System-based testing of a voltage differential protection scheme for shunt capacitor bank

Abstract

Capacitor banks used in substations cause a maintenance problem, which consume time for technicians to identify the root cause of the problem which can result in voltage control issues. Therefore, aim of this project is to identify either the unit or element fails within the capacitor bank using the dedicated voltage differential protection function. The voltage differential across the capacitor bank is calculated using the Capacitor Bank Assistant (CBA) tool in AcSELerator quickset. There are two modes of operation are considered (a) Alarm and (b) Trip. The alarm mode is used to notify the system operator for small change in system voltage due to element fail within capacitor bank, whereas in trip mode operation the change in voltage reaches the maximum threshold value and send the trip signals in order to disconnect the faulty banks from rest of the power system. The paper designed the voltage differential logic in AcSELerator quickset for both alarm and trip modes respectively. The system-based voltage differential protection function testing for shunt capacitor banks is introduced in this paper. The reason for introducing the system-based testing is because two CMCs are used to make a connection for VZ and VY channels of SEL487V IED in order to test the voltage differential function. The two CMCs are synchronized in Relay SimTest software using GPS signals from SEL satellite clock (SEL-2407) and Antenna. Relay SimTest software has a provision to model the capacitor bank and simulations result are analyzed for alarm and trip mode operations respectively. In addition to the main protection (voltage differential), this manuscript provides the protection setting and simulation results for the overload backup protection for SCB’s. However, it is observed that voltage differential scheme for SCB’s is more sensitive in comparison with overcurrent backup protection. The cost of the voltage differential is more expensive than the backup overload protection because of using only with CT signals. In summary, it is a good practice to implement both Main (Voltage differential scheme) and Back-up (Overload) protection schemes in order to effectively protect the SCB’s from any kind of internal faults in the system. Finally, the IEC61850 GOOSE message application is considered for SCB’s. The engineering configuration is performed for two logical nodes A87PDIF1 (alarm mode) and T87PDIF1 (trip mode). The IEC61850 GOOSE simulation results are analyzed using IED Scout. Finally, hardwired and IEC61850 GOOSE simulation results are compared. The GOOSE operation is faster than hardwired signals for shunt capacitor banks voltage differential function.