Case study. Investigation of rotor hotspot temperature of a 325 MVA hydro-generator

Transcription

1 Case study Investigation of rotor hotspot temperature of a 325 MVA hydro-generator Present by : Mounir Essalihi, P.Eng Collaboration : Claude Hudon, IREQ IRCM 2017 Orlando, Florida

2 Presentation Outline Introduction Context of the case study Inspection report FBG measurement principle Instrumentation of the rotor Results of measurements Winter and summer temperatures Flux measurements Discussion and Conclusions 2

3 Introduction The first aim of this presentation to explain how Fiber Bragg grating technology was used to measure the surface temperature of the pole s field winding of a rotor in service. A second goal was to investigate inter-turn insulation using flux measurement. 3

4 Context of the case study Visual inspection done by technical support at the plant revealed significant inter-turn insulation migration on several poles of all units of the plant An abnormal heating seemed to be the cause of this degradation 4

5 Context of the case study We wanted to know the temperature of the hot spots of the field winding IREQ implemented a method using fiber optic temperature sensors for rotors We want to know at the same time if there were any inter-turn short circuits by using the flux measurement The units have been operating for just over thirty years out of 50 years of expected life The poles have class B insulation, maximum of 130 C To know the maximum hotspot will help to decide if re-insulating the poles from class-b(130 C) to class-f insulation (155 C) will provide a full life cycle 5

6 Inspection report Light color Dark color 6

7 Inspection report The deterioration is more marked on the lagging edge of the poles Rotation 7 Rotation

8 FBG measurement principle An internal research project at the IREQ was carried out to evaluate the FBG as a temperature probe (nonconductive) FBGs are commercially available Two years of laboratory measurements under static and rotational conditions have demonstrated the validity of these sensors The transfer of the optical signal from the rotating part to the fixed part is done by a rotating optical joint Rotating optical joint Fixed part Rotating part 8

9 FBG measurement principle Fiber Optic with Bragg Gratings Bragg grating #1 Bragg grating#2 Bragg grating#3 Intensity Intensity Each of the Bragg gratings reflected a wavelength λb 9

10 FBG measurement principle The wavelength λb characteristic of a Bragg grating depends on the temperature λ B1 λ B2 λ B3 λ BN Δλ B = a (T T 0 ) Bragg Grating λ B1 λ B2 λ B3 λ BN 10

11 Instrumentation of the rotor The 4 poles instrumented covered all position in the inhomogeneous cooling of a rotor. The lagging edge is less cooled than the leading edge. The position of the pole relative to the spider arms change de cooling efficiency The four poles selected (21, 22, 23 and 24) cover a sector between two rotor spider arms FBG Flux FBG 11

12 Instrumentation of the rotor The rotating optical joint installed can measure up to 20 FBG in series This rotary joint must be placed on the shaft axis It allows the passage of the light signals between the measuring device and the FBG and back to the instruement Flux Measuring device 12

13 Results of measurements Two measurement campaigns were carried out May (twater = 1,5 C) August (t water = 14,0 C) Test Date time end MW MVAr MVA 1 9 May 24 : May 10 : Flux 3 10 May 16 : Aug. 07 : , Aug. 10 : ,3 13

14 Results of measurements t water = 1,5 C Test conditions were not as stable as desired with a 136 MVAr excursion Test 1 Test 2 Test 3 Power Date and hour 14

15 Results of measurements t water = 1,5 C The temperature of the hot spot on the rotor (T = C) exceeded the average acceptable temperature for a class B insulation (T = 105 C) Test 1 Test 2 Test 3 Power FBG Min et Max RTD Min et Max Flux Date and hour P23 lagging P22 leading RTDs are not very sensitive to rotor heating Tmax RTD < 90 C 15 Date and hour

16 Results of measurements t water = 1,5 C The temperature of the poles depends on their position and the configuration of the ventilation channels of the rim ducts The lagging edges are all hot but the hottest is T lagging 23> 105 C The fact that the bottom of the poles (measured part) is warmer is probably related to the I beam in the bottom of the rim Flux P21 lagging P22 lagging P23 lagging P24 lagging P22 laeading P23 lagging 16

17 Results of measurements t water = 14 C There were some short excursion above of the MVAr limit (100 MVAR), but the major problem is that all probes exceed the limit of 105 C, with Tmaximum = C Test 4 Test 5 Flux 17

18 Results of magnetic flux measurements The magnetic flux in the air gap was measured on units A4 and A8 Flux 18

19 Results of magnetic flux measurements A4 The non-uniformity of the flux of unit A4 seems to be related to the shape of the air gap Flux Compare to the average Compare to the same polarity Compare to the adjacent 19

20 Results of magnetic flux measurements A8 The pole 10 shows the same deviation in the three comparisons, this being the sign of a circuit-circuit on this pole Flux Compare to the average Compare to the same polarity Compare to the adjacent 20

21 Discussion At commissioning, the maximum value of the average rotor temperature did not exceed 105 C At that time there was no criteria of acceptability for the temperature of a hot spot on the rotor It was considered <120 C but was not measured At present, although several poles are showing insulation migration, inter-turn short circuit is only beginning to occur. Flux 21

22 Conclusion The maximum temperature of the measured poles reached C This exceeds the acceptable average temperatures for: The 4 poles measured may not be the hottest of all units in the power plant groups A re-insulation with class F may not be sufficient to guarantee the operation for a lifetime of 50 years A detailed study of ventilation and possible corrections is desirable to keep the rotors with their current design The migration of the inter-turn insulation, does not yet cause generalized short-circuits 22