1. Electrical Insulation Conference – IEEE EIC 2022
2022
Ali Naderian Jahromi1 Pranav Ketharam Pattabi1
Shanon Lo1 John Densley2
1METSCO Energy Solutions, Canada
2Arbolec Solutions, Canada
Comparison of Different Voltage Waveforms for
Partial Discharge Measurement in Medium Voltage
Cables and Accessories
Paper ID: 1169

2. 2022
Electrical Insulation Conference – IEEE EIC 2022
Presentation Outline
▶ Introduction
▶ Partial Discharge Measurement Approaches
▶ Laboratory Investigation
▪ Corona Discharge in Air
▪ Surface Discharge
▪ Termination Cutback Issue
▪ Splice Deficiency
▶ Discussions
▶ Conclusion

3. 2022
Electrical Insulation Conference – IEEE EIC 2022
Introduction
▶ Partial discharge (PD) measurement has been commonly used in the industry as a design,
commissioning, and diagnostic test procedure for medium voltage (MV) and high voltage
(HV) cables since the mid-1970s
▶ PD originates from defective sites anywhere within the cable insulation, semicon, joints, or
terminations. Improper handling, workmanship error, insulation aging, and, rarely,
manufacturing defects can also contribute to PD
▶ High background noise results in the incapability of sensing PD whose magnitude is lower
than the background level. High sensitivity is often critical for the factory and field
commissioning testing of MV cables and accessories
▶ This paper aims to evaluate and compare the performance of offline PD measurement
techniques using different voltage waveforms (sinusoidal AC – 60 Hz, sinusoidal very low
frequency (VLF – 0.1 Hz), and damped alternating current (DAC)), through a comprehensive
laboratory study

4. 2022
Electrical Insulation Conference – IEEE EIC 2022
Partial Discharge Measurement Approaches
▶ Offline PD testing of MV cables can be performed using different voltage sources, depending
on the situation and the associated site constraints or logistics
▶ A few papers are available in the literature that describe the effects of the supply
voltage/frequency on partial discharge inception voltage (PDIV) measurements
Initiative Year Result
To investigate the role of
voltage supply frequency
on PDIV measurement for
cavities embedded in
XLPE
2012 PDIV values measured through DAC are significantly higher (almost
twice) than those obtained using power frequency. PDIV using the
sinusoidal VLF (0.1 Hz) was similar or even lower than that of power
frequency
2018 A 15% to 40% PDIV increase when sinusoidal VLF (0.1 Hz) was used
compared to the sinusoidal AC (60 Hz)
Comparison of certain PD
voltage waveforms for PD
localization
2017 Comparable PDIV values between cosine rectangular VLF (0.1 Hz)
and DAC. Higher PDIV value with sinusoidal VLF (0.1 Hz) as
compared to cosine rectangular (0.1 Hz)

5. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation - Background
▶ To examine the effect of the various voltage waveforms on the PD measurement of MV
cables and their accessories, a comprehensive laboratory was carried out
▶ Some major defect types observed in MV cable systems such as corona discharge in air,
surface discharge, cutback error at the termination, and splice deficiency were created in
different MV cable samples for the study
▶ The cable samples with defects were subject to PD testing using three main power supplies:
sinusoidal AC (60 Hz), sinusoidal VLF (0.1 Hz), and DAC
▶ An HV capacitive divider was used as the PD sensor, alongside an identical PD acquisition
system for the entire study. The average background PD level remained around 2 pC during
the evaluation

6. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation - Background
▶ The PDIV and partial discharge extinction
voltage (PDEV) values were primarily
recorded for the different scenarios
▶ The phase resolved partial discharge
(PRPD) pattern and the absolute PD
magnitude for the relevant defect type
were also verified, to validate the
expected response

7. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation – Corona Discharge in Air
▶ The first examination involved simulating a
corona discharge in air on a 15 kV XLPE cable
sample using a sharp object
PD Power
Supply
PD Parameter
PDIV (kV rms) PDEV (kV rms)
Sinusoidal AC (60 Hz) 6.3 5.5
Sinusoidal VLF (0.1 Hz) 7.7 6.6
DAC 9 8.1

8. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation – Surface Discharge
▶ The second scenario involved creating a surface
discharge defect on a 15 kV XLPE cable sample
PD Power
Supply
PD Parameter
PDIV (kV rms) PDEV (kV rms)
Sinusoidal AC (60 Hz) 7.4 6.5
Sinusoidal VLF (0.1 Hz) 9 7.5
DAC 11.2 8.5

9. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation – Termination Cutback Issue
▶ For MV cables, poor workmanship is a major
failure mode that can particularly be identified
through PD testing
▶ A third evaluation was performed to capture the
presence of a cutback issue at the termination of
a 28 kV TRXLPE cable sample
PD Power
Supply
PD Parameter
PDIV (kV rms) PDEV (kV rms)
Sinusoidal AC (60 Hz) 9.3 6.9
Sinusoidal VLF (0.1 Hz) 10.1 7.4
DAC 14 13

10. 2022
Electrical Insulation Conference – IEEE EIC 2022
Laboratory Investigation – Splice Deficiency
▶ Another weak spot in MV cable systems is the other
cable accessory (splice or joint), prone to
workmanship issues, during cable commissioning.
Such splice defects can also be identified through PD
testing
▶ To demonstrate this application, a splice deficiency
was introduced in a 35 kV TRXLPE type cable sample
PD Power
Supply
PD Parameter
PDIV (kV rms) PDEV (kV rms)
Sinusoidal AC (60 Hz) 6.4 5.7
Sinusoidal VLF (0.1 Hz) 8.3 7.5
DAC 9.6 8.5

11. 2022
Electrical Insulation Conference – IEEE EIC 2022
Discussions
▶ Summary of the PD parameters from the laboratory investigation for the various defects
introduced, based on each of the cable’s rated phase-to-ground voltage (U0)
Defect
Type
Sinusoidal AC
(60 Hz)
Sinusoidal VLF
(0.1 Hz)
DAC
PDIV
(x U0)
PDEV
(x U0)
PDIV
(x U0)
PDEV
(x U0)
PDIV
(x U0)
PDEV
(x U0)
Corona
Discharge in Air
0.72 0.63 0.88 0.76 1.03 0.93
Surface
Discharge
0.85 0.75 1.03 0.86 1.29 0.98
Termination
Cutback Issue
0.57 0.43 0.62 0.46 0.86 0.80
Splice Deficiency 0.31 0.28 0.41 0.37 0.47 0.42

12. 2022
Electrical Insulation Conference – IEEE EIC 2022
Discussions
▶ The sinusoidal AC (60 Hz) power supply
was found to be the most sensitive,
followed closely by the VLF power supply
▶ Testing with the DAC power source
required much higher test voltages for PD
inception, particularly observed in the
surface discharge test scenario
▶ The sinusoidal VLF (0.1 Hz) exhibited a 10%
to 30% increase in PDIV values as
compared to the sinusoidal AC (60 Hz),
while DAC was the least sensitive, based on
a 40% to 50% increase in PDIV values from
sinusoidal AC (60 Hz). DAC was also found
to have a 15% to 40% higher PDIV value, as
compared to sinusoidal VLF (0.1 Hz)

13. 2022
Electrical Insulation Conference – IEEE EIC 2022
Conclusion
▶ Within the scope of this paper, a comprehensive laboratory study was completed to
compare the performance of three main power supplies in detecting the presence of a PD
defect in MV cable samples and their accessories
▶ Order of sensitivity in detecting PD defects: Sinusoidal AC (60 Hz) > Sinusoidal VLF (0.1 Hz) >
DAC. The nature of the DAC waveshape could be a reason for the lower sensitivity, resulting
in different breakdown field strengths from continuous AC voltage application
▶ All three power supplies could pick up the presence of a PD defect within reasonable test
voltage levels for relevant cable diagnostics (up to 1.30 U0), useful for cable maintenance
testing
▶ Background PD plays a huge role in determining the ability of commercial PD equipment
towards detecting the presence of potential defects
▶ Based on the results of this study, continuous AC application (either sinusoidal AC (60 Hz) or
sinusoidal VLF (0.1 Hz)) is preferred for both cable PD commissioning and maintenance
testing. DAC can be a good option for cable PD maintenance testing

14. 2022
Electrical Insulation Conference – IEEE EIC 2022
Thank You!
For more information and
services:
Ali Naderian Jahromi –
ali.naderian@metsco.ca
Pranav Ketharam Pattabi –
pranav.pattabi@metsco.ca
www.metsco.ca
905-232-7300