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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

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Introduction

Insulation Resistance is Temperature influenced

Megger R&D • Patent US8428895, 2013• Patent SE537145, 2015

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Temperature Correction FactorsRotating Equipment Cables

Tem

pera

ture

(°C

)

Cla

ss A

Cla

ss B

Cod

e N

atur

al

Cod

e G

R-S

Perf

orm

ance

Nat

ural

Hea

t Res

ist N

atur

al

Hea

t Res

ist

Perf

orm

ance

GR

-S

Ozo

ne R

esis

t Nat

ural

G

R-S

Varn

ishe

d C

ambr

ic

Impr

egna

ted

Pape

r

0 0.21 0.4 0.25 0.12 0.47 0.42 0.22 0.14 0.1 0.285 0.31 0.5 0.4 0.23 0.6 0.56 0.37 0.26 0.2 0.4310 0.45 0.63 0.61 0.46 0.76 0.73 0.58 0.49 0.43 0.6415.6 0.71 0.81 1 1 1 1 1 1 1 120 1 1 1.47 1.83 1.24 1.28 1.53 1.75 1.94 1.4325 1.48 1.25 2.27 3.67 1.58 1.68 2.48 3.29 4.08 2.1730 2.2 1.58 3.52 7.32 2 2.24 4.03 6.20 8.62 3.235 3.24 2 5.45 14.6 2.55 2.93 6.53 11.65 18.2 4.7740 4.8 2.5 8.45 29.2 3.26 3.85 10.7 25 38.5 7.1545 7.1 3.15 13.1 54 4.15 5.08 17.1 41.4 81 10.750 10.45 3.98 20 116 5.29 6.72 27.85 78 170 1655 15.5 5 6.72 8.83 45 345 2460 22.8 6.3 8.58 11.6 73 775 3665 34 7.9 15.40 11870 50 10 20.3 19375 74 12.6 26.6 313

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Temperature Correction Coefficients

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

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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

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QUESTIONS?