Partial Discharge Detection Methods and Equipment

Timely partial discharge detection can save your high voltage equipment.

by ken wilson

In the field of electrical engineering, the breakdown of an electrical insulation under high voltage is called partial discharge (PD). The consequences of these types of occurrences can be hazardous if not detected in a timely fashion. Regular PD analysis and Bushing monitoring will give an accurate indication of the status of the deterioration process. Early detection can be the key to preventing more serous problems along the way. We offer you the best in partial discharge instruments as well as diagnostic monitors at elec-di.com.

Partial discharges may commence from different sources such as connected transformers or connected cables. Precise localization of the discharge source is extremely important for the initiation of corrective actions such as repairing the weak spots. Problems can be solved by utilizing detection coils at each cable end. Short duration signals are propagated towards both cable ends and therefore allow an accurate measurement of the difference in arrival times. This difference is what indicates the approximate location of the weak spot. Perfect synchronization of the signals is mandatory for an accurate measurement, as they travel through the cable with half the speed of light. To achieve this synchronization, high-frequency pulses are artificially injected into both ends of the cable. Usually, the processing of the measurements occurs on location, including specialized interpretation and database storage. It is generally recommended that a specialist interprets the partial discharge signals, as they can be conf using. For instance, a brief partial discharge in a resin insulated splice calls for immediate precautions as opposed to the same discharge within an oil insulated splice which is of no concern. Whatever the situation or the source of the problem, at elec-di.com you can find a solution.

Partial discharge monitoring is frequent when working with high voltage machines. PD activities usually occur in equipment such as transformers, on-load tap chargers, bushings, cables or switchgear. Transformers convert power level voltages from one level to another. Over time, PD may occur and if left undetected it may cause thermal faults or arcing. On-load tap chargers usually control secondary voltage regulation and tend to fail due to prolonged contact wear, component fatigue, misalignment or overloading. Bushing monitoring is very important because high voltage bushings are often prone to sudden failures. Bushings are meant to transport load currents in and out of grounded enclosures. Therefore, regular bushing monitoring is necessary in order to prevent serous problems in high voltage bushings by detecting increased capacitance before bushing levels become unsafe. Switchgear is prone to failure at the breaker level as it interrupts the high currents caused by fault conditions. With high voltage cables, the problems occur over time because of degradation. In this situation, PD monitors are used to detect small radio frequency current pulses and to correlate the values with the monitored phase.

There are many things to consider when selecting an appropriate PD monitor. First of all you should look at product specifications such as power input, range, memory, input correction, output, dimension and weight. Furthermore, specifications like frequency range, maximum pulse and absolute voltage peak are to be considered as they can make a great difference. Special features are also important. PD monitors can provide network use, integral software, remote access via a local area network and data acquisition systems. Other product features such as noise rejection, rise-time detection, remote alarms, three-phase measurements or individual alert thresholds are also available with PD monitors.

Partial discharge activity usually initiates in old high voltage equipment or flawed insulation. Within time, it propagates until the insulation is completely destroyed and the equipment collapses. Regular PD testing and Bushing monitoring is the only way to make sure a breakdown will be avoided.

About the author:

The partial discharge phenomenon is inevitable. High voltage equipment becomes deteriorated over time and problems occur sooner or later. Visit our website for complete information about partial discharge detection and Bushing monitoring equipment.

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