Selecting an appropriate bus protection scheme requires careful consideration of several factors, including bus layout, permissible switching scenarios, availability of suitable current transformers (CTs), and maintenance requirements.
High-impedance bus relaying is ideal for buses with statically assigned zone currents, provided that suitable CTs are available. These systems do not require disconnect status inputs. However, substations with terminals that switch between different buses must dynamically assign input currents to protection zones based on disconnect auxiliary contact status. To mitigate misoperations caused by disconnect auxiliary contact failures, a secondary trip criterion, such as a check zone, may be necessary.
Low-impedance numerical relays are particularly effective for complex bus configurations requiring dynamic zone selection, as they allow reconfiguration without altering physical CT wiring.
While bus differential relaying ensures protection for all bus arrangements, fast bus tripping and directional elements may suffice for certain configurations. Additionally, the placement, saturation, and ratio of CTs, along with the presence of surge arresters, significantly impact the performance and selection of a protection scheme.
This paper explores various bus configurations, presents suitable protection schemes, and evaluates their complexity, benefits, and limitations.
