WEB database for the evaluation of PD measurements on MV cable system

Abstract

The medium voltage (MV) cable network is an important asset of a distribution system. It represents large investment, and it must guarantee a reliable operation and it is from economic point of view essential to extend the life time of the medium voltage power cables as much as possible. It is known that with increasing age, the number of faults will increase and the power supply reliability might be reduced. Important symptoms of this degradation process can be related to discharging local insulation imperfections or defects which may occur in particular cable sections or cable accessories: joints, terminations. About 50% of the failures in medium voltage power cable networks are related to insulation problems. Insulation problems may have different origins: by new cables in joints and termination due to mounting faults or by cables in service due to degradation of cable insulation, or degradation of joints and terminations. The use of onsite PD measuring systems is more and more common to detect and locate PD faults to prevent service failures and loss of power supply. To perform a PD measurement is quite easy, but the interpretation of the results often raises more questions and makes the decision for replace or repair difficult. The increasing number of joint failures prepared in the past 15 years was an initial point to establish a VDE-working group to collect and share experiences of onsite PD measurements. More than 30 German power utilities and several manufactures of PD measuring equipment and of cable accessories are members of the working group. The outcome of this work is a WEB database, to collect in a clear structure the most important PD parameter of field measurements and the results of visual inspections of the located PD faults. This paper describes the database in detail and presents that the evaluation of PD measurements and severity estimation of the specific PD fault has to be done under consideration of the type of accessory and also the nature of the defect. Because the ignition of PD in a defect depends from the type of excitation voltage the database is structured accordingly. The data collection in the database should not be limited on German power utilities and industry networks, but can be also used for worldwide input and use for interpretation of onsite PD measurements.