PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER – 1

1.1 INTRODUCTION

A traffic light is a collection of two or more coloured lights found at some junctions and pedestrian crossings which indicates whether it is safe and/or legal to continue across the path of other road users. In the United Kingdom, traffic lights are widely used both on major roads and in built-up areas. Their numbers have increased exponentially since they were first invented in 1868.

The operation of standard traffic lights which are currently deployed in many junctions, are based on predetermined timing schemes, which are fixed during the installation and remain until further resetting. The timing is no more than a default setup to control what may be considered as normal traffic. Although every road junction by necessity requires different traffic lighttiming setup, many existing systems operate with an over-simplified sequence. This has instigated various ideas and scenarios to solve the traffic problem. 

A traffic light group is defined as a set of traffic lights which are controlled by the same regulator, which acts as a master or coordinator. The regulator operates under a intelligent system that allows for controlling the lights status depending on time, traffic conditions, etc. In the last 70 years, several innovations on the original concept of traffic light control have been introduced. These innovations consist in the introduction of complex routines such as macro-andmicro-regulation, redundancy to increment the security, more efficient and economical reflectors, etc. However, one aspect that remains the same in all the cases is the use of incandescent lights as the lighting element. During the 80s, a new lighting technology was introduced: Light Emitting Diodes, most commonly known as LED. LEDs can be power supplied with a dc voltage and are able to emit light in a specified wavelength. LED technology is commonly used in displays, panel indicators, remote controls, television screens, etc.

LED technology has experienced a great evolution in the last few years, having a lower fabrication cost wit the possibility of having LED with different illumination colour. LEDs are specially constructed to release a large number of photons outward. Additionally, they are housed in a plastic bulb that concentrates the light in a particulardirection. The application of LEDs in traffic lights has several advantages with respect to incandescent bulbs:• LEDs do not have a filament that burn out, so that they do not get especially hot in contrast toincandescent bulbs;• LEDs last much longer than incandescent lamps, what means that the long term operation andmaintenance costs are significantly lower than for incandescent bulbs;• Light production process is significantly more efficient than in incandescent bulbs, where ahuge portion of the available power supply is used to heat the filament and is not directly usedin the production of light;• A large number of applications can be implemented with LEDs as traffic lightingElements: modification of lighting condition depending on climatic conditions, change in the Crossing time for pedestrians, failure detection, generation of alarms, etc. Figure 1 shows a

Page 1Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

comparison between the emission spectrum of LEDs and incandescent bulb as red traffic lights. The number of LEDs used in a traffic light depends on the manufacturer. In the figure, 680 LEDs are allocated in concentric circles. As it can be seen in the light spectrum for the red light, the LED produces a narrower band of Proceedings of the 6th WSEAS International Conference on Power Systems, Lisbon, Portugal, September 22-24, 2006 256 wavelengths concentrated around the red wavelength (657 nm), which means that the light and color emitted by the traffic light will be much brighter. Moreover, the power supply level needed for the incandescent light is 7.3 dB higher in order to obtain the same intensity. In order to implement the applications indicated, a certain level of intelligence is required in both the traffic light and the regulator. Therefore, a communication link must be established, so that a transceiver must be installed in both sites of the link (traditional traffic control system is unidirectional from regulator to traffic lights, without any response from the status of the traffic lights).

There are different transmission media than can be used. Physical layers based on radio technology are likely to receive the disturbances provided by impulsive noise from car engines, which is a significant interference contribution in different frequency bands. Wired technologies such as fiber, coaxial or copper lines are not available between traffic light and regulator, so that a significant deployment cost is required. Therefore, the use of power lines as transmission media is foreseen as the most appropriate technology as there is no need of deploying new infrastructure.

(b) Incandescent bulb (135 W)Figure 1.1 Traffic light implemented with LED and incandescent bulb.

Page 2Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

The scope of this contribution is to present a PLC-based smart traffic light control, where the communication link is established using the power lines used to feed the traffic light groups. The structure of the paper is as follows. Section 2 describes the architecture of the system. Section 3 details the specifications and requisites of the communication systems, and section 4 shows the selected hardware platform and software tools used to implement the tested.

To design an intelligent and efficient traffic control system, a number of parameters that represent the status of the road conditions must be identified and taken into consideration.

Page 3Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER -2

2.1 WORKING PRINCIPLE

In this project solar panel which gives the electrical energy (dc) & we use two relay (24v dc) in which one relay is connected or disconnected between solar panel PLC & battery & other relay is connected or disconnected between battery PLC & power supply. Both relay controlled by teco PLC

One relay connected between battery & solar panel when battery charging between 20% to 90% . when battery is charging more than 90% then relay is connected between solar panel .

Other relay is connected between solar panel & PLC battery charging is more than 90% then solar panel is directly connected with PLC-2 which control the traffic light signal.

At the time of evening sunlight intensity goes to down. Due to this reason battery charging percentage then relay -2 is connected between battery & PLC(traffic light controller) but at the time of night battery discharges more than 90% then PLC(traffic light controller) is directly connected with SMPS(switched mode power supply). Finally our aim is that 24v dc supply always given to the PLC(traffic light controller). The project are shown in fig 2.1.

Fig -2.1

Page 4Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

2.2 The block diagram

The block diagram of the project are shown in figure 2.2.

Page 5Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

2.3 TABLE OF COMPONENT AND IT’S COST

S. NO. NAME OF COMPONENT RATING COST(RUPIES)PER UNIT

1 SOLER PANEL 21 V, 0.58A12 V, 0.56A

1250 650

2 BATTERY 24V, 7.2AH 1330

3 LED 3V 2

4 LAMP INDICATER 24V 20

5 PLC (MICROLOGIX 1500)PLC (TECHO)

24V,12PIN I/O24V

100006000

6 RELAY 24V, DC,PLA 250

7 BREAD BORD WIRE _ 5/M

Page 6Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER-3

3.1 Basic Traffic Lights

The most basic traffic light consists of three bulbs with different coloured lenses, which from top to bottom are red, amber and green. In the UK, the lights commonly use a sequence of four phases:1. Red— this indicates that traffic must stop behind the line. It is compulsory for all road users to do so. Some traffic lights even have cameras to catch drivers breaking this law.2. Red and Amber— this combination of bulbs indicates that the lights are about to change to green, and gives drivers time to release their handbrake and prepare to drive off as soon as they are allowed to do so. This phase was first introduced in 1958.3. Green— this indicates that traffic may pass through the junction, provided that it is safe to do so and the way is clear. Some junctions are marked with a hash of yellow lines forming a box, which indicates that drivers must not stop on the box unless they are turning right and their exit is clear.4. Amber— this warns traffic that it should stop unless it is unsafe to do so. In the UK it is legal to pass through an amber light, as the phase exists to warn drivers not yet at the junction that they will have to stop.Traffic lights at junctions will always follow this pattern, with conflicting flows of traffic being forced to take turns. Often the green bulb is replaced with two or more green arrows or filter lights, which indicate that traffic turning left or right may go, while a red light remains to instruct oncoming traffic to wait. It is now quite common for vehicles turning right to have to wait for a separate filter light, even if the way is clear. Despite being relatively simple, filter arrows are often 'mistaken' for an instruction to go by drivers who want to turn a different way to that shown. Problems are also known to arise from motorists watching the other lights at junctions and anticipating their own movement, and so shades are used to hide the lights from both drivers and from the sun, which would reduce their visibility

It is interesting to note that the UK is one of only a few countries not to have a 'left on red' rule, where cars are allowed to pass through a red light if it is safe to turn left; in the UK, red lights and filter lights must always be obeyed.A recent improvement in traffic light technology has come with the development of red, amber and green light-emitting diodes (LEDs). Arrays of these tiny bulbs can be used to replace the existing light bulbs in traffic lights and are clearer and more energy-efficient. It is estimated that replacing all the traffic light bulbs in the UK with LEDs would save enough energy to power the city of Norwich.

Page 7Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

3.2 Project scope 1. Construct a model of four way junction of a traffic light model.2. Programme a ladder logic diagram to control the traffic light. 3. Combine the software part and the hardware part to simulate a traffic light system.

3.3 Hardware design

The objective of the hardware design is to develop the interface circuit between the PLC and the elevator system and the elevator control panel, with both external and internal requests. These requests are produced by push buttons that send continuous signals to the PLC when activated. Each push button is connected to an LED to identify the request placed. In addition, the four floors are represented by four LEDs, one for each level. Furthermore, an alarm switch is installed to produce a flashing signal whenever activated. This facility was introduced to simulate the desire for a sudden stoppage of the elevator either for reasons of safety or for requests for a repair job to be carried out on the elevator.

In order to obtain the desired setup, we needed to find a way to capture the pulse generated by a depressed push button. We also needed to make sure that the PLC is recognizing these signals in order for it to correctly perform the required action. As explained below, both issues were resolved by using set/reset flip flops and relays respectively.

The block diagram of the system’s layout is shown in Fig., where both the interfacebetween the PLC and the elevator system with the control panel are drawn

Fig-3.1 Block diagram of the system layout.

3.7 Description of Ladder Logic

The elevator starts at level 1. It opens the door for 5 s, then checks for requests in upper levels. The movement from one level to another is represented by a timer. The transition between two successive levels takes 8 s. As soon as a request is serviced, the door opens for 5 s to take passengers in, and then proceeds to the next request to be serviced. Whenever a level is passed by, its light flashes for 1 s to indicate the current position of the elevator on its way to its

Page 8Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

required destination. The requests whose direction (up or down) is similar to the current direction of the elevator are always serviced before those made in the opposite direction, regardless of which requests were made first. The system continues to service all the remaining requests in a similar way. Whenever no more requests are left to service, the elevator will simply remain at the level it was last at, keeping the door open for 5 s and then closing it until a fresh request is made. However the door is programmed to never open in between levels, and whenever the alarm switch is activated, the alarm signal starts flashing and the elevator stops at the next immediate destination, opens the door and freezes all requests until the alarm is set off again.An illustrative example on the intelligent control of the elevator is explained below:

Assume the following requests: 2D, 3U, 4D, were made and the elevator is currently at level 1. The PLC will then perform the following sequence: First, all up requests are serviced, i.e. in this case only 3U will be serviced. Next the elevator reaches the fourth floor to service 4D, and finally it services the remaining down requests, which in our case is 2D.

3.8 System ArchitectureThe architecture of the communications system must take into account the topology of

the power lines that supply power to each traffic light. In typical situations, low voltage power lines are installed from the regulator to the traffic lights, resulting in a star topology. According to the deployment of traffic light groups, the topology of the communication system from the regulator to the traffic lights follows a pointto- multipoint architecture. This means that a regulator controls several of traffic lights depending on each particular situation. In most of the cases, a regulator controls all the traffic lights used to manage the traffic in a street crossing, as it can be seen in Figure 2. Distances between the regulator and the traffic light groups typically vary in a range from 70 to 400 m. In a traffic light control system, the required bit rate is low enough to be transmitted through power lines. As well, the conditions of the propagation channel are favourable to establish the link as typical conducted interference that appear in a PLC-basedsystem are not found in traffic control scenario (dedicated low voltage lines to power supply the traffic lights are used). On the other hand, the star based topology reduces channel impairments such as impedance mismatching, echoes and multipath propagation. There are different architectures to implement the control system. In present traffic control systems, the intelligence of the system is completely installed in the controller, so that the controller is in charge of switching lights, generate alarms, etc. This is carried out by means of a power interface boards composed of triacs and optocouplers between the traffic lights and the controller. The architecture of the proposed system is based on the installation of a PLC modem in both the traffic light group and in the controller. Apart from the communications tasks, the PLC modem installed in the traffic light takes charge of the light operation. This new concept means that the information flow between traffic light and regulator is significantly reduced, as the controller is no longer responsible for transmitting all the control signals to the traffic lights. On the other hand, traffic light groups will inform the controller of the current status, with special emphasis of alarm situations (fused light, power supply failure etc.).

Page 9Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Fig -3.44.2.5 Programming

PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory. Often, a single PLC can be programmed to replace thousands of relays[4.3].

Under the IEC 61131-3 standard, PLCs can be programmed using standards-based programming languages. A graphical programming notation called Sequential Function Charts is available on certain programmable controllers. Initially most PLCs utilized Ladder Logic Diagram Programming, a model which emulated electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced. This model remains common today.

IEC 61131-3 currently defines five programming languages for programmable control systems: function block diagram (FBD), ladder diagram (LD), structured text (ST; similar to the Pascal programming language), instruction list (IL; similar to assembly language) and sequential function chart (SFC)[4.4]. These techniques emphasize logical organization of operations.

While the fundamental concepts of PLC programming are common to all manufacturers, differences in I/O addressing, memory organization and instruction sets mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.

Page 10Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

4.3 PLC compared with other control systems

Fig -4.2

4.4 Allen-Bradley PLC installed in a control panel

PLCs are well adapted to a range of automation tasks. These are typically industrial

processes in manufacturing where the cost of developing and maintaining the automation system

is high relative to the total cost of the automation, and where changes to the system would be

expected during its operational life. PLCs contain input and output devices compatible with

industrial pilot devices and controls; little electrical design is required, and the design problem

centers on expressing the desired sequence of operations. PLC applications are typically highly

customized systems, so the cost of a packaged PLC is low compared to the cost of a specific

custom-built controller design. On the other hand, in the case of mass-produced goods,

customized control systems are economical. This is due to the lower cost of the components,

which can be optimally chosen instead of a "generic" solution, and where the non-recurring

engineering charges are spread over thousands or millions of units.

For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities.

A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies, input/output hardware and necessary testing and certification) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit buses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomical [4.5].

Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls. Single-board computers using semi-customized or fully proprietary hardware may be chosen for very demanding control applications where the high development and maintenance cost can be supported. "Soft PLCs" running on desktop-type computers can interface with

Page 11Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

industrial I/O hardware while executing programs within a version of commercial operating systems adapted for process control needs.

Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC so that G-code (involving a CNC machine) can be used to instruct machine movements.

PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller". A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. As PLCs have become more powerful, the boundary between DCS and PLC applications has become less distinct.

PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually does not support control algorithms or control loops. As hardware rapidly becomes more powerful and cheaper,RTUs, PLCs and DCSs are increasingly beginning to overlap in responsibilities, and features and vice versa. The industry has standardized on the IEC 61131-3functional block language for creating programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary alternatives and associated development environments.

In recent years "Safety" PLCs have started to become popular, either as standalone models (Pilz PNOZ Multi, Sick etc.) or as functionality and safety-rated hardware added to existing controller architectures (Allen Bradley Guardlogix, Siemens F-series etc.). These differ from conventional PLC types as being suitable for use in safety-critical applications for which PLCs have traditionally been supplemented with hard-wired safety relays. For example, a Safety PLC might be used to control access to a robot cell with trapped-key access, or perhaps to manage the shutdown response to an emergency stop on a conveyor production line. Such PLCs typically have a restricted regular instruction set augmented with safety-specific instructions designed to interface with emergency stops, light screens and so forth. The flexibility that such systems offer has resulted in rapid growth of demand for these controllers.

4.5 PLC

Page 12Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Fig -4.3

4.7 BASIC PLC OPERATIONS

Page 13Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Fig -4.5

Page 14Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

4.8 LOGIC 0, LOGIC 1

Fig -4.6

4.9 Different Types and uses of PLC

The Unitary PLC is typically the smallest and least expensive. It would be used in a small machine or fixed application such as overhead door controls or a stand-alone parts inspection system. They are not expandable so the application is limited to on-board I/O. There are, however, some very powerful units available with built in GSM, color screens, and web servers. Most have 1 or 2 analog I/O channels as well as a high speed input and pulse train output for simple motion control.

The Modular PLCs start with a processor with a few or no on-board I/O. They typically mount to a DIN rail and sometimes require a separate power supply. Additional I/O as well as specialty modules also snap onto the DIN rail and plug into the processor or adjacent module. Modular PLCs are used in applications where a higher I/O count is needed or when using specialty modules such as quadrature encoders, thermocouple inputs, etc. They are also useful in small applications that have options or “upgrades” available to the end user. Systems can be expanded (within certain limits) without adding additional rack space.

Page 15Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Rack style PLCs are usually more expensive, expandable, and powerful than unitary or modular PLCs. The rack provides a power and communication backplane that greatly increases the communication rate between the processor and the modules as well as allowing some specialty modules to communicate with each other without the processor. In some brands, multiple processors can be in the same rack and share the inputs. Racks also allow for redundant processors for critical systems such as waste water pumps or fire control systems. The types of modules available for rack systems are far more extensive than modular systems. The number of available I/O points is also much higher in the rack systems. Around 1000 for some modular PLCs versus over 100,000 for the same brand of rack system.

4.10 Programmable Logic Controllers

4.10.1 MicroLogix 1500 System

Fig -4.7

In a perfect world you would always know what's behind the next door. In the world of automation, the MicroLogix 1500 controller can help you open up new possibilities and get you to where you want to go with ease. This dynamic controller is a more powerful and expandable addition to the MicroLogix family:

Application flexibility and versatility with Compact I/O means a small footprint and expansion to over 100 I/O points

Large onboard non-volatile memory Real Time Clock (RTC) capabilities allow time scheduling of control Program portability allows user programs to be uploaded, downloaded and transported

via Memory Modules Built in PID capabilities Data Access Tool for data monitoring and adjustment Eight Latching (pulse catch) inputs Four event interrupts

4.10.2 Performance

Approximate scan time for a typical 1K user program (includes timers, counters, etc.): 1 millisecond

Page 16Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Simple bit instruction execution: 0.7 microseconds 2 millisecond selectable timed interrupt (STI) 1 millisecond timers Two 20 kHz high-speed counters each with eight modes of operation (up, down,

up/down, quadrature, etc.) Two 20 kHz high-speed outputs (PTO or PWM with acceleration/deceleration profiles) Rugged tongue-and-groove package design, to provide strength and system reliability May be expanded to include up to 16 Compact I/O modules

Base Units continue to support up to eight modules (within the power budget of the base unit) with additional expansion through expansion cables and a number of expansion power supplies.

4.10.3 Optional Features

Data Access Tool (DAT) plug-in device Memory Module Real Time Clock (RTC) Module Combination Memory & RTC Module Expansion I/O modules for discrete and analog applications with a comprehensive

selection of electrical configurations

4.10.4 Advantages of a Modular PLC over a Fixed PLC.

Computers make life easier and more manageable, but people rarely think about the technology that is running in the background. The traffic light signaling drivers to turn, the amusement park ride turning in unfathomable twists, and the factory assembly line using machines in the automobile manufacturing process all have one thing in common, programmable logic controllers (PLCs). These digital computers can be programmed for all sorts of automated actions, and though they come in both fixed and modular form, the modular type is the most popular because of its advantages.

CHAPTER -5

Page 17Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

5.1 Solar Panel

A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged, connected assembly of photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Each panel is rated by its DC output power under standard test conditions, and typically ranges from 100 to 450 watts. The efficiency of a panel determines the area of a panel given the same rated output - an 8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel.

Because a single solar panel can produce only a limited amount of power, most installations contain multiple panels. A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and or solar tracker and interconnection wiring.

5.2 Theory and Construction

Solar panels use light energy (photons) from the sun to generate electricity through the photovoltaic effect. The structural (load carrying) member of a module can either be the top layer or the back layer. The majority of modules use wafer-based crystalline silicon cells or thin-film cells based on cadmium telluride or silicon. The conducting wires that take the current off the panels may contain silver, copper or other non-magnetic conductive transition metals.

The cells must be connected electrically to one another and to the rest of the system. Cells must also be protected from mechanical damage and moisture. Most solar panels are rigid, but semi-flexible ones are available, based on thin-film cells.

Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired current capability.

Separate diodes may be needed to avoid reverse currents, in case of partial or total shading, and at night. The p-n junctions of mono-crystalline silicon cells may have adequate reverse current characteristics that these are not necessary. Reverse currents waste power and can also lead to overheating of shaded cells. Solar cells become less efficient at higher temperatures and installers try to provide good ventilation behind solar panels.[1]

Some recent solar panel designs include concentrators in which light is focused by lenses or mirrors onto an array of smaller cells. This enables the use of cells with a high cost per unit area (such as gallium arsenide) in a cost-effective way.

Depending on construction, photovoltaic panels can produce electricity from a range of frequencies of light, but usually cannot cover the entire solar range (specifically, ultraviolet, infrared and low or diffused light). Hence much of the incident sunlight energy is wasted by solar panels, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into different wavelength ranges and direct the beams onto different cells tuned to those ranges.[2] This has been projected to be capable of raising efficiency by 50%.

Currently the best achieved sunlight conversion rate (solar panel efficiency) is around 21% in commercial products,[3] typically lower than the efficiencies of their cells in isolation. The energy

Page 18Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

density of a solar panel is the efficiency described in terms of peak power output per unit of surface area, commonly expressed in units of watts per square foot (W/ft2). The most efficient mass-produced solar panels have energy density values of greater than 13 W/ft2 (140 W/m2).

5.3 Production

Fig -5.1

In 2010, 15.9 GW of solar PV system installations were completed, with solar PV pricing survey

and market research company PV insights reporting growth of 117.8% in solar PV installation on

a year-on-year basis. With over 100% year-on-year growth in PV system installation, PV module

makers dramatically increased their shipments of solar panels in 2010. They actively expanded

their capacity and turned themselves into gigawatt GW players. According to PV insights, five of

the top ten PV module companies in 2010 are GW players. Suntech, First Solar, Sharp, Yingli

and Trina Solar are GW producers now, and most of them doubled their shipments in 2010

5.4 Mounting Systems

5.4.1 Trackers

Solar trackers increase the amount of energy produced per panel at a cost of mechanical complexity and need for maintenance. They sense the direction of the Sun and tilt the panels as needed for maximum exposure to the light.

5.4.2 Fixed Racks

Fixed racks hold panels stationary as the sun moves across the sky. The fixed rack sets the angle at which the panel is held. Tilt angles equivalent to an installation's latitude are common.

Page 19Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

5.4.3 Ground Mounted

Ground mounted solar power systems consist of solar panels held in place by racks or frames that are attached to ground based mounting supports.

Ground based mounting supports include:

Pole mounts, which are driven directly into the ground or embedded in concrete. Foundation mounts, such as concrete slabs or poured footings Ballasted footing mounts, such as concrete or steel bases that use weight to secure the solar

panel system in position and do not require ground penetration. This type of mounting system is well suited for sites where excavation is not possible such as capped landfills and simplifies decommissioning or relocation of solar panel systems.

Roof mounted

Roof mounted solar power systems consist of solar panels held in place by racks or frames attached to roof based mounting supports.

Roof based mounting supports include:

Pole mounts, which are attached directly to the roof structure and may use additional rails for attaching the panel racking or frames.

Ballasted footing mounts, such as concrete or steel bases that use weight to secure the panel system in position and do not require through penetration. This mounting method allows for decommissioning or relocation of solar panel systems with no adverse effect on the roof structure.

Fig -5.2

Technicians installing photovoltaic panels

on a roof mounted rack.

Fig -5.3

A roof mounted solar panel system installed on a

sloped roof using pole mounts and rails.

5.5 Photovoltaic’s   ( PV )

Photovoltaic’s is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light

Page 20Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

and release electrons. When these free electron’s are captured, an electric current result that can be used as electricity.The photoelectric effect was first noted by a French physicist, Edmund Becquerel, in 1839, who found that certain materials would produce small amounts of electric current when exposed to light. In 1905, Albert Einstein described the nature of light and the photoelectric effect on which photovoltaic technology is based, for which he later won a Nobel prize in physics. The first photovoltaic module was built by Bell Laboratories in 1954. It was billed as a solar battery and was mostly just a curiosity as it was too expensive to gain widespread use. In the 1960s, the space industry began to make the first serious use of the technology to provide power aboard spacecraft. Through the space programs, the technology advanced, its reliability was established, and the cost began to decline. During the energy crisis in the 1970s, photovoltaic technology gained recognition as a source of power for non-space applications.

Fig -5.4The diagram above illustrates the operation of a basic photovoltaic cell, also called a solar cell. Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current -- that is, electricity. This electricity can then be used to power a load, such as a light or a tool.A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module. Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module.

Page 21Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Fig -5.5Multiple modules can be wired together to form an array. In general the larger area of a module or array, the more electricity that will be produced. Photovoltaic modules and arrays produce direct-current (dc) electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.Today's most common PV devices use a single junction, or interface, to create an electric field within a semiconductor such as a PV cell. In a single-junction PV cell, only photons whose energy is equal to or greater than the band gap of the cell material can free an electron for an electric circuit. In other words, the photovoltaic response of single-junction cells is limited to the portion of the sun's spectrum whose energy is above the band gap of the absorbing material, and lower-energy photons are not used.One way to get around this limitation is to use two (or more) different cells, with more than one band gap and more than one junction, to generate a voltage. These are referred to as "multijunction" cells (also called "cascade" or "tandem" cells). Multijunction devices can achieve a higher total conversion

Fig-5.6 efficiency because they can convert more of the energy spectrum of light to electricity.As shown below, a multijunction device is a stack of individual single-junction cells in descending order of band gap (Eg). The top cell captures the high-energy photons and passes the rest of the photons on to be absorbed by lower-band-gap cells.Much of today's research in multijunction cells focuses on gallium arsenide as one (or all) of the component cells. Such cells have reached efficiencies of around 35% under concentrated sunlight. Other materials studied for multijunction devices have been amorphous silicon and copper indium diselenide.

Page 22Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

As an example, the multijunction device below uses a top cell of gallium indium phosphide, "a tunnel junction," to aid the flow of electrons between the cells, and a bottom cell of gallium arsenide

Fig -5.7

Page 23Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER 6

6.1 Battery :-

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery (or "voltaic pile") in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year, with 6% annual growth.[15]

There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power fortelephone exchanges and computer data centers.

6.1.1 History

Fig -5.1

The symbol for a battery in a circuit diagram. It originated as a schematic drawing of the earliest

type of battery, a voltaic pile.

In strict terms, a battery is a collection of multiple electrochemical cells, but in popular usage battery often refers to a single cell. For example, a 1.5-volt AAA battery is a single 1.5-volt cell, and a 9-volt battery has six 1.5-volt cells in series. The first electrochemical cell was

Page 24Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

developed by the Italian physicist Alessandro Volta in 1792, and in 1800 he invented the first battery, a "pile" of many cells in series.[16]

The usage of "battery" to describe electrical devices dates to Benjamin Franklin, who in 1748 described multiple Leyden jars (early electrical capacitors) by analogy to a battery of cannons. Thus Franklin's usage to describe multiple Leyden jars predated Volta's use of multiple galvanic cells. It is speculated, but not established, that several ancient artifacts consisting of copper sheets and iron bars, and known asBaghdad batteries may have been galvanic cells.

Volta's work was stimulated by the Italian anatomist and physiologist Luigi Galvani, who in 1780 noticed that dissected frog's legs would twitch when struck by a spark from a Leyden jar, an external source of electricity. In 1786 he noticed that twitching would occur during lightning storms. After many years Galvani learned how to produce twitching without using any external source of electricity. In 1791, he published a report on "animal electricity." He created an electric circuit consisting of the frog's leg (FL) and two different metals A and B, each metal touching the frog's leg and each other, thus producing the circuit A–FL–B–A–FL–B...etc. In modern terms, the frog's leg served as both the electrolyte and thesensor, and the metals served as electrodes. He noticed that even though the frog was dead, its legs would twitch when he touched them with the metals.

Within a year, Volta realized the frog's moist tissues could be replaced by cardboard soaked in salt water, and the frog's muscular response could be replaced by another form of electrical detection. He already had studied the electrostatic phenomenon of capacitance, which required measurements of electric charge and of electrical potential ("tension"). Building on this experience, Volta was able to detect electric current through his system, also called a Galvanic cell. The terminal voltage of a cell that is not discharging is called its  electromotive force (emf), and has the same unit as electrical potential, named (voltage) and measured in volts, in honor of Volta. In 1800, Volta invented the battery by placing many voltaic cells in series, piling them one above the other. This voltaic pile gave a greatly enhanced net emf for the combination, with a voltage of about 50 volts for a 32-cell pile. In many parts of Europe batteries continue to be called piles.

Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cells were an inexhaustible source of energy, and that the associated corrosion effects at the electrodes were a mere nuisance, rather than an unavoidable consequence of their operation, as Michael Faraday showed in 1834. According to Faraday, cations (positively charged ions) are attracted to the cathode, and anions(negatively charged ions) are attracted to the anode.

Although early batteries were of great value for experimental purposes, in practice their voltages fluctuated and they could not provide a large current for a sustained period. Later, starting with the Daniell cell in 1836, batteries provided more reliable currents and were adopted by industry for use in stationary devices, in particular in telegraph networks where they were the only practical source of electricity, since electrical distribution networks did not exist at the time. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly. Many used glass jars to hold their components, which made them fragile. These characteristics made wet cells unsuitable for portable appliances. Near the end of the nineteenth century, the invention of dry cell batteries, which replaced the liquid electrolyte with a paste, made portable electrical devices practical.

Page 25Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Since then, batteries have gained popularity as they became portable and useful for a variety of purposes.

6.1.2 Principle of Operation

Fig -6.2

A voltaic cell for demonstrate on purposes. In this example the two half-cells are linked by a salt

bridge separator that permits the transfer of ions, but not water molecules.

A battery is a device that converts chemical energy directly to electrical energy.  It consists of a number of voltaic cells; each voltaic cell consists of two half-cells connected in series by a conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the electrode to which anions (negatively charged ions) migrate, i.e., the anode or negative electrode; the other half-cell includes electrolyte and the electrode to which cations (positively charged ions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery, cations are reduced (electrons are added) at the cathode, while anions are oxidized (electrons are removed) at the anode. The electrodes do not touch each other but are electrically connected by the electrolyte. Some cells use two half-cells with different electrolytes. A separator between half-cells allows ions to flow, but prevents mixing of the electrolytes.[17]

Each half-cell has an electromotive force (or emf), determined by its ability to drive electric current from the interior to the exterior of the cell. The net emf of the cell is the difference between the emfs of its half-cells, as first recognized by Volta. Therefore, if the electrodes have emfs   and , then the net emf is  ; in other words, the net emf is the difference between the reduction of the half-reactions.

The electrical driving force or   across the terminals of a cell is known as the terminal voltage (difference) and is measured in volts. The terminal voltage of a cell that is neither charging nor discharging is called the open-circuit voltage and equals the emf of the cell. Because of internal resistance, the terminal voltage of a cell that is discharging is smaller in magnitude than the open-circuit voltage and the terminal voltage of a cell that is charging exceeds the open-circuit voltage. An ideal cell has negligible internal resistance, so it would maintain a constant terminal voltage of   until exhausted, then dropping to zero. If such a cell maintained 1.5 volts and stored a charge of one coulomb then on complete discharge it would perform 1.5 joule of work. In actual cells, the internal resistance increases under discharge, and the open circuit voltage also decreases under discharge. If the voltage and resistance are plotted

Page 26Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

against time, the resulting graphs typically are a curve; the shape of the curve varies according to the chemistry and internal arrangement employed.

As stated above, the voltage developed across a cell's terminals depends on the energy release of the chemical reactions of its electrodes and electrolyte. Alkaline and zinc–carbon cells have different chemistries but approximately the same emf of 1.5 volts; likewise NiCd and NiMH cells have different chemistries, but approximately the same emf of 1.2 volts. On the other hand the high electrochemical potential changes in the reactions of lithium compounds give lithium cells emfs of 3 volts or more.

6.1.3 Categories and types of Batteries

Fig -6.3

From top to bottom: a large 4.5-volt (3R12) battery, a D Cell, a C cell, an AA cell, an AAA cell,

an AAAA cell, an A23 battery, a 9-volt PP3 battery, and a pair of button cells (CR2032 and

LR44).

Batteries are classified into two broad categories, each type with advantages and disadvantages.[31]

Primary batteries irreversibly (within limits of practicality) transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means.

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition[18].

Some types of primary batteries used, for example, for telegraph circuits, were restored to operation by replacing the components of the battery consumed by the chemical reaction. Secondary batteries are not indefinitely rechargeable due to dissipation of the active materials, loss of electrolyte and internal corrosion.

Page 27Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

6.2 Primary Batteries

Primary batteries can produce current immediately on assembly. Disposable batteries are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells.[19]

Common types of disposable batteries include zinc–carbon batteries and alkaline batteries. In general, these have higher energy densities than rechargeable batteries, but disposable batteries do not fare well under high-drain applications with loads under 75 ohms (75 Ω).

6.3 Secondary Batteries

Secondary batteries must be charged before use; they are usually assembled with active materials in the discharged state. Rechargeable batteries or secondary cells can be recharged by applying electric current, which reverses the chemical reactions that occur during its use. Devices to supply the appropriate current are called chargers or rechargers.

The oldest form of rechargeable battery is the lead–acid battery. This battery is notable in that it contains a liquid in an unsealed container, requiring that the battery be kept upright and the area be well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteries during overcharging. The lead–acid battery is also very heavy for the amount of electrical energy it can supply. Despite this, its low manufacturing cost and its high surge current levels make its use common where a large capacity (over approximately 10 Ah) is required or where the weight and ease of handling are not concerns[20].

A common form of the lead–acid battery is the modern car battery, which can, in general, deliver a peak current of 450 amperes. An improved type of liquid electrolyte battery is the sealed valve regulated lead–acid battery (VRLA battery), popular in the automotive industry as a replacement for the lead–acid wet cell. The VRLA battery uses an immobilized sulfuric acid electrolyte, reducing the chance of leakage and extending shelf life. VRLA batteries have the electrolyte immobilized, usually by one of two means:

Gel batteries (or "gel cell") contain a semi-solid electrolyte to prevent spillage. Absorbed Glass Mat (AGM) batteries absorb the electrolyte in a special fiberglass matting.

Other portable rechargeable batteries include several "dry cell" types, which are sealed units and are, therefore, useful in appliances such as mobile and laptop computers. Cells of this type (in order of increasing power density and cost) include nickel–cadmium (NiCd),nickel–zinc (NiZn), nickel metal hydride (NiMH), and lithium-ion (Li-ion) cells. By far, Li-ion has the highest share of the dry cell rechargeable market. Meanwhile, NiMH has replaced NiCd in most applications due to its higher capacity, but NiCd remains in use in power tools, two-way radios, and medical equipment. NiZn is a new technology that is not yet well established commercially.

Page 28Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Recent developments include batteries with embedded electronics such as USBCELL, which allows charging an AA cell through a USB connector, and smart battery packs with state-of-charge monitors and battery protection circuits to prevent damage on over-discharge. Low self-discharge (LSD) allows secondary cells to be recharged prior to shipping.

6.4 Battery Cell types

There are many general types of electrochemical cells, according to chemical processes applied and design chosen. The variation includes galvanic, electrolytic cells, fuel cells, flow cells and voltaic piles.

6.4.1 Wet Cell

A wet cell battery has a liquid electrolyte. Other names are flooded cell, since the liquid covers all internal parts, or vented cell, since gases produced during operation can escape to the air. Wet cells were a precursor to dry cells and are commonly used as a learning tool for electrochemistry. It is often built with common laboratory supplies, such as beakers, for demonstrations of how electrochemical cells work. A particular type of wet cell known as a concentration cell is important in understanding corrosion. Wet cells may be primary cells (non-rechargeable) or secondary cells (rechargeable). Originally, all practical primary batteries such as the Daniel cell were built as open-topped glass jar wet cells. Other primary wet cells are the Leclanche cell, Grove cell, Bunsen cell, Chromic acid cell, Clark cell, and Weston cell. The Leclanche cell chemistry was adapted to the first dry cells. Wet cells are still used in automobile batteries and in industry for standby power for switchgear, telecommunication or large uninterruptible power supplies, but in many places batteries with gel cells have been used instead. These applications commonly use lead–acid or nickel–cadmium cells.

6.4.2 Dry Cell

"Dry cell" redirects here. For the heavy metal band, see Dry Cell (band).

Fig -6.4

Page 29Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Line art drawing of a dry cell:

1. brass cap, 2. plastic seal, 3. expansion space, 4. porous cardboard, 5. zinc can, 6. carbon rod, 7.

chemical mixture.

A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Unlike a wet cell, a dry cell can operate in any orientation without spilling as it contains no free liquid, making it suitable for portable equipment. By comparison, the first wet cells were typically fragile glass containers with lead rods hanging from the open top, and needed careful handling to avoid spillage. Lead–acid batteries did not achieve the safety and portability of the dry cell until the development of the gel battery.

A common dry cell battery is the zinc–carbon battery, using a cell sometimes called the dry Leclanché cell, with a nominal voltage of 1.5 volts, the same as the alkaline battery (since both use the same zinc–manganese dioxide combination).

A standard dry cell comprises a zinc anode (negative pole), usually in the form of a cylindrical pot, with a carbon cathode (positive pole) in the form of a central rod. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode. The remaining space between the electrolyte and carbon cathode is taken up by a second paste consisting of ammonium chloride and manganese dioxide, the latter acting as a depolarizer. In some more modern types of so-called 'high-power' batteries (with much lower capacity than standard alkaline batteries), the ammonium chloride is replaced by zinc chloride.

6.4.3 Reserve cell

A reserve battery is stored in unassembled form and is activated, ready-charged, when its internal parts are assembled, e.g. by adding electrolyte; it can be stored inactivated for a long period of time. For example, a battery for an electronic fuse might be activated by the impact of firing a gun, breaking a capsule of electrolyte to activate the battery and power the fuse’s circuits. Reserve batteries are usually designed for a short service life (seconds or minutes) after long storage (years). A water-activated battery for oceanographic instruments or military applications becomes activated on immersion in water.

6.5 Battery cell performance

A battery's characteristics may vary over load cycle, over charge cycle, and over lifetime due to many factors including internal chemistry current drain, and temperature.

6.6 Battery capacity and discharging

Fig -6.5.A device to check battery voltage.

Page 30Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

A battery's capacity is the amount of electric charge it can store. The more electrolyte and electrode material there is in the cell the greater the capacity of the cell. A small cell has less capacity than a larger cell with the same chemistry, and they develop the same open-circuit voltage.

Because of the chemical reactions within the cells, the capacity of a battery depends on the discharge conditions such as the magnitude of the current (which may vary with time), the allowable terminal voltage of the battery, temperature, and other factors. The available capacity of a battery depends upon the rate at which it is discharged. If a battery is discharged at a relatively high rate, the available capacity will be lower than expected[21].

The capacity printed on a battery is usually the product of 20 hours multiplied by the constant current that a new battery can supply for 20 hours at 68 F° (20 C°), down to a specified terminal voltage per cell. A battery rated at 100 A·h will deliver 5 A over a 20-hour period at room temperature. However, if discharged at 50 A, it will have a lower capacity.

The relationship between current, discharge time, and capacity for a lead acid battery is approximated (over a certain range of current values) by Peukert's law:

where

 is the capacity when discharged at a rate of 1 amp.

 is the current drawn from battery (A).

 is the amount of time (in hours) that a battery can sustain.

 is a constant around 1.3.

For low values of I internal self-discharge must be included.

Internal energy losses and limited rate of diffusion of ions through the electrolyte cause the efficiency of a real battery to vary at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge rates, but if the rate is very low, it will partly self-discharge during the long time of operation, again lowering its efficiency.

Installing batteries with different A·h ratings will not affect the operation of a device (except for the time it will work for) rated for a specific voltage unless the load limits of the battery are exceeded. High-drain loads such as digital cameras can result in delivery of less total energy, as happens with alkaline batteries.[31] For example, a battery rated at 2000 mA·h for a 10- or 20-hour discharge would not sustain a current of 1 A for a full two hours as its stated capacity implies.

Page 31Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER -7

7.1 Solar Tracking Systems

Global warming has increased the demand and request for green energy produced by renewable sources such as solar power. Consequently, solar tracking is increasingly being applied as a sustainable power generating solution.

Solar Tracking System is a device for orienting a solar panel or concentrating a solar reflector or lens towards the sun. Concentrators, especially in solar cell applications, require a high degree of accuracy to ensure that the concentrated sunlight is directed precisely to the powered device. Precise tracking of the sun is achieved through systems with single or dual axis tracking.

A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices.

In flat-panel photovoltaic (PV) applications trackers are used to minimize the angle of incidence between the incoming light and a photovoltaic panel. This increases the amount of energy produced from a fixed amount of installed power generating capacity. In standard photovoltaic applications, it is estimated that trackers are used in at least 85% of commercial installations greater than 1MW from 2009 to 2012.

In concentrated photovoltaic (CPV) and concentrated solar thermal (CSP)applications trackers are used to enable the optical components in the CPV and CSP systems. The optics in concentrated solar applications accept the direct component of sunlight light and therefore must be oriented appropriately to collect energy. Tracking systems are found in all concentrator applications because such systems do not produce energy unless oriented closely toward the sun.

7.2 Basic concept

Fig -7.1

Page 32Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

The effective collection area of a flat-panel solar collector varies with the cosine of the

misalignment of the panel with the Sun.

Sunlight has two components, the "direct beam" that carries about 90% of the solar energy, and the "diffuse sunlight" that carries the remainder - the diffuse portion is the blue sky on a clear day and increases as a proportion on cloudy days. As the majority of the energy is in the direct beam, maximizing collection requires the sun to be visible to the panels as long as possible.

7.3 Trackers

Even though a fixed flat-panel can be set to collect a high proportion of available noon-time energy, significant power is also available in the early mornings and late afternoons when the misalignment with a fixed panel becomes excessive to collect a reasonable proportion of the available energy. For example, even when the Sun is only 10° above the horizon the available energy can already be around half the noon-time energy levels (or even greater depending on latitude, season, and atmospheric conditions).

Thus the primary benefit of a tracking system is to collect solar energy for the longest period of the day, and with the most accurate alignment as the Sun's position shifts with the seasons.

In addition, the greater the level of concentration employed the more important accurate tracking becomes, because the proportion of energy derived from direct radiation is higher, and the region where that concentrated energy is focused becomes smaller.

7.3.1 Single Axis Tracking Systems Solar panels with single axis tracking systems. The panels can turn around the centre

axis. LINAK can provide the actuators that tilt the panels.

Fig -7.2

Page 33Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

7.3.2 Horizontal single axis tracker (HSAT)

Fig -7.3

The axis of rotation for horizontal single axis tracker is horizontal with respect to the ground. The posts at either end of the axis of rotation of a horizontal single axis tracker can be shared between trackers to lower the installation cost.

Field layouts with horizontal single axis trackers are very flexible. The simple geometry means that keeping all of the axis of rotation parallel to one another is all that is required for appropriately positioning the trackers with respect to one another.

Appropriate spacing can maximize the ratio of energy production to cost, this being dependent upon local terrain and shading conditions and the time-of-day value of the energy produced. Backtracking is one means of computing the disposition of panels.

Horizontal trackers typically have the face of the module oriented parallel to the axis of rotation. As a module tracks, it sweeps a cylinder that is rotationally symmetric around the axis of rotation.

In single axis horizontal trackers, a long horizontal tube is supported on bearings mounted upon pylons or frames. The axis of the tube is on a north-south line. Panels are mounted upon the tube, and the tube will rotate on its axis to track the apparent motion of the sun through the day.

7.3.3 Vertical single axis tracker (VSAT)

The axis of rotation for vertical single axis trackers is vertical with respect to the ground. These trackers rotate from East to West over the course of the day. Such trackers are more effective at high latitudes than are horizontal axis trackers.

Field layouts must consider shading to avoid unnecessary energy losses and to optimize land utilization. Also optimization for dense packing is limited due to the nature of the shading over the course of a year.

Page 34Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Vertical single axis trackers typically have the face of the module oriented at an angle with respect to the axis of rotation. As a module tracks, it sweeps a cone that is rotationally symmetric around the axis of rotation.

7.3.4 Dual Axis Tracking Systems

Dual axis tracking is typically used to orient a mirror and redirect sunlight along a fixed axis towards a stationary receiver. But the system can also gain additional yield on your PV cells. LINAK can provide you with quality actuators that

Fig -7.4

7.3.5 Tilted single axis tracker (TSAT)

Fig -7.5

Single axis trackers with roughly 20 degree tilt at Nellis Air Force Base in Nevada, USA. The

arrays form part of the Nellis Solar Power Plant. Credit: U.S. Air Force photo by Senior Airman

Larry E. Reid Jr.

All trackers with axes of rotation between horizontal and vertical are considered tilted single axis trackers. Tracker tilt angles are often limited to reduce the wind profile and decrease the elevated end’s height off the ground.

Field layouts must consider shading to avoid unnecessary losses and to optimize land utilization.

Page 35Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

With backtracking, they can be packed without shading perpendicular to their axis of rotation at any density. However, the packing parallel to their axis of rotation is limited by the tilt angle and the latitude.

Tilted single axis trackers typically have the face of the module oriented parallel to the axis of rotation. As a module tracks, it sweeps a cylinder that is rotationally symmetric around the axis of rotation.

7.3.6 Multi-mirror concentrating PV

Fig -7.6 Reflective mirror concentrator units

This device uses multiple mirrors in a horizontal plane to reflect sunlight upward to a high temperature photovoltaic or other system requiring concentrated solar power. Structural problems and expense are greatly reduced since the mirrors are not significantly exposed to wind loads. Through the employment of a patented mechanism, only two drive systems are required for each device. Because of the configuration of the device it is especially suited for use on flat roofs and at lower latitudes. The units illustrated each produce approximately 200 peak DC watts.

A multiple mirror reflective system combined with a central power tower is employed at the Sierra Sun Tower, located in Lancaster, California. This generation plant operated by Solar is scheduled to begin operations on August 5, 2009. This system, which uses multiple heliostats in a north-south alignment, uses pre-fabricated parts and construction as a way of decreasing startup and operating costs.

Page 36Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER-8

8.1 RelayA relay is an electrically operated switch. Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming

in from one circuit and re-tran smitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

Fig -8.1

A type of relay that can handle the high power required to directly control an electric motor or

other loads is called a contactor. Solid-state relays control power circuits with no moving parts,

instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits from

overload or faults; in modern electric power systems these functions are performed by digital

instruments still called "protective relays".

8.2 Basic Design and Operation

Page 37Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Fig -8.2

8.3 Simple Electromechanical Relay

Fig -8.3

Small "cradle" relay often used in electronics. The "cradle" term refers to the shape of the relay's

armature.

A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core,

an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,

and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to

the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by

a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this

condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.

Other relays may have more or fewer sets of contacts depending on their function. The relay in

the picture also has a wire connecting the armature to the yoke. This ensures continuity of the

circuit between the moving contacts on the armature, and the circuit track on the printed circuit

board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that

activates the armature, and the consequent movement of the movable contact(s) either makes or

breaks (depending upon construction) a connection with a fixed contact. If the set of contacts

was closed when the relay was de-energized, then the movement opens the contacts and breaks

the connection, and vice versa if the contacts were open. When the current to the coil is switched

off, the armature is returned by a force, approximately half as strong as the magnetic force, to its

relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in

industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage

application this reduces noise; in a high voltage or current application it reduces arcing.

When the coil is energized with direct current, a diode is often placed across the coil to

dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise

Page 38Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

generate a voltage spike dangerous to semiconductor circuit components. Some automotive

relays include a diode inside the relay case. Alternatively, a contact protection network

consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil

is designed to be energized with alternating current (AC), a small copper "shading ring" can be

crimped to the end of the solenoid, creating a small out-of-phase current which increases the

minimum pull on the armature during the AC cycle.[8.1]

A solid-state relay uses a thyristor or other solid-state switching device, activated by the

control signal, to switch the controlled load, instead of a solenoid. Anoptocoupler (a light-

emitting diode (LED) coupled with a photo transistor) can be used to isolate control and

controlled circuits.

8.4 Types Of Relay

8.4.1 Latching Relay

Fig -7.4 Latching relay with permanent magnet

A latching relay has two relaxed states (bistable). These are also called "impulse", "keep", or

"stay" relays. When the current is switched off, the relay remains in its last state. This is achieved

with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an

over-center spring or permanent magnet to hold the armature and contacts in position while the

coil is relaxed, or with a remanent core. In the ratchet and cam example, the first pulse to the coil

turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil

turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the

advantage that one coil consumes power only for an instant, while it is being switched, and the

relay contacts retain this setting across a power outage. A remanent core latching relay requires a

current pulse of opposite polarity to make it change state.

8.4.2 Reed Relay

A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts

inside an evacuated or inert gas-filled glass tube which protects the contacts against

atmospheric corrosion; the contacts are made of magnetic material that makes them move under

Page 39Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

the influence of the field of the enclosing solenoid. Reed relays can switch faster than larger

relays, require only little power from the control circuit, but have low switching current and

voltage ratings. In addition, the reeds can become magnetized over time, which makes them stick

'on' even when no current is present; changing the orientation of the reeds with respect to the

solenoid's magnetic field will fix the problem.

Fig -8.5

A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted

with mercury. Such relays are used to switch low-voltage signals (one volt or less) where the

mercury reduces the contact resistance and associated voltage drop, for low-current signals

where surface contamination may make for a poor contact, or for high-speed applications where

the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be

mounted vertically to work properly. Because of the toxicity and expense of liquid mercury,

these relays are now rarely used. See also mercury switch.

8.4.3 Polarized Relay

A polarized relay placed the armature between the poles of a permanent magnet to

increase sensitivity. Polarized relays were used in middle 20th Centurytelephone exchanges to

detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician

could first adjust them for maximum sensitivity and then apply a bias spring to set the critical

current that would operate the relay.

8.4.4 Machine tool Relay

A machine tool relay is a type standardized for industrial control of machine tools,

transfer machines, and other sequential control. They are characterized by a large number of

contacts (sometimes extendable in the field) which are easily converted from normally-open to

normally-closed status, easily replaceable coils, and a form factor that allows compactly

installing many relays in a control panel. Although such relays once were the backbone of

Page 40Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

automation in such industries as automobile assembly, the programmable logic controller (PLC)

mostly displaced the machine tool relay from sequential control applications.

A relay allows circuits to be switched by electrical equipment: for example, a timer

circuit with a relay could switch power at a preset time. For many years relays were the standard

method of controlling industrial electronic systems. A number of relays could be used together to

carry out complex functions (relay logic). The principle of relay logic is based on relays which

energize and de-energize associated contacts. Relay logic is the predecessor of ladder logic,

which is commonly used in Programmable logic controllers.

8.4.5 Ratchet Relay

This is again a clapper type relay which does not need continuous current through its coil

to retain its operation.

8.4.6 Contactor Relay

A contactor is a very heavy-duty relay used for switching electric motors and lighting

loads, although contactors are not generally called relays. Continuous current ratings for

common contactors range from 10 amps to several hundred amps. High-current contacts are

made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize;

however, silver oxide is still a good conductor.[8.2] Such devices are often used for motor starters.

A motor starter is a contactor with overload protection devices attached. The overload sensing

devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot

melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with

the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor

relays can be extremely loud to operate, making them unfit for use where noise is a chief

concern.

8.4.7 Solid-State Relay

Fig -7.6

Page 41Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

A solid state relay (SSR) is a solid state electronic component that provides a similar function to

an electromechanical relay but does not have any moving components, increasing long-term

reliability. Every solid-state device has a small voltage drop across it. This voltage drop limited

the amount of current a given SSR could handle. The minimum voltage drop for such a relay is a

function of the material used to make the device. Solid-state relays rated to handle 100 to

1,200 Amperes, have become commercially available. Compared to electromagnetic relays, they

may be falsely triggered by transients.

8.4.8 Solid State Contactor Relay

A solid state contactor is a heavy-duty solid state relay, including the necessary heat

sink, used for switching electric heaters, small electric motors and lighting loads; where frequent

on/off cycles are required. There are no moving parts to wear out and there is no contact bounce

due to vibration. They are activated by AC control signals or DC control signals

from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or

other microprocessor and microcontroller controls.

8.4.9 Buchholz Relay

A Buchholz relay is a safety device sensing the accumulation of gas in large oil-

filled transformers, which will alarm on slow accumulation of gas or shut down the transformer

if gas is produced rapidly in the transformer oil.

8.4.10 Forced-Guided Contacts Relay

A forced-guided contacts relay has relay contacts that are mechanically linked together,

so that when the relay coil is energized or de-energized, all of the linked contacts move together.

If one set of contacts in the relay becomes immobilized, no other contact of the same relay will

be able to move. The function of forced-guided contacts is to enable the safety circuit to check

the status of the relay. Forced-guided contacts are also known as "positive-guided contacts",

"captive contacts", "locked contacts", or "safety relays".

8.4.11 Overload Protection Relay(used in Project)

Electric motors need overcurrent protection to prevent damage from over-loading the

motor, or to protect against short circuits in connecting cables or internal faults in the motor

windings.[3] One type of electric motor overload protection relay is operated by a heating element

in series with the electric motor. The heat generated by the motor current heats a bimetallic

strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed

to the same environment as the motor, a useful though crude compensation for motor ambient

temperature is provided.

Page 42Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Relays are used to and for:

Amplify a digital signal, switching a large amount of power with a small operating

power. Some special cases are:

A telegraph relay, repeating a weak signal received at the end of a long wire

Controlling a high-voltage circuit with a low-voltage signal, as in some types

of modems or audio amplifiers,

Controlling a high-current circuit with a low-current signal, as in the starter solenoid of

an automobile,

Detect and isolate faults on transmission and distribution lines by opening and

closing circuit breakers (protection relays),

Fig -8.7

Isolate the controlling circuit from the controlled circuit when the two are at different

potentials, for example when controlling a mains-powered device from a low-voltage

switch. The latter is often applied to control office lighting as the low voltage wires are

easily installed in partitions, which may be often moved as needs change. They may also

be controlled by room occupancy detectors to conserve energy,

Logic functions. For example, the boolean AND function is realised by connecting

normally open relay contacts in series, the OR function by connecting normally open

contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or)

function. Similar functions for NAND and NOR are accomplished using normally closed

contacts. The Ladder programming language is often used for designing relay

logic networks.

The application of Boolean Algebra to relay circuit design was formalized by Claude

Shannon in A Symbolic Analysis of Relay and Switching Circuits

Page 43Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Early computing. Before vacuum tubes and transistors, relays were used as logical

elements in digital computers. See electro-mechanical computers such asARRA

(computer), Harvard Mark II, Zuse Z2, and Zuse Z3.

Safety-critical logic. Because relays are much more resistant than semiconductors to

nuclear radiation, they are widely used in safety-critical logic, such as the control panels

of radioactive waste-handling machinery.

Time delay functions. Relays can be modified to delay opening or delay closing a set of

contacts. A very short (a fraction of a second) delay would use a copper disk between the

armature and moving blade assembly. Current flowing in the disk maintains magnetic

field for a short time, lengthening release time. For a slightly longer (up to a minute)

delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape

slowly. The time period can be varied by increasing or decreasing the flow rate. For

longer time periods, a mechanical clockwork timer is installed.

Vehicle battery isolation. A 12v relay is often used to isolate any second battery in cars,

4WDs, RVs and boats.

Switching to a standby power supply.

8.5 Relay Application Considerations

Fig -8.8

A large relay with two coils and many sets of contacts, used in an old telephone switching

system.

Fig -8.9

Page 44Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Several 30-contact relays in "Connector" circuits in mid 20th century 1XB switch and5XB

switch telephone exchanges; cover removed on one

Selection of an appropriate relay for a particular application requires evaluation of many

different factors:

Number and type of contacts – normally open, normally closed, (double-throw)

Contact sequence – "Make before Break" or "Break before Make". For example, the old

style telephone exchanges required Make-before-break so that the connection didn't get

dropped while dialing the number.

Rating of contacts – small relays switch a few amperes, large contactors are rated for up

to 3000 amperes, alternating or direct current

Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC,

automotive types to 50 VDC, special high-voltage relays to about 15 000 Vperating

lifetime, useful life - the number of times the relay can be expected to operate reliably.

There is both a mechanical life and a contact life; the contact life is naturally affected by

the kind of load being switched.

Coil voltage – machine-tool relays usually 24 VAC, 120 or 250 VAC, relays for

switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few

milliamperes

Coil current - including minimum current required to operate reliably and minimum

current to hold. Also effects of power dissipation on coil temperature at various duty

cycles.

Package/enclosure – open, touch-safe, double-voltage for isolation

environment - minimum and maximum operating between circuits, explosion proof,

outdoor, oil and splash resistant, washable for printed circuit board assembly

Operating temperatures and other environmental considerations such as effects of

humidity and salt

Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB

post soldering cleaning, which is removed once assembly is complete.

Mounting – sockets, plug board, rail mount, panel mount, through-panel mount,

enclosure for mounting on walls or equipment

Switching time – where high speed is required

"Dry" contacts – when switching very low level signals, special contact materials may be

needed such as gold-plated contacts

Contact protection – suppress arcing in very inductive circuits

Page 45Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Coil protection – suppress the surge voltage produced when switching the coil current

Isolation between coil contacts

Aerospace or radiation-resistant testing, special quality assurance

Expected mechanical loads due to acceleration – some relays used

in aerospace applications are designed to function in shock loads of 50 g or more

Accessories such as timers, auxiliary contacts, pilot lamps, test buttons

Regulatory approvals

Stray magnetic linkage between coils of adjacent relays on a printed circuit board.

There are many considerations involved in the correct selection of a control relay for a particular

application. These considerations include factors such as speed of operation, sensitivity,

and hysteresis. Although typical control relays operate in the 5 ms to 20 ms range, relays with

switching speeds as fast as 100 us are available. Reed relays which are actuated by low currents

and switch fast are suitable for controlling small currents.

As for any switch, the current through the relay contacts (unrelated to the current through the

coil) must not exceed a certain value to avoid damage. In the particular case of high-

inductance circuits such as motors other issues must be addressed. When a power source is

connected to an inductance, an input surge current which may be several times larger than the

steady current exists. When the circuit is broken, the current cannot change instantaneously,

which creates a potentially damaging spark across the separating contacts.

Consequently for relays which may be used to control inductive loads we must specify the

maximum current that may flow through the relay contacts when it actuates, the make rating; the

continuous rating; and the break rating. The make rating may be several times larger than the

continuous rating, which is itself larger than the break rating.

8.6 Derating Factors

Control relays should not be operated above rated temperature because of resulting

increased degradation and fatigue. Common practice is to

derate 20 degrees Celsius from the maximum rated

temperature limit. Relays operating at rated load are also

affected by their environment. Oil vapors may greatly

decrease the contact tip life, and dust or dirt may cause the

tips to burn before their normal life expectancy. Control

relay life cycle varies from 50,000 to over one million

cycles depending on the electrical loads of the

contacts, duty cycle, application, and the extent to which the relay is derated. When a control

Page 46Department of Electrical And Electronics Engg., Integral University, Lko

Type of load % of rated value

Resistive 75

Inductive 35

Motor 20

Filament 10

Capacitive 75

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

relay is operating at its derated value, it is controlling a lower value of current than its maximum

make and break ratings. This is often done to extend the operating life of the control relay. The

table lists the relay derating factors for typical industrial control applications.

8.7 Undesired Arcing

Without adequate contact protection, the occurrence of electric current arcing causes

significant degradation of the contacts in relays, which suffer significant and visible damage.

Every time a relay transitions either from a closed to an open state (break arc) or from an open to

a closed state (make arc & bounce arc), under load, an electrical arc can occur between the two

contact points (electrodes) of the relay. The break arc is typically more energetic and thus more

destructive.

The heat energy contained in the resulting electrical arc is very high (tens of thousands of

degrees Fahrenheit), causing the metal on the contact surfaces to melt, pool and migrate with the

current. The extremely high temperature of the arc cracks the surrounding gas molecules

creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys the

contact metal, causing some material to escape into the air as fine particulate matter. This very

activity causes the material in the contacts to degrade quickly, resulting in device failure. This

contact degradation drastically limits the overall life of a relay to a range of about 10,000 to

100,000 operations, a level far below the mechanical life of the same device, which can be in

excess of 20 million operations.[8.3]

8.8 Protective Relays

For protection of electrical apparatus and transmission lines electromechanical relays

with accurate operating characteristics were used to detect overload, short-circuits, and other

faults. While many such relays remain in use digital devices now provide equivalent protective

Function

Fig -8.10

Page 47Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

Railway Signaling

Part of a relay interlocking using UK Q-style miniature plug-in relays.

Railway signaling relays are very big and cumbersome compared to the mostly small voltages

(less than 120 V) and currents (perhaps 100 mA) that they switch. Contacts are widely spaced to

prevent dangerous flashovers and short circuits over a lifetime that may exceed fifty year.BR930

series plug-in relays are widely used on railways following British practice. These are 120 mm

high, 180 mm deep and 56 mm wide and weigh about 1400 g, and can have up to 16 separate

contacts, say 12 make and 4 break contacts.

Since rail signal circuits must be highly reliable, special techniques are used to detect and

prevent failures in the relay system. To protect against false feeds,double switching relay

contacts are often used on both the positive and negative side of a circuit, so that two false feeds

are needed to cause a false signal. Not all relay circuits can be proved so there is reliance on

construction features such as carbon to silver contacts to resist lightning induced contact welding

and to provide AC immunity.Opto-isolators are also used in some instances with railway

signalling, especially where only a single contact is to be switched.

Page 48Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER- 9

9.1 Lamp Indicator An indicator lamp is a warning device used to alert drivers of potential problems with their vehicles. Functions such as oil pressure, water temperature and the voltage are all typically wired into dashboard indicator lamps. When there is a potential problem or a dangerous reading from a engine sensor, the indicator lamp will illuminate. Many vehicles have both full-functioning gauges that show the reading of the function as well as an indicator lamp. Typically, lower-optioned and base-packaged vehicles will possess only the indicator lamp system. For every function of the automobile engine, a sensor exists to transmit readings back to the dashboard. This system of warning lights and function indicators allows the driver to have an understanding of how the engine is operating. The sensors are programed to send a signal to the indicator lamp in the case of a non-standard sensor reading. When this signal is sent, the warning light illuminates, telling the driver there is a problem. The situation can then be assessed, and the driver can determine if immediate service is warranted or if the vehicle can continue on and be serviced later. Although rare, an occasional faulty sensor can trigger a reaction from a warning  lamp. When this happens, it can typically only be detected through testing of the sensor itself. While a mechanical gauge is triggered by the actual component being measured, such as water temperature or oil pressure, the indicator lamp uses electrical senders that measure the function against a go, no-go parameter engineered into the sensor. This type of system is not as accurate as the mechanical gauge, though it is more easily understood by the average driver. Many automobile operators have no idea what their proper engine oil pressure or temperature should be before it is considered overheating. Most drivers, on the other hand, do understand that a problem exists when a warning light is illuminated on the vehicle's dashboard. Theindicator lamp typically has the engine's function displayed inside the illuminated light—when the lamp marked "Temp." is illuminated, the driver understands that the vehicle's temperature is presenting a problem. When developing the warning system, it was understood that a driver must posses some mechanical ability or knowledge to decipher the readings of the mechanical gauges. Designers reasoned, however, that everyone could understand that there was a problem with the vehicle if a bright red light suddenly came on within the dashboard.

Page 49Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

9.2 LED   24V   Indicator   Lamp

Fig -9.1

9.3 FOLED 24V Indicator Lamp: 

Color: red,green,yellow,blue,white3V--380V widely used in Household appliances and Lighting system....

Fig -8.2

LED   24V   indicator   lamp

LED 24V indicator lamp(indicator light) CE,ROHS cert panel cutout:22.3mm used for machinery equipment, machine tools

Page 50Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CHAPTER- 10

10.1 Light-Emitting Diode

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

When a light-emitting diode is forward-biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. LEDs are often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster switching. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.

Light-emitting diodes are used in applications as diverse as aviation lighting, automotive lighting, advertising, general lighting, and traffic signals. LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.

Fig -10.1

Page 51Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

10.2 Technology

The LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.

The wavelength of the light emitted, and thus its color depends on the gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radioactive transition, which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible, or near-ultraviolet light.

Fig 10.2 The inner workings of an LED

LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors.

Fig -10.3 I-V diagram for a diode

Page 52Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.

Most materials used for LED production have very high refractive indices. This means that much light will be reflected back into the material at the material/air surface interface. Thus, light extraction in LEDs is an important aspect of LED production, subject to much research and development

10.3 Types

Fig -10.4

The main types of LEDs are miniature, high power devices and custom designs such as alphanumeric or multi-color

10.4 Miniature

Fig -10.5

These are mostly single-die LEDs used as indicators, and they come in various sizes from 2 mm

to 8 mm, through-hole and surface mount packages. They usually do not use a separate heat sink.[83] Typical current ratings ranges from around 1 mA to above 20 mA. The small size sets a

Page 53Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

natural upper boundary on power consumption due to heat caused by the high current density

and need for a heat sink.

10.5 High-Power

Solid-State Lighting   and   LED Lamp

Fig -10.6 High-power light-emitting diodes (Luxeon, Lumileds)

High-power LEDs (HPLED) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit over a thousand lumens.[84][85] Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the device will fail in seconds. One HPLED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp.

Page 54Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

CONCLUSIONS

By using PLC, control of the solar photovoltaic based battery charging could be effectively implemented. The power consumption could be reduced by the connected load, which are driven by the grid supply as it uses LEDs for lighting purposes. The SPV panel size could be reduced.

Nowadays, most of the control system operation in industries used PLC as a controller to control the process. It is used for process control, transportation, domestic appliances etc. Using the PLC to control traffic light can reduce the use of hard-wired relays and other external components. PLC has an internal function such as timer and counter making it become sophisticated but simple for use. It also provides flexibility of control that based on the programming and can execute simple logic instruction which being used in ladder diagram.

An Intelligent Traffic Light using PLC to control a cross-junction has been successfully developed. The PLC program (ladder logic diagram) for implementing three mode of traffic light operation; Normal Mode, Emergency Mode and Night Mode, have been designed completely and can be operated effectively together with the model of emergency sensor (switch) for the Emergency mode and the IR sensor circuit that has been developed especially for the Night mode..

All the testing of the response to incoming emergency vehicle, instant green light during the night and the normal mode of operation has been done successfully. It was repeatedly tested to operate for continuously long time. In past period, the system had been performing well without any error. As such, it can be concluded that the system performance is reliable to response to change on time regarding on traffic volume and approaching emergency vehicle as wished-for. The change from one mode to another is achieved automatically.

Page 55Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

REFERENCES:

1. Maher, Michael J. Real-Time Control and Communications. 18th Annual ESD/SMI International Programmable Controllers Conference Proceedings, 1989, p. 431-436.

2. Kinner, Russell H., P.E. Designing Programable Controller Application Programs Using More than One Designer. 14th Annual International Programmable Controllers Conference Proceedings, 1985, p. 97-110.

3. W. Bolton, Programmable Logic Controllers, Fifth Edition, Newnes, 2009 ISBN 978-1-85617-751-1,

4. Keller, William L Jr. Grafcet, A Functional Chart for Sequential Processes, 14th Annual International Programmable Controllers Conference Proceedings, 1984, p. 71-96

.5. Gregory K. McMillan, Douglas M. Considine (ed), Process/Industrial Instruments and

Controls Handbook Fifth Edition, McGraw-Hill, 1999 ISBN 0-07-012582-1 Section 3 Controllers

6.  Mason, C. R.. "Art & Science of Protective Relaying, Chapter 2, GE Consumer &

Electrical". Retrieved October 09, 2011

.

7.  Kenneth B. Rexford and Peter R. Giuliani (2002). Electrical control for machines (6th

ed.). Cengage Learning. p. 58. ISBN 978-0-7668-6198-5.

8. "Lab Note #105 Contact Life - Unsuppressed vs. Suppressed Arcing". Arc Suppression

Technologies. April 2011. Retrieved October 09, 2011

.

9.  Zocholl, Stan (2003). AC Motor Protection. Schweitzer Engineering Laboratories,

Inc.ISBN 0972502610, 978-0972502610.10. MyOKDB Engineering; How to Configure PLC; January 2011

11. Automation Direct: What Is a PLC?

12. Texas Instruments: Programmable Logic Controller Solutions

Page 56Department of Electrical And Electronics Engg., Integral University, Lko

PLC CONTROL TRAFFIC SIGNALING SYSTEM USING SOLAR PANEL

13. -Purdue University; College of Technology; PLC Fundamentals; T.E. Kostek; August 2009

14. -Texas A&M University; Engineering Technology and Industrial Distribution; Programmable Logic Controllers

15. - "battery" (def. 4b), Merriam-Webster Online Dictionary (2009). Retrieved 25 May 2009

16. - Asimov, Isaac. [1] Retrieved 3 May 2009.

17.  "battery" (def. 6), The Random House Dictionary of the English Language, the Unabridged Edition (2nd edition), 1996 ed.

18.  Buchmann, Isidor. Can the lead–acid battery compete in modern times?. Battery

University. Retrieved 2 September 2007.

19.  What's the best battery?. Battery University. Retrieved 26 August 2008

20.  Battery Capacity – Techlib. Retrieved 10 April 2007.

21.  battery myths vs battery facts – free information to help you learn the difference. Retrieved 10 August 2007.

22. www.datatranslation.com/.../Evolution-of-virtual-Instrumentationpdf\

23. http://www.eeherald.com/section/design-guide/dgni100003.html

24. http://www.scientific-computing.com/features/features.php?feature id

25. www. wikipedia .org

26. www.google.com

27. www.nptel.iitm.ac.in/

Page 57Department of Electrical And Electronics Engg., Integral University, Lko