Classification of PD Patterns in XLPE Cables Under Various

1
Classification of PD Patterns in XLPE Cables
Under Various Soil Conditions using Statistical
Technique
(????? ??? ??? ?? ?? ??? ?? XLPE ????? ? PD
Pattern ??)
?? IEEE ?? April 7-10, 20002 Muhamad
Mansor, Ahmad Basri Abdul Ghani, Dr.
Prodipto Sankar Ghosh (?????)
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Abstract
?? ???? ??? ??? ???? ?? ??? ??? ?? ??? Factor?
PD (Partial Discharge)??. ? ??? Underground
Power Cables?? PD? ???? ?? ? Soil Thermal
Resis- tivity? ??? ?????.
?? Purpose To study the effect of various
soil conditions on the level of PD -. Straight
Detection Method ?? -. PD ???? Haefely
Trench TE 571 -. 11kV, single core, 240mm2
XLPE cable ?? ??? ??? ???? Elliptical Waveform
PD Pattern? ???. Statistical Pattern
Recognition Technique? ??? ??? ?? Various Soil
Conditions ???? PD Pattern?? ????? ?????.
3
Abstract
PD Pattern? Classification? ??? Soil
Condition??? Discharges? Recognition? ?? ???.
? ??? PD LEVEL? ?? ??? ?? ??? ??? ??? ????? ??
?? ?? Backfill Meterial? ???? Cable loading?
??? ????.
Thermal Resistivity(?????) ???? ???? ?? gt ???
?? ??? ???? ???? ?? ??? ?? ????? ? ? ??? ????
??? ?? ???? ??? ???? ??? ??. ??? ????? ???
?? ?????, ???? ?? ??? ?? ? ??? ???? ???
????? ????. ??? ???? ????? ? ??? ??? ?????
?? ???? ????. ?? ?? ???? ?? ?? ??? ??? ? ??
?? ??? ??? ?? ???? ??? ?????? ?? ?? ???? ??(???
??) ? ??. ?? ?? ?????? ??? ??? ?? ???? ????
???? ??? ?? ?? ??. ?? ???????
XLPE(Cross Linking-Polyethylene)?? XLPE?
?????(PolyethylenePE)? ?????? ???? ?????
?????(PE)? ?? (??)?? ????? ??? ????(?? ??)? ???
?????? ????? ??? ??? ??? ??? ??? ????? ?? ????.
?? ?? ? ????? ?? ?????? ??? ? ??? ??? ??? ???.
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INTRODUCTION
??PD? ?? ??? ?? ?? (???? ageing, service life ??)
??? ????(??? ??)
??? ??
??? STRESS (??,???,???? ?, soil thermal condition
??)
?? Purpose To study the effect of various
soil conditions on the level of PD -. Straight
Detection Method ?? -. PD ???? Haefely
Trench TE 571 -. 11kV, single core, 240mm2
XLPE cable ??
gt Cable ?? ?? gt soil thermal resistivity ??
Statistical Technique? PD ??
gt Backfill Material ??? gt Cable Loading ??
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EXPERIMENTAL SET UP

?? ?? 11kV, single core, 240mm2 XLPE cable(??
6m) Dry sand? ??? U-shaped cable trench? ??.
trench 1.4m wide, 1.8m height,
5.4m in total length. Cable trench? current
transformer? ??? ?? Set? TNB Research High
Voltage Testing Laboratory ? Shielded
enclosure?? ???.
XLPE cable
Dry Sand? ??? U-shaped cable trench
PD ???? -. Haefely Trench TE571(PD????
Straight Detection Method? ??) -. 100kV,
1000kVA, 50Hz Resonant Test System? ??
Power? ???.
Fig 1. Equivalent Circuit Diagram for PD
Measurement
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EXPERIMENTAL PROCEDURE
1) ??? ??? ??? Thermal Resistivity?? ?? Dry
Sand?? ??. 2) Sand Thermal Resistivity? reading?
Cable Trench Location 6?? ?. 3) PD? ??? Reading?
ambient ???? ?. (5? ??) -gt Haefely Trench TE571
PD Measurement System? Data ?? 4) ?? Soil
Thermal Resistivity?? Cable ??? 90? ??(Current
transformer ??) 5) Cable ?? 90??? PD Reading. 6)
Second reading?? ?? Cable ??? ???. 7) 1)?? 6)??
??? 5? ??. PD Reading ?? ?, Cable Trench??
Cable? ??? ?? ?? ?? Sand? Thermal Resistivity ?
?? ??. -gt Sand Thermal Resistivity? Reading?
Cable Trench? Location 6 ?? ?. ???? ??? Cable
Temperature? ??? ?? ????. ?? ??? ??, Voltage
rise rate? 1kVrms? ????. Test Voltage? 11kVrms??
60? ?? 18kVrms ???. PD??? ?? ?? 11kVrms? ???. ?
Procedure? IEC 885 Part 2? ???.
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VARIATION OF THERMAL PARAMETERS
Variation of Cable Temperature
-. The variation of the cable temperature is done
to replicate the loading of the cable during
service. -. Cable? Heating? 3-phase, 415V, 50Hz
Current Transformer? ??. -. Cable Temperature?
K-Type thermocouple? ??? ??. -. The cable
temperature is simulating the percentage of the
cable loading during service. -. Cable loading?
??? ??? ? (1)? ??? ????.
? (1)
TC Conductor (core) Temperature(?) TRT
Surrounding (soil) Temperature(?) n
Number of Core r Resistance of the
conductor (core) (?/m) RTH Sum of Thermal
Resistivity(m?W-1)
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VARIATION OF THERMAL PARAMETERS
Variation of Cable Temperature
Thermocouple ? ?? ?? ?? ???(??? ? ??? ??)? ???
??? ? ? ????? ??? ??? ??? ?? ???? ???? ??? ???
???. ?? ?? ?? ?? ?? ?? ? ? ????? ??? ??? ??
???? ?? ?? ? ??? ? ? ???? ???? ??? ???? ????.
Thermocouple? ??? ??? ??? ?? ??? ?? ??? ???
???, ?? ? ???? ???? 0 C?? 2600C ??? ?? ????
??, ??? ?? ?? ? ????. ??? ?????? ????? ??
?? ?? ??? ????? ????, ?? ? ???? ??? ??? ???
????. ???? ?? ?? ?? ??? ???? ?? ????
???,???,?? ??? ? ??? ??? ???? ?? ???? ????
???? ?????? ?????? ? ?? ???? ?? ??? ??? ??
??? ???? ?? ???? ??? MgO ?? ?????? ?? ??? ???
?? ?? ?? ????.
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VARIATION OF THERMAL PARAMETERS
Variation of Cable Temperature
-. Figure 2? Cable loading? Cable ?? ??? ??
????. -. ?? ???? Soil thermal resistivity ??
1.2m?W-1. ? ????, Cable Temperature? 2 Sets??
?? 90?? 28?(ambient temperature). -. The cable
temperature of 28? is reflecting ambient
temperature, which means the cable is
energised without any load. -. The cable
temperature of 90? is reflecting 100 loading of
the cable under normal operating condition.
Cable loading
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VARIATION OF THERMAL PARAMETERS
Variation of Soil Thermal Resistivity
-. The soil thermal resistivity is varied in
order to simulate different soil thermal
condition in the field. -. ? ???? Sand? Cable
Trench? ???? ??. -. This is because sand is used
as a backfill material in the cable trench in
Tenaga Nasional Berhad, Malaysia. -. Sand
thermal resistivity? Cable Trench?? ?? ??? ??
???. -. Sand thermal resistivity? KD2 Thermal
Properties Analyzer? ?? ????. -. The KD2
Properties Analyzer will give direct and
instantaneous reading of the soil thermal
properties. -. ???? sand thermal resistivity 4
sets? ??. Simulating very dry to very wet soil
conditions. s1 6.320m?W-1 s2
2.540m?W-1 s3 0.977m?W-1 s4
1.730m?W-1
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PROPOSED STATISTICAL PATTERN RECOGNITION TECHNIQUE
-. Pattern recognition using statistical method
is one of the established techniques in
classifying PD signals. -. The calculation of
parameters such as skewness, kurtosis, discharge
factor, cross correlation factor and modified
cross correlation factor allows us to determine
the sharpness, shape and symmetry of the PD
waveform from unknown origin. -. ?? values? PD
waveforms? ????? ?? ??? ??. -. ? ???? PD
waveforms? ??? ??? PD Measurement System?? ??
Elliptical form?? ???. -. Elliptical
waveforms? ?? Figure 3?? ?? ??. -. Elliptical
waveform? 3000 phase windows? ??? ??. -. Then
we follow the phase related recognition
technique to represent the average magnitude
of the discharge impulses as a function of the
phase angle. -. ? Discharge ??? ?? ?? ??? ????
Soil thermal resistivity? Cable temperature?
?? ? ??.
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PROPOSED STATISTICAL PATTERN RECOGNITION TECHNIQUE
-. Two-dimensional ??? ?? Figure 4?? ?? ??.
-. Sine wave?? Positive half? ??? ??? Negative
half? ??? ??? ?? ???. -. ?? ??? ??? ??? Soil
Condition ?? ? XLPE Cable??? PD Pattern ?????
Operator?? ??? ????? ?????.
-. 1 skewness(???, ????)
Xi the recorded value Pi the probability of
frequency of appearance for that value Xi in time
window I µ ?Xi Pi is the mean and s is the
variance s2 ?(Xi - µ)2 Pi .
-. Skewness is calculated for both negative and
positive half cycle, which is showing how
symmetry the distribution.
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PROPOSED STATISTICAL PATTERN RECOGNITION TECHNIQUE
-. 2 Kurtosis(???)
???(kurtosis)? ??? ???? ???? ????. ????? ??
0?? ??? ??. Kurtosis ?? ???? ?? ????? ??? ???? ??
? ???? ??? ??? ?? ???.
-. Kurtosis? ??? Sharpness? ????.
-. 3 Cross Correlation Factor(cc)
Xi the mean discharge magnitude in window i of
the positive half cycle Yi the mean discharge
magnitude in the corresponding window in the
negative half cycle n the number of phase
windows per half cycle cc cross correlation
factor Positive negative half cycle??
?? ??? ??? ?? ? ? ??.
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PROPOSED STATISTICAL PATTERN RECOGNITION TECHNIQUE
-. 4 Discharge Factor(Q)
QS- and QS the sum of the mean pulse height
distribution in the positive and negative
half cycle of the voltage cycle N-
and N the number of discharges of the mean
pulse height distribution in the
negative and positive half oh the voltage
cycle
-. Discharge factor is useful to describe the
difference in the mean discharge level in the
negative and positive distribution
-. 5 Modified cross correlation factor(mcc)
mcc Q.cc
-. The value of these operators corresponding to
various PD distributions are then analysed to
classify their patterns.
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RESULTS AND DISCUSSION
-. ????, 4?? Soil thermal resistivity, 2?? cable
temperature? ?? ?? ?? -. ? Cable??? ?? soil
thermal resistivity?? ????? 1.73m?W-1? ??. -gt
cable ???? 1.8 m?W-1? ???? ??. -. Soil thermal
resistivity? Cable Temperature? ?? 5?? ?? ??
-. 6 The standard error of the confidence
interval
s the standard deviation of the statistical
operator from a series of N observations of
one and the same type of soil conditions at a
given cable temperature t a statistical test
parameter depending on N
-. Standard error (????) Standard deviation
(????) standard value Soil thermal
resistivity? ??, Standard error lt standard
value hit or 1 standard error standard
value miss or X recognition rate
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RESULTS AND DISCUSSION
Analysis of recognition rate of PD at 90?
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RESULTS AND DISCUSSION
Analysis of recognition rate of PD at ambient
temperature
-. S1? S3? Recognition Rate? ??. ??? ??? ???
?? Hitting Pattern? ???.
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CONCLUSION
-. PD Pattern ??? ??? Statistical Operators,
1) Skewness 2) Kurtosis 3) Discharge
Factor 4) Cross Correlation Factor 5)
Modified Cross Correlation Factor
-. Recognition Rate
-. Soil Thermal Resistivity Cable Temperature
-gt PD Activity? ??? ??? ??. -gt PD Pattern
Classification (Statistical Technique)? ???
Backfill Meterial? Cable Loading? ????.