There are various factors that influence the performance of insulation system which are electrical, thermal, and mechanical factors; besides, production defects and impurity of insulation production can also result in difference of dielectric constant, and cause non-uniform electric field which could lead to an local electric field exceeding the breakdown voltage, followed by partial discharge phenomenon. Partial discharge was named after its own characteristic which means that it only exists partially in the insulation system instead of the entire system. This phenomenon will accelerate the insulation aging and may lead to short circuit; furthermore, serious consequences will happen if the PD activity is not discovered and handled properly. There are three major techniques of PD avoidance which are periodical diagnostic, PD long-term monitoring, and PD Care. Comparison among these three techniques is shown below.

Periodical diagnostic can reveal mechanism defects through the diagnostic test performed by industry experts. Although professional service is performed periodically, this method cannot minimize the possibility of occurring PD activities. On the other hand, PD long-term monitoring is a method which can effectively lower the risk of PD, but the cost is relatively high; in other words, it is not cost efficient. By combining the advantage of these two methods, PD Care can provide professional service with relatively low cost.

The comparison clearly points out the advantage of each method. Although Periodical Diagnostic cost the least, PD Care proves its cost-efficiency . From the other point of perspective, Periodical Diagnostic holds its advantage only in the short-term which excluding the time-based services , such as rewinding. The following is an example of rewinding a generator.