Temperature Rise Tests Centre for Power Transformer Monitoring, Diagnostics and Life Management (transformerlife) Monash University, Australia Oleg Roizman IntellPower, Australia Valery Davydov Monash University Spring 2009 IEEE Transformers Committee Meeting Miami FL, 21 April 2009
Special Test Transformer Nameplate Data Year of Manufacture 2006 Rated Power HV/MV for ONAN, kva 468/468 Rated Voltage HV/MV/LV, kv 22/4.5/0.415 Rated Current HV/MV Amp 12.3/60.0 Cooling Types ONAN, ONAF, OFAF Number of Phases 3 Vector Symbol YNyn0yn0 Mass Untanking, kg 2420 Mass Each Cooler (excluding oil), kg 115 Mass Total (including oil), kg 6850 Insulating Oil Each Cooler, l 43 Insulating Oil Total, litre 2650 Oil Circulation, l/min 1200
Temperature Sensors and DAQ System 16 Fiber Optic sensors 24 Thermocouples, including magnetic and thermal ribbon types 9 RTDs, including those of moisture/temperature transmitters More than 60 channels of information stored at 1 min interval
Location of Thermocouples and RTDs in Test Transformer Top Oil Temperatures Top Core Yoke Temperatures Top Rings Temp Top Radiator Bottom Radiator
Location of Fibre Optic Probes and Core Thermocouples
Fibre Optic Probe Installation in MV Winding, Phase B
Fibre Optic Probe Installation in HV Winding
Effect of Measuring Instrumentation In the following 4 slides, comparisons are made for the two windings of Phase B (OFAF) MV (layer type) HV (disc type) The comparisons are made for results obtained during the Temperature Rise Tests conducted at Monash using two different instrumentation sets for winding resistance measurement
Comparison of Tavr and FO for MV OFAF Phase B, 100A 1st set of winding resistance measurement instrumentation was used 65 60 Top wnd. temp Mid wnd. temp 55 T, deg C 50 45 Avr wnd. T 40 35 30 Bot wnd. T 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 t, min FO12 MV top FO13 MV middle FO14 MV bottom θwm(i) as measured θw(i) as calculated
Comparison of Tavr and FO for HV OFAF Phase B, 100A 1st set of winding resistance measurement instrumentation was used 51 49 47 Tawr 45 T, deg C 43 41 39 37 35 0 2 4 6 8 10 12 14 16 t, min FO7 HV top FO9 HV middle FO11 HV bottom Measured average winding temperature Calculated average winding temperature
OFAF (100A) HV Phase B 2 nd set of winding resistance measurement instrumentation was used 90 85 80 75 70 65 60 0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24 0:17:17 0:20:10 0:23:02 Twarm Twarm fitted IEC 20mins Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO7 FO1 FO9
OFAF(100 A) MV Phase B 2 nd set of winding resistance measurement instrumentation was used 120 110 100 T, deg C 90 80 70 60 0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24 0:17:17 0:20:10 0:23:02 Time since shut down (mins) Twarm Twarm fitted IEC 20mins Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO13 FO12 FO14 It could be seen that depending on duration of test variations in Twnd (R) is ~10 ºC
Blocked Coolers: 60A 90 Blocked Coolers 60 A 88 86 Phase A Phase C Phase B 84 82 T, degc 80 78 76 74 72 ~4 hours! 70 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 FO6 FO15 FO16
Blocked Coolers: 60 A 2 nd set of winding resistance measurement instrumentation was used 84 82 80 78 Ph A Blocked Cooling Tw = 5.521* exp(-time/ 4.331) - 0.1618 * time + 76.59 Ph C Ph B T, degc 76 74 72 70 68 0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 Twarm A Twarm fitted IEC (A) Twarm C Twarm fitted IEC Twarm B Twarm fitted IEC (B)
Blocked Coolers HV Phase B 60A hottest measured temp mid measured temp 90 85 80 75 T, deg C 70 65 60 55 Winding temp by resistance bottom measured temp 50 45 0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 Time since shutdown (mins) Twarm FO7 FO9 FO11 (TV4+TV5)/2
ONAN(60A) HV phase B 2 nd set of winding resistance measurement instrumentation was used 70 65 T, deg C 60 55 50 45 0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24 0:17:17 Time since shutdown (mins) Twarm Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO9 FO3 FO11
ONAN(60A) MV phase B 2 nd set of winding resistance measurement instrumentation was used 75 70 65 T, deg C 60 55 50 45 40 0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24 0:17:17 Time since shutdown (mins) Twarm Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO12 FO13 FO14
Comparison of FO Data for Phases A, B & C In the following slide a comparison is made for Phases A, B and C for the HV (disc type) winding for the OFAF cooling mode The comparison is made for the measurements obtained during the Temperature Rise Tests conducted at Monash for the FO probes installed in the 2 nd top disc of Phases A, B & C The differences in the FO measurement results were observed due to the following reasons: Phase A is the most remote phase from the oil inlet pipe; the velocity of oil flow through the winding ducts of Phase A is the lowest Phase C is the closest phase to the oil inlet pipe; the velocity of oil flow through the winding ducts of Phase C is the highest Phase B is in the middle between the inlet pipe and Phase A
FO Sensors Data for Phases A, B and C OFAF (100A) 95 Phase A 90 85 Phase B Temperature, deg C 80 75 70 Phase C 65 60 Cooling curves FO6 FO15 FO16 55 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 Time, h:mm
Cooling Curves for A, B and C Phases, OFAF (100A), HV 90 2 nd set of winding resistance measurement instrumentation was used Phase B Phase C Phase A 85 Winding temperautre by R, deg C 80 75 70 65 60 0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 Time since shutdown, min
Effect of first valid time point for MV in OFAF 90 85 1:45 min T, deg C 80 75 70 4:00 min 65 60 0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24 0:17:17 0:20:10 0:23:02 Time since shutdown (mins) Twarm Twarm fitted IEC 20mins (from 1m45s) Twarm fitted IEC 20mins (from 4m)
Factors Affecting Winding Temperature Rise Winding resistance measuring equipment Ambient temperature determination Inadequate calculation of the average oil temperature (leads to wrong g factor) Accuracy of Load Loss measurement Assumed total loss as sum of NL + LL Effect of the Core temperature dynamics Cold resistance measurement errors Not reaching steady state before shutdown
Factors Affecting Winding Temperature Rise (cont d) Connection circuit (two windings at a time) Time interval first and last data point resistance measurement Fitting curve method Ambient oil temperature consideration
Conclusions Depending on winding time constant taking first resistance measurement at 4 min may be too long wait and could lead to significant error in determination of winding temperature at shutdown 10 min cooling curve period could be well justified for small and medium distribution transformers, but does not seem to be adequate for large power transformers, where 20 min should be considered as more appropriate 15 sec acquisition rate was found to be easily achievable with the modern acquisition systems and is recommended, especially for a winding with a short time constant
Conclusions (Cont d) Considerations should be given to the following recommendations when FO sensors are used: a. Number and locations of FO temperature probes should be determined on the basis of analysis of heat and mass transfer with assistance of numerical methods such as FEM and CFD; b. Hot-spot temperature should be continuously measured by FO sensors installed in each winding of each phase and verified by calculations in accordance with the latest relevant standards and/or more detailed inhouse thermo-hydraulic models; c. Average winding temperature rise by resistance should be measured only in the winding of the phase with the highest hot-spot temperature found in b) unless the difference between that temperature and the average of all phases exceeds agreed value (e.g. 3 ºC).