Download OVERALL SUMMARY OF INSULATION

OVERALL SUMMARY OF INSULATION CONDITION OF HT MOTORS – June/July 2012
MOTOR ID
KM 2115
KM 4115
I. R.
(GΩ)
9.44
4.98
P.
I.
9.2
6.5
D.
D.
0.7
2.6
WCA Difference (%)
R
0.4
0.2
NO ACTION REQUIRED,
TEST AFTER 3 YEARS
P. I.
Ø
EAR
Tan delta at 20 % Vp
Tan delta tip - up
Capacitance tip-up
Apparent charge
Z
0.2
0.2
ф
0
0
I/F
0
0
ALAR
M
Surge
Test
(EAR
%)
1
1
Tan δ
at 20 %
Voltage
(%)
0.82
1.78
Tan δ
Tip-up
(%)
0.49
0.30
MONITOR,
TEST AFTER 2 YEARS
Capacitance
Tip-up
(%)
3.56
2.54
Apparent
Charge
(pC)
1070
1570
Inception
Voltage
(V)
4800
3200
Ratio of
+ve to –
ve half
cycle PD
Diagnosis & Action Recommended
1.30
The PD pattern is typical of discharges occurring close
to the conductors. This kind of PD is much more severe
& needs to be monitored closely. The capacitance tipup is extremely high; indicating discharges in internal
voids. Overhauling will not help in such cases.
Rewinding/replacement should be planned.
1.10
The PD pattern indicates that there is improper contact
between the slot portion conductive varnish & the
overhang semi-conductive varnish. The end windings
should be cleaned & then conductive/semi-conductive
varnish applied in the knuckle region. The high D. D. &
tan delta values too indicate contamination; requiring
an overhaul. The motor should be re-tested within 6
months; & overhauled at a given opportunity.
ACTION RECOMMENDED,
TEST AFTER 1 YEAR
ACTION MANDATORY,
THEN RE-TEST
= Polarization Index (> 2, else indicates moisture ingress)
D. D.
= Dielectric Discharge Ratio (< than 2, else indicates contamination)
= Phase Angle (unbalance < 10)
I/F
= Current Frequency Response (unbalance < 2 %)
= Error Area Ratio (< 10 %, else indicates interturn shorts)
< 4.0, else indicates severe aging
= average increment in tan delta between 0.20 VP and phase voltage (< 0.8, else indicates severe voids)
= increment in capacitance between 0.20 VP and phase voltage, divided by the capacitance at 0.20 VP (< 2.5, else indicates significant voids/PD)
= summary of all discharges divided by the number of discharges
If ratio of +ve to –ve half cycle PD is more than 1.5; PD is close to copper conductors (aging). If PD Ratio is less than 0.5, PD is on the slot surface region (loose coils, improper stress grading or
contaminated end-winding). If PD Ratio is between 0.5 to 1.5, PD is distributed throughout the insulation (thermal degradation or de-lamination).
If Ø & I/F unbalance is excessive, interturn insulation degradation is indicated.