Industrial power system protection against transmission system blackouts

Complex industrial power systems that include significant on-site power generation are usually at risk when transmission network blackouts occur. Due to blackouts the on-site generation may suffer inadvertent tripping of the generators and plant shutdown. For continuous processes that have expensive consequences following a shutdown the impact of a blackout has to be mitigated through selection of appropriate protection schemes. Traditionally the protection against blackout is effected by the rate-of-change-of-frequency (ROCOF) relays. The set-up of the ROCOF relays is a delicate operation that requires a good knowledge of the dynamic behaviour of the transmission system where it will be installed. In some cases these conditions are difficult to be fulfilled and alternative solutions should be sought. The paper presents such alternative protection solutions and discusses the implementation practicalities. The paper includes also the results of the dynamic simulations carried out on a model representing a petrochemical plant power system connected to a transmission network experiencing a blackout.