Comparison of Different Voltage Waveforms for Cable PD Testing.pdf
- 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