Protection History: Unbalance Relays

This article continues the series covering generator protection and describes the protection against unsymmetrical load. Developing load-unbalance protection based on the method proposed by the Canadian Charles Legeyt Fortescue in his paper describing the symmetrical components ("Method of Symmetrical Co-Ordinates Applied to the Solution of Polyphase Networks") in 1918. As we all know every rotating system can be divided into zero, positive and negative components. The negative components are used for unbalance protection. More

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