ERF-based fault detection scheme for STATCOM-compensated line

The shunt flexible AC transmission system devices affect the protection schemes because of reactive power injection. Therefore, robust protection schemes are required. This study presents a fault detection scheme, which is based on estimated reactive power factor (ERF) and differential current with modified setting. The ERF is defined as sine of phase difference between the static synchronous compensator tap voltage and differential current. The static synchronous compensator tap voltage can be estimated using local end voltage and current. The ERF is measured at both the relay ends. In capacitive mode, if both ERFs are more than upper threshold, the fault is external, and if any ERF is less than upper threshold, the fault is internal. In inductive mode, if ERF is between upper and lower threshold, fault is internal else, if differential current is more than modified differential current setting, the fault is internal, or else, the fault is external. The performance of presented scheme is investigated for various system configurations with PSCAD/EMTDC simulations. Further, the scheme is successfully validated in real-time digital simulator. It is found that the scheme is robust and selective for various faulty conditions, compensation level variations, and location variations.