Static and dynamic presentation 05 2009

High Volta ge Te sting Te sting motor insula tion a t volta ge le ve ls simila r to those the motor e ncounte rs in it’s norma l e nvironme nt... Tes ting Ins ulation Sys tems• Multimet

Static & Dynamic

Mo to r Te s ting

Dre w No rman

App lic ations Enginee r

VIBRATION INS TITUTE

Pie dmont Chap ter #14

2009 Annual S e minar

Motor Failure Areas

Static Mo to r

Te s ting

Intro to Static Mo tor Monitoring

Defining Static (Off-Line) Electric Motor

Tes ting

WHAT IS IT: Me a suring a nd tra cking e le ctrica l prope rtie s of the

winding circuit in a n e ffort to de te rmine its he a lth a nd re lia bility while the motor is de e ne rgize d

HOW:

Low Volta ge Te sting

Me a suring spe cific e le ctrica l pa ra me te rs a t or be low na me pla te

volta ge s to de te rmine a cha nge in the e le ctrica l circuit prope rtie s.

High Volta ge Te sting

Te sting motor insula tion a t volta ge le ve ls simila r to those the motor

e ncounte rs in it’s norma l e nvironme nt.

Tes ting Ins ulation Sys tems

• Multimeters

• Low voltage circuit evalua tion (i.e Capacitance , Inductance)

• S urge Te sting

• Corona Testing

• Partial Discharge Dete ction

• Infrared, Ultrasonic, Vibration

Failure Me cha nisms

Tes ting Theory

Diele c tric Stre ngth of Goo d Ins ulatio n

October 30, 2007 © SKF Group Slide 10

Pro pe rties of the Diele ctric s

Demons trate the Dielectric Streng th of the Magnet Wire

One S lot of a 460 volt Motor

•Combined Ins ulation to Ground is

Slot Ce ll Line r Phas e Ins ulatio n Wedge

Ins ulation Life Curve

Ins ulation Life Curve

Bus Voltage

Insulation Failure

October 30, 2007

© SKF Group

Slide 16

Caus es of Ins ulation Failure

The rma l Aging (IEEE 101)

• For e ve ry 10C incre a se in te mpera ture of the insula tion, the ra te of insula tion

de gra da tion is doubled.

Ins ulatio n Sys te ms

• S tarting Current & Initia l Tempe rature Rise (Restarts)

• Therma l Insulation from Contamination

• Power Quality

– Ha rmonic Volta ge Fa ctor

– Unde r a nd Over Volta ge

– Volta ge Imba la nce

The rmal Capac ity/ Altitude

October 30, 2007

© SKF Group

Slide 20

Caus es of Ins ulation Failure

The rma l Aging (IEEE 101)

• For e ve ry 10C incre a se in te mpera ture of the insula tion, the ra te of insula tion

de gra da tion is doubled.

Conta mina tion

• Che mica l, de posit on the winding a ctive ly a tta ck the insula tion

– (i.e Acids , Ca us tics , EP -2 Gre a s e )

• Some conta mina tion ca n a lso le a d to therma l insula tion

• Abra sive we a r of insula tion due to impa ct from a ir flow

Me cha nica l

• Move me nt within the winding a t sta rt up

• The rma l growth of ma te ria ls

Ove r Volta ge S pike s

• High Volta ge surge s ca use d by Switching, Lightning, VFD’s

How Long Should a Motor’s Ins ulation Las t?

hours

4 11

4166 24

000 , 100

=

=

Turn to Turn Failure

80% of electrica l s tator failure s start as turn-to-turn fault

Most will fail to ground in the s lot and some phase to

phase, but the root cause will be turn to turn fa ilure

Ge ne ral Ele ctric Pape r

October 30, 2007

© SKF Group

Slide 24

Reas ons why mos t failures beg in as

“turn to turn” failures

• Turn insula tion is the we a ke st insula tion in the motor.

Both Me cha nica lly a nd Die le ctrica lly

• All Contributors to Insula tion De gra da tion a re a cting e ve nly on the winding, howe ve r this winding is more e xpose d to outside influe nce (i.e Conta mina tion, Move me nt, Abra sion, The rma l Insula tion)

• Move me nt from sta rt up rubs the turns toge the r ca using we a r

(D.E Cra wford\Ge ne ra l Ele ctric)

• Da ma ge ca use d by winding a nd ha ndling proce ss.

• S ta rting, S topping, Lighting, a nd VFD’s ca use volta ge spike s which in turn produce high turn to turn volta ge s.

D.E Crawford, “A Mec hanis m o f Motor Failure s ” Ge ne ral Ele c tric

Co mpany, 75CH1014-0-EI-19.

“…Looseness, motion and wear develop as the result of certain stresses applied to the motor windings by the service it sees Careful analysis revealed the following conditions:

 Diffe re ntial the rmal s tre s s e s

 Diffe re nt co efficients of expans ion

 Varnis h we akening at higher te mperatures

 Magnetic force due to winding c urre nts ”

“…Wear between the moving components is a natural consequence of motion and it was found when the likely points were located…”

B.K Gupta, B.A Lloyd, G.C S tone , D.K S harma, N.E Nils s on, and J.P

Fitzge rald, “Turn Ins ulation Capability of Larg e AC Motors Part 3 – Ins ulatio n

Coordination.”, IEEE Trans ac tions o n Ene rgy Conve rs ion, Vol EC-2, No 4,

De c embe r 1987.

“… In 1982, a working group of the IEEE Rota ting Ma chinery Insula tion Subcommitte e

publishe d crite ria which se t a minimum ca pa bility for la rge motors of a ny a ge to withsta nd

volta ge surge s ….Figure 2 shows the highe st surge s from a ll the motors monitored in this study (which ha d no surge prote ction), compa re d to IEEE curve More tha n 50% of the motors

monitore d e xpe rience d surge s which e xce e d the IEEE re commende d withsta nd leve l…”

“…The most common de teriora tion proce ss, especia lly in a motor with a long se rvice re cord, involve s the gra dua l loosening of the insula te d turns due to shrinka ge a nd loss of me cha nica l stre ngth in the insula tion a s a re sult of opera tion a t high te mpe ra tures Unde r the influe nce of

ma gnetic force s ca use d by e ithe r sta rting curre nts or the norma l 60hz curre nt, the turns rub

a ga inst one a nothe r, a bra ding a wa y the turn insula tion Eventua lly e nough insula tion is re move d tha t a mild surge , or e ve n the norma l 60Hz inte rturn volta ge will short circuit the turn.”

October 30, 2007

© SKF Group

Slide 28

Voltage and Ins ulation Breakdown

Motors do not fail at ope rating voltage whe re they see 20

to 30 volts turn to turn

Eve ry time the motor starts it sees voltage spikes of up to

5 pu (per unit) (~2000V for a 460v Motor)

Ins ulation Failure on Start-up

Voltage spikes on S tart-up

EPRI S tudy:

Volts V

L

392 2

3 480

2 3

October 30, 2007

© SKF Group

Slide 30

M

Voltage Spikes on Start-up

Rise time of Voltage spike is 2 to 5 micro seconds

Spike s are ge ne rated

as the s ec ond & third

c ontac ts clos es

0V 1960V

Christiansen & Petersen Denmark IEEE 68C6-EI-87

Two pole Wye - S ix turns pe r coil - ~ 1000 hp

October 30, 2007

© SKF Group

Slide 32

Early Turn Failure

•Ma jority of Turn to Turn fa ilure s sta rt a t the e a rly turns

•Most e a rly turn fa ilure s a re a re sult of high volta ge spike s

A

B C

Neutral or Star Point

“Early” End Turns

Area most likely to have a copper to copper failure.

Lightening caused failure may happen further into the weakened

winding, a result of the slower voltage rise time.

October 30, 2007 © SKF Group Slide 34

E.P Dic k, B.K Gupta, P.Pillai, A Narang, “Prac tic al Calculation of S witc hing

S urge s at Motor Te rminals ” IEEE/PES 1988 Winte r Mee ting, Jan 31, 1988.

“….Given a maximum pres trike voltage on third pole clos ing of 2.82 per unit, the

s tee p-fronte d motor te rminal s urge c an vary be twe en 2 and 5 per unit de pe nding

on the c onfiguration.”

Pete r Zoto s , “Motor Failure s due to Stee p Fro nted S witc hing Surge s : The Ne ed

fo r Surge Pro tec tio n – Us e r’s Expe rie nc e ” IEEE Trans ac tions on Indus try

Applicatio ns , Vol 30, No 6, Nove mbe r/De c embe r 1994.

“…The prime purpos e of the pa pe r is to e s ta blis h tha t motor winding ins ula tion provide d with

“de dica te d inte rturn ins ula tion” ca n withs ta nd stre s s ge ne ra te d by s witching surges with

a mplitude a s high a s 5 p.u a nd with a rise time ra nge of 1-0.1us without the use of s hunt

ca pa citors ”

“…S tudie s show tha t significa nt s urges a re pre s e nt only during bre a ke r closing ope ra tions while

e ne rgizing the motor Mos t s urge s have 1-3 p.u ma gnitude s a nd 0.2 – 0.6us rise time s ……The highe st re corde d s urge wa s 4.6p.u with 0.57us ris e time in norma l ope ra tions.”

“…Inde pe nde nt te s ts , conducte d on a ir bla s t (s ta tion-type ) circuit bre a ke r, s how tha t the highe s t

re corde d s urge wa s 3.44 p.u with a ris e time of 3us for norma l a nd a bortive s ta rts ”

“… Te s ts conducte d by na tiona l orga niza tions show tha t the wors t s urge s ha ve a ma gnitude of

a s high a s 4.6 p.u a nd a ris e time of 0.1us ; howe ve r, mos t motors e xpe rie nce s urge s on the orde r of 3 p.u ma gnitude with a ris e time of 0.2-0.6us Surge te s ts conducte d on motors s how tha t the s tator winding insula tion ha s a surge s trength in e xce s s of 5 p.u to 0.1us rise time.”

October 30, 2007

© SKF Group

Slide 36

Pas chen’s Law

P a sche n’s La w re quire s a minimum of 325 volts to instiga te a n a rc.

Ins ulation Life Curve

Bus Voltage

Insulation below Arcing Voltages

5pu ~ 2000V

October 30, 2007

© SKF Group

Slide 38

Fus ed Shorted Turns

Once the dielectric strength falls below the operating voltage the turns will fuse toge ther!

Burned turn I2R = Heat

Auto Trans former Action of Welded Fault

•Initial shorting of the turns is often in the extension, however, the failure to ground will be in the slots.

According to IEEE the we lde d faulte d turns will burn through

the s lot ce ll line r to ground within 15 minute s

October 30, 2007 © SKF Group Slide 40

Auto Trans former Action of Welded Fault

T2 T3 T1

Auto Trans former Action of Welded Fault

T2 T3

T1

16 Turns

1 Turn 16x Normal Current

» 32x Normal Heat (I 2 R)

R.M Tallam, T.G Habetle r, R.G Harle y, “Trans ie nt Mode l for Inductio n Mac hines with S tator Winding Turn Faults ” IEEE Trans ac tions on Indus try Applic ations ,

Vol 38, No 3, May/June 2002.

“….A turn fa ult in the sta to r wind ing o f a n ind uc tio n m a c hine c a use s a

la rg e c irc ula ting c urre nt to flo w in the sho rte d turns, o f the o rd e r o f twic e

the b lo c ke d ro to r c urre nt If left undetected, turn faults can pro pagate,

le ading to phas e -ground o r phas e -phas e faults Ground curre nt flo w re s ults

in irrevers ible damage to the co re and the mac hine might have to be

removed from s e rvic e Incipie nt dete ction of turn faults is e s s ential to avo id hazardo us ope rating c o nditio ns and re duc e down time ”

Steps of Typical Motor Failure

1) Dielectric S trength of a ne w motor is ve ry high

2) Motor will see normal aging

• The rma l

• Che mica l

• Me cha nica l

3) Dielectric S trength falls below level of switching surge s

• Arcing occurs whe n motor sta rts up

October 30, 2007

© SKF Group

Slide 46

Steps of Typical Motor Failure

4) Insulation begins to deteriorate much fa ste r

5) Dielectric S trength drops below ope rating voltage

• The short fuses

6) Transforme r a ction causes high induce d curre nt - high hea t

7) Rapid Failure

Dielectric Streng th and Voltage Spikes

October 30, 2007

© SKF Group

Slide 48

Baker Off-Line Equipment

Trouble S hooting (TS)

Quality Assurance (QA)

Predictive / Preventive Maintenance (PPM)

October 30, 2007

© SKF Group

Slide 50

Off-Line Motor Tes ting

•Coil Re sistance (PPM, QA, TS )

•PI (polariza tion te st) (PPM, QA)

•Surge Test (PPM, QA, TS )

Delta Res is tance

% 100

% 76

11 85

0

80

0 90

5 85

0

05

deviation Max

October 30, 2007

© SKF Group

Slide 52

Res is tance Tes ting Is s ues

Balance between pha ses

• # of Turns per pha se

• Dia meter coppe r

• High re sista nce connections

• Turn-To-Turn shorts

• Turn-To-Turn Ope ns

Apply tes t potential for 1 minute

Correct to 40° C.

Rule o f thumb:

Re s is tanc e halves for eac h 10° C te mperature inc re as e

Rule o f thumb:

Minimum value ac ce ptable

1 me g ohm + 1 meg ohm / KV (Co rre cte d to 40 C)°

2 R

40

T −

Me g-Ohm Te s ting

– De te rmine if the motor ha s fa ile d to ground

– Dirty motor (Surfa ce le a ka ge )

– P e rform a P ola riza tion Index a nd Diele ctric Absorption Te st.

Meg-Ohm Tes t

• It Cannot:

– De te rmine if a motor is good

– Find a Turn-to-Turn Fa ult

– Find a n Ope n P ha se

– Find a P ha se -to-P ha se Fa ult

October 30, 2007 © SKF Group Slide 56

Megohm Tes t Voltag e

Polarization Index, Dielectric Abs orption Tes t

PI Tes t 10min/1min

DA Test 3min/30sec

October 30, 2007

© SKF Group

Slide 58

Polarization Index Tes t

The ratio of insulation resista nce after te n (10) minutes of minute continuously applied DC, divided by the

insula tion resis tance at one (1)

An indication of age and/or wet insulation

A fre sh dry motor will ea sily exceed 20000 meg-ohms at

10 minutes

PI Tip 1: Test instrument must be capa ble of measuring

at lea st 20,000 meg ohms It is pre ferred to have 50,000

me g ohm measuring ca pability

PI and DA Te s t

PI Tip 2: Apparatus must not be polarized (To depolarize,

find-• De te riora te d ground wa ll insulation

• Dry-rotte d, hard, brittle ground wa ll insula tion, conta mina tion

PI & DA Pas s Fail Levels

• Grea te r than 1 let it run (Common Fie ld Rule)

• IEEE 2 or gre ater

• DA va lue should close ly resemble PI Ra tio (>2)

October 30, 2007

© SKF Group

Slide 62

Polarization Index Tes t

P I Tip 3: Insula tion re a ding a t one (1) minute should e a sily e xce e d

Polarization Index Tes t

P I Tip 5: It is re comme nde d (Industry S ta nda rd) tha t the P I te st

volta ge e qua l or e xce e d the nume rica l va lue of line volta ge

Exa mple : 460VAC - te st a t 500vdc

2300VAC - te st a t 2500vdc 4160VAC - te st a t 5000vdc

P I Tip 6: S ma ll motors a nd ge ne ra tors ca n be come pola rize d in

much le ss tha n 10 minute s.

It is sugge ste d tha t motors/ge ne ra tors 100hp or gre a te r be P I te ste d Appa ra tus sma lle r the n 100hp ofte n ca n be te ste d using the “DA”

te st.

The pa ra me te rs of time ca n va ry, but 3 minute s divide d by ½ minute

se e ms to work we ll.

Standard 6 Lead NEMA Wiring Diagram

DC High Potential Tes ting

ANSI / IEEE Std 95-1977

Apply test potential for 1 minute Correct to 40 C Rule of thumb: Re sista nce halves for ea ch 10 C tempe rature incre ase

5.1 DC Tes t Voltag e = 1.7 X AC Te s t Voltage

5.2 Mainte nanc e Proo f Tes ting

AC 125% to 150% of Te rminal Voltage

Example :

4160 VAC (1.25) (4160) (1.7) = 8800 VDC (1.50) (4160) (1.7) = 10,600 VDC Bake r Ins trume nt s ugge s ts :

Twic e Voltage + 1000 Volts

o r (4160) (2) + 1000 = 9320 VDC

ANSI/IEEE 95-1977

Bake r re c omme nds Twic e Voltage + 1000

For mo tors in s ervic e

1920VDC

Example : 460 Volt Mac hine

Hi-Pot te s ting

October 30, 2007 © SKF Group Slide 70

HiPo t Te s t Vo ltage s IEEE 95-1977

Para 5.2 fo r Mainte nanc e Pro o f Te s ting

35190 29325

11268 13800

17595 14663

5634 6900

10608 8840

3397 4160

5865 4888

1878 2300

1530 1275

490 600

1466 1222

469 575

1224 1020

392 480

Max Te s t V Vline *1.5*1.7

Min Te s t V Vline *1.25X1.7

Per Unit Vline

EASA DC HiPot

(Table 4.2)

31603 48620

16354 25160

10298.6 15844

6188 9520

2431 3740

2375.75 3655

2165.8 3332