Hybrid optical current transformer with optical and power-line energisation

The hybrid optical current transformer (HOCT) has previously been proposed as a suitable device to replace a conventional open-terminal post-type curr ent transformer. The HOCT is much smaller than the conventional device lead ing to lower manufacturing costs. There is also a degree of electrical insu lation inherent as optical fibre is used for connections between the line-m ounted HOCT and ground level instrumentation; this reduces installation cos ts. A performance specification for a HOCT is presented; a HOCT unit satisf ying this specification could, in principle, be a suitable replacement for a conventional device for power system protection purposes without loss of system quality or reliability. A prototype HOCT has been designed and const ructed; initial tests show that it meets the specified accuracy requirement s over the full operating temperature range. As far as call be determined, this is the first alternative to conventional current transformers that has been shown to meet these stringent requirements.