Sometimes electrical discharges occur across a portion of insulation between two conducting electrodes without entirely bridging the gap. This situation is called partial discharge (PD). It can occur in voids within solid insulations, in gas bubbles within liquid insulations or around gas electrodes. PD monitoring is crucial because of the hazardous consequences it may have. Bushing monitoring is also of great importance as it provides information about incipient failures. You can find all the information you need on partial discharge instruments, diagnostic monitors and much more at elec-di.com.



Partial discharge is not something uncommon as it usually occurs under normal working conditions. It generally begins in high voltage equipment where the insulation condition has become subject to deterioration. This deterioration can be the result of many things, such as age or thermal over-stressing. Sometimes PD is determined by improper installation of new electrical equipment or poor design or workmanship. This is particularly obvious in cable joints and terminations and can therefore be quickly prevented. The danger with undetected PD is that it can propagate and develop into electrical trees. This weakens the insulation gradually until it fails completely. A breakdown can have very serious consequences and it's better to try and prevent such occurrences.

Each partial discharge phenomenon is an outcome of the electrical breakdown of an air pocket in the insulation. The electrical breakdown causes a very brief electric current to flow through the air pocket. These breakdown currents are in fact the object of partial discharge measurements. PD analysis and measurements are meant to evaluate the integrity of the electrical equipment. Measurements can be taken either continuously or intermittently and can be detected on-line or off-line. The purpose of these measurements is to determine whether the electrical equipment is in need of maintenance.

There are various manufacturing problems that impair the reliability of high voltage equipment. The electrical insulation is often subject to thermal stress, chemical attack and abrasion due to excessive coil movement. In all these situations, the bonding properties of the epoxy or polyester resins that coat the windings become weakened over time. As a consequence, an air pocket will develop in the windings. The PD phenomenon accelerates the breakdown process of electrical equipment. Once the dielectric strength and mechanical integrity of the insulation is compromised, it's only a matter of time before a ground or phase-to-phase fault occurs.

Transformer bushings are constantly subjected to substantial dielectric strains. Over time, a failure in their insulation is very likely. Such a failure damages the bushing itself and can also lead to the loss of the entire transformer. Bushing monitoring is probably the only reliable way to avoid these dangerous and expensive situations. Bushing monitors perform online screenings of high voltage bushings by measuring stray currents in their normal operation process. The Bushing monitoring process provides all the relevant information through analog outputs, local display, dry contacts and serial communication ports.

High voltage machines are generally pretty reliable and do not break down often. However, occasionally failure does occur and is generally caused by a winding insulation breakdown. Regular partial discharge analysis and Bushing monitoring will surely lead to improvements in the machine's useful operating life, availability and plant economy. Regular and thorough monitoring makes for early detection of problems and possible remedial of the situation. Here at elec-di.com you will find the best monitoring and detecting solutions available.