Instantaneous protection scheme for backup protection of high-voltage transmission lines

The protection scheme focused on in this study is a typical protection system used in high-voltage systems such as 132 kV, 275 kV, and 500 kV. The research will analyze the existing protection scheme for transmission lines that the power utility has implemented and will propose a new protection scheme to improve the performance of the existing scheme. The existing protection scheme currently implemented by the power utility for backup protection operation has a longer fault-clearing time and no restoration time, and it does not utilize support relays. This study will focus on a backup protection operation on high-voltage overhead transmission lines, which take up communication when the main protection has failed to communicate, the relay has failed due to loss of DC supply, or the relay function itself has been blocked. Moreover, all the support relays will be utilized in order to improve the protection system. The improvement will consider three elements, which are the fault-clearing time, fast restoration time, and relay utilization. Each improvement to the protection system will have its own philosophy and concrete rationale, which have advantages or disadvantages for the transmission line. The effect of the improvement scheme will also consider the outcomes in other schemes to ensure that time coordination does not overlap. Every possibility of a fault will be analyzed in order to have a clear understanding of the effects of the three elements. CAPE software will be used as a tool for simulation and to analyze its compatibility with real applications. CAPE software is able to model a real-life transmission line and is also able to simulate faults in the tested area. The results of the simulation show that the backup protection operation improved fault-clearing time and restoration time. It also increased the network's system stability, particularly during the occurrence of maximum fault currents.