Field evaluation of FR5 glass optical current transducer

This paper describes the operation of an optical current transducer (OCT). The OCT operates by measuring changes in the polarisation state of light travelling through a magneto-optic sensor head exposed to the magnetic field of a current carrying conductor. The changes in polarisation state are directly related to the magnitude of the current flowing within the bus bar but is also influenced by external environmental parameters such as temperature and mechanical disturbance. Engineering solutions to these influences have been implemented. Thermally induced errors of greater than 25% are shown to be corrected to less than 0.2% over a range of temperatures from -45 degreesC to 140 degreesC. In addition to this, signal waveform distortion resulting from mechanical vibration is automatically reduced by more than 30 dB over a range of frequencies from 0 Hz to 5 kHz. This paper reports on the design of this OCT and on detailed investigations carried out at the British Short-Circuit Testing Station to establish the operational characteristics of the OCT when subjected to transient current signals often with a significant de component.