Novel capacitor-divider voltage sensors for high-voltage transmission systems

For some time, it has been recognised that conventional capacitor voltage transformers (c.v.t.s) have transient response limitations which affect the performance of modern high-speed protection. To take advantage of existing and new types of distance protective systems, capable of performing accurately withing the first 20 ms of fault inception, a high-fidelity voltage measurement system which overcomes the limitation of conventional c.v.t.s has been developed. The novel high-fidelity voltage sensor comprises a conventional capacitor divider and solid-state amplifier system, the latter being suitable for application with existing designs of capacitor voltage transformer, purpose-designed capacitor voltage dividers, or with capacitor-probe facilities in SF6 metal-clad switchgear installations. A summary of the results of the various tests which have led to the development and design of a fully engineered system are described. Reasonable correlation is shown to exist between actual performance of the novel c.d.v.s on the 400 kV system and laboratory tests. Technical performance requirements for high-speed protection covered by the IEC Recommendations, Publications 186, 1969, and 186 A, 1970, and other special requirements are evaluated in a manner which could be used as a basis for design specifications. The paper concludes by considering economic aspects and future possibilities.