Using phasors to analyze power system negative phase sequence voltages caused by unbalanced loads

An analytical method is demonstrated which allows the level of negative phase sequence (NPS) voltage at a busbar to be expressed as a sum of phasors representing independent sources. The method is extended to enable the balancing capability of Static VAr Compensators (SVCs) with individual phase voltage control to be assessed. The capability of such SVCs and the allowable levels of NPS voltage on the system, including any short term limits, can be combined in a capability chart showing the unbalanced loads which can be supplied from a substation. The approach facilitates the treatment of fixed unbalances due to filters or intentional offsets designed to maximise the SVC balancing range for specific loads. Field test results are presented which validate the analytical methods used