CENTRAL TESTING CIRCLE,DVC, MAITHON TRANSFORMER PROTECTION BY
JAYANTA DUTTA, SUPERINTENDING ENGINEER CRITM, DVC, MAITHON
Slide 2
PHYSICAL ARRANGEMENT OF A THREE PHASE TRANSFORMER
Slide 3
CORE MATERIALS USED FOR CONSTRUCTION OF TRANSFORMER Grain
oriented Electrical Steel CRGO is undoubtedly the most important
soft magnetic material in use today. Whether in small transformer,
distribution transformer or in large transformer & generator,
grain oriented electrical steel CRGO is a must for the production
of energy saving electrical machines. Grain oriented Electrical
Steels are iron-silicon alloys that provide low core loss and high
permeability needed for more efficient and economical electrical
transformers. CRGO Grain oriented grades of electrical steel are
typically used for transformer cores and large generators
Slide 4
CORE MATERIALS USED FOR CONSTRUCTION OF TRANSFORMER Important
physical properties of Electrical steels (CRGO) include
Resistivity, saturation induction, magneto-crystalline anisotropy,
magnetostriction, and Curie temperature. Resistivity, which is
quite low in iron, increases markedly with the addition of silicon.
Higher Resistivity lessens the core loss by reducing the eddy
current component. Raising the silicon content will lower
magnetostriction, but processing becomes more difficult. The high
Curie temperature of iron will be lowered by alloying elements, but
the decrease is of little importance to the user of CRGO Electrical
steels.
Slide 5
DERIVATION EQUATION OF TRANSFORMER
Slide 6
STANDARD CONNECTION GROUP 1 (ZERO DEGREE)
Slide 7
STANDARD CONNECTION GROUP 2 (180 DEGREE)
Slide 8
STANDARD CONNECTION GROUP 3 (-30DEGREE)
Slide 9
STANDARD CONNECTION GROUP 4 (+30DEGREE)
Slide 10
PARALLELLING OF TRANSFORMERS The theoretically ideal conditions
for paralleling transformers are: Identical turn ratios and voltage
ratings. Equal percent impedances required for equal Load sharing.
Equal ratios of resistance to reactance. Same polarity. Same phase
angle shift. (Vector Group) Same phase rotation.
Slide 11
TYPES OF TRANSFORMER FAULTS TRANSFORMER FAULTS ARE GENERALLY
CLASSIFIED INTO FIVE CATEGORIES:- WINDING AND TERMINAL FAULTS.
(ABOUT 60%) CORE FAULTS. (ABOUT 12%) TANK AND TRANSFORMER
ACCESSORIES FAULT. ( ABOUT10%) ONLOAD TAPCHANGER FAULT.(15%)
ABNORMAL OPERATION CONDITIONS.(2%) SUSTAINED AND UNCLEARED EXTERNAL
FAULTS.(1%)
Slide 12
FAULTS IN AUXILLIARY EQUIPMENT Transformer oil Oil level low.
Moisture absorption Transformer cooling system. Failure of
insulation between lamination and core bolt. Badly made joints and
connections.
Slide 13
WINDING AND TERMINAL FAULTS Insulation failure between winding
and core Between (phase to earth) Between phases (phase to phase)
Between HV and LV winding Inter turn faults. Cause may be Excessive
over load, Loose connection Improper Installation and Commissioning
Constant Over voltage, Aging of winding insulation Consequence of
minor faults.
Slide 14
CONSTANT OVER VOLTAGE Over voltage conditions are of two kinds;
TRANSIENT OVER VOLTAGE arise from switching and lightning
disturbances and are liable to cause interturn faults. POWER
FREQUENCY OVER VOLTAGE causes both an increase in stress on the
insulation and proportionate increase in working flux. Increase in
working Flux will increase the working Flux and thereby increase in
the Magnetizing Current.
Slide 15
EXTERNAL FAULTS Sources of abnormal stress in a transformer
are:- External overloads Short circuits Over voltage Reduced system
frequency (v/f ratio) FAULTS IN OLTC FAULTS IN BUSHINGS
Slide 16
TYPES OF TRANSFORMER FAULTS
Slide 17
CRITERION FOR SELECTION OF PROTECTION SCHEME Kva or Mva rating
Voltage ratio Winding connections. Per unit / per cent reactance
Neutral point Earthing resistance Value of system Earthing
resistance. Whether indoor or outdoor Dry or oil filled. With or
without conservator Fault level at the power transformer terminals
Network diagram showing the position of transformer in the system
network.
Slide 18
BASIC PROTECTIONS OF TRANSFORMERS BIASED DIFFERENTIAL
PROTECTION RESTRICTED EARTH FAULT PROTECTION. HV BACK-UP
OVERCURRENT AND EARTH FAULT PROTECTION. EARTH FAULT PROTECTION MAY
HAVE AN ADDITIONAL DIRECTIONAL ELEMENT. LV BACK-UP OVERCURRENT AND
EARTH FAULT PROTECTION. OVERFLUXING PROTECTION
Slide 19
DIFFERENTIAL PROTECTION Protects the transformer against
winding faults such as phase-to-phase fault and phase to earth
fault. It works on circulating current principle. Balanced three
phase through current suffers a phase change (30 degree for Group
3,4) which must be corrected in CT secondary leads by appropriate
connection of the CT secondary windings. Elimination of Zero
sequence through CT secondary Connections for Star Connected
Winding.
Slide 20
DIFFERENTIAL RELAY CURRENT BALANCE CONDITION
Slide 21
Problems / Difficulties, While Incorporating Differential
Protection : Different voltage levels at primary and secondary of
the transformer. Possible ratio mismatch of the current
transformers. 30 phase shift in case of delta / star transformer.
Operation of the transformer at different tap position. Ct ratio
errors Different CT performance at high fault currents. Inherent
difference in the CT characteristic Saturation of CTs cause large
ratio errors ip = k*is + im. Presence of d. C. Component in the
fault current.
Slide 22
MAGNETISING INRUSH 6 to 10 times the rated current. Present
only on the primary side of the transformer. Depends on residual
flux of the transformer and voltage wave position at the instant of
switching (i.e. Zero or peak).
Slide 23
MAGNETISING INRUSH CURRENT WAVEFORM
Slide 24
BIAS OF DIFFERENTIAL RELAY
Slide 25
DUAL SLOPE OF BIAS OF DIFFERENTIAL RELAY
Slide 26
BIAS OF DIFFERENTIAL RELAY There may be some ratio errors in
CTs (upto 5%) and some difference in primary and secondary currents
due to tap changing (upto 10%). Biasing is used to avoid false
trippings from these effects. The differential protection uses some
percentage of through current for biasing (or restraining). say we
use tripping slope as 20% and differential & restraining
currents in a typical relay are : Differential current = |I1+I2|
Restraining current = (|I1|+|I2|)/2 The relay will trip when:
Differential current / Restraining current> 0.2
Slide 27
RESTRICTED EARTH FAULT PROTECTION Provides sensitive,
instantaneous earth fault protection within the protected zone of
the transformer. Operates on circulating current principle. CAG 14
high impedance relay is used with external stabilizing resistor for
the stability against through faults. Operating coil of the relay
is connected with L. C. Circuit in series to immune harmonic
produced by ct saturation. The residual current of 3 CTs is
balanced against the output of a CT in neutral conductor.
Slide 28
HIGH IMPEDENCE RESTRICTED EARTH FAULT PROTECTION RATIO AND
ACCURRACY CLASS ALONG WITH KNEE POINT VOLTAGE OF ALL THE 4 CTS
SHOULD BE IDENTICAL. R R R C B A TRANSFORMERCTs TRANSFORMER A B C
LINE CTs RELAY & SR NEUTRAL CTs
Slide 29
RESTRICTED EARTH FAULT PROTECTION CONNECTIONS
Slide 30
CALCULATION OF STABILISING RESISTANCE FOR R/E/F PROTECTION
Example:- For a 50MVA 230/36KV transformer, through fault Stability
req. up to say 20 Times Full Load Current with Neutral CT assumed
completely saturated. Line CT ratio & Neutral CT Ratio
considered as 400/1. CT resistance = 5ohms. Relay resistance 4.5
ohms Cable and Lead Resistance - 1 ohm. Relay Pick Up - 0.1 Amps.
Calculate the value of Stabilizing Resistance. Full Load current =
50,000/ 3 x 230 = 125.51A Maximum Current Stability = 125.51 x 20 =
2510.218A = 2.5kA Considering the Saturation of the Neutral CT,
Voltage developed across the relay = 2510.218 ( 1+5+1 ) = 43.93
Volts Now Volts to operate the relay: - IR = 0.1 x 4.5 =
0.45Volts.
Slide 31
CALCULATION OF STABILISING RESISTANCE FOR R/E/F PROTECTION To
ensure Stability of Protection Circuit Voltage drop across the S.R
= 2510.218 ( 1+5+1 ) = 43.93 Volts Hence resistance required -
43.47/0.1 = 434.7ohms. Now the relay must pick - up at internal
faults. For 0.1A pickup requires 0.1( 5+1+434.7+4.5+1) = 44.62
Volts. Now Im at Vk = 800mA Total Mag. Current for 4 CT = 4 x 0.8 =
3.2A Effective Relay setting = Irelay + Im = 0.1 + 3.2 = 3.3A Or in
terms of primary the Line Current = 3.3 x 400 = 1320A. Hence for a
internal E/F current of 1320A the relay is found to operate.
Slide 32
COMBINED DIFFERENTIAL AND RESTRICTED EARTH FAULT
PROTECTION
Slide 33
NUMERICAL DIFFERENTIAL RELAY PROTECTION WITH HIGH IMPEDENCE
R/E/F PROTECTION
Slide 34
Connection of transformer differential protection with high
impedance REF (I7) and neutral current measurement at I8
Slide 35
OVERFLUXING PROTECTION E = 4.44 * * f * T E / f WHEN THE FLUX
DENSITY INCREASES BEYOND SATURATION POINT, A SUBSTANTIAL AMOUNT OF
FLUX IS DIVERTED TO STEEL STRUCTURAL PARTS AND INTO THE AIR. AT
SATURATION FLUX DENSITY THE CORE STEEL WILL OVER HEAT. STRUCTURAL
STEEL PARTS WHICH ARE NU-LAMINATED AND ARE NOT DESIGNED TO CARRY
MAGNETIC FLUX WILL HEAT RAPIDLY. FLUX FLOWING IN UNPLANNED AIR
PATHS MAY LINK CONDUCING LOOPS IN THE WINDINGS, LOADS, TANK BASE AT
THE BOTTOM OF THE CORE AND STRUCTURAL PARTS AND THE RESULTING
CIRCULATING CURRENTS IN THESE LOOPS CAN CAUSE DANGEROUS TEMPERATURE
INCREASE. IT MAY BE SEEN THAT METALLIC SUPPORT STRUCTURES FOR CORE
AND COIL, WINDINGS, LEAD CONDUCTORS, CORE LAMINATION, TANK ETC. MAY
ATTAIN SUFFICIENT TEMPERATURE WITH THE EVOLUTION OF COMBUSTIBLE GAS
F=(V/F)/(V n /Fn)1.11.21.251.31.4 Duration of withstand
time(min.)Continuous210.50
Slide 36
BACK UP O/C AND E/F PROTECTION BACKUP PROTECTION OF TRANSFORMER
IS O/C AND E/F PROTECTION APPLIED AGAINST EXTERNAL SHORT CIRCUIT
AND EXCESSIVE OVER LOADS. NORMALLY IDMT RELAYS WITH STANDARD
INVERSE OR VERY INVERSE CURVES. GENERALLY INSTALLED IN THE HV AND
LV SIDE OF THE TRANSFORMER. FOR HV SIDE, THE TRIPPING SHOULD BE OF
BOTH SIDES. FOR LV SIDE, THE TRIPPING WILL ONLY BE FOR THE LV SIDE.
BACKUP PROTECTION OF TRANSFORMER HAS FOUR ELEMENTS, THREE OVER
CURRENT RELAYS CONNECTED EACH IN EACH PHASE AND ONE EARTH FAULT
RELAY CONNECTED TO THE COMMON POINT OF THREE OVER CURRENT
RELAYS.
Slide 37
INHERENT PROTECTIONS OF TRANSFORMERS BUCHOLZ PROTECTION FOR
MAIN TANK. OIL SURGE RELAY PROTECTION FOR DIVERTOR TANK. PRESSURE
RELEASE VALVE (PRV). OIL TEMEPRATURE HIGH ALARM AND TRIP. WINDING
TEMPERATURE HIGH ALARM AND TRIP. OIL LEVEL LOW ALARM.
Slide 38
BUCHOLZ RELAY
Slide 39
TRANSFORMER PROTECTIONS PROTECTIONTRANSFORMER RATED BELOW
500KVA TRANSFORMER RATED BETWEEN 500KVA AND 5MVA TRANSFORMER RATED
ABOVE 5MVA DIFFERENTIALXX R.E.F.XX BACK UP O/CX BACK UP E/FX
TRANSFORMER OVERFLUXING XX BUCHOLZX P.R.V.X O.T.I AND W.T.I.X OIL
LEVEL MONITORING X FUSES XX
Slide 40
EARTHING SYSTEM FOR UNGROUNDED DELTA
Slide 41
POWER TRANSFORMER PROTECTION IN DVC
Slide 42
PRESENT DAY POWER TRANSFORMER PROTECTION IN 132KV FOR DVC
Slide 43
PRESENT DAY POWER TRANSFORMER PROTECTION IN 220KV FOR DVC
Slide 44
PRESENT DAY ICT PROTECTION IN 400KV INSTALLATION FOR DVC (6 CT
SCHEME)
Slide 45
STANDARD A.C. SCHEMATIC OF TRANSFORMER PROTECTION.
Slide 46
MAINATAINANCE PRACTICES REQUIRED FOR TRANSFORMER The general
cleaning of bushings and transformer top on main tank. The small
oil leakage attending. The tightness checking of control wire and
terminal blocks. The cleaning of contactor coils at marshalling
box. The test of Buch. relay by loss of oil method. The OTI &
WTI checking by both hot oil bath method and dial rotating method.
The cooling system also are checked.
Slide 47
MAINTAINANCE PRACTICES REQUIRED FOR TRANSFORMER The OTI &
WTI pocket oil are checked. The alarm for Main tank & diverter
tank low oil level. The trip test by PRV and diver tank OSR. The
Phase marking of bushings. The IR Value of Transformer are measured
by 5.0KV Megger. The power factor test. The main tank oil BDV and
moisture content test. The DGA test of both main tank and diverter
tank oil at CRITL
Slide 48
MAINATAINANCE PRACTICES REQUIRED FOR TRANSFORMER Without shut
down activities. Checking of bushing oil level :- M/D2 Checking of
oil level in conservator :- M/D3. Checking of oil level in OLTC
conservator :-M/D4. Manual actuation of cooler oil pumps and fans
:- M/D5. Checking of oil leaks :-M/D6. Checking condition of silica
gel in breather :- M/D7. Checking of oil level in oil seal of
breather :-M/D8. Testing of oil for DGA and other oil parameters
:-HY
Slide 49
CHANGE OF DIFERENTIAL CIRCUIT WITH CHANGE OF VECTOR GROUP
THROUGH PRIMARY CONNECTIONS.
Slide 50
Monitoring test on a Transformer There are certain tests, which
after rectifying the value nearer to permissible limit, minimizes
the failure of transformers due to internal fault. DGA test: DGA
will indicate heating, burning, sparking/arcing, loose joint, etc.
inside the xmer. Capacitance Tan Delta / P.I. & A.I. tests:
Capacitance Tan Delta and P.I. & A.I. values will indicate
insulation condition of transformer. Oil sample test: As per IS -
1866. Also, the trend of change in the oil gives useful information
(can be known from its colour and odor) Oil sample test will
indicate oil quality, which is directly affecting transformer
health and life both.
Slide 51
MONITORING OF TRANSFORMER BY INSULATING OIL EVALUATION MINERAL
OILS USED IN TRANSFORMERS AS COOLANTS AND INSULANT SHOULD HAVE THE
FOLLOWING PROPERTIES:- HIGH DIELECTRIC STRENGTH TO WITHSTAND
ELECTRICAL STRESS IMPOSED IN SERVICE. SUFFICIENTLY LOW VISCOCITY SO
THAT ITS ABILITY TO CIRCULATE AND TRANSFER HEAT IS NOT IMPAIRED.
ADEQUATE LOW TEMPERATURE PROPERTIES DOWN TO THE LOWEST TEMPERATURE
EXPECTED AT THE INSTALLATION SITE. RESISTANCE TO OXIDATION TO
MAXIMISE SERVICE LIFE.
Slide 52
TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE
ACTION TESTS RECOMMENDED BRIEF EXPLANATION BREAKDOWN VOLTAGE
(IEC60156) MEASURES THE OILS ABILITY TO WITHSTAND ELECTRICAL STRESS
WATER CONTENT (IEC 60814) WATER ACCELERATES THE DETERIORATION OF
BOTH THE INSULATING OIL AND THE PAPER INSULATION, LIBERATING MORE
WATER IN THE PROCESS. ACIDITY (NEUTRALIZATION FACTOR) (IEC 62021-1)
ORIGINATES FROM OIL DECOMPOSITION. SOMETIMES ALSO FROM ATMOSHPHERIC
CONTAMINATION.
Slide 53
TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE
ACTION TESTS RECOMMENDED BRIEF EXPLANATION INTERFACIAL TENSION
(ASTMD971-99A) THE INTERFACIAL TENSION (IFT) MEASURES THE TENSION
AT THE INTERFACE BETWEEN TWO LIQUID (OIL AND WATER) WHICH DO NOT
MIX AND IS EXPRESSED IN DYNE/CM OR mN/m. DEFINITE RELATIONSHIP WITH
IFT AND ACIDITY. INCREASE IN ACIDITY CAUSES DROP IN IFT. RATIO OF
IFT/ACIDITY GIVES QUALITY INDEX SYSTEM. AND A NEW OIL CAN HAVE A QI
OF >1500(45/.03) DIELECTRIC DISSIPATION FACTOR OR RESISTIVITY
(IEC60247) THE DISSIPATION TEST MEASURES THE LEAKAGE CURRENT
THROUGH AN OIL. REVEALS PRESENCE OF CONTAMINATION AND PRESENCE OF
MOISTURE RESIN, VARNISH, FOREIGN CONTAMINANTS.ETC
Slide 54
TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE
ACTION TESTS RECOMMENDED BRIEF EXPLANATION DISSOLVED GAS ANALYSIS
(DGA) IEC60567 GASES ANALYSED :- HYDROGEN - H 2 METHANE CH 4 ETHANE
C 2 H 6 ETHYLENE C 2 H 4 ACETYLENE C 2 H 2 CARBON MONOXIDE CO
CARBON DIOXIDE CO 2 NITROGEN N 2 OXYGEN O 2 ADVANCE WARNING OF
DEVELOPING FAULTS. A MEANS FOR CONVENIENTLY SCHEDULING REPAIRS.
MONITOR THE RATE OF FAULT DEVELOPMENT ORIGIN OF GASES PARTIAL
DISCHARGE MAJOR GAS HYDROGEN AND MINOR GAS IS METHANE THERMAL
FAULTS - 300 DEG :- ETHYLENE MORE THE TEMP. MORE IS THE PRODUCTION
OF ETHYLENE. ARCHING HIGH ENERGY DISCHARGE. MAJOR GAS
ACETYLENE.
Slide 55
DISSOLVED GAS ANALYSIS Transformer Chemistry Services method of
interpretation is based upon : Key gases : CSUS values (Age
compensated) BS 5800/IEC 599 ratios (providing the Total
Combustible Gases present are above 300 ppm) Rogers Ratios Trend
(Production rates of gases) Morgan-Schaffer Tables Total
Combustible Gas Production Rates TDCG(c57.104-1991) Total
Combustible Gas Westinghouse Guidelines Age of transformer. History
of transformer (Repaired, degasses, etc).
Slide 56
GAS CONCENTRATION LIMITS OF TRANSFORMER (IEEE)
GASNORMALCAUTIONWARNINGINTERPRETATION HYDROGEN - H 2 700PPMARCHING
CORONA METHANE CH 4 400PPMSPARKING ETHANE C 2 H 6 100PPMLOCAL
OVERHEATING ETHYLENE C 2 H 4 100PPMSEVERE OVERHEATING ACETYLENE C 2
H 2 5 PPMARCHING CARBON MONOXIDE CO 570PPM SEVERE OVERLOADING
CARBON DIOXIDE CO 2 10000PPM SEVERE OVERLOADING TCG1900PPM
Slide 57
TOTAL DISSOLVABLE COMBUSTABLE GAS. Total Combustible Gases
Recommended Action 0-500 PPM NORMAL AGING ANALYZE AGAIN IN 6-12
MONTHS 501 to 1200 PPM DECOMPOSITION MAYBE IN EXCESS OF NORMAL
AGING 1201 to 2500 PPM MORE THAN NORMAL DECOMPOSITION ANALYZE IN 1
MONTH 2500 PPM and above MAKE WEEKLY ANALYSIS TO DETERMINE GAS
PRODUCTION RATES CONTACT MANUFACTURER
Slide 58
TESTS OF OIL TO ASSESS ITS CONDITION AND SUGGEST CORRECTIVE
ACTION TESTS RECOMMENDED BRIEF EXPLANATION FURAN ANALYSIS
(IEC61619) ANALYSIS OF THE CONDITION OF PAPER INSULATION. DIRECT
TEST OF PAPER IS THE TENSILE STRENGTH OR DEGREE OF POLIMERISATION
(DP). INDIRECT METHOD IS FURAN ANLYSIS WHICH MEASURES THE QUANTITY
OF 2- FURALDEHYDE (IN PPM) IN OIL IS DIRECTLY RELATED TO THE DP OF
THE PAPER INSIDE THE TRANSFORMER.
Slide 59
ANALYSIS OF THE DP VALUES DP RANGE REMARKS
Slide 60
ANALYSIS OF THE DP VALUES DP RANGE REMARKS 360- 450 THE PAPER
IS STARTING TO APPROACH THE CRITICAL CONDITION. SUGGEST A RE-SAMPLE
IN 1-2 YEARS TIME. 460- 600 SIGNIFICANT PAPER DETERIORATION BUT
STILL WELL AWAY FROM THE CRITICAL POINT 610- 900 MILD TO MINIMAL
PAPER AGEING. >900NO DETECTABLE PAPER DEGRADATION
Slide 61
RECOMMENDED LIMITS OF INSULATING OILS (OLD) AS PER IS1866 -
2000 TESTSTRANSFORMER VOLTAGE RATING LIMITS INTERFACIAL TENSION
(N/m) FOR ALL VOLTAGE LEVELS 0.015(Min) NEUTRALIZATION VALUE MG OF
KOH/G FOR ALL VOLTAGE LEVELS 0.3 (MAX) BREAKDOWN VOLTAGE ABOVE
170KV BETWEEN 72.5 170KV BELOW 72.5KV 50(MIN) 40(MIN) 30(MIN)
DIELECTRIC DISSIPATION FACTOR @90C ABOVE 170KV BELOW 170KV 0.2(MAX)
1.0(MAX)
Slide 62
RECOMMENDED LIMITS OF INSULATING OILS (OLD) AS PER IS1866 -
2000 TESTSTRANSFORMER VOLTAGE RATING LIMITS RESISTIVITY X 10 12,
OHM-CM@ @90C FOR ALL VOLTAGES0.1(MIN) WATER CONTENT PPM ABOVE 170KV
BETWEEN 72.5 170KV BELOW 72.5KV 20(MAX) 40(MAX) NO FREE MOISTURE
SEDIMENT AND SLUDGE FOR ALL VOLTAGESNIL
Slide 63
RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 -
2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV
APPEARANCECLEAR FREE FROM SEDIMENT AND SUSPENDED MATTER DENSITY
@29.5C(G/C M) MAX 0.89 VISCOSITY @27C(CST) MAX 27 FLASH POINT C
(MIN) 140 POUR POINT C (MAX) -6
Slide 64
RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 -
2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV NEUTRALIZAT
ION VALUE MG OF KOH/G (MAX) 0.03 WATER CONTENT PPM (MAX) 201510
INTERFACIAL TENSION (N/m) Min.035
Slide 65
RECOMMENDED LIMITS OF UNUSED INSULATING OILS AS PER IS1866 -
2000 PROPERTIESHIGHEST VOLTAGE OF EQUIPMENT (KV) 170KV DIELECTRIC
DISSIPATION FACTOR @90C (MAX) 0.015 0.010 RESISTIVITY X 10 12, OHM-
CM@ @90C (MIN) 666 BREAKDOWN VOLTAGE (Min) 405060
Slide 66
MEASUREMENTS MODES FOR TAN DELTA GST MODE :- GROUNDED SPECIMEN
TEST IS REFFERED TO AS MEASUREMENT OF AN INSULATION SAMPLE THAT HAS
ONE OF ITS TERMINAL GROUNDED. GSTg- MODE :- GSTg MODE MEANS
GROUNDED SPECIMEN TEST WITH GUARDING UST MODE :- THE UNGROUNDED
SPECIMEN TEST IS REFERRED TO AS THE TEST OF AN INSULATION SAMPLE
THAT IS NOT GROUNDED.
Slide 67
OVERALL POWER FACTOR AND CAPACITANCE
Slide 68
OVERALL POWER FACTOR AND CAPACITANCE GST MODE ICH + ICHL
Slide 69
OVERALL POWER FACTOR AND CAPACITANCE GSTG-A MODE. ( CAPACITANCE
CH)
Slide 70
OVERALL POWER FACTOR AND CAPACITANCE UST-A (CAPACITANCE
CHL)
Slide 71
OVERALL POWER FACTOR AND CAPACITANCE MEASUREMENTS OF HV SIDE
MEASUREME NT TEST MODE SWEEP V TEST FREQ. WATT LOSSE S CAP MEAS PF
MEAS. ICH+ICH L GSTNONE50 HZ ICH GST g - A NONE50 HZ ICH(f) GST g -
A FREQUEN CY 50 HZ TO 400 HZ ICHL UST-A50 HZ ICHL(f) UST-A 50 HZ TO
400 HZ
Slide 72
MEASUREMENTS FOR TAN DELTA AT DIFFERENT FREQUENCY
Slide 73
OVERALL POWER FACTOR AND CAPACITANCE LV SIDE (CALCULATION OF
CL)
Slide 74
OVERALL POWER FACTOR AND CAPACITANCE GST MODE ICL + ICHL
Slide 75
OVERALL POWER FACTOR AND CAPACITANCE GSTG-A MODE. ( CAPACITANCE
CL)
Slide 76
OVERALL POWER FACTOR AND CAPACITANCE UST-A (CAPACITANCE
CL)
Slide 77
OVERALL POWER FACTOR AND CAPACITANCE MEASUREMENTS OF LV SIDE
MEASUREME NT TEST MODE SWEEP V TEST FREQ. WATT LOSSE S CAP MEAS PF
MEAS. ICL+ICL H GSTNONE 50 HZ ICLGST g - A NONE 50 HZ ICL(f)GST g -
A FREQU ENCY 50 HZ TO 400 HZ ICLHUST- A 50 HZ ICLH(f)UST- A 50 HZ
TO 400 HZ
Slide 78
CONDENSER TYPE BUSHINGS
Slide 79
Slide 80
MERITS OF CONDENSER BUSHING
Slide 81
MEASUREMENT OF TANDELTA OF BUSHING C1
Slide 82
Slide 83
MEASUREMENT OF TANDELTA OF BUSHING C2
Slide 84
Slide 85
RANGE OF DISSIPATION FACTOR ITEMS TYPICAL POWER FACTOR VALUES @
20C OF 400KV GRADE NEWOLDWARNING/ALA RM LIMIT POWER TRANSFORMERS,
OIL INSULATED 0.2- 0.4% 0.3- 0.5% >0.5% BUSHING0.2- 0.3% 0.3-
0.5% >0.5%
SHUNT REACTOR PROTECTION SCHEME CT AND VT PHASE CT PROVIDES
INFORMATION FROM PHASE SIDE, NCT PROVIDES INFORMATION FROM NEUTRAL
SIDE AND GROUND CT IS SINGLE PHASE CONNECTED BETWEEN NEUTRAL AND
GROUND. GROUND CT MEASURES 3i0 ACCURATELY AND HELPS IN DETECTING
LOW CURRENT FAULTS LIKE TURN TO TURN ETC.