Power Cases

In following cases, a method of equivalencing is used. We need equivalencing to reduce simulation time. It is useful especially when we want to study a large system with hundreds of thousand components by reducing the size of the power grid to a model system with fewer components than the original one. However, one disadvantage of an equivalent is that the reduced system can`t be used to study another behavior that the one for which reduction has been done. But if we focus of specific behaviors of the original, the equivalent can generate those behaviors similar enough and save a lot of time. Therefore, engineering insight is required between the size of the equivalent and the accuracy of the simulation results.

The first equivalencing method was developed by Ward in 1949 and it is still widely used. Another classic method is called a REI (radial, equivalent and independent) method. PowerWorld uses one of the Ward type methods. Moreover, there are basically two types of equivalencing, static equivalencing and dynamic equivalencing. Static network reduction is usually used for system planning and development as well as for system on-line monitoring and control purposes. Dynamic equivalencing methods are usually employed to create equivalent synchronous machines in order to mimic the transient stability behaviors of the original system. Also, it can be used to model equivalent loads. [1]

[1] By Wonhyeok Jang’s comments