To remain competitive, electrical utility companies continually strive to improve system operation and reliability while reducing costs. To meet these challenges, utility companies are developing techniques for increasing the life of installed equipment, as well as, diagnosing and monitoring their utility networks.
An example of the type of installed equipment used by utility companies to address voltage instability and collapse problems is the static VAR compensator (SVC), which serves to remove the losses contributing to the huge increase in current by temporarily injecting reactive power into the network. An SVC typically includes valves or switching elements in the form of thyristor-switched capacitors (TSC) and thyristor switched reactors (TSR). These semiconductor switching elements are packaged in a cylindrical ceramic “press-pack” and arranged in pairs between two flat, copper plates. The plates are electrically and thermally conductive members, and are used as heat sinks for the semiconductor switching elements, as well as to apply an external clamping pressure to the press-pack, which is required to permit the silicon semiconductor within the package to make electrical and thermal contact with the soft copper pole faces of the package. Multiple assemblies of switching element pairs sandwiched between plate pairs are required to be connected in series to conduct and/or control both polarities of the AC current. Thus, multiple assemblies are stacked to facilitate the series connection of multiple lower voltage rated devices to achieve compensation for the higher system voltage. The resulting valve is operated under dielectric oil which serves as high voltage insulation and as a thermal heat transfer fluid. Because of the high thermal conductivity of the dielectric oil, the plates which sandwich the semiconductor switching elements serve as heat sinks to transfer heat generated in the power semiconductors to the oil. In addition, the plates establish the electrical connection between semiconductor switching element pairs of a given assembly.