case study investigation of rotor hotspot temperature of a … · · 2017-06-30fbg measurement...

Case study

Investigation of rotor hotspot temperature of a 325 MVA hydro-generator

IRCM 2017– Orlando, Florida

Present by : Mounir Essalihi, P.EngCollaboration : Claude Hudon, IREQ

COMET-2014, Austin, TX

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

19 mai 20172 IRMC 2017, Orlando, FL


Introduction

The first aim of this presentation to explain how FiberBragg 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.





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




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


Inspection report


Light color Dark

color


Inspection report


Rotation

Rotation

The deterioration is more marked on the lagging edge of the poles




Rotating optical joint

Fixed partRotating part

An internal research project at the IREQ was carried out to evaluate the FBG as a temperature probe (non-conductive) 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




Bragg grating #1

Bragg grating#2

Bragg grating#3

Fiber Optic with Bragg Gratings

Intensity Intensity

Each of the Bragg gratings reflected a wavelength λB




λB1 λB2 λB3

Bragg Grating

λBN

λB1 λB2 λB3 λBN

ΔλB = a (T – T0)

The wavelength λB characteristic of a Bragg grating depends on the temperature




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

FBGFlux

FBG




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


Results of measurements


Two measurement campaigns were carried out May 9-10 2016 (twater = 1,5◦C) August 25-26 2016 (twater = 14,0◦C)

Flux

Test Date time end MW MVAr MVA

1 9 May 24 :00 280 0 280

2 10 May 10 :20 255 83 268

3 10 May 16 :15 268 83 281

4 25 Aug. 07 :25 255 103 274,8

5 26 Aug. 10 :15 270 89 284,3


Results of measurements twater= 1,5 °C


Test conditions were not as stable as desired with a 136 MVAr excursion

Test 1Test 2

Test 3

Date and hour

Pow

er




The temperature of the hot spot on the rotor (T = 133.5 ° C) exceeded the average acceptable temperature for a class B insulation (T = 105 ° C)

Flux

Test 1Test 2

Test 3

FBG Min et Max

RTD Min et Max

RTDs are not very sensitive to rotor heating Tmax RTD < 90°C

Date and hour

P23 laggingP22 leadingDate and hour

Pow

er




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 Tlagging

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

P24 lagging

P23 lagging

P22 laeading

P23 lagging


Results of measurements twater= 14 °C


There were some short excursion above of the MVArlimit (100 MVAR), but the major problem is that all probes exceed the limit of 105°C, with Tmaximum = 137.9 ◦ C

Flux

Test 4 Test 5


Results of magnetic flux measurements


The magnetic flux in the air gap was measured on units A4 and A8

Flux


Results of magnetic flux measurements A4


Flux

Compare to the average Compare to the same polarity Compare to the adjacent

The non-uniformity of the flux of unit A4 seems to be related to the shape of the air gap


Results of magnetic flux measurements A8


Flux

Compare to the average Compare to the same polarity Compare to the adjacent

The pole 10 shows the same deviation in the three comparisons, this being the sign of a circuit-circuit on this pole


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


Conclusion


The maximum temperature of the measured poles reached 137.9 °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

case study investigation of rotor hotspot temperature of a … · · 2017-06-30fbg measurement...

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