Download TRANSFORMER

BASICS OF
TRANSFORMER
1
NEED
WORKING PRINCIPLE
TYPES OF TRANSFORMERS
CONSTRUCTION FEATURES
TRANSFORMERS ACCESSORIES
MAJOR TRANSFORMERS IN POWER PLANTS
TRANSFORMER LOSSES
CONDITION MONITORING OF TRANSFORMERS
2
HISTORICALLY, THE FIRST ELECTRICAL POWER
DISTRIBUTION SYSTEM DEVELOPED BY EDISON
IN 1880s WAS TRANSMITTING DC (DIRECT
CURRENT)
IT WAS DESIGNED FOR LOW VOLTAGES (SAFETY
AND DIFFICULTIES IN VOLTAGE CONVERSION);
THEREFORE, HIGH CURRENTS WERE NEEDED TO
BE GENERATED AND TRANSMITTED TO DELIVER
NECESSARY POWER
THIS SYSTEM SUFFERED SIGNIFICANT ENERGY
LOSSES!
THE SECOND GENERATION OF POWER DISTRIBUTION
SYSTEMS (WHAT WE ARE STILL USING) WAS PROPOSED BY
TESLA FEW YEARS LATER.
HIS IDEA WAS TO GENERATE AC POWER OF ANY
CONVENIENT VOLTAGE, STEP UP THE VOLTAGE FOR
TRANSMISSION (HIGHER VOLTAGE IMPLIES LOWER
CURRENT AND, THUS, LOWER LOSSES),
TRANSMIT AC POWER WITH SMALL LOSSES, AND FINALLY
STEP DOWN ITS VOLTAGE FOR CONSUMPTION
POWER LOSS IS PROPORTIONAL TO THE SQUARE OF THE
CURRENT TRANSMITTED
THE STEP UP AND STEP DOWN VOLTAGE CONVERSION WAS
BASED ON THE USE OF TRANSFORMERS.
O OPTIMISE COST OF BULK TRANSMISSION OF
POWER FROM GENERATORS TO CONSUMERS
REDUCTION IN TRANSMISSION LOSS
O REDUCE OR INCREASE VOLTAGE IN AC SYSTEM
NABLES SAFE SUPPLY VOLTAGE TO CONSUMERS
SOLATION OF
REGULATION
TWO
SYSTEMS
FOR
VOLTAGE
A TRANSFORMER IS A DEVICE
HAT CONVERTS ONE AC VOLTAGE TO ANOTHER
T THE SAME FREQUENCY
AC VOLTAGE
CONSISTS OF ONE OR MORE COIL(S) OF WIRE WRAPPED
ROUND A COMMON FERROMAGNETIC CORE
HESE COILS ARE USUALLY NOT CONNECTED ELECTRICALLY
OGETHER
OWEVER, THEY ARE CONNECTED THROUGH THE COMMON
AGNETIC FLUX CONFINED TO THE CORE
SSUMING THAT THE TRANSFORMER HAS AT LEAST TWO
INDINGS, ONE OF THEM (PRIMARY) IS CONNECTED TO A
OURCE OF AC POWER; THE OTHER (SECONDARY) IS
ONNECTED TO THE LOADS.
CORE TYPE
 CIRCULAR SHAPED
WINDINGS
SHELL TYPE:
 RECTANGULAR SHAPED
WINDINGS
CORE
HE CORE WILL WORK AS A CAGE FOR THE MAGNETIC FLUX
OST OF THE FLUX WILL BE KEPT INSIDE THE CORE
HE CORE IS MADE WITH A VERY SPECIAL ELECTRICAL STEEL
HE STEEL IS MADE AS THIN INSULATED SHEETS WHICH
UST BE MOUNTED ONE BY ONE
HE FINAL GOAL IS TO MINIMIZE THE SIZE OF THE CORE
ND LOSSES.
THE CORE:
WHICH PROVIDES A PATH FOR THE
MAGNETIC LINES OF FLUX
THE PRIMARY WINDING:
WHICH RECEIVES
ENERGY FROM THE AC SOURCE
THE SECONDARY WINDING:
ENERGY FROM THE PRIMARY
DELIVERS IT TO THE LOAD
THE ENCLOSURE:
WHICH RECEIVES
WINDING
AND
WHICH PROTECTS THE ABOVE
COMPONENTS
FROM
DIRT,
MOISTURE,
AND
MECHANICAL DAMAGE.
2 ADJACENT COILS
COILS NOT PHYSICALLY CONNECTED TO EACH OTHER
HE PRIMARY WINDING IS CONNECTED TO A 50 HERTZ
OLTAGE SOURCE
AC
HE MAGNETIC FIELD (FLUX) BUILDS UP (EXPANDS) AND
OLLAPSES (CONTRACTS) ABOUT THE PRIMARY WINDING
HE EXPANDING AND CONTRACTING MAGNETIC FIELD
ROUND THE PRIMARY WINDING CUTS THE SECONDARY
INDING AND INDUCES AN ALTERNATING VOLTAGE INTO
HE WINDING
HIS VOLTAGE CAUSES ALTERNATING CURRENT TO FLOW
HROUGH THE LOAD
HE VOLTAGE MAY BE STEPPED UP OR DOWN DEPENDING ON
HE DESIGN OF THE PRIMARY AND SECONDARY WINDINGS.
HEN A LOAD DEVICE IS CONNECTED ACROSS THE SECONDARY
INDING OF A TRANSFORMER, CURRENT FLOWS THROUGH THE
CONDARY AND THE LOAD
E MAGNETIC FIELD PRODUCED BY THE CURRENT IN THE
CONDARY INTERACTS WITH THE MAGNETIC FIELD PRODUCED BY
E CURRENT IN THE PRIMARY
IS INTERACTION RESULTS FROM THE MUTUAL INDUCTANCE
TWEEN THE PRIMARY AND SECONDARY WINDINGS.
 SIMPLE TRANSFORMER INDICATING
PRIMARY- AND SECONDARY-WINDING
FLUX RELATIONSHIP
THE VOLTAGES IN THE PRIMARY & SECONDARY
COILS DEPEND ON NUMBER OF TURNS IN COILS
Vp = PRIMARY VOLTAGE
Vs = SECONDARY VOLTAGE
Np = NUMBER OF TURNS OF PRIMARY COIL
Ns = NUMBER OF TURNS OF SECONDARY COIL
THERE ARE 2 TYPES OF TRANSFORMERS
STEP-UP TRANSFORMER
Vs  Vp
Ns  Np
CIRCUIT
SYMBOL
STEP-DOWN TRANSFORMER
CIRCUIT
SYMBOL
Vs < Vp
Ns < Np
IF NO POWER IS LOST IN A TRANSFORMER
(NO POWER LOSS)
F THE SECONDARY OF A TRANSFORMER HAS TWO TIMES AS
ANY TURNS AS THE PRIMARY, THE VOLTAGE INDUCED INTO
HE SECONDARY WILL BE TWO TIMES THE VOLTAGE ACROSS
HE PRIMARY
F THE SECONDARY HAS ONE-HALF AS MANY TURNS AS THE
RIMARY, THE VOLTAGE ACROSS THE SECONDARY WILL BE
NE-HALF THE VOLTAGE ACROSS THE PRIMARY.
OWEVER, THE TURNS RATIO AND THE CURRENT RATIO OF A
RANSFORMER HAVE AN INVERSE RELATIONSHIP.
HUS, A 1:2 STEP-UP TRANSFORMER WILL HAVE ONE-HALF
HE CURRENT IN THE SECONDARY AS IN THE PRIMARY.
2:1 STEP-DOWN TRANSFORMER WILL HAVE TWICE THE
URRENT IN THE SECONDARY AS IN THE PRIMARY.
POWER
TRANSFORMERS
:
USED
IN
TRANSMISSION NETWORK OF HIGHER VOLTAGES,
DEPLOYED FOR STEP-UP AND STEP DOWN
TRANSFORMER APPLICATION (765 kV, 400 kV,
220 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)
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 IN TRANSFORMERS ARE STAR/STAR
CONNECTED.
TRANSFORMER CONNECTIONS
STAR / STAR CONNECTION
STAR / DELTA CONNECTION
O-LOAD LOSSES TAKE PLACE MAINLY IN THE CORE SHEETS. IT
ORRESPONDS TO ABOUT 25% OF THE TRANSFORMER LOSSES
HE DC LOSSES TAKE PLACE EXCLUSIVELY IN WINDINGS
HE EDDY/STRAY LOSSES TAKE PLACE IN ALL PIECES OF METAL
NSIDE THE TRANSFORMER (FRAMES, CORE, WINDING, TANKS
TC), A LARGE PART OF IT ARE GENERATED IN THE WINDINGS
SPECIALLY DANGEROUS LOSSES ARE THE ONES CONCENTRATED IN
SMALL VOLUME SINCE THEY MAY CAUSE A HOT-SPOT.
TO MODEL A REAL TRANSFORMER ACCURATELY, WE
NEED TO ACCOUNT FOR THE FOLLOWING LOSSES:
COPPER LOSSES:RESISTIVE HEATING IN THE WINDINGS I2R
EDDY CURRENT LOSSES :
RESISTIVE HEATING IN THE
CORE, PROPORTIONAL TO THE SQUARE OF VOLTAGE APPLIED TO
THE TRANSFORMER
HYSTERESIS LOSSES :
ENERGY NEEDED TO REARRANGE
MAGNETIC DOMAINS IN THE CORE
LEAKAGE FLUX :
FLUX THAT ESCAPES FROM THE CORE AND
FLUX THAT PASSES THROUGH ONE WINDING ONLY.
NOT ALL THE MAGNETIC FIELD PRODUCED BY
THE PRIMARY IS INTERCEPTED BY THE
SECONDARY.
A PORTION OF THE LEAKAGE FLUX MAY INDUCE
EDDY CURRENTS WITHIN NEARBY CONDUCTIVE
OBJECTS, SUCH AS THE TRANSFORMER'S
SUPPORT STRUCTURE, AND BE CONVERTED TO
HEAT.
SSES IN THE TRANSFORMER ARE OF THE ORDER OF 1% OF ITS
LL LOAD KW RATING
ESE LOSSES GET CONVERTED IN THE HEAT THEREBY THE
MPERATURE OF THE WINDINGS, CORE, OIL AND THE TANK RISES
E HEAT IS DISSIPATED FROM THE TRANSFORMER TANK AND THE
ADIATOR IN TO THE ATMOSPHERE
RANSFORMER
COOLING
HELPS
IN
MAINTAINING
THE
MPERATURE RISE OF VARIOUS PARTS WITHIN PERMISSIBLE
MITS
CASE OF TRANSFORMER, COOLING IS PROVIDED BY THE
RCULATION OF THE OIL
RANSFORMER OIL ACTS AS BOTH INSULATING MATERIAL AND ALSO
OOLING MEDIUM IN THE TRANSFORMER
R SMALL RATING TRANSFORMERS HEAT IS REMOVED FROM THE
RANSFORMER BY NATURAL THERMAL CONVECTION
R LARGE RATING TRANSFORMERS THIS TYPE OF COOLING IS NOT
DIFFERENT TRANSFORMER COOLING METHODS
ARE:
AIR COOLING FOR DRY TYPE TRANSFORMERS:
AIR NATURAL TYPE (A.N.)
AIR FORCED TYPE (A.F.)
COOLING FOR OIL IMMERSED TRANSFORMERS:
OIL NATURAL AIR NATURAL TYPE (O.N.A.N.)
OIL NATURAL AIR FORCED TYPE (O.N.A.F.)
OIL FORCED AIR NATURAL TYPE (O.F.A.N.)
OIL FORCED AIR FORCED TYPE (O.F.A.F.)
OIL IMMERSED WATER COOLING:
OIL NATURAL WATER FORCED (O.N.W.F.)
OIL FORCED WATER FORCED (O.F.W.F.)
RANSFORMERS ABOVE 60 MVA EMPLOY A COMBINATION OF FORCED OIL
ND FORCED AIR COOLING
IL NATURAL AIR FORCED TYPE OF COOLING IS NOT ADEQUATE TO REMOVE
HE HEAT CAUSED BY THE LOSSES WHICH IS APPROXIMATELY EQUAL TO
% OF THE TRANSFORMER RATING (0.6MW)
N CASE OF FORCED OIL AND FORCED AIR COOLING SYSTEM A SEPARATE
OOLER IS MOUNTED AWAY FROM THE TRANSFORMER TANK
HIS COOLER IS CONNECTED TO THE TRANSFORMER WITH PIPES AT THE
OTTOM AND THE TOP
HE OIL IS CIRCULATED FROM THE TRANSFORMER TO THE COOLER
HROUGH THE PUMP
HE COOLER IS PROVIDED WITH THE FANS WHICH BLAST AIR ON THE
OOLING TUBES
HIS TYPE OF COOLING IS PROVIDED FOR THE HIGHER RATING
RANSFORMERS AVAILABLE AT THE SUBSTATIONS AND POWER STATIONS.
IS TYPE OF COOLING SYSTEM NEEDS A HEAT EXCHANGER IN
HICH THE HEAT OF THE TRANSFORMER OIL IS GIVEN TO THE
OOLING WATER
E COOLING WATER IS TAKEN AWAY AND COOLED IN SEPARATE
OOLERS
E OIL IS FORCED THROUGH THE HEAT EXCHANGER
E OIL PUMP PUMPS THE OIL FROM TRANSFORMER TO THE HEAT
CHANGER THOUGH THE TOP PIPES
L FROM THE HEAT EXCHANGER IS PUMPED BACK TO THE
RANSFORMER THROUGH THE BOTTOM PIPE
IS TYPE OF COOLING IS PROVIDED FOR VERY LARGE
RANSFORMERS WHICH HAVE RATINGS OF SOME HUNDREDS OF MVA
ENERATING TRANSFORMER WILL HAVE VERY HIGH RATING AND
ATING EQUAL TO THE RATING OF THE GENERATOR)
IS TYPE OF TRANSFORMERS IS USED IN LARGE SUBSTATIONS AND
GENERATOR TRANSFORMER (GT)
STATION TRANSFORMER (ST)
UNIT AUXILIARY TRANSFORMER (UAT)
EXCITATION TRANSFORMER
NEUTRAL GROUNDING TRANSFORMER
AUXILIARY TRANSFORMERS
AUTO TRANSFORMER
GENERATOR TRANSFORMER:
THE GENERATOR
S CONNECTED TO THIS TRANSFORMER BY MEANS OF
SOLATED BUS DUCTS.
THIS TRANSFORMER IS USED TO STEP UP THE
GENERATING VOLTAGE OF AROUND 15KV TO GRID
VOLTAGE.
THIS TRANSFORMER IS GENERALLY PROVIDED WITH
OFAF COOLING.
T IS ALSO PROVIDED WITH OFF CIRCUIT/ON LOAD
TAPS ON THE HIGH VOLTAGE SIDE.
THIS TRANSFORMER HAS ELABORATE COOLING
SYSTEM CONSISTING OF NUMBER OF OIL PUMPS AND
COOLING FANS APART FROM VARIOUS ACCESSORIES.
HE UAT DRAWS ITS INPUT FROM THE MAIN BUSDUCT
CONNECTING GENERATOR TO THE GENERATOR
RANSFORMER.
HE
TOTAL
KVA
CAPACITY
OF
UNIT
AUXILIARY
RANSFORMER REQUIRED CAN BE DETERMINED BY
ASSUMING 0.85 POWER FACTOR AND 0.9 EFFICIENCY FOR
OTAL AUXILIARY MOTOR LOAD.
T IS SAFE AND DESIRABLE TO PROVIDE ABOUT 20% EXCESS
CAPACITY THAN CIRCULATE SO AS TO PROVIDE FOR
MISCELLANEOUS AUXILIARIES AND POSSIBLE INCREASE IN
AUXILIARY LOAD.
WITH HIGHER UNIT RATINGS AND HIGHER STEAM
CONDITIONS, THE AUXILIARY POWER REQUIRED ALSO
NCREASES
AND
LIMITATIONS
IMPOSED
BY
THE
WITCHGEAR
VOLTAGES
AVAILABLE,
INDICATE
THE
MAXIMUM SIZE OF UNIT AUXILIARY TRANSFORMER WHICH
THE STATION TRANSFORMER IS REQUIRED TO FEED
POWER TO THE AUXILIARIES DURING START UPS.
THIS TRANSFORMER IS NORMALLY RATED FOR THE
NITIAL AUXILIARY LOAD REQUIREMENTS OF UNIT.
N TYPICAL CASES, THIS LOAD IS OF THE ORDER OF
60% OF THE LOAD AT FULL GENERATING CAPACITY.
BUT IN LARGE STATIONS WHERE MORE THAN ONE
UNITS ARE OPERATING, THE STATION TRANSFORMERS
SHOULD HAVE SUFFICIENT CAPACITY TO START TWO
UNITS AT A TIME IN ADDITION TO FEEDING THE
COMMON AUXILIARIES.
T IS ALSO PROVIDED WITH ON LOAD TAP CHANGER TO
CATER TO THE FLUCTUATING VOLTAGE OF THE GRID.
HESE TRANSFORMERS ARE EMPLOYED IN THE POWER PLANTS FOR
ELIVERING POWER TO LOW VOLTAGE LOADS (VOLTAGE BELOW
KV).
HESE TRANSFORMERS CONNECTS BETWEEN HV DISTRIBUTION
USES AND LV DISTRIBUTION BUSES OF THE PLANT.
HEIR RATING WILL BE AROUND 1 TO 5MVA, NATURAL OIL
OOLING OR AIR COOLED TRANSFORMERS ARE USED.
OME OF THE POINTS RELATED
RANSFORMERS ARE LISTED BELOW:
TO
STATION
AUXILIARY
HESE TRANSFORMERS ARE LOCATED IN POWER PLANT TO STEP
OWN VOLTAGE FROM 6.6KV TO 415V.
HE RATING FOR THIS TRANSFORMER CORRESPONDS TO THE
ATING OF THE AUXILIARY LOAD IT SHOULD BE BEARING.
HESE TRANSFORMERS ARE INDOOR TYPE AND USUALLY DRY TYPE
RANSFORMERS ARE USED.
CUTAWAY VIEW OF OIL
MMERSED CONSTRUCTION
TRANSFORMER
 THE CONSERVATOR (RESERVOIR)
AT TOP PROVIDES OIL TO
ATMOSPHERE
ISOLATION
AS
COOLANT
LEVEL
AND
TEMPERATURE CHANGES.
 THE WALLS AND FINS PROVIDE
REQUIRED HEAT DISSIPATION
BALANCE
AUTOTRANSFORMER IS AN ELECTRICAL TRANSFORMER WITH ONLY ONE
NDING. THE "AUTO“ PREFIX REFERS TO THE SINGLE COIL ACTING ON
SELF AND NOT TO ANY KIND OF AUTOMATIC MECHANISM.
AN AUTOTRANSFORMER, PORTIONS OF THE SAME WINDING ACT AS BOTH
E PRIMARY AND SECONDARY SIDES OF THE TRANSFORMER. THE WINDING
S AT LEAST THREE TAPS WHERE ELECTRICAL CONNECTIONS ARE MADE.
TOTRANSFORMERS HAVE THE ADVANTAGES OF OFTEN BEING SMALLER,
GHTER, AND CHEAPER THAN TYPICAL DUAL-WINDING TRANSFORMERS, BUT
TOTRANSFORMERS HAVE THE DISADVANTAGE OF NOT PROVIDING
ECTRICAL ISOLATION.
SINGLE-PHASE TAPPED AUTOTRANSFORMER
WITH OUTPUT VOLTAGE RANGE OF 40% –
115% OF INPUT
STEP DOWN VALUES TO SAFE LEVELS FOR
MEASUREMENT
OTENTIAL TRANSFORMERS
ALSO CALLED VOLTAGE TRANSFORMERS
STANDARD OUTPUT 120V
URRENT TRANSFORMERS
STANDARD OUTPUT OF 1 OR 5 AMPS
METERING AND RELAYING STANDARDS
CAN PRODUCE HIGH VOLTAGES IF OPEN CIRCUITED
TANK
RADIATOR/ FAN/PUMP
BUSHINGS
TAP CHANGER
CONSERVATOR
BREATHER
TEMPERATURE INDICATORS
BUCHHOLZ RELAY/OIL SURGE RELAY
OIL LEVEL GAUGE
PRESSURE RELIEF DEVICE (PRD)
VALVES
ROLLER
COOLER CONTROL CUBICLE (MARSHALLING BOX)
REMOTE TAP CHANGER CONTROL CUBICLE (RTCC)
 RADIATORS ARE USED TO
INCREASE THE COOLING
AREA
 DUE TO TRANSFORMER OIL
GETS HEATED UP, HOT OIL
RISES TO TOP & FLOW TO
RADIATOR
 IN
RADIATOR
WHILE
FLOWING
DOWN,
OIL
DISSIPATES
HEAT
TO
COOLING MEDIUM
 COLD OIL AGAIN ENTERS
TRANSFORMER AT BOTTOM
OF RADIATOR
ITH THE VARIATION OF TEMPERATURE
THERE
ORRESPONDING VARIATION IN THE OIL VOLUME
IS
O ACCOUNT FOR THIS, AN
EXPANSION VESSEL CALLED
ONSERVATOR
IS ADDED TO THE TRANSFORMER WITH A
ONNECTING PIPE TO THE MAIN TANK
SMALLER
TRANSFORMERS THIS VESSEL IS OPEN
O ATMOSPHERE THROUGH DEHYDRATING BREATHERS
O KEEP THE AIR DRY)
LARGER TRANSFORMERS, AN AIR BAG IS MOUNTED
SIDE THE CONSERVATOR WITH THE INSIDE OF BAG OPEN
O ATMOSPHERE THROUGH THE BREATHERS AND THE
UTSIDE SURFACE OF THE BAG IN CONTACT WITH THE OIL
URFACE.
ICA GEL BREATHER
OTH TRANSFORMER OIL AND CELLULOSIC PAPER ARE
IGHLY HYGROSCOPIC
APER BEING MORE HYGROSCOPIC THAN THE MINERAL OIL
O THE MOISTURE, IF NOT EXCLUDED FROM THE OIL
URFACE IN CONSERVATOR, THIS WILL FIND ITS WAY
INALLY INTO THE PAPER INSULATION AND CAUSES
EDUCTION INSULATION STRENGTH OF TRANSFORMER.
O MINIMISE THIS THE CONSERVATOR IS ALLOWED TO
REATHE ONLY THROUGH THE SILICAGEL COLUMN, WHICH
BSORBS THE MOISTURE IN AIR BEFORE IT ENTERS THEONSERVATOR AIR SURFACE.
OST OF THE TRANSFORMER (SMALL
TRANSFORMERS
AVE ONLY OTI) ARE PROVIDED WITH INDICATORS
HAT
DISPLACE
OIL
TEMPERATURE
AND WINDING
EMPERATURE
HERE ARE THERMOMETERS POCKETS PROVIDED IN THE
ANK
TOP COVER WHICH HOLD THE SENSING BULLS IN
HEM
IL TEMPERATURE MEASURED IS THAT OF THE TOP OIL,
WHERE AS THE WINDING TEMPERATURE MEASUREMENT IS
NDIRECT, THIS
IS
DONE
BY
ADDING
THE
EMPERATURE RISE
OR PROPER FUNCTIONING OR OTI & WTI IT IS ESSENTIAL
O KEEP THE THERMOMETERS POCKET CLEAN AND FILLED
WITH OIL.
RANSFORMERS TANK IS A PRESSURE VESSEL AS THE INSIDE
RESSURE CAN GROUP STEEPLY WHENEVER THERE IS A
AULT IN THE WINDINGS AND THE SURROUNDING OIL IS
UDDENLY VAPORIZED
ANKS ARE TESTED FOR A PRESSURE WITHSTAND CAPACITY
F 0.35 kg/ cm2 TO PREVENT BURSTING OF THE TANK, THESE
ANKS ARE IN ADDITION PROVIDED WITH EXPANSION VENTS
ITH
A
THIN
DIAPHRAGM
MADE
OF
AKELITE/COPPER/GLASS AT THE END
N PRESENT DAY TRANSFORMERS, PRESSURE RELIEF
EVICES ARE REPLACING THE EXPANSION VENTS, THESE ARE
MILAR TO SAFETY VALVES ON BOILERS (SPRING LOADED).
 WORKS AS A PRESSURE
RELEASING VALVE
 EQUIPPED WITH ALARM/TRIP
CONTACT
 OPERATING PRESSURE:8 kg/ cm2
WINDING AND TERMINAL FAULTS
CORE FAULTS
TANK AND TRANSFORMER ACCESSORY FAULTS
ON–LOAD TAP CHANGER FAULTS
ABNORMAL OPERATING CONDITIONS
SUSTAINED OR UNCLEARED EXTERNAL FAULTS
 THE APPROXIMATE
PROPORTION OF
FAULTS DUE TO
EACH OF THE
CAUSES LISTED
ABOVE IS SHOWN
IN FIGURE
FAILURES IN TRANSFORMERS CAN BE CLASSIFIED
NTO
INDING FAILURES DUE TO SHORT CIRCUITS (TURN-TURN
AULTS, PHASE-PHASE FAULTS, PHASE-GROUND, OPEN
INDING)
ORE FAULTS
AMINATIONS)
(CORE
INSULATION
FAILURE,
SHORTED
RMINAL FAILURES (OPEN LEADS, LOOSE CONNECTIONS,
HORT CIRCUITS)
N-LOAD
TAP
CHANGER
FAILURES
(MECHANICAL,
ECTRICAL, SHORT CIRCUIT, OVERHEATING)
BNORMAL
OPERATING
CONDITIONS
VERLOADING, OVERVOLTAGE)
(OVERFLUXING,
SOURCES OF ABNORMAL STRESS IN A
TRANSFORMER ARE:
OVERLOAD
SYSTEM FAULTS
OVERVOLTAGE
REDUCED SYSTEM FREQUENCY
VERLOAD CAUSES INCREASED 'COPPER LOSS' AND A
ONSEQUENT TEMPERATURE RISE, OVERLOADS CAN BE
ARRIED FOR LIMITED PERIODS
YSTEM SHORT CIRCUITS PRODUCE A RELATIVELY INTENSE
ATE OF HEATING OF THE FEEDING TRANSFORMERS, THE
OPPER LOSS INCREASING IN PROPORTION TO THE SQUARE
F THE PER UNIT FAULT CURRENT
RANSIENT
OVERVOLTAGES
ARISE
FROM
FAULTS,
WITCHING, AND LIGHTNING DISTURBANCES AND ARE
IABLE TO CAUSE INTERTURN FAULTS
EDUCTION OF SYSTEM FREQUENCY HAS AN EFFECT WITH
EGARD TO FLUX DENSITY, SIMILAR TO THAT OF
VERVOLTAGE.
NSUFFICIENT OIL LEVEL
EEPAGE OF WATER IN OIL
ROLONGED OVER LOADING
NGLE PHASE LOADING
NBALANCED LOADING
AULTY TERMINATION (IMPROPER SIZED LUGS ETC)
OWER THEFT
ROLONGED SHORT CIRCUIT
AULTY OPERATION OF TAP CHANGER SWITCH
ACK OF INSTALLATION CHECKS
OURLY
THE FOLLOWING PARAMETERS ARE TO BE CHECKED EVERY
HOUR AND RECORDED, IF THE OBSERVED VALUE EXCEEDS
THE VALUE GIVEN BY THE SUPPLIER, IMMEDIATE REMEDIAL
ACTION SHOULD BE TAKEN.
1. WINDING TEMPERATURE
2. OIL TEMPERATURE
3. LOAD CURRENT
4. TERMINAL VOLTAGE
NORMALLY, MAXIMUM ALLOWED WINDING TEMPERATURE
IS 55ºC ABOVE AMBIENT AND OIL TEMPERATURE IS 45ºC
ABOVE AMBIENT (ACTUAL ALLOWED VALUE MAY VARY
FROM SUPPLIER TO SUPPLIER).
AILY
. OIL LEVEL IN MAIN CONSERVATOR
. OIL LEVEL IN OLTC
. OIL LEVEL IN BUSHING
4. LEAKAGE OF WATER INTO COOLER (OFWF)
. WATER TEMPERATURE (OFWF)
. WATER FLOW (OFWF)
. COLOUR OF SILICA GEL
UARTERLY CHECKING/ REPLACEMENT
RECONDITIONING OF SILICA GEL BREATHER
CHECKING OF WATER COOLER FUNCTIONING
CHECKING OF COOLING FANS FUNCTIONING
GEAR OIL FOR TAP CHANGER MECHANISM
CHECKING OF COOLING PUMPS AND MOTOR FUNCTIONING
ALF YEARLY
INSPECTION OF ALL GASKETS AND JOINTS
NNUALLY
1. PROTECTIVE RELAYS, ALARMS, METERS AND CIRCUITS
TO BE CHECKED AND CALIBRATED
2. IR (INSULATION RESISTANCE) VALUE AND
POLARISATION INDEX
3. TAN DELTA AND CAPACITANCE OF BUSHINGS
4. BDV (BREAK DOWN VOLTAGE) OF TRANSFORMER OIL
5. OIL RESISTIVITY
6. POWER FACTOR OF OIL
7. INTERFACIAL TENSION OF OIL
8. ACIDITY AND SLUDGE OF OIL
ANNUALLY
9. FLASH POINT OF OIL
10. WATER CONTENT OF OIL
11. DISSOLVED GAS ANALYSIS
12. REPLACING OF OLTC OIL
13. THERMO VISION SCANNING
14. EARTHING MEASUREMENTS
15. TAN DELTA AND CAPACITANCE OF WINDING
NCE IN FIVE YEARS
1. FURAN ANALYSIS (ONCE IN A YEAR AFTER THE
FIRST 5 YEARS)
. OVERHAULING OF OLTC DIVERTER SWITCH (ONCE
IN 5 YEARS OR AFTER COMPLETION OF 50,000
OPERATIONS WHICHEVER IS EARLIER).
NCE IN TEN YEARS
OVERHAUL, INSPECTION INCLUDING LIFTING OF
CORE AND WINDING.
URAN ANALYSIS ON TRANSFORMER OIL INDICATES THE
EGREE OF DEGRADATION OF THE TRANSFORMER PAPER
NSULATION.
HIS IS USUALLY DONE IN TRANSFORMERS AGING ABOVE 15
EARS.
URAN INDICATES THE COMPOUNDS OF CARBON AND
YDROGEN.
WHEN THE FURAN COUNT IS ABOVE 2500PPB, IT MEANS THE
RANSFORMER IS ABOUT TO FAIL.
URAN ANALYSIS IS IMPORTANT IN DECIDING WHEN TO
ISCARD A TRANSFORMER UNIT OR RETAIN.
THANK YOU!
RK
JAISWAL
NK
TUTEJA
• +91 9650993009
• [email protected]
• +91 9810174125
• [email protected]