Understanding the Types of Partial Discharge

  • Partial discharge breakdown of insulation results in various effects, including rays, warmth, scent, sound, electromagnetic waves, and high-frequency electric current. It can occur in different types of insulation (air, oil, solid, GIS) and at various voltage levels (from 3kV to 769kV and beyond). The three main types of partial discharge are:
  • Surface PD Discharge: The most common form, occurring across the surface of the insulation, is influenced by environmental factors humidity, temperature and pollution.
  • Internal PD Discharge: These discharges happen within f defects or voids within solid insulation.
  • Corona PD Discharge: Occurs in gaseous dielectrics when inhomogeneous fields are present, often involving discharges from conductors into the surrounding air.

Effective Detection Methods


To detect partial discharge in MV/HV switchgear, bus ducts, cables, etc., it is preferable to perform the detection while the system is live, without disrupting the power supply. Several practical methods rely on detecting different frequency signals, using a combination of sensors to identify different types of partial discharge:


Ultrasonic Methods: Highly effective in identifying corona partial discharge, detecting ultrasonic acoustic emissions beyond the human ear’s capability.

Transient Earth Voltages (TEV): Excel at detecting internal PD, measuring TEV signals that propagate along the metal surfaces of switchgear till ground.

UHF Detection: Excellent non-contact method for identifying electromagnetic PD signals in  Gas Insulated Switch Gears and Cable Terminations

HFCT/RFCT Online Cable Testing: Utilize high-frequency current transformers (HFCT) or radio frequency current transformers (RFCT) for online cable testing, measuring PD pulses that reach an external cable ground while keeping the cable in service during testing.


Technomax: Your Experts in Partial Discharge Testing


At Technomax, we specialize in Online partial discharge testing, offering advanced techniques for accurate electrical insulation health assessment. Our experts are adept at identifying and mitigating potential issues, ensuring the reliable and safe operation of your electrical assets. Contact us today to explore our partial discharge testing services and safeguard the health of your electrical infrastructure. Trust in Technomax for expertise and excellence in partial discharge testing.

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