Testing busbar protection (BBP) systems using process bus technology

Busbar protection (BBP) is the most complex protection system in a substation, as it interfaces to all bays in the substation. Every required current, disconnector status, and circuit breaker status and control point must be wired into the BBP relay in some manner. As a result, BBP relays are the most difficult and time consuming to test. A conventional centralized busbar protection has complicated wiring, as wiring for all currents, status, and control points must be installed to the main unit. Conventional distributed busbar protection simplifies field wiring by using bay units as the interface point to field wiring. Most use dedicated point-to-point fiber optic connections between the bay units and the central unit, requires requiring a fiber optic cable and communications port at the central unit for each bay. Process bus is distributed I/O for protection and control, converting analog interfaces to digital data at the source, using merging units (MUs) for currents and voltages and switchgear control units (SCUs) for status and control, and process interfaces units (PIUs), MUs and SCUs as one, as interface devices. Integrating process bus in busbar protection keeps field wiring the same as with distributed protection: wiring for each bay is connected to a merging unit. The advantage is that the merging units and the busbar protection unit are connected to the process bus communications network, using IEC 61850-based communications and standard time synchronization. The busbar protection unit needs only a single port or redundant ports with high availability network protocols such as PRP (Parallel Redundancy Protocol) and HSR (High-availability Seamless Redundancy) as defined in IEC 62439-3 [1] to collect all data needed for protection. Boundary clock time synchronization technology can be built in the relay to allow the process bus busbar protection relay to act as a master clock to synchronize all the merging units in the system, extending the process bus busbar protection to be used in both digital substation and conventional substation without requiring GPS clock synchronization. Utilizing the process bus technology in busbar protection simplifies the busbar protection testing also. This paper reviews busbar protection under process bus, along with general concepts in testing process bus protection systems. Specifically, the paper outlines testing strategies for a busbar protection relay that can subscribe to, and use, up to 24 SV data streams, including both commissioning and maintenance testing. Included in these strategies is the proper use of test modes and simulated SV and GOOSE messages. An important learning from these discussions is how testing a bus bar protection relay under IEC 61850-based process bus is simpler, and carries less risk, than testing a conventional busbar protection relay.