1 INDIVIDUAL TEMPERATURE CORRECTION (ITC) for INSULATION RESISTANCE MEASUREMENTS May 2017 S. Zurek*, A. El-Rasheed*, M. Ohlen** *Megger Instruments Ltd., Archcliffe Road, Dover, Kent, CT17 9EN, UK **Megger Sweden, AB, Box 724, 182 17, Danderyd, Sweden
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INDIVIDUAL TEMPERATURE CORRECTION (ITC) for ... 2.4 A.El-Rasheed-M.Ohlen.pdfTest Methods Results from Motor trials Results from Transformer trials Conclusions & Future Work 3 Introduction
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INDIVIDUAL TEMPERATURE CORRECTION (ITC) for INSULATION RESISTANCE
MEASUREMENTS
May 2017
S. Zurek*, A. El-Rasheed*, M. Ohlen**
*Megger Instruments Ltd., Archcliffe Road, Dover, Kent, CT17 9EN, UK **Megger Sweden, AB, Box 724, 182 17, Danderyd, Sweden
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Contents
Introduction Temperature Correction Factors Individual Temperature Correction Concept AC and DC excitation Test Methods Results from Motor trials Results from Transformer trials Conclusions & Future Work
Different publications provide different coefficients for the same material
Coefficients are average values at spot temperatures
0.1
1
10
100
‐10 0 10 20 30 40 50 60 70 80 90
T (deg C)
Insulatio
n resistan
ce
tempe
rature coe
fficien
t
Rot A"Rule of thumb"Rot BW.I.M.
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Individual Temperature Correction Concept
Based on activation energy of a material (in eV) ITC algorithm:
• where: E – material-specific activation energy (J), kB – Boltzmann constant 1.3806488 x 10-23(J/K), T1 and T2 temperatures (K) of interest
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11
21 ),( TTkE
BeTTA
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Correction in Frequency & Time Domains
In AC excitation: “temperature is frequency and frequency is temperature”
In DC excitation: temperature affects both resistance and response time
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Test Methods on Motor & Transformer
Environment chamber used provides adjustable and consistent conditions
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Motor Trial: Correction in Time Domain
Algorithm used to correct measurements after 1min and after 10min
0
1
2
3
4
5
6
10 20 30 40 50 60
T (deg C)
IR (GOhm)
10 min, measured 1 min, measured
10 min, corrected 1 min, corrected
10
Motor Trial: Time affects Polarisation Index
PI result is temperature dependant So, correction must be two dimensional:
Resistance & Time
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
10 20 30 40 50 60
T (deg C)
PI
corrected
as measured
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Dry Transformer Trial: Time Domain Correction
Polarisation Index correction (1 min and 10 min) At 40°C the PI is 1.35 (“bad”),
but corrected is 3.05 (“good”)
0
1
2
3
4
10 20 30 40 50 60
T (deg C)
PI
corrected
as measured
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Conclusions & Future Work
Current temperature correction coefficient method is based on average values at spot temperatures
Patent granted for new ITC concept and algorithm ITC algorithm is based on material activation energy Temperature correction for both resistance & time PI measurements are affected by temperature and
must be corrected
Research on multi-material insulation is ongoing Commercialisation work is ongoing