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INTERNSHIP REPORT

OPERATED AT: MAVOOR WATER TREATMENT PLANT, KOOLIMADU PUMPING STATION

CONTROLLED BY:

SUBMITTED BY

ARAVIND N KUMAR

BL.EN.U4EEE13006

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AMRITA SCHOOL OF ENGINEERING BENGALURU

Sl No Content Page nos 1 Acknowledgement 4 2 Introduction 5 3 Water Treatment 6­7 4 Water Treatment Process 8­14 a) Pumping 8­9

b)Aeration 10­12 c) Chemical Treatment

12

d) Chlarifloculator 12 e)Filtrations bed 13 f) Chlorination 13 g) Clear water pump house 14 5 Malfunctioning Encountered 15­16 6 Electrical Installation 17­30 7 Transformers 17 8 Main parts 1.Core 2 Constructional detail :

Shell type Core type

3.Insulator 4.Bushing 5.Types of Cooling 22 6. Protection arrangement

Bucholtz relay Silica Gel Breather Tap changer

24 25 26 26

9 Three phase transformers 27

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Construction 10

Different Windings in a three phase transformer

28­30

11 Three winding transformers 31 112 Substation Distribution & Components 31 13 What happens to incoming high voltage at

KSEB substation? 32­71

a)Lightning Arrester(L A) b) Earth Switch c) Isolator d) SF6 Circuit Breaker e)Current transformer f)Potential transformer g)Bus Bar

14 Incomer 1 Oil Circuit Breaker(OCB) 2 Over Current Relay 3 DC Battery and Charger

47­72

15 Induction Motors 55­63 16 Starters 64­72 17 Electrical Installation Images 72­80

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ACKNOWLEDGEMENT

"Gratitude is not a thing of expression; it is more a matter of feeling."

I would like to express my deep gratitude to the Chief Engineer (Northern Region) Kerala Water Authority,Malaparamba,

Superintending Engineer P.H Circle Kerala Water Authority, Malaparamba, Executive Engineer P.H.Division Kerala Water Authority, Malaparamba , Assistant Executive Engineer Head Works Sub Division Malaparamba, Assistant Engineer Augmentation and Medical College Section Mavoor, Kozhikode for permitting me to have an internship training at Mavoor treatment plant which helped me enrich my knowledge in the field of electrical installations and maintenance at a water treatment plant.

It was my privilege being trained under the guidance of Mrs. Rajalakshmi Assistant Executive Engineer(Civil) Mavoor Division, Mrs. Hemalatha Assistant Executive Engineer(Electrical) Mavoor Division. I would like to thank them for their active support and continuous guidance without which it would have been difficult for me to complete this training. They were generous enough to take time out of their regular work to lend a helping hand whenever I needed one and enabling me to complete this tenure.

I would also like to mention the generous guidance of Mr.Prabodh, Overseer Electrical Mavoor division and Mr. Abdul Salam, Electrician Mavoor division , together with all the staff at Mavoor division whose guidance helped me settle down in the organization and successfully complete the project within the relatively short time frame of 10 days, from 1st June, 2015 to 10th June, 2015. They were supporting enough to give me an opportunity to be a part of such a prestigious organization for 10 days and learn the day to day functioning. Last but not the least i would like to thank Mr.Suresh

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(Retd. CE)for guiding me the pathway towards this journey of knowledge.

INTRODUCTION

Kerala Water Authority is an autonomous authority established for the development and regulation of water supply and waste water collection and disposal in the state of Kerala, India. It is a government­owned organization and hence a monopoly in most parts of the state. The authority was founded on 1 April 1984. Kerala Water Authority is governed by a board chaired by the Chairman, usually the Principal Secretary / Secretary, Department of Water Resources, Government of Kerala. The board also includes the secretaries of the departments of finance, local self­government, the executive director of KRWSA, Managing Director, Technical member, Accounts Member of Kerala Water Authority and three members from local self­government institutions.

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Water Treatment

Water treatment plant is a very integral part of the municipal water distribution process. Water distribution to Kozhikode city starts from the Mavoor water treatment plant located on the banks of Challiyar River. The river water is not fit for drinking so there is a rising need to treat this water and make it potable before supplying for domestic use.

Chaliyar is the fourth longest river in Kerala at 169 km in length. The Chaliyar is also known as Chulika River or Beypore River as it nears the sea. Nilambur, Edavanna, Areekode, Kizhuparamba, Cheruvadi, Edavannappara, Mavoor, Peruvayal, Feroke and Beypore are some of the towns/villages situated along the banks of Chaliyar.

The Chaliyar originates in the Western Ghats range at Elambalari Hills in the Wayanad Plateau of Kerala and flows through Malappuram District for most of its length and then for around 17 km it forms the boundary between Malappuram District and Kozhikode District before entering the city of Kozhikode for its final 10 km journey and finally empties into the Lakshadweep Sea.

This river water is termed as raw water (raw material for the plant).Then it has to undergo a series of processes before it reaches

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the customer. The full responsibility of pumping is being governed by the Kerala Water Authority.

All the process emerges right near the challiyar river banks. The pumping station pumps the raw water from the river using vertical motorised pumps. The plant has a capacity to deliver 54 MLD (million litres per day) + 18 MLD.This happens in two stages Stage 1: 54 MLD

Stage 2: 18 MLD

At present the plant is supplying 34+18 MLD, the rest demand is being fed by the JICA Project at Peruvannamozhi.

Earlier till 2000 the plant had only 54 MLD capacity but in due course of time the demand also increased which led to the additional production of 18 MLD.

The whole plant is controlled by the tireless efforts of the Assistant Executive Engineer (Civil), Assistant Executive Engineer (Electrical), and Overseers, office staff, operators &Electricians.

The plant works 24 hours a day. The operators, electricians, cleaning staff are put on shifts. There are totally three shifts

Shift A: 7:00a.m. – 2:00p.m.

Shift B: 2:00p.m. – 10:00p.m.

Shift C: 10:00p.m. – 7:00a.m.

The cleaning of filter beds takes place twice a day i.e. 8:00a.m. & 3:00 p.m.There are working staff on PSC, employment & daily wages.

Most of the Motors pumps and installations at the mavoor treatment plant are more than 40 years old.

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Water Treatment Process

A)Pumping

Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low­lying land, and the removal of sewage to processing sites.

There are two pump houses at the plant. One feeds the Stage I & the other Stage II .The Stage 1 pump house has 3 motors & stage II also houses 3 motors.

Sl No.

Specification Quantity Location

1 600 HP 1 Stage 1 2 250 HP 2 Stage 1 3 150 Hp 2 Stage 2

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There motors used to pump are of two types i) Slip Ring Induction ii)Squirrel Cage induction motor.

Starters of two types are used for the stage 1 has old starters and stage 2 has soft starters.

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b)Aeration

The water is aerated first. Aeration is the intimate exposure of water

and air. It is a way of thoroughly mixing the air and water so that

various reactions can occur between the components of the air and

the components of the water.

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Aeration removes or modifies the constituents of water using two methods ­ scrubbing action and oxidation. Scrubbing action is caused by turbulence which results when the water and air mix together. The scrubbing action physically removes gases from solution in the water, allowing them to escape into the surrounding air. In the picture above, carbon dioxide and hydrogen sulphide are shown being removed by scrubbing action. Scrubbing action will remove tastes and odours from water if the problem is caused by relatively volatile gases and organic compounds. Oxidation is the other process through which aeration purifies water. Oxidation is the addition of oxygen, the removal of hydrogen,

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or the removal of electrons from an element or compound. When air is mixed with water, some impurities in the water, such as iron and manganese, become oxidized. Once oxidized, these chemicals fall out of solution and become suspended in the water. The suspended material can then be removed later in the treatment process through filtration.

c) Chemical Treatment

The aerated water is treated with alum and lime. First alum and lime are taken in separate chemical tanks and then mixed with water using motors they are stirred well and a solution is made, then through a pipe outlet they are let into the raw water outlet. Adding of lime and alum helps in coagulation as well as killing of microorganisms.

d) Chlarifloculator

Now the coagulated water with impurities needs to be sediment so it moves to an instrument called chlarifloculator,it is similar to a well first the water moves to the inner ring where motorised limbs connected to bridge rotates during this action so the impurities settle down towards the centre of the tank, and the water escapes to the other well by here 75 % of the impurities gets removed to the river via pipes to the river. If there is more precipitation of impurities in the water ,the bridge runs over the well this circular motion helps in settling down the impurities.

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e)Filtration bed

The water moves to the filtration bed, here the water is made to stand on coarse,grain,sand arrangement & this gets filtered from the bottom of the the tank,clear water moves to the chlorination unit.

At times the mud and impurities choke the bed at that particular instant a blower is used to blow the impurities out of the bed this blower is powered by a motor.

f) Chlorination

The water has to be chlorinated this is done using the chlorine from the chlorine tanks of 2000g capacity connected to the aqua chlorinator. These tanks or cylinders are manufactured at Travancore Cochin Chemicals. While these cylinders are connected to the chlorinator the connections has to be tight to prevent leakage ammonium chloride solution is used as an indicator over the rim, the white fumes indicate leakage.

g) Clear water pump house

The clear water moves to sump after chlorination and gets stored. From the sump the water is pumped by 3 motors to the overhead tank located at the hill.

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The water moves through pipe in gravity flow towards Kuttikatoor booster Station. From here the water is pumped and the supply is boosted. There are2 booster stations across the road. A newly built for stage 2 & other for stage 1.It is also accompanied by a 66 KV substation of KSEB.Now the boosted water goes to overhead tanks located at various locations off the district such as Medical College, Malaparamba and the water gets distributed through pipelines through gravity flow.

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Malfunctioning Encountered

Burning of the halum sheet in the starter due to overheating on 5/07/15.

Detection of the problem

Usually the pointer of the ammeter remains constant but as the problem arises in the circuit deflections were observed in the pointer of ammeter which was noted as an abnormality.

Then the motor was switched off & the incoming live wires from transformer were checked, then the rotor connection was checked.

When the starter was opened the problem was detected, due to the overheating of the contacts the halum sheet got burnt & a hole was observed.

Solution

First the starter was removed from the oil tank .Then a considerably big hole was observed in the halum sheet so the whole sheet had to be replaced.

The halum sheet was separated from the frame and it was sent to the industrial shop for redesign then the resistances were connected back again and put back into the oil tank.

Note: while connecting the resistances to the halum sheet considerable care has to be taken that the connections are correct. All the large turn resistances were connected at the ending slots. Care has to be taken that the resistances are to be connected in series.

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Specification of the coil

Small turns 27

Large turns 38

Causes

The instruments are old and each part has its own tensile strength. These machines are working from past 40 years and there are higher chances of sparking in the circuit.

The contacts get loosened over time as the gap widen sparks are produced and the board and associated parts get burnt up.

Burnt up starter

Replaced halum sheet

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Electrical Installation

Transformers

An A.C. device used to change high voltage low current A.C. into low voltage high current A.C. and vice­versa without changing the frequency

In brief,

1. Transfers electric power from one circuit to another

2. It does so without a change of frequency

3. It accomplishes this by electromagnetic induction

4. Where the two electric circuits are in mutual inductive influence of each other.

Transformer forms an Integral part of Electricity distribution

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Transformers providing 440V supply to stage 2 stepping down 11 KV

Name plate details of 11 KV transformer

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Main parts

1. Core Provide low reluctance flux path

Support to windings

CRGOS

Silicon steel

Based on lamination winding the transformers are of 2 types

a)Shell Type

b)Core Type

2) Constructional detail:

Shell type

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• Windings are wrapped around the center leg of a laminated core.

Core type

•Windings are wrapped around two sides of a laminated square core.

Sectional view of transformers

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CoreType

Fig1: Coil and laminations of Fig2: Various types of cores

core type transformer

Shell type

•The HV and LV windings are split into no. of sections

•Where HV winding lies between two LV windings

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•In sandwich coils leakage can be controlled

Fig: Sandwich

windings

•Cu or Al conductors

•HV­­­­Crossover,disc,multilayer

•LV­­­­Helix,disc,disc helix

3. Insulator

•Electrical isolation

•Paper, transformer oil, synthetic resin

•Major and minor

4. Bushing

To provide external electrical connection

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5. Types of Cooling

•AN

•AB

•ONAN

•OFAF

•ONWF

•OFWF

ONAN

ONAF

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OFAF

6. Protection arrangement

Protect against faults has been carried out using the following instruments

•Bucholtz relay

•Conservator breather –Silica gel

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Silica Gel Breather

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Whenever electrical power transformer is loaded, the temperature of the transformer insulating oil increases, consequently the volume of the oil is increased. As the volume of the oil is increased, the air above the oil level in conservator will come out. Again at low oil temperature; the volume of the oil is decreased, which causes the volume of the oil to be decreased which again causes air to enter into conservator tank. The natural air always consists of more or less moisture in it and this moisture can be mixed up with oil if it is allowed to enter into the transformer. The air moisture should be resisted during entering of the air into the transformer, because moisture is very harmful for transformer insulation. A silica gel breather is the most commonly used way of filtering air from moisture. Silica gel breather for transformer is connected with conservator tank by means of breathing pipe

7. Tap changer

It is used to control voltage, the two types of tap changers are

•On load tap changer

•Off load tap changer

Tap changing

•System voltage control is essential for

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1. Adjustment of consumer’s terminal voltage within prescribed limits.

2. Control of real and reactive power in the network

1.Varying secondary voltage

2.Maintaining the secondary voltage constant with a varying primary voltage

3.For providing an auxiliary secondary voltage for a special purpose

4.To provide low voltage for starting rotating machines

5.For providing neutral point

Cut view of transformer

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Transformer with conservator and breather

Three phase transformers

Construction

•A three­phase transformer is constructed by winding three single­phase transformers on a single core.

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•Three­phase transformers are connected in either wye or delta configurations

•Two or three single­phase transformers can be connected together to deliver three­phase power. This is referred to as a transformer bank.

•This allows greater maintenance and replacement options.

Different Windings in a three phase transformer

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Three winding transformers

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Substation Distribution & Components

Transformers have been setup in the plant for distribution. Being an industrial plant the various units require electricity. There is a 66 KV Kerala State Electricity Board (KSEB) substation at the KWA compound. This substation provides a 11KV feeder to the plant.

The current is generated at the Nallalam Power generation Unit of KSEB.Then this power has to be transmitted at high voltage to various substation among which one of them is 66 KV substation Ambalaparamba.Here the 66KV is stepped down to 11KV by 6.6MVA transformers. This substation provides one feeder to KWA, one to Edavannapara, one each to Chennamangalur,Mavoor.

What happens to incoming high voltage at KSEB substation?

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First the high voltage 66KV incomer approaches the substation through transmission towers, first it moves to the lightning arrester.

a)Lightning Arrester(L A)

A lightning arrester is a device used on electrical power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high­voltage terminal and a ground terminal. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices. Lightning­produced extreme voltage spikes in incoming power lines can damage electrical home appliances.

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Then it passes through the Earth Switch attached to LA

b) Earth Switch

Earthing switch connect the live parts/ line conductors and earth. This switch is normally open.

Earthing switch is used to earth the live parts during maintenance and during testing. During maintenance although circuit is open still there are some voltages on line , due to which capacitance between line and earth is charged. Before proceeding to maintenance work the voltage s discharged to earth, by closing the earth switch.

1. Maintenance Earthing Switch: These are two or three pole units with a manual operating mechanism.

2. High Speed Earthing Switch: These are operated by spring energy. Spring is charged by motor­mechanism.

Earthing switches are mounted on the base of mainly line side isolator. Earthing switches are normally vertically break switches. Earthing arms (contact arm of earthing switch) are normally aligned horizontally at off condition. during switching on operation, these earthing arms rotate and move to vertical position and make contact with earth female contacts fitted at the top of the post insulator stack of isolator at its outgoing side. The earthing arms are so interlocked with main isolator moving contacts that it can be closed only when the main contacts of isolator are in open position. Similarly the main

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isolator contacts can be closed only when the earthing arms are in open position.

Then the supply passes through an isolator

c) Isolator

Electrical Isolator or Electrical Isolation Switch

Under Electrical Transmission

Definition of Isolator

Circuit breaker always trip the circuit but open contacts of breaker cannot be visible physically from outside of the breaker and that is why it is recommended not to touch any electrical circuit just by switching off the circuit breaker. So for better safety there must be some arrangement so that one can see open condition of the section of the circuit before touching it. Isolator is a mechanical switch which isolates a part of circuit from system as when required. Electrical isolators separate a part of the system from rest for safe maintenance works.

So definition of isolator can be rewritten as Isolator is a manually operated mechanical switch which separates a part of the electrical power system normally at off load condition.

Types of Electrical Isolators

There are different types of isolators available depending upon system requirement such as 1)Double Break Isolator 2) Single Break Isolator 3) Pantograph type Isolator.

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Depending upon the position in power system, the isolators can be categorized as

1) Bus side isolator – the isolator is directly connected with main bus 2) Line side isolator – the isolator is situated at line side of any feeder 3) Transfer bus side isolator – the isolator is directly connected with transfer bus.

Constructional Features of Double Break Isolators

Lets have a discussion on constructional features of Double Break Isolators. These have three stacks of post insulators as shown in the figure. The central post insulator carries a tubular or flat male contact which can be rotated horizontally with rotation of central post insulator. This rod type contact is also called moving contact.

The female type contacts are fixed on the top of the other post insulators which fitted at both sides of the central post insulator. The female contacts are generally in the form of spring loaded figure contacts. The rotational movement of male contact causes to come itself into female contacts and isolators becomes closed. The rotation of male contact in opposite direction make to it out from female contacts and isolators becomes open. Rotation of the central post insulator is done by a driving lever mechanism at the base of the post insulator and it connected to operating handle (in case of hand operation) or motor (in case of

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motorized operation) of the isolator through a mechanical tie rod.

Constructional features of Single Break Isolators

The contact arm is divided into two parts one carries male contact and other female contact. The contact arm moves due to rotation of the post insulator upon which the contact arms are fitted. Rotation of both post insulators stacks in opposite to each other causes to close the isolator by closing the contact arm. Counter rotation of both post insulators stacks open the contact arm and isolator becomes in off condition. This motorized form of this type of isolators is generally used but emergency hand driven mechanism is also provided.

Operation of Electrical Isolator

As no arc quenching technique is provided in isolator it must be operated when there is no chance current flowing through the circuit. No live circuit should be closed or open by isolator operation. A complete live closed circuit must not be opened by isolator operation and also a live circuit must not be closed and completed by isolator operation to avoid huge arcing in between isolator contacts. That is why isolators must be open after circuit breaker is open and these must be closed before circuit breaker is closed. Isolator can be operated by hand locally as well as by motorized mechanism from remote position. Motorized operation arrangement costs more compared to hand operation; hence decision must be taken before choosing an isolator for system whether hand operated or motor

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operated economically optimum for the system. For voltages up to 145KV system hand operated isolators are used whereas for higher voltage systems like 245 KV or 420 KV and above motorized isolators are used.

Then the connection is connected in series with the SF6 circuit breaker.

d) SF6 Circuit Breaker

A circuit breaker in which the current carrying contacts operate in sulphur hexafluoride or SF6 gas is known as an SF6 circuit breaker.

SF6 has excellent insulating property. SF6 has high electro­negativity. That means it has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule, it is absorbed by that gas molecule and forms a negative ion. The attachment of electron with SF6 gas molecules may occur in two different ways,

These negative ions obviously much heavier than a free electron and therefore over all mobility of the charged particle in the SF6 gas is much less as compared other common gases. We know that mobility of charged particle is majorly responsible for conducting current

through a gas. Hence, for heavier

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and less mobile charged particles in SF6 gas, it acquires very high dielectric strength. Not only the gas has a good dielectric strength but also it has the unique property of fast recombination after the source energizing the spark is removed. The gas has also very good heat transfer property. Due to its low gaseous viscosity (because of less molecular mobility) SF6 gas can efficiently transfer heat by convection. So due to its high dielectric strength and high cooling effect SF6 gas is approximately 100 times more effective arc quenching media than air. Due to these unique properties of this gas SF6 circuit breaker is used in complete range of mediumvoltage and high voltage electrical power system. These circuit breakers are available for the voltage ranges from 33KV to 800KV and even more.

Disadvantages of SF6 CB

The SF6 gas is identified as a greenhouse gas, safety regulation are being introduced in many countries in order to prevent its release into atmosphere.

Puffer type design of SF6 CB needs a high mechanical energy which is almost five times greater than that of oil circuit breaker.

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Types of SF6 Circuit Breaker

There are mainly three types of SF6 CB depending upon the voltage level of application­

1. Single interrupter SF6 CB applied for up to 245 KV(220 KV) system.

2. Two interrupter SF6 CB applied for up to 420 KV(400 KV) system.

3. Four interrupter SF6 CB applied for up to 800 KV(715 KV) system.

Working of SF6 Circuit Breaker

The working of SF6 CB of first generation was quite simple it is some extent similar to air blast circuit breaker. Here SF6 gas was compressed and stored in a high pressure reservoir. Duringoperation of SF6 circuit breaker this highly compressed gas is released through the arc in breaker and collected to relatively low pressure reservoir and then it pumped back to the high pressure reservoir for re utilize.

The working of SF6 circuit breaker is little bit different in modern time. Innovation of puffer type design makes operation of SF6 CB much easier. In buffer type design, the arc energy is utilized to develop pressure in the arcing chamber for arc quenching.

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Here the breaker is filled with SF6 gas at rated pressure. There are two fixed contact fitted with a specific contact gap. A sliding cylinder bridges

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these to fixed contacts. The cylinder can axially slide upward and downward along the contacts. There is one stationary piston inside the cylinder which is fixed with other stationary parts of the SF6 circuit breaker, in such a way that it can not change its position during the movement of the cylinder. As the piston is fixed and cylinder is movable or sliding, the internal volume of the cylinder changes when the cylinder slides.

During opening of the breaker the cylinder moves downwards against position of the fixed piston hence the volume inside the cylinder is reduced which produces compressed SF6 gas inside the cylinder. The cylinder has numbers of side vents which were blocked by upper fixed contact body during closed position. As the cylinder move further downwards, these vent openings cross the upper fixed contact, and become unblocked and then compressed SF6 gas inside the cylinder will come out through this vents in high speed towards the arc and passes through the axial hole of the both fixed contacts. The arc is quenched during this flow of SF6 gas.

During closing of the circuit breaker, the sliding cylinder moves upwards and as the position of piston remains at fixed height, the volume of the cylinder increases which introduces low pressure inside the cylinder compared to the surrounding. Due to this pressure difference SF6 gas from surrounding will try to enter in the cylinder. The higher pressure gas will come through the axial hole of both fixed contact and enters into cylinder via vent and during this flow; the gas will quench the arc.

Then the supply passes through a current transformer

e)Current transformer

A current transformer (CT) is used for measurement of alternating electric currents. Current transformers, together with voltage (or potential) transformers (VT or PT), are known as instrument transformers. When current in a circuit is too high to apply directly to measuring instruments, a current transformer produces a reduced

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current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry.

Current transformers are basically used to take the readings of the currents entering the substation. This transformer steps down the current from 800 amps to 1 amp. This is done because we have no instrument for measuring of such a large current. The main use of this transformer is

a. Distance Protection

b. Backup Protection

c. Measurement

A current transformer is defined as an instrument transformer in which the secondary current is substantially proportional to the primary current (under normal conditions of operation) and differs in phase from it by an angle which is approximately zero for an

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appropriate direction of the connections. This highlights the accuracy requirement of the current transformer but also important is the isolating function, which means no matter what the system voltage the secondary circuit need to be insulated only for a low voltage.

The current transformer works on the principle of variable flux. In the ideal current transformer, secondary current would be exactly equal (when multiplied by the turns ratio) and opposite to the primary current. But, as in the voltage transformer, some of the primary current or the primary ampere­turns are utilized for magnetizing the core, thus leaving less than the actual primary ampere turns to be transformed into the secondary ampere­turns. This naturally introduces an error in the transformation. The error is classified into current ratio error and the phase error

Then the circuit is parallel branched into two lines which passes through an isolator, a SF6 circuit breaker, a current transformer, followed by a LA(note: always a transformer in distribution is associated with an LA before the line reaches the transformer) connecting to the transformer. There are two transformers of 60/11 ,6.3 MVA at the substation which convert 66KV to 11KV.Then it passes through a CT,VCB& an isolator. Then the distribution of 11KV through various feeders takes place.

A Potential transformer is connected in parallel to the circuit

f)Potential transformer

There are two potential transformers used in the bus connected both side of the bus. The potential transformer uses a bus isolator to protect itself. The main use of this transformer is to measure the voltage through the bus. This is done so as to get the detail information of the voltage passing through the bus to the instrument. There are two main parts in it

a. Measurement

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b. Protection

The standards define a voltage transformer as one in which the secondary voltage is substantially proportional to the primary voltage and differs in phase from it by an angle which is approximately equal to zero for an appropriate direction of the connections. This in essence means that the voltage transformer has to be as close as possible to the ideal transformer.

In an ideal transformer, the secondary voltage vector is exactly opposite and equal to the primary voltage vector when multiplied by the turn’s ratio.

In a practical transformer, errors are introduced because some current is drawn for the magnetization of the core and because of drops in the primary and secondary windings due to leakage reactance and winding resistance. One can thus talk of a voltage error which is the amount by which the voltage is less than the applied primary voltage and the phase error which is the phase angle by which the reversed secondary voltage vector is displaced from the primary voltage vector.

g)Bus Bar

The bus is a line in which the incoming feeders come into and get into the instruments for further step up or step down. The first bus is used for putting the incoming feeders in la single line. There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop. The two lines in the bus are separated by a little distance by a conductor having a connector between them. This is so that one can work at a time and the other works only if the first is having any fault.

A bus bar in electrical power distribution refers to thick strips of copper or aluminum that conduct electricity within a switchboard, distribution board, substation, or other electrical apparatus. The size

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of the bus bar is important in determining the maximum amount of current that can be safely carried. Bus bars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross sectional area ratio. The skin effect makes 50­60 Hz AC bus bars more than about 8 mm (1/3 in) thick inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow section has higher stiffness than a solid rod of equivalent current carrying capacity, which allows a greater span between bus bar supports in outdoor switchyards. A bus bar may either be supported on insulators or else insulation may completely surround it. Bus bars are protected from accidental contact either by a metal enclosure or by elevation out of normal reach.

Neutral bus bars may also be insulated. Earth bus bars are typically bolted directly onto any metal chassis of their enclosure. Bus bars may be enclosed in a metal housing, in the form of bus duct or bus way, segregated­phase bus, or isolated­phase bus.

66KV KSEB Substation

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The substation is under the jurisdiction of KSEB.The KEY diagram of the substation is as given below.

The 11 KV feeder enters the plant through poles into a switchyard where the protection is provide by the airbrake switch to a current transformer attached to a metre which displays the no of units consumed based on which the current consumption is calculated. The three phase supply enters the Incomer control panel room. This room

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is located near the pump house. This room receives feeder of 11KV from KSEB.This room contains 46 year old analog control panel, from where the supply is separated to different lines i.e. supply to Ram water 1(pump house 1),Raw water 2,Clear water pump house,contol panel room(newly constructed).So these line move through the electric cables beneath the ground towards distribution transformers.

There are 6 distribution transformers in the plant.

Sl No Location

No of transformers

1 Raw water I 1 2 Raw water II 1(working)

1(not working) 3 Control Room newly constructed 1(supply to stage II)

1(supply to stage I) 4 Clear pump house 1 Incommer Room

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Incommer at the old contol panel room

CTPT­80/5 CTR­100/5 Incoming supply 11KV Current 56A.

The specifications of the incomer are as follows

1 Oil Circuit Breaker(OCB)

Mineral oil has better insulating property than air. In oil circuit breaker the fixed contact and moving contact are immerged inside the insulating oil. Whenever there is a separation of current carrying contacts in the oil, the arc in circuit breaker is initialized at the moment of separation of contacts, and due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately creates a hydrogen bubble around the arc. This highly compressed gas bubble around the arc prevents re­striking of the arc after current reaches zero crossing of the cycle. The oil circuit breaker is the one of the oldest type of circuit breakers.

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When the current carrying contacts in the oil are separated an arc is established in between the separated contacts.

Operation

Actually, when separation of contacts has just started, distance between the current contacts is small as a result the voltage gradient between contacts becomes high. This high voltage gradient between the contacts ionized the oil and consequently initiates arcing between the contacts. This arc will produce a large amount of heat in surrounding oil and vaporizes the oil and decomposes the oil in mostly hydrogen and a small amount of methane, ethylene and acetylene. The hydrogen gas cannot remain in molecular form and its is broken into its atomic form releasing lot of heat. The arc temperature may reach up to 5000° K. Due to this high temperature the gas is liberated surround the arc very rapidly and forms an excessively fast growing gas bubble around the arc. It is found that the mixture of gases occupies a volume about one thousand times that of the oil decomposed. From this figure we can assume how fast the gas bubble around the arc will grow in size. If this growing gas bubble around the arc is compressed by any means then rate of de – ionization process of ionized gaseous media in between the contacts will accelerate which rapidly increase the dielectric strength between the contacts and consequently the arc will be quenched at zero crossing of the current cycle. This is the basic operation of oil circuit breaker. In addition to that cooling effect of hydrogen gas surround the arc path also helps, the quick arc quenching in oil circuit breaker.

Now at present the role of the oil circuit breakers is being carried out by the vacuum circuit breakers (VCBs).

Types of Oil Circuit Breakers

Bulk Oil Circuit Breaker or BOCB

Arc Quenching in Bulk Oil Circuit Breaker

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Bulk oil circuit breaker or BOCB is such types of circuit breakers where oil is used as arc quenching media as well as insulating media between current carrying contacts and earthed parts of the breaker. The oil used here is same as transformer insulating oil.

Minimum Oil Circuit Breaker or MOCB

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These types of circuit breakers utilize oil as the interrupting media. However, unlike bulk oil circuit breaker, a minimum oil circuit breaker places the interrupting unit in insulating chamber at live potential. The insulating oil is available only in interrupting chamber. The features of designing MOCB are to reduce requirement of oil, and hence these breaker are called minimum oil circuit breaker.

Working Principle or Arc Quenching in Minimum Oil Circuit Breaker

Working Principle of minimum oil circuit breaker or arc quenching in minimum oil circuit breaker is described below. In a minimum oil circuit breaker, the arc drawn across the current carrying contacts is contained inside the arcing chamber.

Hence the hydrogen bubble formed by the vaporized oil is trapped inside the chamber. As the contacts continue to move, after its certain travel an exit vent becomes available for exhausting the trapped hydrogen gas. There are two different types of arcing chamber is available in terms of venting are provided in the arcing chambers. One is axial venting and other is radial venting. In axial venting, gases (mostly Hydrogen), produced due to vaporization of oil and decomposition of oil during arc, will sweep the arc in axial or longitudinal direction.

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Working principle Minimum Oil Circuit Breaker with axial venting arc chamber.

The moving contact has just been separated and arc is initiated in MOCB.

The ionized gas around the arc sweep away through upper vent and cold oil enters into the arcing chamber through the lower vent in axial direction as soon as the moving contact tip crosses the lower vent opening and final arc quenching in minimum oil circuit breaker occurs.

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The cold oil occupies the gap between fixed contact and moving contact and the minimum oil circuit breaker finally comes into open position.

Whereas in case of radial venting or cross blast, the gases (mostly Hydrogen) sweep the arc in radial or transverse direction.

The axial venting generates high gas pressure and hence has high dielectric strength, so it is mainly used for interrupting low current at high voltage.

On the other hand radial venting produces relatively low gas pressure and hence low dielectric strength so it can be used for low voltage and high current interruption. Many times the combination of both is used

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in minimum oil circuit breaker so that the chamber is equally efficient to interrupt low current as well as high current. These types of circuit breaker are available up to 8000 MVA at 245 KV.

It contains two relays at the top for protection

Over Current Relays 2 Nos

Earth Fault Relay ­1 No

2 Over Current Relay

The over current relay responds to a magnitude of current above a specified value. There are four basic types of construction: They are plunger, rotating disc, static, and microprocessor type. In the plunger type, a plunger is moved by magnetic attraction when the current exceeds a specified value. In the rotating induction­disc type, which is a motor, the disc rotates by electromagnetic induction when the current exceeds a specified value.

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Static types convert the current to a proportional D.C mill volt signal and apply it to a level detector with voltage or contact output. Such relays can be designed to have various current­versus­time operating characteristics. In a special type of rotating induction­disc relay, called the voltage restrained over current relay. The magnitude of voltage restrains the operation of the disc until the magnitude of the voltage drops below a threshold value. Static over current relays are equipped with multiple curve characteristics and can duplicate almost any shape of electromechanical relay curve. Microprocessor relays convert the current to a digital signal. The digital signal can then be compared to the setting values input into the relay. With the microprocessor relay, various curves or multiple time­delay settings can be input to set the relay operation. Some relays allow the user to define the curve with points or calculations to determine the output characteristics.

3. DC Battery and Charger

DC battery chargers at the control panel room for operating protective relays.

All but the smallest substations include auxiliary power supplies. AC power is required for substation building small power, lighting, heating and ventilation, some communications equipment, switchgear

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operating mechanisms, anti­condensation heaters and motors. DC power is used to feed essential services such as circuit breaker trip coils and associated relays, supervisory control and data acquisition (SCADA) and communications equipment. This describes how these auxiliary supplies are derived and explains how to specify such equipment. It has Single 100% battery and 100% charger, Low capital cost, No standby DC System outage for maintenance. Need to isolate battery/charger combination from load under boost charge conditions in order to prevent high boost voltages.

Induction Motors

One of the most common electrical motor used in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than synchronous speed. In this, we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depend upon the input supply ­ single phase induction motor and three phase induction motor. Single phase induction motor is not a self starting motor which we will discuss later and three phase induction motor is a self­starting motor. Now in general we need to give two supply i.e. double excitation to make a machine to rotate. For example if we consider aDC motor, we will give one supply to the stator and another to the rotor through brush arrangement.

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Working Principle of Induction Motor

But in induction motor we give only one supply, so it is really interesting to know that how it works. It is very simple, from the name itself we can understand that there is induction process occurred. Actually when we are giving the supply to the stator winding, flux will generate in the coil due to flow of current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday's law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type.

Types Induction Motor

SINGLE PHASE INDUCTION MOTOR

Split phase induction motor

Capacitor start induction motor

Capacitor start capacitor run induction motor

Shaded pole induction motor

THREE PHASE INDUCTION MOTOR

a)Squirrel cage induction motor

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b) Slip ring induction motor

Construction of Three Phase Induction Motor

Under Induction Motor

The three phase induction motor is the most widely used electrical motor. Almost 80% of the mechanical power used by industries is provided by three phase induction motors because of its simple and rugged construction, low cost, good operating characteristics, absence of commutator and good speed regulation. In three phase induction motor the power is transferred from stator to rotor winding through induction. The Induction motor is also called asynchronous motor as it runs at a speed other than the synchronous speed.

Like any other electrical motor induction motor also have two main parts namely rotor and stator

1. Stator: As its name indicates stator is a stationary part of induction motor. A stator winding is placed in the stator of induction motor and the three phase supply is given to it.

2. Rotor: The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft.

The rotor of the three phase induction motor are further classified as

1. Squirrel cage rotor,

2. Slip ring rotor or wound rotor or phase wound rotor.

Depending upon the type of rotor construction used the three phase induction motor are classified as:

1. Squirrel cage induction motor,

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2. Slip ring induction motor or wound induction motor or phase wound induction motor.

The construction of stator for both the kinds of three phase induction motor remains the same and is discussed in brief in next paragraph.

The other parts, which are required to complete the induction motor, are:

1. Shaft for transmitting the torque to the load. This shaft is made up of steel.

2. Bearings for supporting the rotating shaft.

3. One of the problems with electrical motor is the production of heat during its rotation. In order to overcome this problem we need fan for cooling.

4. For receiving external electrical connection Terminal box is needed.

5. There is a small distance between rotor and stator which usually varies from 0.4 mm to 4 mm. Such a distance is called air gap.

Stator of Three Phase Induction Motor

The stator of the three phase induction motor consists of three main parts :

1. Stator frame,

2. Stator core,

3. Stator winding or field winding.

Stator Frame

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It is the outer most part of the three phase induction motor. Its main function is to support the stator core and the field winding. It acts as a covering and it provide protection and mechanical strength to all the inner parts of the induction motor. The frame is either made up of die cast or fabricated steel. The frame of three phase induction motor should be very strong and rigid as the air gap length of three phase induction motor is very small, otherwise rotor will not remain concentric with stator, which will give rise to unbalanced magnetic pull.

Stator Core

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The main function of the stator core is to carry the alternating flux. In order to reduce the eddy current loss, the stator core is laminated. These laminated types of structure are made up of stamping which is about 0.4 to 0.5 mm thick. All the stamping are stamped together to form stator core, which is then housed in stator frame. The stamping is generally made up of silicon steel, which helps to reduce the hysteresis loss occurring in motor.

Stator Winding or Field Winding

The slots on the periphery of stator core of the three phase induction motor carries three phase windings. This three phase winding is supplied by three phase ac supply. The three phases of the winding are connected either in star or delta depending upon which type of starting method is used. The squirrel cage motor is mostly started by star – delta stater and hence the stator of squirrel cage motor is delta connected. The slip ring three phase induction motor are started by inserting resistances so, the stator winding of slip ring induction motor can be connected either in star or delta. The winding wound on the stator of three phase induction motor is also called field winding and when this winding is excited by three phase ac supply it produces

a rotating magnetic field.

Types of Three Phase Induction Motor

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1. Squirrel cage three phase induction motor: The rotor of the squirrel cage three phase induction motor is cylindrical in shape and have slots on its periphery. The slots are not made parallel to each other but are bit skewed (skewing is not shown in the figure of squirrel cadge rotor beside) as the skewing prevents magnetic locking of stator and rotor teeth and makes the working of motor more smooth and quieter. The squirrel cage rotor consists of aluminium, brass or copper bars (copper bras rotor is shown in the figure beside). These aluminium, brass or copper bars are called rotor conductors and are placed in the slots on the periphery of the rotor. The rotor conductors are permanently shorted by the copper or aluminium rings called the end rings. In order to provide mechanical strength these rotor conductor are braced to the end ring and hence form a complete closed circuit resembling like a cage and hence got its name as "squirrel cage induction motor". The squirrel cage rotor winding is made symmetrical. As the bars are permanently shorted by end rings, the rotor resistance is very small and it is not possible to add external resistance as the bars are permanently shorted. The absence of slip ring and brushes make the construction of Squirrel cage three phase induction motor very simple and robust and hence widely used three phase induction motor. These motors have the advantage of adapting any number of pole pairs. The below diagram shows squirrel cage induction rotor having aluminium bars short circuit by aluminium end rings.

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Advantages of squirrel cage induction rotor­

1. Its construction is very simple and rugged.

2. As there are no brushes and slip ring, these motors requires less maintenance.

Applications: Squirrel cage induction motor is used in lathes, drilling machine, fan, blower printing machines etc

2. Slip ring or wound three phase induction motor : In this type of three phase induction motor the rotor is wound for the same number of poles as that of stator but it has less number of slots and has less turns per phase of a heavier conductor. The rotor also carries star or delta winding similar to that of stator winding. The rotor consists of numbers of slots and rotor winding are placed inside these slots. The three end terminals are connected together to form star connection. As its name indicates three phase slip ring induction motor consists of slip rings connected on same shaft as that of rotor. The three ends of three phase windings are permanently connected to these slip rings. The external resistance can be easily connected through the brushes and slip rings and hence used for speed control and improving the starting torque of three phase induction motor. The brushes are used to carry current to and from the rotor winding. These brushes are further connected to three phase star connected resistances. At starting, the resistance are connected in rotor circuit and is gradually cut out as the rotor pick up its

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speed. When the motor is running the slip ring are shorted by connecting a metal collar, which connect all slip ring together and the brushes are also removed. This reduces wear and tear of the brushes. Due to presence of slip rings and brushes the rotor construction becomes somewhat complicated therefore it is less used as compare to squirrel cage induction motor.

Advantages of slip ring induction motor ­

1. It has high starting torque and low starting current.

2. Possibility of adding additional resistance to control speed.

Application:

Slip ring induction motor are used where high starting torque is required i.e. in hoists, cranes, elevator etc.

Difference between Slip Ring and Squirrel Cage Induction Motor

Slip ring or phase wound Induction motor Squirrel cage induction motor

Construction is complicated due to presence of slip ring and brushes Construction is very simple

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The rotor winding is similar to the stator winding

The rotor consists of rotor bars which are permanently shorted with the help of end rings

We can easily add rotor resistance by using slip ring and brushes

Since the rotor bars are permanently shorted, its not possible to add external resistance

Due to presence of external resistance high starting torque can be obtained

Staring torque is low and cannot be improved

Slip ring and brushes are present Slip ring and brushes are absent

Frequent maintenance is required due to presence of brushes Less maintenance is required

The construction is complicated and the presence of brushes and slip ring makes the motor more costly

The construction is simple and robust and it is cheap as compared to slip ring induction motor

This motor is rarely used only 10 % industry uses slip ring induction motor

Due to its simple construction and low cost. The squirrel cage induction motor is widely used

Rotor copper losses are high and hence less efficiency

Less rotor copper losses and hence high efficiency

Speed control by rotor resistance method is possible

Speed control by rotor resistance method is not possible

Slip ring induction motor are used where high starting torque is required i.e in hoists, cranes, elevator etc

Squirrel cage induction motor is used in lathes, drilling machine, fan, blower printing machines etc

An induction motor is similar to a poly­phase transformer whose secondary is short circuited. Thus, at normal supply voltage, like in

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transformers, the initial current taken by the primary is very large for a short while. (Unlike in DC motor, large current at starting is due to back emf.) If an induction motor is directly switched on from supply, it takes 5 to 7 times its full load current, and develops a torque which is only 1.5 to 2.5 times the full load torque. This large starting current will produce large voltage drop in line, which may affect the operation of other devices connected in the line. From the torque equation of induction motor, it can be seen that starting torque can be improved by increasing the rotor resistance. Rotor resistance can be easily increased in case of slip­ring induction motors, but for squirrel cage motorsstarting current can be controlled by applying reduced stator voltage. Methods of starting induction motor are described below.

Starting Of Squirrel Cage Motors

Adding external resistance to the rotor of a squirrel cage motor is not possible. Starting in­rush current in squirrel cage motors is controlled by applying reduced voltage to the stator. For this purpose, following methods are used:

1. By using primary resistors or reactors

2. Autotransformer

3. Star­delta switches

1. Using primary resistors:

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Obviously, purpose of primary resistors is to drop some voltage, consequently applying reduced voltage to the stator. Hence, the initial current will be reduced. Here, one thing should be noted that, current varies directly to thee voltage whereas torque varies as square of the applied voltage. That is, if the applied voltage is reduced by 50% :­ current will be reduced by 50% but the torque will be reduced by 25%. 2.Auto­transformers:

Auto­transformer

Auto­transformers are also known as auto­starters or compensators. They can be used for both star connected or delta connected squirrel cage motors. The internal connections of an auto­starter is as shown in the figure. At starting, switch is at "start" position, and reduced voltage is applied across the stator. When the motor gathers speed, say upto 80% of its rated speed, auto­transformer automatically disconnects from the circuit as the switch goes to "run" position. The switch changing the connection from start to run position may be air­break (small motors) or oil­immersed (large motors). There are

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also provisions for no­voltage and over­load, with time delay circuits. Many auto­transformers also come with options of reduced voltage drop of 80%, 65% and 50% of the line voltage. 3.Star­delta starter: This method is used in the motors, which are designed to run on delta connected stator. A two way switch is used to connect the stator winding in star while starting and in delta while running with normal speed. When stator winding is star connected, voltage over each phase in motor will be reduced by a factor 1/(sqrt. 3) that it would be for delta connected winding. The starting torque will 1/3 to that of it will be for delta connected winding. Hence a star­delta starter is equivalent to an auto­transformer of ratio 1/(sqrt. 3) or 58% reduced voltage.

Starting Of Slip­Ring Motors

Slip­ring motors are started with full line voltage, as external resistance can be easily added in the rotor circuit with the help of slip­rings. A star connected rheostat is connected in series with rotor via slip­rings as shown in the fig. Introducing resistance in rotor current will decrease the starting current in rotor (and hence in stator). Also, it improves power factor and the torque is increased. The connected rheostat may be hand­operated or automatic. As, introduction of additional resistance in rotor improves the starting torque, slip­ring motors can be started on load.

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The external resistance introduced is only for starting purposes, and is gradually cut out as the motor gathers the speed.

How does soft start work?

A soft starter is any device which controls the acceleration of an electric motor by means of controlling the applied voltage. An Induction motor has the ability to self start owing to the interaction between the rotating magnetic field flux and the rotor winding flux, causing a high rotor current as torque is increased. As a result the stator draws high current and by the time the motor reaches to full speed, a large amount of current (greater than the rated current) is drawn and this can cause heating up of the motor, eventually damaging it. To prevent this, motor starters are needed. Motor starting can be in 3 ways:

1. Applying full load voltage at intervals of time: Direct On Line Starting

2. Applying reduced voltage gradually: Star Delta Starter and Soft starter

3. Applying part winding starting: Autotransformer starter

Soft Start Definition

In technical terms, a soft starter is any device which reduces the torque applied to the electric motor. It generally consists of solid state devices like thyristors to control the application of supply voltage to the motor. The starter works on the fact that the torque is proportional to the square of the starting current, which in turn is proportional to the applied voltage. Thus the torque and the current can be adjusted by reducing the voltage at the time of starting the motor.

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There can be two types of control using soft starter: 1) Open Control: A start voltage is applied with time, irrespective of the current drawn or the speed of the motor. For each phase two SCRs are connected back to back and the SCRs are conducted

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initially at a delay of 180 degrees during the respective half wave cycles (for which each SCR conducts). This delay is reduced gradually with time until the applied voltage ramps up to the full supply voltage. This is also known as Time Voltage Ramp System. This method is not relevant as it doesn’t actually control the motor acceleration. 2) Closed Loop Control: Any of the motor output characteristics like the current drawn or the speed is monitored and the starting voltage is modified accordingly to get the required response. The current in each phase is monitored and if it exceeds a certain set point, the time voltage ramp is halted. Thus basic principle of soft starter is by controlling the conduction angle of the SCRs the application of supply voltage can be controlled. Components of a basic soft starter

Power switches like SCRs which need to be phase controlled such that they are applied for each part of the cycle. For a 3 phase motor, two SCRs are connected back to back for each phase. The switching devices need to be rated at least three times more than the line voltage.

Control Logic using PID controllers or Microcontrollers or any other logic to control the application of gate voltage to the SCR, i.e. to control the firing angle of SCRs in order to make the SCR conduct at the required part of the supply voltage cycle.

Working Example of Electronic Soft Start System for 3 phase induction motor The system consists of the following components:

Two back to back SCRs for each phase, i.e. 6 SCRs in total.

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Control Logic circuitry in form of two comparators­ LM324 and LM339 to produce the level and the ramp voltage and an opto­isolator to control the application of gate voltage to the each SCR in each phase.

A power supply circuitry to provide the required dc supply voltage.

The level voltage is generated using the comparator LM324 whose inverting terminal is fed using a fixed voltage source and the non inverting terminal is fed through a capacitor connected to the collector of an NPN transistor. The charging and discharging of the capacitor causes the output of the comparator to change accordingly and the voltage level to change from high to low. This output level voltage is applied to the non inverting terminal of another comparator LM339 whose inverting terminal is fed using a ramp voltage. This ramp voltage is produced using another comparator LM339 which compares the pulsating DC voltage applied at its inverting terminal to the pure DC voltage at its non inverting terminal and generates a zero voltage reference signal which is converted to a ramp signal by the charging and discharging of a electrolyte capacitor.

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The 3rd comparator LM339 produces a High pulse width signal for every high level voltage, which decreases gradually as the level voltage reduces. This signal is inverted and applied to the Opto isolator, which provides gate pulses to the SCRs. As voltage level falls, the pulse width of the Opto isolator increases and more the pulse width, lesser is the delay and gradually the SCR is triggered without any delay. Thus by controlling the duration between the pulses or delay between applications of pulses, the firing angle of SCR is controlled and the application of supply current is controlled, thus controlling the motor output torque. The whole process is actually an open loop control system where the time of application of gate triggering pulses to each SCR is controlled based on the how earlier the ramp voltage decreases from the level voltage.

Advantages of Soft Start

Now that we have learnt about how an electronic soft start system works, let us recollect few reasons why it is preferred over other methods.

Improved Efficiency: The efficiency of soft starter system using solid state switches is more owing to the low on state voltage.

Controlled startup: The starting current can be controlled smoothly by easily altering the starting voltage and this ensures smooth starting of the motor without any jerks.

Controlled acceleration: Motor acceleration is controlled smoothly.

Low Cost and size: This is ensured with the use of solid state switches.

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The problem with the soft starter is the companies that make the soft starter hoarding the parts, when the soft starter fails the company wants the customer to send the whole soft starter in for repairs vice allowing the customer to rebuild on site..if you have 30 soft starters in a particular building or a ship per say in 1­2 years all of those soft starters should need to go back to the company just to replace an SCR, how about building a better soft starter that could possibly last 4­6 years or allow the customer to make repairs on site.The loud clunk coming from the soft starter is present in over 60% of the soft starter upon motor start up.

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Electrical Installations with images

Blower at the filter bed attached to motor

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Panel control

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Flowmeter­Used to check the amount of eater flowing new installation at the pump house it gives digital output based on the sensor signals and the readings integrated through SCADA can be monitored from remote locations.

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In house Transformers

Incommer Room

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Relays in the control panel

CT ratio 60/5

11KV feeder

240MM^2 PILC CABLE

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Energy meter Getting supply from Current transformer

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New Installations at the plant

New control boards

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