SVC behaviour under voltage collapse conditions

Under stressed conditions, it may be necessary for a power system to operate at a point where a voltage-susceptance characteristic has a negative slope. The authors demonstrate that static VAR compensators (SVCs) can extend stable operation into that region. It is shown that short-term system stability is primarily governed by the interaction between the SVC control system and instantaneous voltage-susceptance characteristics. Given that SVCs are stable in the short term, then long-term behavior is dependent on transformer trapping. These effects are explored. The consequences of SVCs encountering limits are also considered