The paper presents the performance of a novel distributed bus differential protection scheme, which utilizes independent multi-principle advanced protection algorithms, including differential percent slope,
delta phase directional comparison, rate of change of differential (ROCOD) currents, delta phase directional comparison on neutral current differential, and a check zone to secure the electrical bus bars up to three zones (two main and one transfer bus).
This bus protection scheme measures currents from conventional CTs, converts them into digital signals
and publish them using IEC 61850 process bus based (9-2) sampled values as Merging Unit. It also
subscribes the sampled values amongst all the other relay units (within protection scheme) using fiber
optic / copper Ethernet communication. High-speed GOOSE messages (IEC 61850, 8-1) is used to
monitor the real time Isolator / Circuit Breaker status, enabling dynamic reconfiguration of the CT inputs
to different bus protection relay units depending on the load – generation availability. The proposed bus
protection scheme does not need any external Ethernet switch for the sampled value (9-2) exchange. Once the sampled values are received by each protection relay unit, they all act as MASTER relays, and all the relays respond (trip/block) simultaneously to the system event. This also adds redundancy into the bus protection scheme.
Rigorous validation and testing has been carried out to validate the performance of the relay scheme using a transmission system simulated in a RTDS (Real Time Digital Simulator). The test cases include
switching, loading, inrush currents, and extreme CT saturation conditions for external and internal faults.
Many test cases to reflect the practical situation such as high impedance faults, evolving faults, and faults
on lightly loaded conditions have also been performed and will be discussed.
K. Narendra, N. Perera, Presented at the CIGRÉ Canada Conference on Power Systems, Winnipeg, Canada, Sep. 2015., paper CIGRE 660
KEYWORDS: Bus Differential Protection, sub-cycle, IEC 61850, Sampled Values, Process Bus (9-2), Station Bus (8-1), GOOSE