ATEC carries partial discharge testers, corona test sets, corona cameras and more partial discharge test equipment from leading manufacturers like Megger, Omicron, and Hipotronics. ATEC’s inventory of PD test instruments can be paired with other industrial electrical test equipment for insulation testing, dielectric testing, ground testing, and more.
What is Partial Discharge?
A partial discharge (PD) is a small spark within electrical insulation caused by insulation breakdown. PDs occur when an electrical insulation system experiences high voltage stress. A dielectric breakdown of a small portion of the insulation generates electrical discharges, which bridge the gap between two conducting electrodes. These dielectric breakdowns manifest across the surface of insulation material, in pockets found in solid insulation, within gas bubbles in liquid forms of insulation, and proximal to electrodes in gases.
Partial discharge eventually destroys insulation, which leads to electrical breakdowns, and at times even degradation or total failure of the equipment. Cracks, voids, and other dielectric faults are generally the origins of partial discharges. These gaps in insulating material are the perfect environment for partial discharges to occur. PDs can also happen at the boundary between different types of insulation.
Signs of PD include the smell of ozone, the smell of burning wire, a metallic smell, discolorations, and carbon tracks branching out from the insulation, which form in a process known as “treeing.” Discharges begin branching out across the insulation, spreading over the equipment. Treeing manifests as tree-looking marks, surface tracking, and carbonization.
Damage caused by partial discharge can be:
- Mechanical - In the form of ionic bombardment
- Thermal - Heating at the site of the discharge
- Chemical - The discharges dissolve chemical bonds in the insulation
Switchgear partial discharges, for example, can manifest both as corona, the ionization of fluid/air around the conductor, which is generally visible, and also surface tracking, branching marks of the corrosion and degradation that spread due to faulty insulation.
Arcing is another common type of discharge in switchgear, in which the electrical breakdown of gas creates plasma discharge. Arc-flashes in switchgear can occur with force equivalent to being hit with a grenade, giving nearby personnel severe burns and even hearing and memory loss.
Electrical Equipment Vulnerable to Partial Discharges
- Switchgear
- Test cables
- Splices
- Motors
- Terminations
- Transformers
- Generators
What is Partial Discharge Testing?
Partial discharge testing, or PD testing, detects the presence of partial discharges in high voltage equipment.
As aging HV equipment continues to operate at high levels all around us, PD testing is more critical than ever to diagnose insulation failure before electrical stress shuts systems down and incurs expensive maintenance.
Planning out your insulation strategy, having a detailed design, and selecting the right materials can all help to prevent partial discharge from occurring. PD testing is often performed both during manufacturing and throughout the device’s life cycle, ensuring that discharges or signs of insulation breakdown are discovered and can be planned for and prevented.
What is a Partial Discharge Tester?
Partial discharge testers empower operators to perform effective and reliable insulation testing of these high voltage devices in applications like factory acceptance testing, on-site commissioning, and routine electrical maintenance. PD analysis techniques must adhere to IEC 60270, the international standard for the measurement of electrical discharges in insulation.
A complete partial discharge test system is composed of a low inductance coupling capacitor, a high voltage power supply that possesses low background noise, a high voltage filter that minimizes any background noise the power supply may generate, and the key instrument, a partial discharge detector. Partial discharge testers find insulation anomalies with time domain reflectometry, or TDR: the PD detector automatically analyzes reflectograms gathered when the measurement is taken, allowing the cable or device under test to be mapped out.
Equipped with this sophisticated technology, partial discharge testers can discover the precise location of the fault. This data is cross referenced with measurements performed on the same cable during acceptance testing or standard factory quality control specifications. Test personnel are then able to determine the device’s dielectric condition, which can range from new to faulty, and indicates what repairs in maintenance need to be performed on the device going forward.
How to Choose the Right Partial Discharge Tester
Choosing the right partial discharge measurement system is essential, as interpreting PD data points and predicting damage or failures is a difficult process. A modern system with sophisticated data analysis features is ideal. Also, consider whether you need to perform conventional PD detection, verifying the equipment fulfills IEC 60270, or more sophisticated detection, which may require an advanced PD and RIV detector.