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Temperature Rise TestsCentre for Power Transformer Monitoring, Diagnostics
and Life Management (transformerLIFE)Monash University, Australia
Oleg RoizmanIntellPower, Australia
Spring 2009 IEEE Transformers Committee MeetingMiami FL, 21 April 2009
Valery DavydovMonash University
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 RTDsin Test Transformer
Top Oil Temperatures
Top Core Yoke Temperatures
Top Rings Temp
Top Radiator
Bottom Radiator
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 OFAFPhase B, 100A
30
35
40
45
50
55
60
65
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
t, min
T, d
eg C
FO12 MV top FO13 MV middle FO14 MV bottom θwm(i) as measured θw(i) as calculated
Avr wnd. T
Top wnd. temp
Mid wnd. temp
Bot wnd. T
1st set of winding resistance measurement instrumentation was used
Comparison of Tavr and FO for HV OFAFPhase B, 100A
35
37
39
41
43
45
47
49
51
0 2 4 6 8 10 12 14 16
t, min
T, d
eg C
FO7 HV top FO9 HV middle FO11 HV bottomMeasured average winding temperature Calculated average winding temperature
Tawr
1st set of winding resistance measurement instrumentation was used
OFAF (100A) HV Phase B
60
65
70
75
80
85
90
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 5minsTwarm fitted exp 5mins FO7 FO1 FO9
2nd set of winding resistance measurement instrumentation was used
OFAF(100 A) MV Phase B
60
70
80
90
100
110
120
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)
T, d
eg C
Twarm Twarm fitted IEC 20mins Twarm fitted IEC 15mins Twarm fitted IEC 5minsTwarm fitted exp 5mins FO13 FO12 FO14
It could be seen that depending on duration of test variations in Twnd (R) is ~10 ºC
2nd set of winding resistance measurement instrumentation was used
Blocked Coolers: 60A
70
72
74
76
78
80
82
84
86
88
90
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12
T, d
egC
FO6 FO15 FO16
Blocked Coolers 60 A
Phase A Phase C Phase B
~4 hours!
Blocked Coolers: 60 A
Blocked Cooling
68
70
72
74
76
78
80
82
84
0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36
T, d
egC
Twarm A Twarm fitted IEC (A) Twarm C Twarm fitted IEC © Twarm B Twarm fitted IEC (B)
Ph A
Ph C
Ph B
76.59+time*0.1618-4.331)exp(-time/*5.521 = Tw
2nd set of winding resistance measurement instrumentation was used
Blocked Coolers HV Phase B 60A
45
50
55
60
65
70
75
80
85
90
0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36
Time since shutdown (mins)
T, d
eg C
Twarm FO7 FO9 FO11 (TV4+TV5)/2
hottest measured temp mid measured temp
bottom measured tempWinding temp by resistance
ONAN(60A) HV phase B
45
50
55
60
65
70
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)
T, d
eg C
Twarm Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO9 FO3 FO11
2nd set of winding resistance measurement instrumentation was used
ONAN(60A) MV phase B
40
45
50
55
60
65
70
75
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)
T, d
eg C
Twarm Twarm fitted IEC 15mins Twarm fitted IEC 5mins Twarm fitted exp 5mins FO12 FO13 FO14
2nd set of winding resistance measurement instrumentation was used
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 2nd 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 COFAF (100A)
55
60
65
70
75
80
85
90
95
8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time, h:mm
Tem
pera
ture
, deg
C
FO6 FO15 FO16
Phase A
Phase B
Phase C
Cooling curves
Cooling Curves for A, B and C Phases, OFAF (100A), HV
60
65
70
75
80
85
90
0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36
Time since shutdown, min
Win
ding
tem
pera
utre
by
R, d
eg C
Phase B Phase C Phase A
2nd set of winding resistance measurement instrumentation was used
Effect of first valid time point for MV in OFAF
60
65
70
75
80
85
90
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)
T, d
eg C
Twarm Twarm fitted IEC 20mins (from 1m45s) Twarm fitted IEC 20mins (from 4m)
1:45 min
4:00 min
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 in-house 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 temperaturefound in b) unless the difference between that temperature and the average of all phases exceeds agreed value (e.g. 3 ºC).