System dynamics modelling near voltage stability limits considering distributed automatic reactive compensation and on load tap changer transformers

The concenlratio~i of gcncration away from load centres together with load growth has produced a large element of bulk transmission wiUiin inany systems making them more vulnerable to voltage collapse. Substantial amounts of capacitive compensation are oflen required to maintain acceptable voltage levels. Varying system conditions dictate tliat compensation cannot be permanently connected but controlled accordingly. When installing static reactive compensation electric companies are faced with a choice of Static var compensators (SVC) or mechanically switched capacitors (MSC), the latter wlicli are less expensive but whose automatic control may pose difllculties. In this paper long term dynamic studies have identified possible undesired interactions between MSC and on load tap-changers under critical conditions. A novel control strategy for MSC is proposed.