Static and dynamic presentation 05 2009
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S tatic & Dynamic
Mo to r Te s ting
Dre w No rman
Ap p lic atio ns Eng ine e r
VIBRATION INS TITUTE
Pie d m o nt Chap te r #14
2009 Annual S e m inar
Mo to r Failure Are as
IEEE Study (Early 1990’s)
EPRI Study (Mid 1990’s)
S tatic Mo to r
Te s ting
Intro to S tatic Mo to r Mo nito ring
De fining S tatic (Off-Line ) Ele c tric Mo to r
Te s ting
WHAT IS IT: Me a s uring 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 s ting
Me a s uring s pe 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 s ting
Te s ting motor ins ula tion a t volta ge le ve ls s imila r to thos e the motor
e ncounte rs in it’s norma l e nvironme nt.
Winding De s ig n
Ra ndom Winding
(Mus h Winding)
Form Coil
Te s ting Ins ulatio n S ys te ms
• Multime te rs
• Me g-Ohm-Me te r
• Re s is ta nce Me te rs (DLRO, Bridge s )
• Low volta ge circuit e va lua tion (i.e . Ca pa cita nce ,
Inducta nce )
• High P ote ntia l Te s t – AC-DC
• S urge Te s ting
• Corona Te s ting
• P a rtia l Dis cha rge De te ction
• Infra re d, Ultra s onic, Vibra tion
To pic s o f Dis c us s io n
Ins ula tion S tre ngth
Fa ilure Me cha nis ms
Te s ting The ory
• Te s t P a ra me te rs
• P a ss / Fa il Crite ria
Me thods of Te s ting
P re dictive Indica tors in Ele ctrica l Motor Te s ting
Die le c tric S tre ng th o f Go o d Ins ulatio n
Pro pe rtie s o f the Die le c tric s
Dielectric Strength
Puncture/Breakdown
Wire fo r a 460V AC mo to r has
6000VAC ins ulatio n c apability (NEMA MG-1)
8400 Volts Peak 6000V RMS
Or:
6000 AC 2 = 8400VDC
De mo ns trate the Die le c tric S tre ng th o f the
Mag ne t Wire
One S lot of a 460 volt Motor
Pro pe rtie s o f the Die le c tric s
We dg e
S lo t Ce ll Line r
Phas e Ins ulatio n
Slot liner is 20,000 VDC
Nomex-Mylar-Nomex
Single slot in a
random wound
3 Φ Motor
•Co mbine d Ins ulatio n to Gro und is
8400 VDC + 20,000 VDC = 28,400 VDC
Ins ulatio n Life Curve
N WODKAE RB
E GATL OV
Cu-Ground
28,400VDC
Cu-Cu
16,800VDC
TIME (Years)
Impo rtant Po int
The Die le ctric S tre ngth of Good Ins ula tion is Ve ry High!
MUCH HIGHER THAN THE NAMEP LATE RATING!
Ins ulatio n Life Curve
Cu-Ground
28,400VDC
Cu-Cu
16,800VDC
What is causing it to
degrade over time?
Why is the curve shaped this way?
N WODKAE RB
E GATL OV
Insulation
Failure
Bus Voltage
TIME (Years)
Caus e s o f Ins ulatio n Failure
The rma l Aging (IEEE 101)
• For e ve ry 10C incre a s e in te mpe ra ture of the ins ula tion, the ra te of ins ula tion
de gra da tion is double d.
Ins ulatio n S ys te ms
The rmal Co ntributo rs
• Loa d (Incre a s e d curre nt cre a te s he a t by I2R)
• Ambie nt Conditions
– Te mpe ra ture
– Altitude
• S ta rting Curre nt & Initia l Te mpe ra ture Ris e (Re s ta rts )
• The rma l Ins ula tion from Conta mina tion
• P owe r Qua lity
– Ha rmonic Volta ge Fa ctor
– Unde r a nd Ove r Volta ge
– Volta ge Imba la nce
The rmal Capac ity/ Altitude
Caus e s o f Ins ulatio n Failure
The rma l Aging (IEEE 101)
• For e ve ry 10C incre a s e in te mpe ra ture of the ins ula tion, the ra te of ins ula tion
de gra da tion is double d.
Conta mina tion
• Che mica l, de pos it on the winding a ctive ly a tta ck the ins ula tion
–
(i.e . Acids , Ca us tics , EP -2 Gre a s e )
• S ome conta mina tion ca n a ls o le a d to the rma l ins ula tion
• Abra s ive we a r of ins ula tion due to impa ct from a ir flow
Me cha nica l
• Move me nt within the winding a t s ta rt up
• The rma l growth of ma te ria ls
Ove r Volta ge S pike s
• High Volta ge s urge s ca us e d by Switching, Lightning, VFD’s
Ho w Lo ng S ho uld a Mo to r’s
Ins ulatio n Las t?
100,000 hours
11.4 ye a rs – All Da y, Eve ry Da y, Eve ry Ye a r
100,000 hours
= 4166 days = 11.4 years
24 hours
33 ye a rs – 8 hours a Da y, Eve ry Da y
1
Failure Mechanisms
Turn to Turn Failure
80% of e le ctrica l s ta tor fa ilure s s ta rt a s turn-to-turn fa ult
Mos t will fa il to ground in the s lot a nd s ome pha s e to
pha s e , but the root ca us e will be turn to turn fa ilure
Ge ne ral Ele c tric Pape r
Re as o ns why mo s t failure s be g in as
“turn to turn” failure s
• Turn ins ula tion is the we a ke s t ins ula tion in the motor.
Both Me cha nica lly a nd Die le ctrica lly
• All Contributors to Ins ula tion De gra da tion a re a cting e ve nly on the
winding, howe ve r this winding is more e xpos e d to outs ide influe nce .
(i.e . Conta mina tion, Move me nt, Abra s ion, The rma l Ins ula tion)
• Move me nt from s ta rt up rubs the turns toge the r ca us ing we a r.
(D.E. Cra wford\Ge ne ra l Ele ctric)
• Da ma ge ca us e d by winding a nd ha ndling proce s s .
• S ta rting, S topping, Lighting, a nd VFD’s ca us e volta ge s pike s which in
turn produce high turn to turn volta ge s .
D.E. Crawfo rd, “A Me c hanis m o f Mo to r 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
Varnis h we ake ning at hig he r te mpe rature s
Diffe re nt c o e ffic ie nts o f e xpans io n
Mag ne tic fo rc e 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…”
