Simulating the steady state and transient response of protective relays

This paper describes a generic approach to modelling the steady state and transient behaviour of protection devices. A protective relay (overcurrent, distance or any other type) is modelled using a multi-level approach, where a relay frame (which describes the topology), a relay type (which specifies the actual algorithms used), and a relay element (which specifies the actual settings used for a specific application) is defined. Using a simplified current transformer (CT) and voltage transformer (VT) model the steady state response of a relay in a network can be studied, using a normal short circuit simulation. The effect of CT saturation can be studied by performing a time based electromagnetic transient simulation with a detailed CT model. The transient behaviour of capacitor coupled VTs can be investigated using a detailed VT model. A graphic user interface displays any parameter on a flexible single line diagram or on a time based plot