Current measurements using optical power

Fiber optic systems are becoming increasingly important for measurements of current, voltage and temperature in high voltage environments. Conventional electrical wiring such as a current transformer can readily be replaced by noise-free fiber optics. With an optically powered data link and a transducer, direct current, voltage and temperature measurements have been successfully demonstrated. The system includes two modules connected by optical fiber up to 1 km in length. One module is placed at a control site. It supplies optical power for transmission to, and receives data from, the measurement module, which is placed at a remote site, in this case at high voltage. This remote module converts the optical power into electrical power for the electronic circuitry, the transducer and a data communications link. The analog voltage from the transducer is fed into an analog to digital converter. Test results verify successful operation with a sampling rate of 33.3 kHz. Taking anti-aliasing filters into account, an equivalent analog bandwidth of 10 kHz was achieved with an overall resolution of 0.025% (12 bits) and a 0.2% accuracy. Together with modern digital relays this technology offers new reliable ways to improve the protection of high voltage systems. Fully operational over the temperature range -40°C to +85°C, the system is sufficient for most electric power applications