Mutual Zero Sequence Coupling

Main Features

Electrical networks often contain circuits in which lines are constructed in close proximity to each other, especially overhead lines. In these circumstances, the effect of mutual coupling between two adjacent circuits is to alter the zero sequence network and hence fault levels for unbalanced faults, such as L-G. The difference in fault levels between a circuit with mutual zero sequence coupling (MZSC) modelled and a circuit without is significant.

	The inclusion of mutual coupling within fault analysis is relevant where adjacent over head circuits run in close proximity to each other, for example in cases where circuits are constructed on tower lines or where more than one voltage construction is located on the same support.
	Under such circumstances the effect of mutual coupling may significantly alter the fault flows for cases involving earth faults.
	Under extreme cases the effect of mutual coupling can cause sufficient fault current to be induced into circuits adjacent to the faulted circuit that a protection mal-operation occurs. Clearly the ability to model such effects allows users to avoid such problems occurring by adjusting settings accordingly.
	The Mutual Coupling facility will allow Distribution Companies, within the UK, to comply with the requirements of the NGC.