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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