Megger (Germany)

Power swing which is primarily caused by sudden addition or removal of load in a transmission line, consequent to an enormous interruption in power system, which if not blocked, could cause wrong operation to the distance relay which may lead to tripping the healthy part of the transmission line. In the absence of power swing function it may result in severe damage to the machines or cascading tripping in the grid resulting in blackouts. To prevent such scenarios, intelligent electronic devices (IEDs) have power swing block (PSB) detection and trip logics incorporated with distance schemes. This logic provides severe challenges to T & C engineers, where the conventional methods of using several states and multiple configuration steps while testing the IEDs complicates the process of testing. Further, the variations in logics due to manufacturer specific algorithm add to the complications. To address such complications, a new testing philosophy has been developed in, where PSB, PSD and PST functionality testing methodology and detailed discussion on the oscillography file is explained in this paper.

Underground medium voltage (MV) cables are an important component of modern MV distribution networks. However, experience from MV network operations, has shown that local degradation, cable joints and terminations often constitute weak spots on MV cable systems, sequel to factors such as ageing, water ingress, inadequate workmanship and utilization of inappropriate or defective cable accessories. Hence, the need to deploy testing and diagnosis techniques on new and serviced-aged MV cable systems, as outlined in guidelines and standards, such as, the IEEE 400 [1] and IEC 60502–2 [2], to ensure they are as reliable, as possible.

The continuously increasing installation complexity for medium voltage power cables, results in many weak spots and cable failures due to bad workmanship. This is mainly caused by the large variety of cable accessories as well as the reduction in insulation thickness and therefore in the margin of error throughout the entire cable installation process. The necessity for both commissioning testing of new cables as well as diagnostic measurements as part of a condition based maintenance is just a logical given fact. Nowadays cable testing as well as condition monitoring are well proven measurement methods for MV power cables which are guided by IEEE 400 [1] and IEC 60502-2 [2] standards.