Modeling and Practical Verification of PD Occurrence in Installation

Modeling and practical verification of PD occurrence
in installation defects of 150kV joints
Ed Gulski, Piotr Cichecki
Delft University of Technology, The Netherlands
Paul P. Seitz
Seitz Instruments AG, Switzerland
Riccardo Bodega, Theo Hermans
Prysmian Cables and Systems, The Netherlands
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Problem definition
1.
Imperfect installation of HV cable system in the field can generate
different defects in cable accessories.
2.
Basically in PD detection we have to deal with two basic aspects. First
aspect is measurement process which determined by PD detection
methods and testing voltages.
3.
The second issue is PD occurrence that depends on defect size, volume,
position in cable system and the electric field.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Experimental test set-up (full scale 100m 150kV transmission class power
cable with two outdoor termination and joint)
Laboratory set-up:
100m of 87/150 kV 1x1200 XLPE cable
including accessories: 2 terminations type OTC170-X and 1 joint type type CFJ-170A
Internal inductive VHF sensor
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
External inductive VHF sensor
Experimental test set-up (full scale 100m 150kV transmission class power
cable with two outdoor termination and joint)
Continuous AC voltage
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Damped AC voltage
PD-patterns (no defect) of experimental test set-up (full scale 100m 150kV
transmission class power cable with two outdoor termination and joint)
Continuous AC voltage
Damped AC voltage
IEC 602070 PD-pattern at AC 50Hz
IEC 602070 PD-pattern at DAC 412Hz
VHF full spectrum at AC 50Hz
IEC 602070 PD-pattern at DAC 84Hz
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Two artificial defects for investigation:
1.
Missing outer semi-conductive screen
2.
Electrode-bounded cavity
Investigation methods:
1.
Field plotting simulation by Ansoft
2.
PD measurements:
a)
50 Hz AC energizing and conventional IEC60270 PD detection
b)
400 Hz and 84 Hz DAC energizing and conventional IEC60270 PD detection
c)
50 Hz AC energizing and un-conventional PD detection
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Field plotting for: missing insulation screen (defect 1)
PDIV (by 50Hz AC energizing and conventional IEC60270 PD detection) for different sizes
Simulation at 28 kVpeak
Without defect 1
Defect 1 (5mm)
Defect 1 (10mm)
Defect 1 (15mm)
Missing outer semi-conductive
screen: 5mm…15mm
 Field concentration occurs at the end of removed outer semi-conductive screen.
 By applying the same voltage stress at different sizes of defect 1, the field concentration will decrease with the size
of the defect.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Plot of E (kV/mm) as a function of voltage applied up to 1.7U0, (defect 1)

The larger the size of defect 1 shows steeper increase of E (kV/mm) with the increase of voltage applied.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50 Hz AC energizing and conventional IEC60270 PD detection (defect 1)
PDIV
15mm (28 kVpeak)
10mm (30 kVpeak)
5mm (31 kVpeak)
10mm
5mm
60 kVpeak
15mm
 At PDIV an asymmetric PD patterns occur whereas at higher voltage the PD patterns become symmetric.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
qV-Plot at 50Hz AC energizing and
conventional IEC60270 PD detection (defect 1)
 Changing the size of defect 1 does not give significant change in PDIV and the increase of the PD amplitude
as a function of applied voltage will be steeper if the size of defect 1 is larger.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Result from 84Hz and 400Hz DAC energizing and conventional
IEC60270 PD detection (defect 1)
0.8xUo = 70kV/98kV
1.2xUo = 106kV/150kV
DAC 400 Hz
DAC 84 Hz
PDIV
 There is no significant difference in PDIV between 84Hz and 400Hz damped AC voltages.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
qV-Plot at 400Hz DAC energizing and
conventional IEC60270 PD detection (defect 1)
 Changing the size of defect 1 does not change the PDIV and the increase of the PD amplitude as a function of
applied voltage will be steeper if the size of defect 1 is larger.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50Hz AC energizing and un-conventional PD detection (defect 1)
Termination
------------------ (90 m) ----------------------------------------------- Joint -------------------------------- ( 10m) -------------- Termination
Internal S1
External S1
Internal S3
External S3
Internal S2
External S2
 Different types of sensors at different sensor locations (distances to the defect) detect different PD signal
occurrences.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50Hz AC energizing and un-conventional PD detection (defect 1)
Internal
External
PD Patterns for sensor S3, at joint 0m
distance to the defect site
36 MHz
126 MHz
126 MHz
132 MHz
243 MHz
243 MHz
 To detect defects in an accessory internal sensors are more sensitive than the external sensors.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Field plotting for electrode-bounded cavity (defect 2)
Field simulation at 50 kVpeak
Electrode-bounded cavity



Field enhancement: 4.11 – 4.63 kV/mm occurs inside the cavity and breakdown of gas inside the cavity
follows the Paschen curve.
Defect is assumed has length 10mm and depth 1mm.
PDIV was found at 50 kVpeak using IEC6270 detection method.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Plot of E (kV/mm) as a function of voltage applied up to 1.7U0, (defect 2)
E (kV/mm) vs Voltage applied
 The higher the voltage stress applied, the steeper increase in the field enhancement inside the electrode-bounded
cavity.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50Hz AC energizing and conventional IEC60270 PD detection (defect 2)
50 kVpeak (PDIV)
60 kVpeak
54 kVpeak
qV-Plot at 50Hz AC energizing and
conventional IEC60270 PD detection

the symmetric PD phase-resolved patterns occur at both
positive and negative period of the 50Hz AC voltage
cycle.

PD amplitude is increasing by increasing the voltage but
tends to decrease by long duration of voltage applied.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
400Hz DAC energizing and conventional IEC60270 PD detection (defect 2)
PDIV : 64 kVpeak
150 kVpeak
qV-Plot at 400Hz DAC
energizing and
conventional IEC60270 PD
detection

PDIV is slightly higher than at 50Hz AC energizing due
to short and decreasing of DAC voltage stress and the
high resonant frequency (400 MHz).

Short stress of DAC and small number of DAC shots (2)
for each voltage results in varying of PD amplitude due
to stochastic process of PD.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50Hz AC energizing and un-conventional PD detection (defect 2)
Termination
------------------ (90 m) ----------------------------------------------- Joint -------------------------------- ( 10m) -------------- Termination
Internal S1
External S1
Internal S3
External S3
Internal S2
External S2
Internal S2
 Different types of sensors at different sensor locations (distances to the defect) detect different PD signal
occurrences.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
50Hz AC energizing and un-conventional PD detection (defect 2)
Internal
External
PD Patterns for sensor S3, at joint 0m
distance to the defect site
39 MHz
18 MHz
42 MHz
81 MHz
75 MHz
84 MHz
 To detect defects in an accessory internal sensors are more sensitive than the external sensors.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
External sensor sensitivity dependence on the distance to the accessories
500 pC injection from calibrator at termination 2.
Full PD spectra of noise and PD calibration signals are obtained from 2 positions (0m and 6m) of
external sensor for each accessory: S1, S3, and S2
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
External sensor sensitivity dependence on the distance to the accessory

PD signal coupling is selective and the best S/N ration has been observed at 42MHz, 66MHz, 100MHz.

Distance changes 0m…6m between external sensor S2 and termination has direct influence on signal
attenuation in the range 30 MHz – 114 MHz: the longer the distance the higher the attenuation.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
External sensor sensitivity dependence on the distance to the accessory

The external sensor S3 (at joint) shows different less selective coupling as external sensor S1 and S2.

Distance changes 0m …6m between external sensor S2 and termination has direct influence on signal
attenuation in the range 60 MHz – 80 MHz: the longer the distance the higher the attenuation.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
External sensor sensitivity dependence on the distance to the accessory
 As compared to direct coupling the presence of 100m power cable has large influence on the signal
attenuation starting from 80 MHz.
 PD signal coupling is selective and the best S/N ration has been observed at 30MHz, 54MHz, 66MHz.
 Distance changes 0m…6m between external sensor S1 and termination has direct influence on signal
attenuation in the range up to 66 MHz: the longer the distance the higher the attenuation.
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,
Conclusions
1.
PD occurrence in insulation defects depends on the electric field stress as it is present at
the defect site.
2.
Size and the type of the defect in combination with electric stresses may influence the
PDIV, the measurable PD magnitudes and PD-patterns.
3.
Application of continues 50 Hz voltages and damped AC voltages to artificial defects in
cable accessories results in similar PD behavior: PDIV, PD-amplitudes and PD-pattern.
4.
Application of standardized PD-detection method (IEC60270) provides reproducible PDlevels in [pC].
5.
Application of non-standardized PD detection (VHF) has to consider a number of effects
on measurable PD levels:
a) VHF frequency range as used to detect the PD signals and to estimate the PD
magnitude,
b) location and the type of discharging defect
c) the type of the VHF sensor,
d) distance between the VHF sensor and the accessory
IEEE ICC Spring 2010 F10D Diagnostic Testing for Cable Joits & Terminations Meeting, Nashville TN, USA,