PPT ON TRANSFORMERS

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Transformers  Presentation Transcript

1.Transformers

2.TRANSFORMERS

3.Presentation outline
Need
Working Principle
Types of Transformers
Construction Features
Transformers Accessories
Major Transformers in Power Plants
Transformer Losses
Condition Monitoring of Transformers

4.WHY TRANSFORMER
TO OPTIMISE COST OF BULK TRANSMISSION OF POWER FROM GENERATORS TO CONSUMERS
REDUCTION IN TRANSMISSION LOSS
TO REDUCE OR INCREASE VOLTAGE IN AC SYSTEM
ENABLES SAFE SUPPLY VOLTAGE TO CONSUMERS
ISOLATION OF TWO SYSTEMS FOR VOLTAGE REGULATION

5.Definition of Transformer as per Stds
IEC 60076-1 A static piece of apparatus with two or more windings which, by electromagnetic induction, transforms a system of alternating voltage and current into another system of voltage and current usually of different values and at the same frequency for the purpose of transmitting electrical power. IEEE C57.12.80-2002 A static device consisting of a winding, or two or more coupled windings with or without a magnetic core for introducing mutual coupling between electrical circuits.

6.What are the Types of Transformers
Power transformers : Used in transmission network of higher voltages, deployed for step-up and step down transformer application (400 kV, 200 kV, 110 kV, 66 kV, 33kV,22kV)
Distribution transformers: Used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V)

7.Working Principle
If a time-varying voltage   is applied to the primary winding of turns, a current will flow in it producing a magnetomotive force (MMF). Just as an electromotive force (EMF) drives current around an electric circuit, so MMF tries to drive magnetic flux through a magnetic circuit. The primary MMF produces a varying magnetic flux   in the core, and, with an open circuit secondary winding, induces a back electromotive force (EMF). In accordance with Faraday's law of induction, the voltage induced across the primary winding is proportional to the rate of change of flux:    

8.Classifications
Transformers are adapted to numerous engineering applications and may be classified in many ways:
By power level:
     (from fraction of a volt-ampere(VA) to over a thousand MVA),
By application:
    (power supply, impedance matching, circuit isolation),
By frequency range:
    (power, audio, radio frequency(RF))
By voltage class:
    (a few volts to about 765 kilovolts)

9.By cooling type:
     (air cooled, oil filled, fan cooled, water cooled (Natural/ Forced) etc.)
By purpose:
     (distribution, rectifier, arc furnace, amplifier output, etc.).
By ratio of the number of turns in the coils
Step-up The secondary has more turns than the primary.
      Step-down The secondary has fewer turns than the     primary.
Connection :
     Single phase, Star / star,  Star delta etc
Construction :
    Core Type     Shell Type

10.Basic Components of a Transformer
•Current conductors – Primary & Secondary Windings •Magnetic flux conductor - Laminated Steel Core and also Insulation •Cooling •Protection •Supporting accessories

11.COMPONENTS - CORE
Core -The “conductor” for the flux -The skeleton for mechanical  rigidity of the active part -The core, an unbroken path for magnetic flux CRGO or Cold Rolled Grain Oriented Steel is available in various grades (generally called M3, M4, M5 & M6).

12.The transformers are of two general types distinguished from each other by the manner in which the primary and secondary coils are placed around the laminated steel core. They are
shell type and
core type.

13.Transformer Insulation
Minor insulation Like inter turn insulation, is achieved using cellulogic paper.
Major insulation   Between primary and secondary, phase to phase and inner coil to core. This is achieved by Bakelite, wooden blocks, cellulogic paper cylinders.
Transformer Oil: derivative or petroleum crude. This has good dielectric strength.
    also a good cooling medium and absorbs heat from the windings in transformer.

14.Thus mineral oil has a flash point of 140°C and 160°C fire point. This also 'can Sustain the combustion with its own energy, once it catches fire. Thus this is unsuitable for the transformer located indoors.
The indoor transformers are filled with a synthetic liquid known as silicate liquid. This  has flash point well above 300°C.

15.Transformer Oil

16.USE OF TRANSFORMER OIL WITH CRUDE BASE
NAPTHANIC BASE OILS GENERALLY HAVE HIGHER RESISTIVITY VALUES
OIL PARAMETERS ARE IMPORTANT.
PRESENT NTPC SPEC. IS IN LINE WITH IS:335 (1993).
SUGGESTED IS TO HAVE OIL WITH LOW VISCOSITY AS COMPARED TO PRESENTLY BEING USED FOR BETTER COOLING AND FOR BETTER OIL FLOW.

17.Accessories & Auxiliaries
Tap Changer(s)-(On load/Off load)
Tank
Radiators
cooling fans, oil pumps, oil to water heat exchangers (Cooling ONAN / ONAF/ OFAF/ OFWF external coolers)
Bushings

18.Buchholz Relay/Oil Surge Relay
Temperature Indicators- WTI ,  OTI
Oil Level Indicators
Pressure Relief Device
Marshalling Box/Control cubicle
Oil Preservation Systems: Conservators (gas sealed, Bellows/membrane sealed) Breathers Thermo siphon Filters

19.Buchholz Relay

20.BUCHHOLZ PROTECTION

21.Off Load Tap Changer

22.A CONSERVATOR IS A CYLIDERICAL VESSEL WHICH PROVIDES SPACE FOR EXPANSION OF OIL INSIDE THE TRANSFORMER OR SUPPLIES OIL TO THE TRANSFORMER WHEN THE TRANSFORMER OIL COOLS AND CONTRACTS IN VOLUME.
A CONSERVATOR IS ALWAYS PLACED ABOVE THE TRANSFORMER.

23.SILICA  GEL BREATHER

24.Pressure Relief Device( PRD)

25.Cooling of Transformers
Heat is produced in the windings due to current flowing in the conductors (I- R) and in the core on account of eddy currents and hysteresis losses.
Types: ONAN, ONAF, OFAF, OFWF
Air Cooled: In small dry type transformer heat is dissipated directly to the atmosphere.
Oil Cooled: In oil immersed transformers heat is dissipated by thermo-syphon system action. The oil serves as the medium for transferring the heat produced inside the transformer to the outside atmosphere. Based on Thermo-syphon principle.

26.Different transformers in a power Plant
Generator Transformer (GT)
Station Transformer (ST)
Unit Auxiliary Transformer (UAT)
Excitation Transformer
Neutral Grounding Transformer
Auxiliary transformers
Tie / Auto transformer

27.SPECIFICATION
                    STAGE -1 GT-Vindhyachal
   RATED O/P                   250MVA
   RATED VOLT. (HV)        420KV
   RATED VOLT. (LV)        15.75KV
   RATED CURRENT(HV)  344A
   RATED CURRENT(LV)   9175A
   VECTOR GROUP            Ynd11     

28.Instrument Transformers
. Step down values to safe levels for measurement
. Potential Transformers
. Also called voltage transformers
. Standard output 120V
. Current Transformers
. Standard output of 1 or 5 amps
. Metering and relaying standards
. Can produce high voltages if open circuited

29. Rectifier transformers
Output of the main transformer is connected to the rectifier unit.

30. Transformer connections :
       - Delta/Star…used in Generating stations for Step-up
.
        - Star/Delta…used in Receiving stations for Step-down

 * All GTs are Delta/Star connected.

    All Tie T/Fs are Star/Star connected.

31.Transformer losses
Load loss (or copper loss)
No load loss (or iron loss)
The total transformer loss, PTOTAL, at any load level can then be calculated from:
 PTOTAL = PNO-LOAD+ (% Load)2 x PLOAD

32.THE FOLLOWING TESTS ARE GENERALLY PERFORMED ON THE
TRANSFORMER REFERENCE STANDARD : IEC 60076
                ROUTINE TESTS
MEASUREMENT OF WINDING RESISTANCE
MEASUREMENT OF VOLTAGE RATIO, POLARITY AND CHECK OF VOLTAGE VECTOR RELATIONSHIP
MEASUREMENT OF NO-LOAD LOSS AND EXCITATION CURRENT
MEASUREMENT OF INSULATION RESISTANCE
SWITCHING IMPULSE VOLTAGE WITHSTAND TEST
LIGHTNING IMPULSE VOLTAGE WITHSTAND TEST

33.MECHANICAL TESTS
MEASUREMENT OF VIBRATION ON TRANSFORMER TANK
VACUUM TEST ON TRANSFORMER TANK
OIL PRESSURE TEST ON COMPLETELY ASSEMBLED TRANSFORMER
PRESSURE RELIEF DEVICE TEST

34.TYPE TESTS
TEMPERATURE RISE TEST
MEAUREMENT OF POWER TAKEN BY COOLING CIRCUITS

35.SPECIAL TESTS
MEASUREMENT OF ACOUSTIC SOUND LEVEL
DETERMINATION OF CAPACITANCES  AND TAN DELTA BETWEEN WINDING-TO-EARTH AND BETWEEN WINDINGS

36.On-Line Monitoring

37.ON LINE MONITORING EQUIPMENT ON TRANSFORMER
DGA to be monitored on all transformers periodically.

 Periodicity depends on the nature of evaluation of gases.

38.3. Acoustic PD measurement.
    In case DGA results indicate the presence of high discharges  Acoustic PD measurement is done.
    Acoustic PD detector consists of sensor which can sense sound vibrations produced due to occurrence of discharges in oil.
    The sensor has pre-amplifier and filter circuit to eliminate environmental noise

4    Infrared thermography
    With the help of infrared thermo-vision camera, the thermo-image of transformer is prepared
    This scanning helps in detecting overheated zones, loose & corroded connection.

39.1. Frequency Response Analysis
Short circuit forces could move the winding.

Can also change winding inductance and capacitance.

Conventional tests are not sensitive to winding movement

Such changes can be effectively detected by FRA

40.4.    Resistance & magnetizing current.
Maintenance schedule call for daily , quarterly, yearly, two     yearly maintenance requirement.
Over and above after 7 to     10     years, thorough overhauling and inspection of core-coil         assembly by lifting tank top cover / core-coil assembly             needed
    In overhauling sludge deposited on coil is removed and coil     assembly which may become loose is tightened. All other         clampings & cleats etc. are also tightened