Configurable multifunction protection and control unit design and application

The advent of powerful microprocessors has enabled the development of multifunction protection and control units equipped with inputs and outputs, programming facilities and serial communications. The protection and control unit consists of a standard hardware platform which is configured with the appropriate software modules according to the application. The main advantages when compared with the conventional approach are: reduced size and complexity of the switchgear instrument cabinets; minimal wiring; single CT for protection and instrumentation; and ease of adaptation. Multifunction protection and control units allow MV switchgear manufacturers to standardize the circuit breaker panel designs, leading to reduced cost, improved quality and shorter delivery times. This paper describes the approach taken by one manufacturer in the design of such configurable multifunction device. Particular attention is given to the practical application of ladder logic programming facilities in the implementation of complex protection schemes, such as feeder unit protection using directional blocking principle