High voltage dry-type air-core shunt reactors

摘要

Dry-type air-core shunt reactors are now being used more frequently on high voltage power transmission systems to limit overvoltages. Recently, high voltage dry-type air-core shunt reactors have been designed, manufactured and installed directly connected to the transmission systems at voltages up to and including 345 kV. Applications at 500 kV are presently being considered. These ratings require appropriate analysis in terms of switching transient overvoltages and electrical and magnetic clearances since dry-type air-core reactors have some saliently unique characteristics as compared to traditionally applied liquid-immersed units. Dry-type air-core reactors have a stray magnetic field that extends beyond the periphery of the equipment. Hence the magnetic clearances to surrounding metallic objects and for personnel must be established. High voltage dry-type air-core reactors are typically made with a modular winding design that allows use of a lower cost partial phase spare unit. This design technique also allows use of shunt connected surge arrester protection of each series connected winding module. High voltage direct connected liquid-immersed iron-core reactors have a higher inherent capacitance value to ground than dry-type air-core devices. Hence the magnitude and/or frequency of the switching transient overvoltages can be significantly higher where dry-type air-core units are employed. The transient overvoltages to be considered are the transient recovery voltage (TRV) at current interruption which stresses the circuit breaker and the reignition overvoltage which stresses the reactor. The TRV is the significant quantity for the circuit breaker or other load break device. This paper discusses these important aspects of dry-type air-core reactors and their ramifications with respect to the application of these devices for shunt connection on high voltage power transmission systems. Further, information concerning reactor protection, calculation methods for magnetic field levels around reactors, guidance regarding specification and type testing and appropriate methods to mitigate TRV frequency and magnitude, where necessary, are provided.