To assist with the introduction of the IPEC range of Partial Discharge (PD) testing equipment in New Zealand and Australia, HV Power will be making customer presentations (Sept/Oct) supported by a factory expert. Watch out for details to your inbox soon.
Partial discharge is generally accepted as the predominant cause of long term degradation and eventual failure of electrical insulation. As a result, its measurement is common practice in factory testing of many types of high voltage equipment, and, many utilities now undertake an annual PD survey of installed equipment. However, with the latest generation of technology, PD monitoring products are now sufficiently cost effective and reliable (in the sense of not giving false warnings) to be permanently installed – without the need to have a 'guru' in your organisation decoding the resulting data. Permanently-installed devices are ideal for older switchgear, where periodic inspection may be too infrequent.
What is Partial Discharge?
Partial Discharge (PD) is an electrical discharge that does not completely bridge the space between two conducting electrodes. The discharge may be in, for example, a gas-filled void in a solid insulating material, in a gas bubble in a liquid insulator, or around an electrode in a gas.
Partial Discharge occurs at normal working voltages as the defects or cavities in solid insulation are usually filled with a gas of significantly lower breakdown strength than the surrounding material. In addition to this, the permittivity of the gas is invariably lower than that of the solid insulation, causing the electric field intensity in the cavity to be higher than that in the surrounding dielectric. Therefore, under the normal working stress of the insulation, the voltage across the cavity may exceed the breakdown value and initiate electrical breakdown, or ‘partial discharge’ in the void.
How do PD monitors work?
A combination of methods are best used, dependent upon the application:
IPEC combine these detection methods with sophisticated noise detection algorithms - distinguishing between noise and PD - to help avoid false positive results.
- Ultrasonic sensors are generally used to detect insulator surface tracking, where, for example, deposits on the surface over time cause tracking (PD). Tracking/corona generates a characteristic signature in its ultrasonic emission.
- Transient Earth Voltage (TEV) sensors are used to measure internal PD in the equipment. They achieve this as the partial discharge induces small voltage impulses (called TEVs) on the surface of the metal switchgear. The TEV sensor is capacitively coupled to the switchgear.
IPEC’s PD Alarm Switchgear PD Monitoring System and Ultrasonic sensor.
See our website for more details, or contact us.