Online, Non-Intrusive Partial Discharge Screening of Electrical Asset

Electrical systems reliability is of utmost importance for industries and utilities alike. As per NFPA 70B and IEEE Gold Book insulation failure is number one cause of failure of Electrical assets like cables, switchgear, motors, generators, AIS/GIS equipment, transformers etc. Failure of these assets can cause prolonged downtimes and they can be catastrophic as well. For all MV and HV equipment rated 6.6 KV and above, partial discharge is found to be a major failure mode, Prescon engineering is providing this exclusive service in order to cater the need of our valued customer

What is Partial Discharge ?                     

“A localized electrical discharge that only partially bridges the insulation between conductors and which can or cannot occur adjacent to a conductor” quoted from IEC60270 verbatim.

Why it occurs?

When voltage stress exceeds a certain maximum limit of breakdown for that portion of the insulation, partial discharge occurs and continues to happen as long as the excitation voltage is greater than the inception voltage

What are different types of partial discharges?

It depends upon asset, rated voltage, insulation type, shape of conductors, proximity to other phases/ground

• Corona – discharges to air
• Floating Electrode – metal to metal
• Voids – gaps in solid insulation or cavities as well as gas bubbles in liquid insulation
• Surface Discharge – tracking on outside surface of insulation travelling towards other conductor or ground
• Partial Discharges – conductive particles contaminate insulation medium

PD Detection

PD can be detected using following non-conventional techniques in various electrical assets:

• Acoustic Emissions (AE)
• Airborne – ultrasonic microphone 40kHz center frequency
• Contact Probe – broad range 20kHz -300 Khz (PD in oil or SF6 gas) Electromagnetic –
• RFI/UHF Ultra-High Frequency 100 MHz-1 GHz
• TEV Transient Earth Voltage 1 MHz-100 MHz
• HFCT High Frequency Current Transformer 500kHz-50MHz
  • Transformer
  • Motor/generator
  • HV air insulated substation
  • MV switchgear
  • GIS substation
  • cables