Bus Bar Protection

Bus Bar Protection

A busbar is a strip or bar of copper, brass or aluminum that conducts electricity within a switchboard, a substation or a battery bank. Its purpose is to conduct a substantial current of electricity.

ABB's busbar protection is designed for phase-segregated short-circuit protection, control, and supervision of single busbars. The busbar protection relay is intended for use in high-impedance-based applications within utility substations and industrial power systems. The relay can also be utilized in restricted earth-fault and residual earth-fault applications for the protection of generators, motors, transformers and reactors.

The correct method of setting the CT ratios for the busbar differential protection. It can be seen that the CT ratios of all the CTs are equal and are based on the primary current of that feeder which carries the maximum current ratios are 3000/1 A. Therefore, as can be seen from the figure, there is no spill current through the OC relay connected in the spill path and the scheme remains stable.

This figure shows a busbar, having two incoming feeders and one outgoing feeder, being protected by a simple differential protection scheme. The currents shown are for normal load flow. Let us decide the CT ratios on the basis of maximum primary load current seen by each CT. Thus, the CTs on the incoming feeder will have CT ratios of 1000:1 A and 2000:1 A, respectively. The CT on the outgoing feeder will have a CT ratio of 3000:1 A. However, with this choice of CT ratios, it can be seen from the diagram that there is a spill current even during the healthy condition. Thus, the method of selecting CT ratio on the basis of maximum primary current seen by the feeder is not correct.