Summary Nr

Event Date

Report ID Fat SIC Event

Description

41 201085701

07/14/2004

0950625

1731

Employee'S Fingers Crushed By Jaws Of Crimper Head

42 201058633

04/19/2004

0950642

3711

Employee Is Injured In Fall From Hydraulic Press

43 200822450

03/17/2004

0521400

3469

Employee Injured When Operating A Hydraulic Press

44 201165941

03/17/2004

0950641

3492

Employee'S Fingers Partially Amputated In Press

45 202086609

12/01/2003

0524700

3493

Employee'S Arm Is Caught In Hydraulic Press

46 201691037

11/21/2003

0950662

3444

Employee Thumb Is Amputated After Being Crushed

47 201157880

07/12/2003

0950633

3499

Employee Amputates Fingers When Caught In Hydraulic Press

48 201157807

07/07/2003

0950633

7629

Employee Injures Fingers While Operating Hydraulic Press

49 201157682

06/03/2003

0950633

3089

Employee'S Hand Crushed In Hydraulic Press

50 202086484

04/25/2003

0524700

3714

Employee Injured When Hand Lacerated By Hydraulic Press

51 201690849

02/20/2003

0950662

3443

Employee'S Fingers Amputated While Setting Up A Press

52 202339404

11/22/2002

0352430

3544 Employee Suffers Finger Amputation

53 171135080

09/09/2002

1055360

5521

Employee'S Fingers Are Crushed In Hydraulic Press Brake

54 200800712

09/03/2002

0523300

3585

Employee'S Fingers Are Amputated In Press Brake

55 200772200

08/20/2002

0134000

3499

Employee'S Thumb Is Amputated In Press

56 200821841

07/08/2002

0521400

3363

Employee Ampuataes Arm In Hydraulic Press Accident

57 201796018

06/07/2002

0950644

3398

Employee'S Finger Amputated By Hydraulic Press

58 201795614

03/25/2002

0950644

3089

Employee Struck In The Head By Flying Object

59 201503273

03/06/2002

0950614

3444

Hand Crushed In Hydraulic Shearing Press

60 201056272

12/15/2001

0950642

3444

Employee Injured When Right Fingertip Is Caught By Press

Safety regulators are investigating the death of a 38-year-old worker after a hydraulic press accident yesterday in Oakford, south of Perth.

According to a WorkSafe, the man was working with a manual hydraulic press in the workshop

when a metal cylinder shattered, striking him in the chest.

Inspectors travelled to the site soon after the incident to interview witnesses and investigate the

circumstances.

A WorkSafe WA spokesperson told Safe to Work that the investigation will continue, and it still

too early in the process to determine the exact circumstances of the incident.

The hydraulic press will be examined thoroughly to find out what went wrong and what other

factors may have contributed to the worker’s death.

WorkSafe WA Commissioner Lex McCulloch said any work-related death was a tragedy, and

relayed his sincere condolences to the man’s family.

In a statement, the safety regulator reiterated that its mission is to thoroughly investigate serious

work-related injuries and deaths in WA with a view to preventing future incidents of a similar

nature.

ABC Radio Australia 's news site  and ABC News online also ran stories about this

incident.

ACCIDENT INVOLVING HYDRAULIC PILING MACHINE

Photo 1: Hydraulic Piling Machine at accident sceneAn accident took place on 20th May 2008 at around 8:00pm when piling work was being carried out. The accident occurred AT a construction site which is situated next to the public parking area. The Hydraulic Pile Jacking Machine (model YZY 240) was equipped with a crane and a hydraulic piling press. Investigation revealed that the machine is located about 2 meters from the site hoarding which is adjacent to the public parking area. During the accident,

one of the concrete piles which weigh about 2.8 tonnes with the dimensions of 12 meters (Length) x 300 mm (Width) X 300mm (Thickness) fell and crushed two vehicles in the parking area. The accident happened due to the failure of the lifting lug and sling which were used to tie the concrete pile.

Recommendations:

Hazard identification, risk assessment and risk control (HIRARC) shall be implemented before any piling activity.

Adequate lighting is crucial if the piling activity is carried out at night. Piling activity should only be done during broad daylight.

Safe lifting procedure should be updated. Use of spreader device is necessary to ensure the stability of the 12 meters length concrete pile during lifting. Use of

spreader will ease the process and prevent the concrete pile from colliding with the crane boom section due to limited clearance between pile and crane boom.

Routine inspection of lifting gear should be carried out prior to any lifting activity to check for defects. Furthermore, all attachments involving sling or shackle with lifting lug must be done correctly to ensure safe lifting.

Good communication between crane operator and signalman is vital during such piling activity:Signalman appointed should be properly trained to provide clear two-way communication and correct information to the crane operator

Lifting and piling should be supervised and adequate number of workers should be provided.

References:

RIKEN OPTECH

RIKEN OPTECH - Safety Light curtain sensor for Press machine, Area safety sensor for Press Machine, Safety of Stamping machine.The Safety and Automation Systems of RIKEN OPTECH is involved in

developing and marketing equipment for use in stamping operations, such as safety equipment for preventing accidents, malfunction detectors and load monitor for maintaining quality control. -www.tjsolution.com

RIKEN Optech - Safety Device product lineup

1. Riken Optech - SE2 Safety Light curtain sensor (Reflection Type)

Feature of SEII

1. Reflection type, light can be adjusted easily. 2. Special filter protects device from dirt and fog. 

3. Tolerant of ambient light. 4. Built-in self-check circuit automatically checks the electronic circuit to monitor the safety of operation. 

5. It is designed to be vibration resistant so as to mitigate the influence from the action of the press machine.

All Riken Optech SE2 model : SEII-24 (H.200 mm.), SEII-32 (H.280 mm.), SEII-40 (H.360 mm.), SEII-48 (H.480 mm.)

2. Riken Optech - RPH4 Safety Light curtain sensor (Direct Protection Type)

Spec. of Press machine that can apply this model(RPH4) to use

Type of the machine a press machine ---> having an emergency stop and nor-repeat mechanism. Emergency stop time ---> 300ms or less 

Safety distance ---> (Response Time + emergency stop time of the press machine) x 1.6 or more Pressure Capacity ---> (50,000kN or less) 

Scope of the die size ---> within the width of the bolster -www.tjsolution.com

Feature of RPH4

1. It will turn off the output through the action of a self-diagnosis function. Fail-safe design is thoroughly pursued. 

2. When an abnormal incident occurs, the press machine will be stopped instantly! We have created a system that provides a high level of safety. 

3. The goal of creating a safety system supported by technology has been realized. 4. This safety equipment is the result of using the highest level of safety design expertise and FMEA analysis. 

5. The system complies with global standards for safety sensors. 6. The Type 4 Sensor conforms to the IEC Standards and EN Standards. 

7. Various safety functions are built in to the sensor. 8. The introduction of an LED bar supports ease of use. -www.tjsolution.com

9. The compact size is perfect for installation in dangerous areas. 10. The detection width and the sensor length are identical thus keeping the space required to the minimum.

All Riken Optech RPH4 model : (RPH425-n ; n=13~120 <no.of beam>), (RPH414-n ; n=21~125<no.of beam>)

3. Riken Optech - RBS(PSDI) Presence Sensing Device Initiaion System. Photo-electric safety device withactivation function will improve production efficiency and reduce production fatigue.

Riken Optech - RBS(PSDI) Function

- Optional functions for RBS type devices designed to elevate labor efficiency and safety also have acquired the official approval of the Ministry of Health, Labor and Welfare of Japan.

1. Movable GuardsThe movable guard not only will reduce the time required to exchange dies, confirm the safety, and resume

formal work but also will improve the overall safety of the press machine. 2. Three-Optical-Axes Floating Blanking Function is available.

This is an optional item for enhancing the function of the light curtain used for processing long strip work-pieces with pass the sensing field of the light curtain. Press machines will not be stopped even when up to three

optical axes are interrupted. When four optical axes are interrupted, the press machine will be forcibly stopped.

Spec. of Press machine that can apply this model(RBS) to use -www.tjsolution.com

- Press machines with an emergency stop mechanism and an anti-reactivation mechanism that can accept a safety light curtain. 

- Height of the bolster is 75mm or more. - Depth of the bolster is 1,000mm or less. - Length of the stroke is 600mm or less. 

- Set angle of overrun is within 15 degrees. (excluding hydraulic press machines) - Emergency stopping time is 300ms or less. 

- Pressure capacity is 5,000t or less.

4. Riken Optech - Safety Laser Scanner sensor for safety area (RS-4)

Riken Optech model RS-4 Laser scanner safety sensor, it performs continuous scanning over the wide range of 190 degrees covering the entire operating range and if an object or person happens to enter the protective

area, it outputs a stop signal. The specifications of this equipment conform to the Type 3, IEC61496-3 Standards. Therefore, it is best suited for safety-related uses. The area sensor with high sensitivity and high

resolution has wide-ranging applications. RS-4 is best suited for the protection of humans from mobile systems and static systems requiring safety measures up to the extent of the EN954-1 Type 3 Standards.

- Four Protection Areas are ProgrammableAreas can randomly be set with the radius of 4 meters for the protection of humans or for an area with the

radius of 15 meters for the detection of objects.

- Setting up the Protective Area. There are two ways to set the protective area.

1. Directly inputting the data from a PCAs a rectangular area by using numerical data. 

2. Learning functionsMake an outline of a protective area out of cardboard and place it before this equipment. The read-in process starts when the learning function command is executed. The device will scan the outline of the cardboard. A

new protective area will be decided based on the data acquired. It also has a function to store the parameters into the database.

- Protection by PasswordInput process can be restricted to specific passwords so that it runs only when the specified passwords are

inputted. Passwords corresponding to the levels of importance and safety can be set to the equipment. -www.tjsolution.com

1. Small BodyDimensions 140 x 155 x 135 (W x H x D) in mm

4. Number of detection zones: 4 (changeover via switch inputs)

2. High Speed Scanning / High resolution- Scanning rate: 25 scans/s or 40 ms/scan

- Angle range: 190 degrees(Max.)- Angle resolution: 0.36 degrees

5. The protection area is set by a personal computer.

3. With 2 different protection areas are programmable at the same time.- Caution Area: 4m

- Warning Area: 15m

6. EN regulation- IEC 61496-1 type 3- IEC 61496-3 type 3

For more information about "RIKEN Optech" please contact our sale engineer.

Machine pressFrom Wikipedia, the free encyclopedia

This article's tone or style may not reflect the encyclopedic tone used on Wikipedia. See Wikipedia's guide to writing better articles for suggestions. (February

2013)

Manual goldsmith press

Power press with a fixed barrier guard

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged

and removed. (November 2009)

A forming press, commonly shortened to press, is a machine tool that changes the shape of a workpiece by

the application of pressure.[1]Presses can be classified according to

their mechanism: hydraulic, mechanical, pneumatic;

their function: forging presses, stamping presses, press brakes, punch press, etc.

their structure, e.g. Knuckle-joint press, screw press

their controllability: conventional vs. servo-presses

Contents

[hide]

1   An example of peculiar press structure: shop press

2   Some examples of presses by application

3   An example of peculiar press control: servo-press

4   A table of comparison among presses

5   History

6   Safety

7   References

8   External links

An example of peculiar press structure: shop press[edit]

A simple frame, fabricated from steel, containing a bottle jack or simple hydraulic cylinder. Good for general-

purpose work in the auto mechanic shop, machine shop, garage or basement shops, etc. Typically 1 to 30 tons

of pressure, depending on size and expense. Classed with engine hoists andengine stands in many tool

catalogs.

Some examples of presses by application[edit]

A press brake is a special type of machine press that bends sheet metal into shape. A good example of

the type of work a press brake can do is the backplate of a computer case. Other examples include

brackets, frame pieces and electronic enclosures just to name a few. Some press brakes

have CNC controls and can form parts with accuracy to a fraction of a millimetre. Bending forces can

exceed 4,000 kilonewtons (900,000 lbf).[citation needed]

A punch press is used to form holes.

A screw press is also known as a fly press.

A stamping press is a machine press used to shape or cut metal by deforming it with a die. It generally

consists of a press frame, a bolster plate, and a ram.

Capping presses form caps from rolls of aluminium foil at up to 660 per minute.

An example of peculiar press control: servo-press[edit]

A servomechanism press, also known as a servo press or a 'electro press, is a press driven by an AC servo

motor. The torque produced is converted to a linear force via a ball screw. Pressure and position are controlled

through a load cell and an encoder. The main advantage of a servo press is its low energy consumption; its

only 10-20% of other press machines. Another advantage is a quiet and clean work environment.

A table of comparison among presses[edit]

Comparison of various machine presses

Type of

press

Type of framePosition of

frameAction Method of actuation Type of drive

Suspension

Ram Bed

Open-

Gap

Straight-si

Arch

Pille

Solid

Tie

Vertical

Horizontal

Inclinable

Incline

Single

Doubl

Triple

Cran

Front-

Eccentric

Toggl

Screw

Cam

Rack & pi

Piston

Over d

Geared,

ov

Under

Geared, under

One-p

Two-p

Four-p

Single

Multipl

Solid

Open

Adjustable

back

de rrod

d e k

to-back crank

enion

irect

erdrive

direct

drive

oint

oint

oint

e

Bench

X X X X X X X X X X X X X X X X X

Open-back 

inclinable

X X X X X X X X X X X X X X X X X X

Gap-frame

X X X X X X X X X X X X X X X X X X X X X X X X

Adjustable-bed 

horn

X X X X X X X X X X X X X X X

End-

X X X X X X X X X X X X

wheel

Arch-frame

X X X X X X X X X X X X

Straight-side

X X X X X X X X X X X X X X X X X X X X X X X X X X

Reducing

X X X X X X X X X X X X X X X

Knuckle-lever

X X X X X X X X X X X X X X X X

Toggle-

draw

X X X X X X X X X X X X X X X X

Cam-drawing

X X X X X X X X X X X X X X X

Two-point single-

action

X X X X X X X X X X X X X X X

High-

production

X X X X X X X X X X X X X X

Dyeing 

machine

X X X X X X X X X X

Transfer

X X X X X X X X X X X X X X X

Flat-edge trimming

X X X X X X X X

Hydra

X X X X X X X X X X X X X X X X X X

ulic

Press 

brake

X X X X X X X X X X X X

History[edit]

Historically, metal was shaped by hand using a hammer. Later, larger hammers were constructed to press

more metal at once, or to press thicker materials. Often a smith would employ a helper or apprentice to swing

the sledgehammer while the smith concentrated on positioning the workpiece. Adding windmill or steam power

yielded still larger hammers such as steam hammers. Most modern machine presses use a combination of

electric motors and hydraulics to achieve the necessary pressure. Along with the evolution of presses came the

evolution of the dies used within them.

Safety[edit]

Machine presses can be hazardous, so safety measures must always be taken. Bi-manual controls (controls

the use of which requires both hands to be on the buttons to operate) are a very good way to prevent

accidents, as are light sensors that keep the machine from working if the operator is in range of the

DC motorFrom Wikipedia, the free encyclopedia

Workings of a brushed electric motor with a two-pole rotor (armature) and permanent magnet stator. "N" and "S" designate

polarities on the inside faces of the magnets; the outside faces have opposite polarities. The + and - signs show where the

DC current is applied to the commutator which supplies current to the armature coils

Electromagnetism

Electricity

Magnetism

Electrostatics   [show]   

Magnetostatics   [show]   

Electrodynamics   [show]   

Electrical network   [show]   

Covariant formulation   [show]   

Scientists[show]

V

T

E

The Pennsylvania Railroad's class DD1 locomotive running gear was a semi-permanently coupled pair of third rail direct

current electric locomotive motors built for the railroad's initial New York-area electrification when steam locomotives were

banned in the city (locomotive cab removed here).

A DC motor relies on the fact that like magnet poles repel and unlike magnetic poles attract each other. A coil

of wire with a current running through it generates a electromagnetic field aligned with the center of the coil. By

switching the current on or off in a coil its magnet field can be switched on or off or by switching the direction of

the current in the coil the direction of the generated magnetic field can be switched 180°. A simple DC

motor typically has a stationary set of magnets in the stator and an armature with a series of two or more

windings of wire wrapped in insulated stack slots around iron pole pieces (called stack teeth) with the ends of

the wires terminating on a commutator. The armature includes the mounting bearings that keep it in the center

of the motor and the power shaft of the motor and the commutator connections. The winding in the armature

continues to loop all the way around the armature and uses either single or parallel conductors (wires), and can

circle several times around the stack teeth. The total amount of current sent to the coil, the coil's size and what

it's wrapped around dictate the strength of the electromagnetic field created. The sequence of turning a

particular coil on or off dictates what direction the effective electromagnetic fields are pointed. By turning on

and off coils in sequence a rotating magnetic field can be created. These rotating magnetic fields interact with

the magnetic fields of the magnets (permanent or electromagnets) in the stationary part of the motor (stator) to

create a force on the armature which causes it to rotate. In some DC motor designs the stator fields use

electromagnets to create their magnetic fields which allow greater control over the motor. At high power levels,

DC motors are almost always cooled using forced air.

The commutator allows each armature coil to be activated in turn. The current in the coil is typically supplied via

two brushes that make moving contact with the commutator. Now, some brushless DC motors have electronics

that switch the DC current to each coil on and off and have no brushes to wear out or create sparks.

Different number of stator and armature fields as well as how they are connected provide different inherent

speed/torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage

applied to the armature. The introduction of variable resistance in the armature circuit or field circuit allowed

speed control. Modern DC motors are often controlled by power electronics systems which adjust the voltage

by "chopping" the DC current into on and off cycles which have an effective lower voltage.

Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction

applications such as electric locomotives, and trams. The DC motor was the mainstay of electric traction

drives on both electric and diesel-electric locomotives, street-cars/trams and diesel electric drilling rigs for many

years. The introduction of DC motors and an electrical grid system to run machinery starting in the 1870s

started a new second Industrial Revolution. DC motors can operate directly from rechargeable batteries,

providing the motive power for the first electric vehicles and today's hybrid cars and electric carsas well as

driving a host of cordless tools. Today DC motors are still found in applications as small as toys and disk

drives, or in large sizes to operate steel rolling mills and paper machines.

If external power is applied to a DC motor it acts as a DC generator, a dynamo. This feature is used to slow

down and recharge batteries on hybrid car and electric cars or to return electricity back to the electric grid used

on a street car or electric powered train line when they slow down. This process is calledregenerative

braking on hybrid and electric cars. In diesel electric locomotives they also use their DC motors as generators

to slow down but dissipate the energy in resistor stacks. Newer designs are adding large battery packs to

recapture some of this energy.

Contents

[hide]

1   Brush

2   Brushless

3   Uncommutated

4   Permanent magnet stators

5   Wound stators

o 5.1   Series connection

o 5.2   Shunt connection

o 5.3   Compound connection

6   See also

7   External links

8   References

Brush[edit]

Main article: Brushed DC electric motor

A brushed DC electric motor generating torque from DC power supply by using an internal mechanical commutation.

Stationary permanent magnets form the stator field. Torque is produced by the principle that any current-carrying conductor

placed within an external magnetic field experiences a force, known as Lorentz force. In a motor, the magnitude of this

Lorentz force (a vector represented by the green arrow), and thus the output torque,is a function for rotor angle, leading to a

phenomenon known as torque ripple) Since this is a single phase two-pole motor, the commutator consists of a split ring, so

that the current reverses each half turn ( 180 degrees).

The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal

commutation, stationary magnets (permanent or electromagnets), and rotating electrical magnets.

Advantages of a brushed DC motor include low initial cost, high reliability, and simple control of motor speed.

Disadvantages are high maintenance and low life-span for high intensity uses. Maintenance involves regularly

replacing the carbon brushes and springs which carry the electric current, as well as cleaning or replacing

the commutator. These components are necessary for transferring electrical power from outside the motor to

the spinning wire windings of the rotor inside the motor. Brushes consist of conductors.

Brushless[edit]

Main articles: Brushless DC electric motor and Switched reluctance motor

Typical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current/coil

magnets on the motor housing for the stator, but the symmetrical opposite is also possible. A motor controller

converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of

transferring power from outside the motor to the spinning rotor. Advantages of brushless motors include long

life span, little or no maintenance, and high efficiency. Disadvantages include high initial cost, and more

complicated motor speed controllers. Some such brushless motors are sometimes referred to as "synchronous

motors" although they have no external power supply to be synchronized with, as would be the case with

normal AC synchronous motors.

Uncommutated[edit]

Other types of DC motors require no commutation.

Homopolar motor  – A homopolar motor has a magnetic field along the axis of rotation and an electric

current that at some point is not parallel to the magnetic field. The name homopolar refers to the absence

of polarity change.

Homopolar motors necessarily have a single-turn coil, which limits them to very low voltages. This has

restricted the practical application of this type of motor.

Ball bearing motor  – A ball bearing motor is an unusual electric motor that consists of two ball bearing-type

bearings, with the inner races mounted on a common conductive shaft, and the outer races connected to a

high current, low voltage power supply. An alternative construction fits the outer races inside a metal tube,

while the inner races are mounted on a shaft with a non-conductive section (e.g. two sleeves on an

insulating rod). This method has the advantage that the tube will act as a flywheel. The direction of rotation

is determined by the initial spin which is usually required to get it going.

Permanent magnet stators[edit]

Main article: Permanent-magnet electric motor

A PM motor does not have a field winding on the stator frame, instead relying on PMs to provide the magnetic

field against which the rotor field interacts to produce torque. Compensating windings in series with the

armature may be used on large motors to improve commutation under load. Because this field is fixed, it

cannot be adjusted for speed control. PM fields (stators) are convenient in miniature motors to eliminate the

power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which have stator

windings. Historically, PMs could not be made to retain high flux if they were disassembled; field windings were

more practical to obtain the needed amount of flux. However, large PMs are costly, as well as dangerous and

difficult to assemble; this favors wound fields for large machines.

To minimize overall weight and size, miniature PM motors may use high energy magnets made

with neodymium or other strategic elements; most such are neodymium-iron-boron alloy. With their higher flux

density, electric machines with high-energy PMs are at least competitive with all optimally designed singly

fed synchronous and induction electric machines. Miniature motors resemble the structure in the illustration,

except that they have at least three rotor poles (to ensure starting, regardless of rotor position) and their outer

housing is a steel tube that magnetically links the exteriors of the curved field magnets.

Wound stators[edit]

A field coil may be connected in shunt, in series, or in compound with the armature of a DC machine (motor or generator)

Main article: universal motor

See also: Excitation (magnetic)

There are three types of electrical connections between the stator and rotor possible for DC electric motors:

series, shunt/parallel and compound ( various blends of series and shunt/parallel) and each has unique

speed/torque characteristics appropriate for diffent loading torque profiles/signatures.[1]

Series connection[edit]

A series DC motor connects the armature and field windings in series with a common D.C. power source. The

motor speed varies as a non-linear function of load torque and armature current; current is common to both the

stator and rotor yielding current squared (I^2) behavior [citation needed]. A series motor has very high starting torque

and is commonly used for starting high inertia loads, such as trains, elevators or hoists. [2] This speed/torque

characteristic is useful in applications such as dragline excavators, where the digging tool moves rapidly when

unloaded but slowly when carrying a heavy load.

With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding

is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage.

The motor can be damaged by over speed. This is called a runaway condition.

Series motors called "universal motors" can be used on alternating current. Since the armature voltage and the

field direction reverse at (substantially) the same time, torque continues to be produced in the same direction.

Since the speed is not related to the line frequency, universal motors can develop higher-than-synchronous

speeds, making them lighter than induction motors of the same rated mechanical output. This is a valuable

characteristic for hand-held power tools. Universal motors for commercial power frequency are usually small,

not more than about 1 kW output. However, much larger universal motors were used for electric locomotives,

fed by special low-frequency traction power networks to avoid problems with commutation under heavy and

varying loads.

Shunt connection[edit]

A shunt DC motor connects the armature and field windings in parallel or shunt with a common D.C. power

source. This type of motor has good speed regulation even as the load varies, but does not have the starting

torque of a series DC motor.[3] It is typically used for industrial, adjustable speed applications, such as machine

tools, winding/unwinding machines and tensioners.

Compound connection[edit]

A compound DC motor connects the armature and fields windings in a shunt and a series combination to give it

characteristics of both a shunt and a series DC motor.[4] This motor is used when both a high starting torque

and good speed regulation is needed. The motor can be connected in two arrangements: cumulatively or

differentially. Cumulative compound motors connect the series field to aid the shunt field, which provides higher

starting torque but less speed regulation. Differential compound DC motors have good speed regulation and

are typically operated at constant speed.

TransformerFrom Wikipedia, the free encyclopedia

This article is about the electrical device. For the media and toy franchise, see Transformers. For other uses,

see Transformer (disambiguation).

Pole-mounted distribution transformerwith center-tapped secondary winding used to provide 'split-phase' power for

residential and light commercial service, which in North America is typically rated 120/240 volt.[1][2]

A transformer is an electrical device that transfers energy between two circuits through electromagnetic

induction. A transformer may be used as a safe and efficient voltage converter to change the AC voltage at its

input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without

changing voltage and impedance conversion.

A transformer most commonly consists of two windings of wire that are wound around a common core to

provide tight electromagnetic coupling between the windings. The core material is often a laminated iron core.

The coil that receives the electrical input energy is referred to as the primary winding, while the output coil is

called the secondary winding.

An alternating electric current flowing through the primary winding (coil) of a transformer generates a varying

electromagnetic field in its surroundings which causes a varying magnetic flux in the core of the transformer.

The varying electromagnetic field in the vicinity of the secondary winding induces anelectromotive force in the

secondary winding, which appears a voltage across the output terminals. If a load impedance is connected

across the secondary winding, a current flows through the secondary winding drawing power from the primary

winding and its power source.

A transformer cannot operate with direct current; although, when it is connected to a DC source, a transformer

typically produces a short output pulse as the current rises.

Contents

[hide]

1   Invention

2   Applications

3   Basic principles

4   Basic transformer parameters and construction

5   Construction

6   Classification parameters

7   Types

8   Applications

9   History

10   See also

11   Notes

12   References

13   Bibliography

14   External links

Invention[edit]

The invention of transformers during the late 1800s allowed for longer-distance, cheaper, and more energy

efficient transmission, distribution, and utilization of electrical energy. In the early days of commercial electric

power, the main energy source was direct current (DC), which operates at low-voltage high-current. According

to Joule's Law, energy losses are directly proportional to the square of current. This law revealed that even a

tiny decrease in current or rise in voltage can cause a substantial lowering in energy losses and costs. Thus,

the historical pursuit for a high-voltage low-current electricity transmission system took shape. Although high

voltage transmission systems offered many benefits, the future fate of high-voltage alternating current still

remained unclear for several reasons: high-voltage sources had a much higher risk of causing severe electrical

injuries; many essential appliances could only function at low voltage. Regarded as one of the most influential

electrical innovations of all time, the introduction of transformers had successfully reduced the safety concerns

associated with alternating current and had the ability to lower voltage to a value that was required by most

essential appliances.[3]

Applications[edit]

Transformers perform voltage conversion; isolation protection; and impedance matching. In terms of voltage

conversion, transformers can step-up voltage/step-down current from generators to high-voltage transmission

lines, and step-down voltage/step-up current to local distribution circuits or industrial customers. The step-up

transformer is used to increase the secondary voltage relative to the primary voltage, whereas the step-down

transformer is used to decrease the secondary voltage relative to the primary voltage. Transformers range in

size from thumbnail-sized used in microphones to units weighing hundreds of tons interconnecting the power

grid. A broad range of transformer designs are used in electronic and electric power applications, including

miniature, audio, isolation, high-frequency, power conversion transformers, etc.

Basic principles[edit]

The functioning of a transformer is based on two principles of the laws of electromagnetic induction: An electric

current through a conductor, such as a wire, produces a magnetic field surrounding the wire, and a changing

magnetic field in the vicinity of a wire induces a voltage across the ends of that wire.

The magnetic field excited in the primary coil gives rise to self-induction as well as mutual induction between

coils. This self-induction counters the excited field to such a degree that the resulting current through the

primary winding is very small when no load draws power from the secondary winding.

The physical principles of the inductive behavior of the transformer are most readily understood and formalized

when making some assumptions to construct a simple model which is called theideal transformer. This model

differs from real transformers by assuming that the transformer is perfectly constructed and by neglecting that

electrical or magnetic losses occur in the materials used to construct the device.

Ideal transformer[edit]

Ideal transformer with a source and a load. NP and NS are the number of turns in the primary and secondary windings

respectively.

The assumptions to characterize the ideal transformer are:

The windings of the transformer have no resistance. Thus, there is no copper loss in the winding, and

hence no voltage drop.

Flux is confined within the magnetic core. Therefore, it is the same flux that links the input and output

windings.

Permeability of the core is infinitely high which implies that net mmf (amp-turns) must be zero (otherwise

there would be infinite flux) hence IP NP - IS NS = 0.

The transformer core does not suffer magnetic hysteresis or eddy currents, which cause inductive loss.

If the secondary winding of an ideal transformer has no load, no current flows in the primary winding.

The circuit diagram (right) shows the conventions used for an ideal, i.e. lossless and perfectly-coupled

transformer having primary and secondary windings with NP and NS turns, respectively.

The ideal transformer induces secondary voltage VS as a proportion of the primary voltage VP and respective

winding turns as given by the equation

,

where,

a is the winding turns ratio, the value of these ratios being respectively higher and lower than unity for

step-down and step-up transformers,[4][5][a][b]

VP designates source impressed voltage,

VS designates output voltage, and,

According to this formalism, when the number of turns in the primary coil is greater than the

number of turns in the secondary coil, the secondary voltage is smaller than the primary

voltage. On the other hand, when the number of turns in the primary coil is less than the

number of turns in the secondary, the secondary voltage is greater than the primary voltage.

Any load impedance ZL connected to the ideal transformer's secondary winding allows

energy to flow without loss from primary to secondary circuits. The resulting input and

output apparent powerare equal as given by the equation

.

Combining the two equations yields the following ideal transformer identity

.

This formula is a reasonable approximation for the typical commercial transformer,

with voltage ratio and winding turns ratio both being inversely proportional to the

corresponding current ratio.

The load impedance ZL and secondary voltage VS determine the secondary current

IS as follows

.

The apparent impedance ZL' of this secondary circuit load referred to the

primary winding circuit is governed by a squared turns ratio multiplication factor

relationship derived as follows[7][8]

.

For an ideal transformer, the power supplied to the primary and the power

dissipated by the load are equal. If ZL = RL where RL is a pure resistance

then the power is given by:[9][10]

The primary current is given by the following equation:[9][10]

Induction law[edit]

A varying electrical current passing through the primary coil

creates a varying magnetic field around the coil which induces a

voltage in the secondary winding. The primary and secondary

windings are wrapped around a core of very high magnetic

permeability, usually iron,[c] so that most of the magnetic flux

passes through both the primary and secondary coils. The

current through a load connected to the secondary winding and

the voltage across it are in the directions indicated in the figure.

Ideal transformer and induction law

The voltage induced across the secondary coil may be calculated

from Faraday's law of induction, which states that:

where Vs is the instantaneous voltage, Ns is the number of

turns in the secondary coil, and dΦ/dt is the derivative [d]  of

the magnetic flux Φ through one turn of the coil. If the turns

of the coil are oriented perpendicularly to the magnetic field

lines, the flux is the product of the magnetic flux

density B and the area A through which it cuts. The area is

constant, being equal to the cross-sectional area of the

transformer core, whereas the magnetic field varies with time

according to the excitation of the primary. Since the same

magnetic flux passes through both the primary and

secondary coils in an ideal transformer,[7] the instantaneous

voltage across the primary winding equals

Taking the ratio of the above two equations gives the

same voltage ratio and turns ratio relationship shown

above, that is,

.

The changing magnetic field induces an emf across

each winding.[11] The primary emf, acting as it does

in opposition to the primary voltage, is sometimes

termed the counter emf.[12] This is in accordance

with Lenz's law, which states that induction of emf

always opposes development of any such change

in magnetic field.

As still lossless and perfectly-coupled, the

transformer still behaves as described above in the

ideal transformer.

Polarity[edit]

Instrument transformer, with polarity dot and X1 markings

on LV side terminal

The relationships of the instantaneous polarity at

each of the terminals of the windings of a

transformer depend on the direction the windings

are wound around the core. Identically wound

windings produce the same polarity of voltage at

the corresponding terminals. This relationship is

usually denoted by the dot convention in

transformer circuit diagrams, nameplates, and on

terminal markings, which marks the terminals

having an in-phase relationship.[13][14][15][e][f]

Real transformer[edit]

The ideal transformer model neglects the following

basic linear aspects in real transformers.

Core losses, collectively called magnetizing current

losses, consist of[18]

Hysteresis  losses due to nonlinear application

of the voltage applied in the transformer core,

and

Eddy current  losses due to joule heating in the

core that are proportional to the square of the

transformer's applied voltage.

Whereas windings in the ideal model have no

impedance, the windings in a real transformer have

finite non-zero impedances in the form of:

Joule losses due to resistance in the primary

and secondary windings[18]

Leakage flux that escapes from the core and

passes through one winding only resulting in

primary and secondary reactive impedance.

If a voltage is applied across the primary terminals

of a real transformer while the secondary winding is

open without load, the real transformer must be

viewed as a simple inductor with an impedance Z:

.

Leakage flux[edit]

Main article: Leakage inductance

Leakage flux of a transformer

The ideal transformer model assumes that

all flux generated by the primary winding

links all the turns of every winding,

including itself. In practice, some flux

traverses paths that take it outside the

windings.[19] Such flux is termed leakage

flux, and results in leakage

inductance in series with the mutually

coupled transformer windings.[12] Leakage

flux results in energy being alternately

stored in and discharged from the

magnetic fields with each cycle of the

power supply. It is not directly a power

loss, but results in inferior voltage

regulation, causing the secondary voltage

not to be directly proportional to the

primary voltage, particularly under heavy

load.[19]Transformers are therefore

normally designed to have very low

leakage inductance. Nevertheless, it is

impossible to eliminate all leakage flux

because it plays an essential part in the

operation of the transformer. The

combined effect of the leakage flux and

the electric field around the windings is

what transfers energy from the primary to

the secondary.[20]

In some applications increased leakage is

desired, and long magnetic paths, air

gaps, or magnetic bypass shunts may

deliberately be introduced in a transformer

design to limit the short-circuit current it

will supply.[12] Leaky transformers may be

used to supply loads that exhibit negative

resistance, such as electric arcs, mercury

vapor lamps, and neon signs or for safely

handling loads that become periodically

short-circuited such as electric arc

welders.[21]

Air gaps are also used to keep a

transformer from saturating, especially

audio-frequency transformers in circuits

that have a DC component flowing in the

windings.[22]

Knowledge of leakage inductance is also

useful when transformers are operated in

parallel. It can be shown that if the percent

impedance (Z) and associated winding

leakage reactance-to-resistance (X/R)

ratio of two transformers were

hypothetically exactly the same, the

transformers would share power in

proportion to their respective volt-ampere

ratings (e.g. 500 kVA unit in parallel with

1,000 kVA unit, the larger unit would carry

twice the current). However, the

impedance tolerances of commercial

transformers are significant. Also, the Z

impedance and X/R ratio of different

capacity transformers tends to vary,

corresponding 1,000 kVA and 500 kVA

units' values being, to illustrate,

respectively, Z ~ 5.75%, X/R ~ 3.75 and Z

~ 5%, X/R ~ 4.75.[23][24]

Equivalent circuit[edit]

See also: Steinmetz equivalent circuit

Referring to the diagram, a practical

transformer's physical behavior may be

represented by an equivalent

circuit model, which can incorporate an

ideal transformer.[25]

Winding joule losses and leakage

reactances are represented by the

following series loop impedances of the

model:

Primary winding: RP, XP

Secondary winding: RS, XS.

In normal course of circuit equivalence

transformation, RS and XS are in practice

usually referred to the primary side by

multiplying these impedances by the turns

ratio squared, (NP/NS) 2 = a2.

Real transformer equivalent circuit

Core loss and reactance is represented by

the following shunt leg impedances of the

model:

Core or iron losses: RC

Magnetizing reactance: XM.

RC and XM are collectively termed

the magnetizing branch of the model.

Core losses are caused mostly by

hysteresis and eddy current effects in the

core and are proportional to the square of

the core flux for operation at a given

frequency.[26] The finite permeability core

requires a magnetizing current IM to

maintain mutual flux in the core.

Magnetizing current is in phase with the

flux, the relationship between the two

being non-linear due to saturation effects.

However, all impedances of the equivalent

circuit shown are by definition linear and

such non-linearity effects are not typically

reflected in transformer equivalent circuits.[26] With sinusoidal supply, core flux lags

the induced emf by 90°. With open-

circuited secondary winding, magnetizing

branch current I0 equals transformer no-

load current.[25]

The resulting model, though sometimes

termed 'exact' equivalent circuit based

on linearity assumptions, retains a number

of approximations.[25] Analysis may be

simplified by assuming that magnetizing

branch impedance is relatively high and

relocating the branch to the left of the

primary impedances. This introduces error

but allows combination of primary and

referred secondary resistances and

reactances by simple summation as two

series impedances.

Transformer equivalent circuit impedance

and transformer ratio parameters can be

derived from the following tests: open-

circuit test,[g] short-circuit test, winding

resistance test, and transformer ratio test.

Basic transformer parameters and construction[edit]

Effect of frequency[edit]

Transformer universal emf equation

If the flux in the core is purely sinusoidal,

the relationship for either winding between

its rmsvoltage Erms of the winding, and the

supply frequency f, number of turns N,

core cross-sectional area a in m2 and peak

magnetic flux density Bpeakin Wb/m2 or T

(tesla) is given by the universal emf

equation:[18]

If the flux does not contain

even harmonics the following equation can

be used for half-cycle average

voltage Eavg of any waveshape:

The time-derivative term in Faraday's Law

shows that the flux in the core is

the integral with respect to time of the

applied voltage.[28]Hypothetically an ideal

transformer would work with direct-current

excitation, with the core flux increasing

linearly with time.[29] In practice, the flux

rises to the point where magnetic

saturation of the core occurs, causing a

large increase in the magnetizing current

and overheating the transformer. All

practical transformers must therefore

operate with alternating (or pulsed direct)

current.[29]

The emf of a transformer at a given flux

density increases with frequency.[18] By

operating at higher frequencies,

transformers can be physically more

compact because a given core is able to

transfer more power without reaching

saturation and fewer turns are needed to

achieve the same impedance. However,

properties such as core loss and

conductor skin effect also increase with

frequency. Aircraft and military equipment

employ 400 Hz power supplies which

reduce core and winding weight.[30] Conversely, frequencies used for

somerailway electrification systems were

much lower (e.g. 16.7 Hz and 25 Hz) than

normal utility frequencies (50 – 60 Hz) for

historical reasons concerned mainly with

the limitations of early electric traction

motors. As such, the transformers used to

step-down the high over-head line

voltages (e.g. 15 kV) were much heavier

for the same power rating than those

designed only for the higher frequencies.

Power transformer over-excitation condition

caused by decreased frequency; flux (green),

iron core's magnetic characteristics (red) and

magnetizing current (blue).

Operation of a transformer at its designed

voltage but at a higher frequency than

intended will lead to reduced magnetizing

current. At a lower frequency, the

magnetizing current will increase.

Operation of a transformer at other than its

design frequency may require assessment

of voltages, losses, and cooling to

establish if safe operation is practical. For

example, transformers may need to be

equipped with 'volts per hertz' over-

excitation relays to protect the transformer

from overvoltage at higher than rated

frequency.

One example of state-of-the-art design is

traction transformers used for electric

multiple unit and high-speed train service

operating across the country border and

using different electrical standards, such

transformers' being restricted to be

positioned below the passenger

compartment. The power supply to, and

converter equipment being supply by,

such traction transformers have to

accommodate different input frequencies

and voltage (ranging from as high as

50 Hz down to 16.7 Hz and rated up to 25

kV) while being suitable for multiple AC

asynchronous motor and DC converters &

motors with varying harmonics mitigation

filtering requirements.

Large power transformers are vulnerable

to insulation failure due to transient

voltages with high-frequency components,

such as caused in switching or by

lightning.[31]

Energy losses[edit]

A theoretical (ideal) transformer does not

experience energy losses, i.e. it is 100%

efficient. The power dissipated by its load

would be equal to the power supplied by

its primary source. In contrast, a real

transformer is typically 95 to 99% efficient,

due to several loss mechanisms, including

winding resistance, winding capacitance,

leakage flux, core losses, and hysteresis

loss. Larger transformers are generally

more efficient than small units, and those

rated for electricity distribution usually

perform better than 98%.[32]

Experimental transformers

using superconducting windings achieve

efficiencies of 99.85%.[33] The increase in

efficiency can save considerable energy in

a large heavily loaded transformer; the

trade-off is in the additional initial and

running cost of the superconducting

design.

As transformer losses vary with load, it is

often useful to express these losses in

terms of no-load loss, full-load loss, half-

load loss, and so on. Hysteresis and Eddy

current losses are constant at all load

levels and dominate overwhelmingly

without load, while variable winding joule

losses dominating increasingly as load

increases. The no-load loss can be

significant, so that even an idle

transformer constitutes a drain on the

electrical supply. Designing energy

efficient transformers for lower loss

requires a larger core, good-quality silicon

steel, or even amorphous steel for the

core and thicker wire, increasing initial

cost. The choice of construction

represents a trade-off between initial cost

and operating cost.[34]

Transformer losses arise from:

Winding joule losses

Current flowing through winding conductors causes joule heating. As frequency increases, skin effect

and proximity effect causes winding resistance and, hence, losses to increase.

Core losses

Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the

core. According to Steinmetz's formula, the heat energy due to hysteresis is given by

, and,

hysteresis loss is thus given by

where, f is the frequency, η is the hysteresis coefficient and βmax is the maximum flux density, the

empirical exponent of which varies from about 1.4 to 1 .8 but is often given as 1.6 for iron.[34][35][36]

Eddy current losses

Ferromagnetic materials are also good conductors and a core made from such a material also

constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate

within the core in a plane normal to the flux, and are responsible for resistive heating of the core

material. The eddy current loss is a complex function of the square of supply frequency and inverse

square of the material thickness.[34] Eddy current losses can be reduced by making the core of a stack

of plates electrically insulated from each other, rather than a solid block; all transformers operating at

low frequencies use laminated or similar cores.

Magnetostriction related

transformer hum

Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract

slightly with each cycle of the magnetic field, an effect known as magnetostriction, the frictional energy

of which produces an audible noise known as mains hum or transformer hum.[4][37] This transformer

hum is especially objectionable in transformers supplied at power frequencies [h]  and in high-

frequency flyback transformers associated with PAL system CRTs.

Stray losses

Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned

to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive

materials such as the transformer's support structure will give rise to eddy currents and be converted

to heat.[38] There are also radiative losses due to the oscillating magnetic field but these are usually

small.

Mechanical

vibration and

audible noise

transmission

In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the

primary and secondary windings. This energy incites vibration transmission in interconnected

metalwork, thus amplifying audible transformer hum.[39]

Core form and shell

form transformer

s[edit]

Core form = core

type; shell form

= shell type

Closed-core

transformers

are

constructed in

'core form' or

'shell form'.

When windings

surround the

core, the

transformer is

core form;

when windings

are surrounded

by the core,

the transformer

is shell form.

Shell form

design may be

more prevalent

than core form

design for

distribution

transformer

applications

due to the

relative ease in

stacking the

core around

winding coils.[40] Core form

design tends

to, as a

general rule,

be more

economical,

and therefore

more

prevalent, than

shell form

design for high

voltage power

transformer

applications at

the lower end

of their voltage

and power

rating ranges

(less than or

equal to,

nominally, 230

kV or 75 MVA).

At higher

voltage and

power ratings,

shell form

transformers

tend to be

more

prevalent.[40][41]

[42][43] Shell form

design tends to

be preferred

for extra high

voltage and

higher MVA

applications

because,

though more

labor-intensive

to

manufacture,

shell form

transformers

are

characterized

as having

inherently

better kVA-to-

weight ratio,

better short-

circuit strength

characteristics

and higher

immunity to

transit

damage.[43]

Construction[edit]

Cores[edit]

Laminated steel

cores[edit]

Laminated core

transformer

showing edge of

laminations at

top of photo

Power

transformer

inrush current

caused by

residual flux at

switching instant;

flux (green), iron

core's magnetic

characteristics

(red) and

magnetizing

current (blue).

Transformers

for use at

power or audio

frequencies

typically have

cores made of

high

permeability sil

icon steel.[44] The steel

has a

permeability

many times

that of free

space and the

core thus

serves to

greatly reduce

the

magnetizing

current and

confine the flux

to a path which

closely couples

the windings.[45] Early

transformer

developers

soon realized

that cores

constructed

from solid iron

resulted in

prohibitive

eddy current

losses, and

their designs

mitigated this

effect with

cores

consisting of

bundles of

insulated iron

wires.[46] Later

designs

constructed

the core by

stacking layers

of thin steel

laminations, a

principle that

has remained

in use. Each

lamination is

insulated from

its neighbors

by a thin non-

conducting

layer of

insulation.[47]The

universal

transformer

equation

indicates a

minimum

cross-sectional

area for the

core to avoid

saturation.

The effect of

laminations is

to confine eddy

currents to

highly elliptical

paths that

enclose little

flux, and so

reduce their

magnitude.

Thinner

laminations

reduce losses,[48] but are

more laborious

and expensive

to construct.[49] Thin

laminations are

generally used

on high-

frequency

transformers,

with some of

very thin steel

laminations

able to operate

up to 10 kHz.

Laminating the

core greatly

reduces eddy-

current losses

One common

design of

laminated core

is made from

interleaved

stacks of E-

shaped steel

sheets capped

with I-shaped p

ieces, leading

to its name of

'E-I

transformer'.[49] 

Such a design

tends to exhibit

more losses,

but is very

economical to

manufacture.

The cut-core or

C-core type is

made by

winding a steel

strip around a

rectangular

form and then

bonding the

layers

together. It is

then cut in two,

forming two C

shapes, and

the core

assembled by

binding the two

C halves

together with a

steel strap.[49] They have

the advantage

that the flux is

always

oriented

parallel to the

metal grains,

reducing

reluctance.

A steel

core's remane

nce means

that it retains a

static magnetic

field when

power is

removed.

When power is

then reapplied,

the residual

field will cause

a high inrush

current until

the effect of

the remaining

magnetism is

reduced,

usually after a

few cycles of

the applied AC

waveform.[50] O

vercurrent

protection

devices such

as fuses must

be selected to

allow this

harmless

inrush to pass.

On

transformers

connected to

long, overhead

power

transmission

lines, induced

currents due

to geomagneti

c

disturbances d

uring solar

storms can

cause

saturation of

the core and

operation of

transformer

protection

devices.[51]

Distribution

transformers

can achieve

low no-load

losses by

using cores

made with low-

loss high-

permeability

silicon steel

or amorphous

(non-

crystalline)

metal alloy.

The higher

initial cost of

the core

material is

offset over the

life of the

transformer by

its lower losses

at light load.[52]

Solid cores[edit]

Powdered iron

cores are used

in circuits such

as switch-

mode power

supplies that

operate above

mains

frequencies

and up to a

few tens of

kilohertz.

These

materials

combine high

magnetic

permeability

with high bulk

electrical resist

ivity. For

frequencies

extending

beyond

the VHF band,

cores made

from non-

conductive

magnetic cera

mic materials

called ferrites a

re common.[49] Some radio-

frequency

transformers

also have

movable cores

(sometimes

called 'slugs')

which allow

adjustment of

the coupling

coefficient (and 

bandwidth) of

tuned radio-

frequency

circuits.

Toroidal cores[edit]

Small toroidal

core transformer

Toroidal

transformers

are built

around a ring-

shaped core,

which,

depending on

operating

frequency, is

made from a

long strip

of silicon

steel o

rpermalloy wou

nd into a coil,

powdered iron,

or ferrite.[53] A

strip

construction

ensures that

the grain

boundaries are

optimally

aligned,

improving the

transformer's

efficiency by

reducing the

core's reluctan

ce. The closed

ring shape

eliminates air

gaps inherent

in the

construction of

an E-I core.

[21] The cross-

section of the

ring is usually

square or

rectangular,

but more

expensive

cores with

circular cross-

sections are

also available.

The primary

and secondary

coils are often

wound

concentrically

to cover the

entire surface

of the core.

This minimizes

the length of

wire needed,

and also

provides

screening to

minimize the

core's

magnetic field

from

generating ele

ctromagnetic

interference.

Toroidal

transformers

are more

efficient than

the cheaper

laminated E-I

types for a

similar power

level. Other

advantages

compared to

E-I types,

include smaller

size (about

half), lower

weight (about

half), less

mechanical

hum (making

them superior

in audio

amplifiers),

lower exterior

magnetic field

(about one

tenth), low off-

load losses

(making them

more efficient

in standby

circuits),

single-bolt

mounting, and

greater choice

of shapes. The

main

disadvantages

are higher cost

and limited

power capacity

(see Classificat

ion

parameters bel

ow). Because

of the lack of a

residual gap in

the magnetic

path, toroidal

transformers

also tend to

exhibit higher

inrush current,

compared to

laminated E-I

types.

Ferrite toroidal

cores are used

at higher

frequencies,

typically

between a few

tens of

kilohertz to

hundreds of

megahertz, to

reduce losses,

physical size,

and weight of

inductive

components. A

drawback of

toroidal

transformer

construction is

the higher

labor cost of

winding. This

is because it is

necessary to

pass the entire

length of a coil

winding

through the

core aperture

each time a

single turn is

added to the

coil. As a

consequence,

toroidal

transformers

rated more

than a few kVA

are

uncommon.

Small

distribution

transformers

may achieve

some of the

benefits of a

toroidal core

by splitting it

and forcing it

open, then

inserting a

bobbin

containing

primary and

secondary

windings.

Air cores[edit]

A physical core

is not an

absolute

requisite and a

functioning

transformer

can be

produced

simply by

placing the

windings near

each other, an

arrangement

termed an 'air-

core'

transformer.

The air which

comprises the

magnetic

circuit is

essentially

lossless, and

so an air-core

transformer

eliminates loss

due to

hysteresis in

the core

material.[12] The

leakage

inductance is

inevitably high,

resulting in

very poor

regulation, and

so such

designs are

unsuitable for

use in power

distribution.[12] 

They have

however very

high bandwidt

h, and are

frequently

employed in

radio-

frequency

applications,[54] 

for which a

satisfactory

coupling

coefficient is

maintained by

carefully

overlapping

the primary

and secondary

windings.

They're also

used

for resonant

transformers s

uch as Tesla

coils where

they can

achieve

reasonably low

loss in spite of

the high

leakage

inductance.

Windings[edit]

Windings are

usually arranged

concentrically to

minimize flux

leakage.

It has been su

ggested that Compensation winding be merged i

nto this article. (Discuss) Proposed

since

March

2

014.

The conductin

g

material used

for the

windings

depends upon

the application,

but in all cases

the individual

turns must be

electrically

insulated from

each other to

ensure that the

current travels

throughout

every turn.[55] For small

power and

signal

transformers,

in which

currents are

low and the

potential

difference

between

adjacent turns

is small, the

coils are often

wound

from enamelle

d magnet wire,

such as

Formvar wire.

Larger power

transformers

operating at

high voltages

may be wound

with copper

rectangular

strip

conductors

insulated by

oil-

impregnated

paper and

blocks

ofpressboard.[56]

Cut view through

transformer

windings. White:

insulator. Green

spiral: Grain

oriented silicon

steel. Black:

Primary winding

made of oxygen-

free copper.

Red: Secondary

winding. Top left:

Toroidal

transformer.

Right: C-core,

but E-core would

be similar. The

black windings

are made of film.

Top: Equally low

capacitance

between all ends

of both windings.

Since most

cores are at

least moderately

conductive they

also need

insulation.

Bottom: Lowest

capacitance for

one end of the

secondary

winding needed

for low-power

high-voltage

transformers.

Bottom left:

Reduction

ofleakage

inductance woul

d lead to

increase of

capacitance.

High-frequency

transformers

operating in

the tens to

hundreds of

kilohertz often

have windings

made of

braided Litz

wire to

minimize the

skin-effect and

proximity effect

losses.[28] Larg

e power

transformers

use multiple-

stranded

conductors as

well, since

even at low

power

frequencies

non-uniform

distribution of

current would

otherwise exist

in high-current

windings.[56] Ea

ch strand is

individually

insulated, and

the strands are

arranged so

that at certain

points in the

winding, or

throughout the

whole winding,

each portion

occupies

different

relative

positions in the

complete

conductor. The

transposition

equalizes the

current flowing

in each strand

of the

conductor, and

reduces eddy

current losses

in the winding

itself. The

stranded

conductor is

also more

flexible than a

solid conductor

of similar size,

aiding

manufacture.[56]

The windings

of signal

transformers

minimize

leakage

inductance and

stray

capacitance to

improve high-

frequency

response.

Coils are split

into sections,

and those

sections

interleaved

between the

sections of the

other winding.

Power-

frequency

transformers

may

have taps at

intermediate

points on the

winding,

usually on the

higher voltage

winding side,

for voltage

adjustment.

Taps may be

manually

reconnected,

or a manual or

automatic

switch may be

provided for

changing taps.

Automatic on-

load tap

changers are

used in electric

power

transmission or

distribution, on

equipment

such as arc

furnace transfo

rmers, or for

automatic

voltage

regulators for

sensitive

loads. Audio-

frequency

transformers,

used for the

distribution of

audio to public

address

loudspeakers,

have taps to

allow

adjustment of

impedance to

each speaker.

A center-

tapped

transformer is

often used in

the output

stage of an

audio

power amplifier 

in a push-pull

circuit.

Modulation

transformers

in AM transmitt

ers are very

similar.

Dry-type

transformer

winding

insulation

systems can

be either of

standard open-

wound 'dip-

and-bake'

construction or

of higher

quality designs

that

include vacuu

m pressure

impregnation (

VPI), vacuum

pressure

encapsulation (

VPE), and cast

coil

encapsulation 

processes.[57] I

n the VPI

process, a

combination of

heat, vacuum

and pressure

is used to

thoroughly

seal, bind, and

eliminate

entrained air

voids in the

winding

polyester resin

insulation coat

layer, thus

increasing

resistance to

corona. VPE

windings are

similar to VPI

windings but

provide more

protection

against

environmental

effects, such

as from water,

dirt or

corrosive

ambients, by

multiple dips

including

typically in

terms of final

epoxy coat.[58]

Cooling[edit]

Cutaway view of

liquid-immersed

construction

transformer. The

conservator

(reservoir) at top

provides liquid-

to-atmosphere

isolation as

coolant level and

temperature

changes. The

walls and fins

provide required

heat dissipation

balance.

See

also: Arrhenius

equation

To place the

cooling

problem in

perspective,

the accepted

rule of thumb

is that the life

expectancy of

insulation in

all electric

machines inclu

ding all

transformers is

halved for

about every

7 °C to 10 °C

increase

in operating

temperature,

this life

expectancy

halving rule

holding more

narrowly when

the increase is

between about

7 °C to 8 °C in

the case of

transformer

winding

cellulose

insulation.[59][60]

[61]

Small dry-type

and liquid-

immersed

transformers

are often self-

cooled by

natural

convection

and radiation h

eat dissipation.

As power

ratings

increase,

transformers

are often

cooled by

forced-air

cooling,

forced-oil

cooling, water-

cooling, or

combinations

of these.[62] Large

transformers

are filled

with transform

er oil that both

cools and

insulates the

windings.[63] Tr

ansformer oil is

a highly

refined mineral

oil that cools

the windings

and insulation

by circulating

within the

transformer

tank. The

mineral oil

and paper insu

lation system

has been

extensively

studied and

used for more

than 100

years. It is

estimated that

50% of power

transformers

will survive 50

years of use,

that the

average age of

failure of

power

transformers is

about 10 to 15

years, and that

about 30% of

power

transformer

failures are

due to

insulation and

overloading

failures.[64][65] Pr

olonged

operation at

elevated

temperature

degrades

insulating

properties of

winding

insulation and

dielectric

coolant, which

not only

shortens

transformer life

but can

ultimately lead

to catastrophic

transformer

failure.[59] With

a great body of

empirical study

as a

guide, transfor

mer oil

testing includin

g dissolved

gas

analysis provid

es valuable

maintenance

information.

This underlines

the need to

monitor,

model,

forecast and

manage oil

and winding

conductor

insulation

temperature

conditions

under varying,

possibly

difficult, power

loading

conditions.[66][67]

Building

regulations in

many

jurisdictions

require indoor

liquid-filled

transformers to

either use

dielectric fluids

that are less

flammable

than oil, or be

installed in fire-

resistant

rooms.[68] Air-

cooled dry

transformers

can be more

economical

where they

eliminate the

cost of a fire-

resistant

transformer

room.

The tank of

liquid filled

transformers

often has

radiators

through which

the liquid

coolant

circulates by

natural

convection or

fins. Some

large

transformers

employ electric

fans for forced-

air cooling,

pumps for

forced-liquid

cooling, or

have heat

exchangers for

water-cooling.[63] An oil-

immersed

transformer

may be

equipped with

a Buchholz

relay, which,

depending on

severity of gas

accumulation

due to internal

arcing, is used

to either alarm

or de-energize

the

transformer.[50] 

Oil-immersed

transformer

installations

usually include

fire protection

measures such

as walls, oil

containment,

and fire-

suppression

sprinkler

systems.

Another

protection

means

consists in fast

depressurizatio

n

systems which

are activated

by the first

dynamic

pressure peak

of the shock

wave, avoiding

transformer

explosion

before static

pressure

increases.

Many

explosions are

reported to

have been

avoided thanks

to this

technology.[69]

Polychlorinate

d

biphenyls have

properties that

once favored

their use as

a dielectric

coolant,

though

concerns over

their environm

ental

persistence led

to a

widespread

ban on their

use.[70] Today,

non-toxic,

stable silicone-

based oils,

or fluorinated

hydrocarbons 

may be used

where the

expense of a

fire-resistant

liquid offsets

additional

building cost

for a

transformer

vault.[68][71] PCB

s for new

equipment was

banned in

1981 and in

2000 for use in

existing

equipment in

United

Kingdom[72] Le

gislation

enacted in

Canada

between 1977

and 1985

essentially

bans PCB use

in transformers

manufactured

in or imported

into the

country after

1980, the

maximum

allowable level

of PCB

contamination

in existing

mineral oil

transformers

being 50 ppm.[73]

Some

transformers,

instead of

being liquid-

filled, have

their windings

enclosed in

sealed,

pressurized

tanks and

cooled

by nitrogen or 

sulfur

hexafluoride g

as.[71]

Experimental

power

transformers in

the 500-to-

1,000 kVA

range have

been built

with liquid

nitrogen or heli

um cooled sup

erconducting w

indings, which

eliminates

winding losses

without

affecting core

losses.[74][75]

Insulation drying[edit]

Construction of

oil-filled

transformers

requires that

the insulation

covering the

windings be

thoroughly

dried of

residual

moisture

before the oil is

introduced.

Drying is

carried out at

the factory,

and may also

be required as

a field service.

Drying may be

done by

circulating hot

air around the

core, or by

vapor-phase

drying (VPD)

where an

evaporated

solvent

transfers heat

by

condensation

on the coil and

core.

For small

transformers,

resistance

heating by

injection of

current into the

windings is

used. The

heating can be

controlled very

well, and it is

energy

efficient. The

method is

called low-

frequency

heating (LFH)

since the

current used is

at a much

lower

frequency than

that of the

power grid,

which is

normally 50 or

60 Hz. A lower

frequency

reduces the

effect of

inductance, so

the voltage

required can

be reduced.[76] The LFH

drying method

is also used for

service of older

transformers.[77]

Bushings[edit]

Larger

transformers

are provided

with high-

voltage

insulated bushi

ngs made of

polymers or

porcelain. A

large bushing

can be a

complex

structure since

it must provide

careful control

of the electric

field

gradient withou

t letting the

transformer

leak oil.[78]

Classification

parameters[edit]

Transformers

can be

classified in

many ways,

such as the

following:

Power

capacity:

From a

fraction of

a volt-

ampere

(VA) to

over a

thousand

MVA.

Duty of a

transforme

r:

Continuou

s, short-

time,

intermitten

t, periodic,

varying.

Frequency

range: Po

wer-

frequency, 

audio-

frequency,

or radio-

frequency.

Voltage

class:

From a

few volts

to

hundreds

of

kilovolts.

Cooling

type: Dry

and liquid-

immersed

- self-

cooled,

forced air-

cooled;

liquid-

immersed

- forced

oil-cooled,

water-

cooled.

Circuit

applicatio

n: Such as

power

supply,

impedanc

e

matching,

output

voltage

and

current

stabilizer

or circuit

isolation.

Utilization: 

Pulse, po

wer,

distributio

n, rectifier, 

arc

furnace,

amplifier

output,

etc..

Basic

magnetic

form: Core

form, shell

form.

Constant-

potential

transforme

r

descriptor:

Step-up,

step-

down, isol

ation.

General

winding

configurati

on: By EIC

vector

group -

various

possible

two-

winding

combinati

ons of the

phase

designatio

ns delta,

wye or

star,

and zigza

g or

interconne

cted star;[i] other -

autotransf

ormer, Sc

ott-T, zigz

ag

grounding

transforme

r winding.[79][80][81][82]

Rectifier

phase-

shift

winding

configurati

on: 2-

winding,

6-pulse; 3-

winding,

12-pulse; .

. . n-

winding,

[n-1]*6-

pulse;

polygon;

etc..

Types[edit]

Various

specific

electrical

application

designs

require a

variety

of transformer

types.

Although they

all share the

basic

characteristic

transformer

principles, they

are customize

in construction

or electrical

properties for

certain

installation

requirements

or circuit

conditions.

Autotransf

ormer:

Transform

er in which

part of the

winding is

common

to both

primary

and

secondary

circuits.[83]

Capacitor

voltage

transforme

r:

Transform

er in which

capacitor

divider is

used to

reduce

high

voltage

before

application

to the

primary

winding.

Distributio

n

transforme

r, power

transforme

r:

Internation

al

standards

make a

distinction

in terms of

distributio

n

transforme

rs being

used to

distribute

energy

from

transmissi

on lines

and

networks

for local

consumpti

on and

power

transforme

rs being

used to

transfer

electric

energy

between

the

generator

and

distributio

n primary

circuits.[83]

[84][j]

Phase

angle

regulating

transforme

r: A

specialise

d

transforme

r used to

control the

flow of

real power

on three-

phase

electricity

transmissi

on

networks.

Scott-T

transforme

r:

Transform

er used for

phase

transforma

tion from

three-

phase

to two-

phase and

vice versa.[83]

Polyphase

transforme

r: Any

transforme

r with

more than

one

phase.

Grounding

transforme

r:

Transform

er used for

grounding

three-

phase

circuits to

create a

neutral in

a three

wire

system,

using a

wye-delta

transforme

r,[80][85] or

more

commonly

, a zigzag

grounding

winding.[80]

[82][83]

Leakage

transforme

r:

Transform

er that has

loosely

coupled

windings.

Resonant

transforme

r:

Transform

er that

uses

resonance

to

generate a

high

secondary

voltage.

Audio

transforme

r:

Transform

er used in

audio

equipment

.

Output

transforme

r:

Transform

er used to

match the

output of a

valve

amplifier

to its load.

Instrument

transforme

r: Potential

or current

transforme

r used to

accurately

and safely

represent

voltage,

current or

phase

position of

high

voltage or

high

power

circuits.[83]

Applications[edit]

An electrical

substation in Mel

bourne, Australia 

showing three of

five 220 kV –

66 kV

transformers,

each with a

capacity of

150 MVA[86]

Transformer at

the Limestone

Generating

Station in Manito

ba, Canada

Transformers

are used to

increase

voltage before

transmitting

electrical

energy over

long distances

through wires.

Wires

have resistanc

e which loses

energy through

joule heating at

a rate

corresponding

to square of

the current. By

transforming

power to a

higher voltage

transformers

enable

economical

transmission of

power and

distribution.

Consequently,

transformers

have shaped

the electricity

supply

industry,

permitting

generation to

be located

remotely from

points

of demand.[87] 

All but a tiny

fraction of the

world's

electrical

power has

passed

through a

series of

transformers

by the time it

reaches the

consumer.[38]

Transformers

are also used

extensively

in electronic

products to

step-down the

supply voltage

to a level

suitable for the

low voltage

circuits they

contain. The

transformer

also electrically

isolates the

end user from

contact with

the supply

voltage.

Signal and

audio

transformers

are used to

couple stages

of amplifiers an

d to match

devices such

as microphone

s and record

players to the

input of

amplifiers.

Audio

transformers

allowe

dtelephone circ

uits to carry on

a two-way

conversation o

ver a single

pair of wires.

A balu

ntransformer

converts a

signal that is

referenced to

ground to a

signal that

has balanced

voltages to

ground, such

as between

external cables

and internal

circuits.

History[edit]

Discovery of

induction[edit]

Faraday's

experiment with

induction

between coils of

wire[88]

Electromagneti

c induction, the

principle of the

operation of

the

transformer,

was

discovered

independently

and almost

simultaneously

by Joseph

Henry and Mic

hael

Faraday in

1831. Although

Henry's work

likely having

preceded

Faraday's work

by a few

months,

Faraday was

the first to

publish the

results of his

experiments

and thus

receive credit

for the

discovery.[89] T

he relationship

between emf

and magnetic

flux is an

equation now

known

as Faraday's

law of

induction:

.

where   

is the

magnitude

of the emf

in volts

and ΦB is

the

magnetic

flux

through

the circuit

in webers.[90]

Faraday

performed

the first

experimen

ts on

induction

between

coils of

wire,

including

winding a

pair of

coils

around an

iron ring,

thus

creating

the

first toroid

al closed-

core

transforme

r.[91] Howe

ver he

only

applied

individual

pulses of

current to

his

transforme

r, and

never

discovere

d the

relation

between

the turns

ratio and

emf in the

windings.

Induction

coils[edit]

Faraday's

ring

transformer

Induction

coil, 1900,

Bremerhav

n, Germany

The first

type of

transforme

r to see

wide use

was

the inducti

on coil,

invented

by

Rev. Nich

olas

Callan of 

Maynooth

College,

Ireland in

1836. He

was one

of the first

researcher

s to

realize the

more turns

the

secondary

winding

has in

relation to

the

primary

winding,

the larger

the

induced

secondary

emf will

be.

Induction

coils

evolved

from

scientists'

and

inventors'

efforts to

get higher

voltages

from

batteries.

Since

batteries

produce di

rect

current

(DC)rather

than AC,

induction

coils relied

upon

vibrating e

lectrical

contacts t

hat

regularly

interrupted

the current

in the

primary to

create the

flux

changes

necessary

for

induction.

Between

the 1830s

and the

1870s,

efforts to

build

better

induction

coils,

mostly by

trial and

error,

slowly

revealed

the basic

principles

of

transforme

rs.

First alternati

ng current transformers[ed

it]

By the

1870s,

efficient g

enerators 

producing 

alternating

current

(AC) were

available,

and it was

found AC

could

power an

induction

coil

directly,

without

an interrup

ter.

In 1876,

Russian

engineer 

Pavel

Yablochko

v invented

a lighting

system

based on

a set of

induction

coils

where the

primary

windings

were

connected

to a

source of

AC. The

secondary

windings

could be

connected

to

several 'el

ectric

candles' (

arc lamps)

of his own

design.[92] [

93] The

coils

Yablochko

v

employed

functioned

essentially

as

transforme

rs.[92]

In 1878,

the Ganz

factory,

Budapest,

Hungary,

began

manufactu

ring

equipment

for electric

lighting

and, by

1883, had

installed

over fifty

systems in

Austria-

Hungary.

Their AC

systems

used arc

and

incandesc

ent lamps,

generators

, and other

equipment

.[94]

Lucien

Gaulard a

nd John

Dixon

Gibbs first

exhibited

a device

with an

open iron

core

called a

'secondar

y

generator'

in London

in 1882,

then sold

the idea to

the Westin

ghouse co

mpany in

the United

States.[46] 

They also

exhibited

the

invention

in Turin,

Italy in

1884,

where it

was

adopted

for an

electric

lighting

system.[95] 

However,

the

efficiency

of their

open-core

bipolar

apparatus

remained

very low.[95]

Early series circuit

transformer

distribution[edit]

Induction

coils with

open

magnetic

circuits

are

inefficient

at

transferrin

g power

to loads.

Until about

1880, the

paradigm

for AC

power

transmissi

on from a

high

voltage

supply to

a low

voltage

load was a

series

circuit.

Open-core

transforme

rs with a

ratio near

1:1 were

connected

with their

primaries

in series

to allow

use of a

high

voltage for

transmissi

on while

presenting

a low

voltage to

the lamps.

The

inherent

flaw in this

method

was that

turning off

a single

lamp (or

other

electric

device)

affected

the

voltage

supplied

to all

others on

the same

circuit.

Many

adjustable

transforme

r designs

were

introduced

to

compensa

te for this

problemati

c

characteri

stic of the

series

circuit,

including

those

employing

methods

of

adjusting

the core or

bypassing

the

magnetic

flux

around

part of a

coil.[95] Effi

cient,

practical

transforme

r designs

did not

appear

until the

1880s, but

within a

decade,

the

transforme

r would be

instrument

al in

the War of

Currents,

and in

seeing AC

distributio

n systems

triumph

over their

DC

counterpar

ts, a

position in

which they

have

remained

dominant

ever

since.[96]

Shell form

transformer

. Sketch

used by

Uppenborn

to describe

ZBD

engineers'

1885

patents and

earliest

articles.[95]

Core form,

front; shell

form, back.

Earliest

specimens

of ZBD-

designed

high-

efficiency

constant-

potential

transformer

s

manufactur

ed at the

Ganz

factory in

1885.

The ZBD

team

consisted

of Károly

Zipernowsk

y, Ottó

Bláthy and 

Miksa Déri

Stanley's

1886

design for

adjustable

gap open-

core

induction

coils[97]

Closed-core

transformers and

parallel power

distribution[edit]

In the

autumn of

1884, Kár

oly

Zipernows

ky, Ottó

Bláthy and 

Miksa

Déri (ZBD)

, three

engineers

associated

with the

Ganz

factory,

had

determine

d that

open-core

devices

were

impractica

ble, as

they were

incapable

of reliably

regulating

voltage.[98] 

In their

joint 1885

patent

application

s for novel

transforme

rs (later

called

ZBD

transforme

rs), they

described

two

designs

with

closed

magnetic

circuits

where

copper

windings

were

either a)

wound

around

iron wire

ring core

or

b) surroun

ded by

iron wire

core.[95] Th

e two

designs

were the

first

application

of the two

basic

transforme

r

constructi

ons in

common

use to this

day, which

can as a

class all

be termed

as either

core form

or shell

form (or

alternative

ly, core

type or

shell

type), as

in a) or b),

respectivel

y (see

images).[40][41][99][100] 

The Ganz

factory

had also

in the

autumn of

1884

made

delivery of

the world's

first five

high-

efficiency

AC

transforme

rs, the first

of these

units

having

been

shipped

on

Septembe

r 16, 1884.[101] This

first unit

had been

manufactu

red to the

following

specificati

ons: 1,400

W, 40 Hz,

120:72 V,

11.6:19.4

A, ratio

1.67:1,

one-

phase,

shell form.[101]

In both

designs,

the

magnetic

flux linking

the

primary

and

secondary

windings

traveled

almost

entirely

within the

confines

of the iron

core, with

no

intentional

path

through air

(see Toroi

dal

cores belo

w). The

new

transforme

rs were

3.4 times

more

efficient

than the

open-core

bipolar

devices of

Gaulard

and

Gibbs.[102] 

The ZBD

patents

included

two other

major

interrelate

d

innovation

s: one

concernin

g the use

of parallel

connected

, instead

of series

connected

, utilization

loads, the

other

concernin

g the

ability to

have high

turns ratio

transforme

rs such

that the

supply

network

voltage

could be

much

higher

(initially

1,400 to

2,000 V)

than the

voltage of

utilization

loads (100

V initially

preferred).[103][104] Wh

en

employed

in parallel

connected

electric

distributio

n systems,

closed-

core

transforme

rs finally

made it

technically

and

economic

ally

feasible to

provide

electric

power for

lighting in

homes,

businesse

s and

public

spaces.[105]

[106] Bláthy

had

suggested

the use of

closed

cores,

Zipernows

ky had

suggested

the use

of parallel

shunt

connectio

ns, and

Déri had

performed

the

experimen

ts;[107]

Transform

ers today

are

designed

on the

principles

discovere

d by the

three

engineers.

They also

popularize

d the word

'transform

er' to

describe a

device for

altering

the emf of

an electric

current,[105]

[108] althou

gh the

term had

already

been in

use by

1882.[109]

[110] In

1886, the

ZBD

engineers

designed,

and the

Ganz

factory

supplied

electrical

equipment

for, the

world's

first power

station tha

t used AC

generators

to power a

parallel

connected

common

electrical

network,

the steam-

powered

Rome-

Cerchi po

wer plant.[111]

Although 

George

Westingho

use had

bought

Gaulard

and Gibbs'

patents in

1885,

the Edison

Electric

Light

Company 

held an

option on

the US

rights for

the ZBD

transforme

rs,

requiring

Westingho

use to

pursue

alternative

designs

on the

same

principles.

He

assigned

to William

Stanley th

e task of

developin

g a device

for

commerci

al use in

United

States.[112] 

Stanley's

first

patented

design

was for

induction

coils with

single

cores of

soft iron

and

adjustable

gaps to

regulate

the emf

present in

the

secondary

winding

(see

image).[97] 

This

design[113] 

was first

used

commerci

ally in the

US in

1886[96]but

Westingho

use was

intent on

improving

the

Stanley

design to

make it

(unlike the

ZBD type)

easy and

cheap to

produce.[113]

Westingho

use,

Stanley

and

associates

soon

developed

an easier

to

manufactu

re core,

consisting

of a stack

of thin

'E-shaped'

iron

plates,

insulated

by thin

sheets of

paper or

other

insulating

material.

Prewound

copper

coils could

then be

slid into

place, and

straight

iron plates

laid in to

create a

closed

magnetic

circuit.

Westingho

use

applied for

a patent

for the

new low-

cost

design in

December

1886; it

was

granted in

July 1887.[107][114]

Other early

transformers[ed

it]

In 1889,

Russian-

born

engineer 

Mikhail

Dolivo-

Dobrovols

ky develop

ed the

first three-

phase tran

sformer at

the Allgem

eine

Elektricität

s-

Gesellsch

aft('Gener

al

Electricity

Company'

) in

Germany.[115]

In

1891, Niko

la

Tesla inve

nted

the Tesla

coil, an

air-cored,

dual-tuned

resonant

transforme

r for

generating

very high

voltages a

t high

frequency.[116][117]

See als

o[edit]

Step Down TransformerPosted by P. Marian in Power supply, Theory with 37 comments Tagged with: transformers

   

What is a step down transformer: is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “steps down” the voltage applied to it.

As a step-down unit, the transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. The primary winding, which doesn’t have to conduct as much current, may be made of smaller-gauge wire.

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Step Down Tranformer Considerations how to wire a step down transformer how to check a step down transformer

Step-Down Tranformer Considerations

It is possible to operate either of these transformer types backwards (powering the secondary winding with an AC source and letting the primary winding power a load) to perform the opposite function: a step-up can function as a step-down and visa-versa. One convention used in the electric power industry is the use of “H” designations for the higher-voltage winding (the primary winding in a step-down unit; the secondary winding in a step-up) and “X” designations for the lower-voltage winding.

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One of the most important considerations to increase transformer efficiency and reduce heat is choosing the metal type of the windings. Copper windings are much more efficient than aluminum and many other winding metal choices, but it also costs more. Transformers with copper windings cost more to purchase initially, but save on electrical cost over time as the efficiency more than makes up for the initial cost.

Step-down transformers are commonly used to convert the 220 volt electricity found in most parts of the world to the 110 volts required by North American equipment.

How to Wire a Step Down Transformer

1. Observe and identify the schematic and rating of the step down transformer to be installed. Remove the terminal connection box cover placed at the lower side of the transformer. Only the high amperage types will have this enclosure, while lower powered transformers will have an exposed screw terminal.

2. Know termination identification follows for all step down transformers: H1, H2, H3 and H4 signify the high voltage side or power feed end of the transformer. This holds

true regardless of the size of the transformer. Interconnection of the transformer will vary depending on the manufacturer and voltage used for feeding the transformer.

3. Terminate the feed power wires first by cutting the wires to length. If you are using large wire lugs be sure to take into consideration the length of the lug and the amount of wire that can be inserted into the female crimp area.

4. Strip back the outer insulating of the wires with the pocketknife or wire strippers. Insert the eye ring or wire lug over the bare copper wire and crimp the connection device, using the appropriate-size crimper, permanently to the wire.

5. Terminate the high side, high voltage of the step down transformer. If the high side terminals are bolts, be sure to follow any torque requirements that are listed by the manufacturer.

6. Terminate the low side, low voltage of the transformer. Note these terminals will be identified by X1, X2, X3 and X4. Again follow the manufacturer’s individual schematics for that particular type of transformer. Note that on small control transformers there will only be an X1 and X2. X1 is the power or “hot” side and X2 is generally the grounding and neutral portion of the low voltage.

7. Terminate the small control transformer for X1 and X2. X1 will go directly to the control circuit after passing through a small fuse that is rated for the circuit. X2 will be terminated not only to the neutral side of the control circuit, but the grounding safety as well. In other words, the X2 side of the small control transformer must be tied to the grounding system of the electrical circuit.

8. Replace all covers on the transformer and any enclosures that protect you from electricity. Apply the high voltage to the transformer by switching on the feeder power circuit. Turn on the low side safety circuit control.

9. Use a volt meter to test for proper voltage on the step down side of the transformer. It should be the same that is listed on the specs tag provided by the manufacturer.

How to Check a Step Down Transformer

1. Remove all wires from the transformer terminals using the screwdriver. Identify the wires if they are not already identified. Use a clear tape and pen. Write the terminal that the wires are attached to and place the identified tape on the wire’s end.

2. Turn the volt ohmmeter to the “Ohms” position and place the red lead into the connector identified as “Ohms.” Touch the black lead to the metal frame of the transformer.

3. Touch the red lead to the transformer’s terminals in the following order: H1, H2, X1 and then X2. The meter should read infinite ohms or wide open. Infinite ohms on a digital meter will be identified as a blank screen or a wide open will have the word “Open” displayed. If the meter registers any form of resistance, there is an internal problem with the windings. The copper coils may be shorted to the metal frame of the transformer. The transformer will have to be replaced.

4. Check the continuity of each separate coil using the ohmmeter. Touch the black lead to H1 and the red lead to H2. The meter should give a resistance reading. Generally,

it should read in the range of 3 to 100 ohms, depending on the style and type of transformer. Perform the same test to the X1 and X2 terminals. You should receive the same results. If the meter reads infinite ohms or a wide open when checking between the terminals of the same coil, the wires are broken. Replace the transformer.

5. Use the ohmmeter to conduct the transformers isolation circuit. Touch the red lead to H1 and the black lead to X1. The meter should read infinite ohms or a wide-open circuit. Perform the same test, but to H2 and X2 respectively. If any resistance at all is read on the meter other than a wide-open circuit, the isolation of the transformer has been compromised and must be replaced.

An Introduction to Interrupts

Difficulty

 

Beginner, small amount of advanced code

Skills Required

 

Familiarity with microcontrollers.

Parts Required

 

Arduino, to run examples. Any microcontroller will do though.

Introduction to InterruptsWhy would I need an interrupt? Robots spend a lot of time waiting for things to happen. A common example: your robot wants to drive straight until an IR sensor says that an object is too close. Seems fairly simple:

Code:driveForward();while(sensor_value == DIGITAL_HIGH){ // maybe do some other stuff, like follow a wall.

};stop();

This code is "polling" the sensor. It keeps checking the value over and over again manually (in software). This works of course, but what if your "other stuff" starts to be a really long process - you might overshoot and run into the wall. What happens if the event we are trying to detect is really short - you might miss it. In these instances you want to use an interrupt. Common examples where interrupts are used:

Counting pulses from an encoder (they are really short, and come very often)

Catching some short pulse (like the 10ms pulse given off by a UVTron sensor)

Using switches or digital IR sensors as bumpers (and you want an instant stop)

What is an interrupt?The really cool thing about microcontrollers is they have fancy hardware that can do things like PWM, analog-to-digital conversion -- and interrupts. An interrupt is a little piece of hardware that sits, waiting to detect a trigger event, such as a particular pin going from a low state to a high state. When this event happens:

1. the interrupt triggers2. the microcontroller stops executing it's current program3. the microcontroller starts executing an Interrupt Service Routine, or ISR4. when the ISR is done, we return to the original program

So a hardware interrupt is sort of like when the President interrupts your nightly TV viewing to tell you the economy has crashed. The trigger event is the economy crashing, and immediately as that happens the hardware (President) runs an ISR (his talk to the nation). 

In your ISR, you would have code that does some processing to handle the event. For instance, your ISR would:

Increment the value of a counter, if you were counting pulses from an encoder

Set a flag to say "fire found" if you were monitoring a UVTron Stop the robot if you were using interrupt bumpers

Most microcontrollers support a wide variety of interrupt triggers:

A particular pin state going from low to high A particular pin state going from high to low Any change on a particular pin

Typically, microcontrollers only have a few interrupts, on specific pins. We'll discuss a slight change to this below in the section "Wait, I've run out of interrupts". Another interesting point to note, that won't really be discussed much here, is that PWM and hardware timer/counters rely entirely on hardware that is similar to interrupts.

The Interrupt-Driven BumperLet's now implement an example using the Arduino. The Arduino is based on an ATMEGA168 AVR. This chip has 2 hardware interrupts (named 0 and 1). The pins that can be used for interrupt triggers are tied to digital 2 and 3, respectively. The Arduino makes using interrupts quite easy, they have a function AttachInterrupt(interrupt, ISR, trigger):

interrupt is which hardware interrupt 0 (Digital 2) or 1 (digital 3). ISR is the function with is to be used as the ISR trigger is either: RISING, FALLING, or CHANGE, for which events to

trigger on

The code below will use several psuedo functions which you will need to implement for your particular robot:

DriveForward() - make the robot move forward at some regular speed DriveBackward() - make the robot move backward at some regular

speed Stop() - stops the robot TurnLeft() - make a little turn left, like 45 degrees or so

For our example, we will assume you have a bump switch. It should be tied between ground and the digital input pin (we'll use a pullup resistor to keep them at 5V when not pressed).

There are a few things going on here. First, we start rolling forward. We have an integer used as a flag, that is either 0 when we have not hit an object, or 1 when we hit something. An interrupt occurs when we hit something, it will stop the robot to avoid any damage, and also set our flag. Then, our main loop will handle backing the robot up when it gets a chance. There are a few reasons to implement our code like this. First, delay() relies on interrupts. Second, you don't ever want interrupts to run for very long, as they will typically stop other interrupts from occurring -- this can be devastating when you have something like a system clock that relies on interrupts (as the Arduino does). 

Code:// Interrupt-Driver Bumper Example// A bumper switch on the front of the robot should be tied to digital pin 2 and ground

#include <avr/interrupt.h>

volatile int bumper; // have we hit something

void setup(){ pinMode(2, INPUT); // Make digital 2 an input digitalWrite(2, HIGH); // Enable pull up resistor

// attach our interrupt pin to it's ISR attachInterrupt(0, bumperISR, FALLING); // we need to call this to enable interrupts interrupts();

// start moving bumper = 0; DriveForward();}

// The interrupt hardware calls this when we hit our left bumpervoid bumperISR(){ Stop(); bumper = 1;}

void loop(){ // if bumper triggered if(bumper > 0){ DriveBackward(); // set motors to reverse delay(1000); // back up for 1 second TurnRight(); // turn right (away from obstacle) bumper = 0; DriveForward(); // drive off again... } // we could do lots of other stuff here.}

Wait, I ran out of interrupts!The Arduino library only supports 2 pin interrupts, because it only uses the 2 dedicated hardware interrupts. However, the ATMEGA168 (the chip that the Arduino is built out of) can actually generate interrupts on every port, it's just slightly more complicated. These are called the Pin Change Interrupts. Each port of the AVR has it's own interrupt vector, and you can turn on interrupts for as many of the pins as you want. There are a few limitations though. First, an interrupt is generated for any pin change, you can't limit the hardware to rising or falling only, although you could implement that in your ISR. Second, because all of the pins in a port share an interrupt vector, if you use more than one pin in a port you will have to manually check which pin generated the interrupt. It should be noted that switching into the ISR takes several clock cycles, so your ISR will not run instantaneously, and thus it may be difficult to "check" which pin generated the interrupt.Lastly, because there isn't a library out there, you have to write a little more code.

Note that the Arduino has arbitrary names for its pins, that have no relevance to the AVR names, you'll have to use the ATMEGA168 datasheet, plus the Arduino pin out chart to sort out register values. This is definately an advanced topic, but it is a great way to learn a few more details of the AVR architecture.

Code:// Quick example of using pin change interrupts// This shows how to use Digital Pin 4 (PCINT18/PD2) as an interrupt

#include <avr/interrupt.h>

// we need to remember that the Arduino environment uses different pin numbers// than the ATMEGA168 itself.

void setup(){ // Make digital 4 (PCINT18/PD2) an input pinMode(4, INPUT); // this is ATMEGA168 specific, see page 70 of datasheet

// Pin change interrupt control register - enables interrupt vectors // Bit 2 = enable PC vector 2 (PCINT23..16) // Bit 1 = enable PC vector 1 (PCINT14..8) // Bit 0 = enable PC vector 0 (PCINT7..0) PCICR |= (1 << PCIE2); // Pin change mask registers decide which pins are enabled as triggers PCMSK2 |= (1 << PCINT18);

// enable interrupts interrupts();}

void loop(){ // do nothing...}

// we have to write our own interrupt vector handler..ISR(PCINT2_vect){ // this code will be called anytime that PCINT18 switches // (hi to lo, or lo to hi)}

Some Warnings for Arduino UsersDon't use the delay() or millis() functions inside an ISR on the Arduino. The reason being that they depend on the system clock, which itself is generated from an interrupt. On the AVR architecture, when one interrupt starts processing its ISR, all other intterupts are disabled temporarily. For this same reason, you want to keep your ISR as short as possible (to avoid messing with the system clock itself).

End NotesThat about covers the basics of interrupts, with some examples using the Arduino. Take a look at my tutorial on closed loop feedback for more information about using encoders