Off-Line Partial Discharge Cable Testing

Virginia Balitski, Magna IV Engineering Columns, Tech Quiz, Winter 2022 Columns

NETA Certified Technicians must continually adjust to advancing technology and diagnostic testing techniques. Over the years, cable testing has advanced to where multiple testing methods can be selected.

After careful consideration of system requirements, a site owner may choose off-line partial discharge (PD) testing as one of their cable testing methods. This quiz looks at some details on partial discharge testing of cables.

  1. 1. What is partial discharge?
    a. A localized electrical discharge that only partially bridges the insulation
    b. Complete loss of a voltage signal
    c. A low-frequency (0.1Hz) failure
    d. Severe arcing that exists inside insulators that is usually detected by IR scanning
  2. Which of the following cables are suitable for off-line PD testing?
    a. 3-conductor tape-shielded cable
    b. 1-conductor concentric neutral cable
    c. Non-shielded cable
    d. a & b
  3. What other limitations might make off-line PD testing of a cable not feasible?
    a. Cable length
    b. Electrical noise on site
    c. Resistive shield connections at the termination
    d. All of the above
  4. What are the typical test set components of an off-line PD test set?
    a. PD measuring instrument, 60Hz hipot, and series capacitor
    b. PD measuring instrument only
    c. PD measuring instrument, VLF hipot, and a parallel coupling capacitor
    d. PD measuring instrument, DC hipot, and a parallel resistor
  5. What units are usually used to quantify PD activity?
    a. Micro-amps
    b. Pico-coulombs
    c. Giga-ohms
    d. Ampere-hour
  6. Do all data points from off-line testing indicate PD activity?
    a. Yes. The analyzer is filtered for high-frequency signals, so any data is concerning.
    b. No. High-frequency signals are recorded, including electrical noise and corona discharges.
    c. No. You will almost always receive mostly corona discharge signals, and only major issues will make it through.
    d. Yes. Any concerning PD will produce a vast number of data points.


Virginia Balitski, CET, Manager – Training and Development, has worked for Magna IV Engineering since 2006. Virginia started her career as a Field Service Technologist and has achieved NETA level 4 Senior Technician Certification. She has since dedicated her time to the advancement of training and safety in the electrical industry. Virginia is a Certified Engineering Technologist through ASET – The Association of Science & Engineering Technology Professionals of Alberta. She serves on NETA’s Board of Directors, is the current Vice-Chair of CSA Z462, Workplace Electrical Safety, and is a member of the NFPA 70E, Electrical Safety in the Workplace Technical Committee.