Compensation of simple fiber optic faraday effect sensors
A monitoring system for detecting earth faults in an electrical power supply grid providing a power signal includes a plurality of monitoring devices, each of the monitoring devices including a detector for detecting the level of harmonics in the power signal, wherein the level of harmonics is detected in a specific frequency range. Each of the monitoring devices further includes a memory for storing a harmonics reference value, a processor for comparing the detected level of harmonics with the reference level, and a communication device for transmitting an alarm if the detected level of harmonics is above the reference level for a specific period of time. Each of the detectors includes an optical sensor for detecting the harmonics by use of the Faraday effect.
1. A system for monitoring and/or determining voltage conditions at a high voltage side of a step-down voltage transformer of a transformer station, the system comprising:
an electrical conductor connected to the high voltage side of the transformer;
an optical unit including an optical transmitter and an optical receiver connected by an optical conduit, the optical conduit including an optical current sensor mounted on the electrical conductor and configured for sensing current-sensitive electrical fields at the electrical conductor, and for generating a sensor output signal indicative of optical power received by the optical receiver from the optical transmitter through the optical conduit;
a memory unit configured for storing transformer related information relating to characteristics of the transformer; and
a processor unit, operatively connected to the optical current sensor and the memory unit, and configured for (a) measuring currents in the electrical conductor in response to the sensor output signal, (b) receiving a voltage signal indicative of measured voltages at a low voltage side of the transformer, and (c) calculating voltage conditions on the high voltage side of the transformer in response to the measured currents, the voltage signal, and the transformer related information received from the memory unit.
2. The system according to claim 1 , further comprising an output unit operatively connected to the processor unit and configured for outputting data representing the voltage conditions at the high voltage side of the transformer.