The theory and application of differential protection of multi-terminal lines without synchronization using vector difference as restraint quantity - simulation study

This paper presents an application of a new novel differential relay algorithm for EHV three terminal as well as multi-terminal transmission line, using phase measurement units in a form of an incremental current. The new method presented is based on a vector sum as an operating quantity as most methods known today. However the restraint quantity used the vector difference between the largest incremental current and the vector sum of incremental currents of other terminals. This tripping criterion reduces the need to provide synchronization between the signals at the line terminal ends for up to 400 km circuit length, as well as reducing the additional restraint when current transformer saturation occurred during an external fault. A simulation study carried and the results of which show that the scheme gives the response correctly under sever conditions/cases.