Temperature Rise Tests - IEEE Standards Working Group Areas

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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

Rated Power HV/MV for ONAN, kVA

Rated Voltage HV/MV/LV, kV

Rated Current HV/MV

Cooling Types

Amp

Number of Phases

Vector Symbol

Mass Untanking, kg

Mass Each Cooler (excluding oil), kg

2006

468/468

22/4.5/0.415

12.3/60.0

ONAN, ONAF,

OFAF

3

YNyn0yn0

2420

115

Mass Total (including oil), kg

Insulating Oil Each Cooler, l

Insulating Oil Total,

Oil Circulation, l/min litre

6850

43

2650

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

55

60

65

Comparison of Tavr and FO for MV OFAF

Phase B, 100A

1st set of winding resistance measurement instrumentation was used

Top wnd. temp

Mid wnd. temp

50

45

40

Avr wnd. T

35

30

0 1 2

FO12 MV top

3

Bot wnd. T

4 5

FO13 MV middle

6 7 8

t, min

FO14 MV bottom

9 10 11 12

θ wm(i) as measured

13 14 15

θ w(i) as calculated

16

Comparison of Tavr and FO for HV OFAF

Phase B, 100A

1st set of winding resistance measurement instrumentation was used

51

49

47

45

43

41

39

37

35

0

Tawr

2 4

FO7 HV top

Measured average winding temperature

6 8

t, min

10

FO9 HV middle

Calculated average winding temperature

12

FO11 HV bottom

14 16

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

Twarm

Twarm fitted exp 5mins

0:08:38 0:11:31

Twarm fitted IEC 20mins

FO7

0:14:24 0:17:17

Twarm fitted IEC 15mins

FO1

0:20:10

Twarm fitted IEC 5mins

FO9

0:23:02

OFAF(100 A) MV Phase B

2 nd set of winding resistance measurement instrumentation was used

120

110

100

90

80

70

60

0:00:00 0:02:53 0:05:46 0:08:38 0:11:31 0:14:24

Time since shut down (mins)

0:17:17 0:20:10 0:23:02

Twarm

Twarm fitted exp 5mins

Twarm fitted IEC 20mins

FO13

Twarm fitted IEC 15mins

FO12

Twarm fitted IEC 5mins

FO14

It could be seen that depending on duration of test variations in Twnd (R) is ~10

º

C

84

82

80

78

76

74

72

90

88

86

70

7:12 8:24

Blocked Coolers: 60A

Phase A

Phase C

Blocked Coolers 60 A

Phase B

~4 hours!

9:36 10:48 12:00

FO6

13:12

FO15

14:24

FO16

15:36 16:48 18:00 19:12

72

70

68

0:00

78

76

74

84

82

80

Blocked Coolers: 60 A

2 nd set of winding resistance measurement instrumentation was used

Blocked Cooling

Ph A

Tw = 5.521

* exp(-time/ 4.331) 0.1618

* time + 76.59

Ph C

Ph B

2:24

Twarm A

4:48 7:12

Twarm fitted IEC (A)

9:36

Twarm C

12:00

Twarm fitted IEC ©

14:24

Twarm B

16:48 19:12

Twarm fitted IEC (B)

21:36

90

85

80

75

70

65

60

55

50

45

0:00

Blocked Coolers HV Phase B 60A hottest measured temp mid measured temp

2:24 4:48

Winding temp by resistance bottom measured temp

16:48 19:12 7:12 9:36 12:00

Time since shutdown (mins)

14:24

Twarm FO7 FO9 FO11 (TV4+TV5)/2

21:36

ONAN(60A) HV phase B

2 nd set of winding resistance measurement instrumentation was used

70

65

60

55

50

45

0:00:00

Twarm

0:02:53

Twarm fitted IEC 15mins

0:05:46 0:08:38

Time since shutdown (mins)

0:11:31

Twarm fitted IEC 5mins Twarm fitted exp 5mins

0:14:24

FO9 FO3

0:17:17

FO11

ONAN(60A) MV phase B

2 nd set of winding resistance measurement instrumentation was used

75

60

55

50

45

70

65

40

0:00:00

Twarm

0:02:53

Twarm fitted IEC 15mins

0:05:46 0:08:38

Time since shutdown (mins)

0:11:31

Twarm fitted IEC 5mins Twarm fitted exp 5mins

0:14:24 0:17:17

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

90

85

80

75

70

65

60

55

8:24

Phase B

Phase C

9:36

Cooling curves

10:48 12:00

Phase A

13:12

Time, h:mm

14:24 15:36

FO6 FO15

16:48

FO16

18:00

75

70

65

60

0:00

Cooling Curves for A, B and C Phases,

OFAF (100A), HV

2 nd set of winding resistance measurement instrumentation was used

90

Phase B Phase C Phase A

85

80

2:24 4:48 7:12 9:36 12:00

Time since shutdown, min

14:24 16:48 19:12 21:36

Effect of first valid time point for MV in OFAF

80

75

70

90

85

65

60

0:00:00

1:45 min

4:00 min

0:02:53

Twarm

0:05:46 0:08:38 0:11:31 0:14:24

Time since shutdown (mins)

Twarm fitted IEC 20mins (from 1m45s)

0:17:17 0:20:10

Twarm fitted IEC 20mins (from 4m)

0:23:02

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.

b.

c.

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;

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;

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

º

C).

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