RTDs vs Slot Couplers

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    COMPARISON OF PARTIAL DISCHARGE PERFORMANCEUSING RTDs AND SLOT COUPLER

    Unit #4 LP

    Operating Conitions Na!ep"ate Inor!ationAmbient Temperature 0F

    HumidityManufacturer/Type GE Hydrogen/water

    cooling/ATV 4 poles

    oad !M"/MVA#$/Amps/%& '()/*0/+*00/,0

    -ate of MFG. (+*

    Volts (000 Maintenance !rebuild1rewound&

    2o

    $tator Temperature 03oint (

    40.( ower MVA at *0/4) $5G *06/**6.6

    ' *.6 Volts '0000

    * 40.4 Amps 66(/,604 4(.( #M *+00

    ) 4'.( E7citer Volts )00

    + 4(.) E7citer Amps ('0+/('+

    .F. 0.6)

    Temperature rise 03$tator/#otor

    4)/,4

    5nsulation type Mica Epo7y

    $E#5A 8 (609((

    General observation

    $lot coupler is installed:; A p=ase?( > @ p=ase?

    (* > 3 p=ase; A p=ase?+0 > @ p=ase?,' > 3 p=ase

    - actiity wit= magnitudes up to *)0 mV and repetition rates (40 pulses

    per +0 HB cycle =ae been detected wit= slot couplers.-ominating - pattern corresponds to p=ase to ground disc=arge and =as

    distinctie pulse polarity predominance on negatie =alf wae T=is pattern of -actiity may correspond to a slot disc=arge or to a disc=arge in deteriorated gradinglayer w=ere stator bars are emerging slots. Measurements wit= significant differencein load and winding temperature can distinguis= t=ose types of - actiity. 3ontinuousmonitoring does it automatically.

    Measurements wit= #T- sensors =ae been performed wit= connections to#T-Cs 88+(1 +* ; A p=ase1 (1 * ; @ p=ase1 (* and () located under/aboe first bars in

    (

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    t=e first coils of bot= parallels in A1 @ and 3 p=ases. T=ose #T-s are located at eit=ercollector or turbine ends.

    Additional measurements =ae been performed wit=:(. #T-s located in slots )61 ++1 '(1 ))1 ** and +, > ne7t coil to Dumpers between

    coils connected in eac= parallel ; in mid winding location.'. #T-s located in slots 461+01,' > same location as $lot 3oupler at collector end fordirect comparison of two types of sensors.

    5n total t=e mac=ine =as ,' #T-s located in ,' slots at collector and turbine ends andin t=e middle. Multiple sensing points along t=e stator let obtain more reliableinformation on stator insulation conditions.

    Hig= - actiity wit= magnitudes up to 4'0 mV and repetition rates ''0pulses per +0 HB cycle =ae been detected wit= #T- sensors. Hig=est - actiitywas obsered wit= #T-s 88);++ located deeply inside stator winding along statorbars.

    -ominating - pattern coincides wit= - pattern detected by slot couplers. Most oft=e detected - actiity are p=ase to ground disc=arges wit= positie pulse polaritypredominance !on negatie =alf wae&. Howeer p=ase to p=ase disc=arges =aebeen obsered also.

    ulse distributions along +0 HB cycle and e7amples of - pulse waeformsfrom t=e sensors are presented in Figures ( ; *.

    - signals from $lot 3ouplers >

    distribution along +0 HB power cyclea

    - signals from #T- sensors >

    distribution along +0 HB power cycle$

    Fig%re &

    '

    #T-

    #T-+*

    #T-0(

    #T-0*

    #T-(*

    #T-()$3,'

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    - pulse from $3 in slot 8+(!A p=ase&.

    a

    - pulse from $3 in slot 8(6 !A and 3p=ases&.

    $Fig%re '

    Si!%"taneo%s ete(tion o PD p%"se $) RTD an SC sensors

    $imilar response of #T-+0 and $3+0bot= located at t=e collector end anddifferent response in faor of #T- in

    slot ,'

    a

    $imilar response of #T-,' and $3,'bot= located at t=e collector end

    $Fig%re *

    An automatically generated reports containing bar grap=s for - intensity1ma7imum detected magnitudes1 repetition rates1 p=ase;magnitude plane proDectionsof *- p=ase resoled - distributions and t=e table wit= numerical - data from t=esensors are presented below.

    *

    $3,'

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    Partial Discharge Diagnostic ReportCreate+ &&,&-,'../

    Co!pan) Na!e+ Mi0est Generation1 LLCO$2e(t+ Unit#4 LPE3%ip!ent Rate o"tage 567 '.8.

    Test Res%"ts 9S"ot Co%p"ers:

    P;ase Reso"

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    $ensor-ate

    Magnitude0.(ppc

    n3l

    5ntensitym"

    owerm"

    ulse#epetition#ate ppc

    Ma7imumMagnitude

    n3l

    $ensitiityn3l/V

    Aboen3l

    $3+( ((;(0;'00) 0.), '.4+ '.(' 4+.) 0.,) (0 0.0)

    $30( ((;(0;'00) 0.4( ,., 4.)' (44 (.'+ (0 0.0)

    $3(* ((;(0;'00) 0.*(+ ).( ,.+, (06 0 .,) (0 0.0)

    $346 ((;(0;'00) 0.44, ,.4 )., ()' 0.+66 (0 0.0)

    $3+0 ((;(0;'00) 0.), '.0( (.(( '4.6 0.6(, (0 0.0)

    $3,' ((;(0;'00) '. ('.+ (+.* (*4 *.)) (0 0.0)

    Test Res%"ts 9RTD sensors:

    )

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    P;ase Reso"

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    Partia" Dis(;arge Para!eter Ta$"e

    $ensor-ate

    Magnitude0.(ppc

    n3l

    5ntensitym"

    owerm"

    ulse#epetition#ate ppc

    Ma7imumMagnitude

    n3l

    $ensitiityn3l/V

    Aboen3l

    #T-0( ((;(0;'00) (.4 '( ('. ((4 '.* (0 0.(

    #T-0* ((;(0;'00) (.() '+.' (4.4 ''4 '.)( (0 0.(

    #T-(* ((;(0;'00) 0.,' 4.*, ).)) *).6 (.) (0 0.(#T-() ((;(0;'00) '.* ,.(6 .0* 4+., *.6, (0 0.(

    #T-'( ((;(0;'00) 0.)*( ).4* 4.+( )(.6 0.,) (0 0.(

    #T-** ((;(0;'00) 0.'++ (.4+ (.4( (,.* 0.44, (0 0.(

    #T-46 ((;(0;'00) 0.,) *.) *.'( *).+ (.'+ (0 0.(

    #T-)) ((;(0;'00) 0.((' 0.0(+6 0.00*( 0.'0( 0.''4 (0 0.(

    #T-)6 ((;(0;'00) 0.)*( (. 0.,, (,. 0.6(, (0 0.(

    #T-+0 ((;(0;'00) 0.), *.) '.)6 *)., (.'+ (0 0.(

    #T-+( ((;(0;'00) 0.44, (.)4 (.* (4.( 0.+*( (0 0.(

    #T-+* ((;(0;'00) *.)) (6.6 (+.+ ('6 4.'' (0 0.(

    #T-++ ((;(0;'00) 0.), '.*' '.*( '(.( 0.,) (0 0.(

    #T-+, ((;(0;'00) 0.(4) 0.0++4 0.0**4 0.,' 0.''4 (0 0.(

    #T-,' ((;(0;'00) *.6, (6.4 (6.4 (*6 **.) (0 0.(

    Comparison of Slot Couplers and RTDs sensors-irect comparison =ae been made apple to apple for $lot 3ouplers and #T- sensorslocated in slots:

    - 46 ; top bar A p=ase1 bottom bar 3 p=ase?- +0 ; top bar @ p=ase1 bottom bar A p=ase?- ,' ; top bar 3 p=ase1 bottom bar @ p=ase.

    As it can be seen from t=e picture below sensors gie are pretty comparable results.Howeer #T-s more sensitie to - actiity in bottom bar because $lot 3ouplers ares=ielded from t=e bottom bar by t=e top bar.

    ,

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    Conclusions and recommendations

    $ignificant - actiity =as been detected wit= bot= slot couplers and #T-sensors. Magnitudes up to *)0 mV and repetition rates (40 pulses per +0 HB cycle=ae been found on $lot 3ouplers. Magnitudes up to 4'0 mV and repetition rates ''0 pulses per +0 HB cycle =ae been obsered wit= #T- sensors. -ominating -

    pattern corresponds to p=ase to ground disc=arge and =as distinctie pulse polaritypredominance on negatie =alf wae T=is pattern of - actiity may correspond to aslot disc=arge or to a disc=arge in deteriorated grading layer w=ere stator bars areemerging slots. $lot disc=arge mec=anism is more probable. Measurements wit=significant difference in load and winding temperature can distinguis= t=ose types of- actiity.

    Tree measurements wit= #T- sensors =ae been performed wit= connectionsto () #T-s located in different parts of t=e winding. Multiple sensing points along t=estator let obtain more reliable information on stator insulation conditions.

    For direct comparison of two types of sensors special test =as been performedwit= connections to t=e $lot 3ouplers and #T-s located in slots 461+01,' at t=e

    collector end. Test came up wit= pretty comparable results. Howeer #T-s are moresensitie to - actiity in bottom bars because $lot 3ouplers are s=ielded from t=ebottom bar by t=e top bar.

    - actiity and #is of Failure can be classified as MODERATE toELEATED."e would recommend repeating measurements in t=ree mont=s. 5t is preferable toperform measurements wit= different operating conditions > load and temperature. -actiity s=ould be monitored on regular basis."e would recommend installing continuous - monitoring system on t=e generator.

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