The key state parameters and relevant monitoring methods of fiber optical current transformer

Fiber optical current transformer (FOCT) can be influenced by a variety of external factors (such as ambient temperature, vibration, shock, electromagnetic interference, etc.) and internal factors (such as degradation of optoelectronic devices, increase of optical loss, etc.) in the field operation process, these factors cause the change of internal key state parameters in FOCT, thus reduced the accuracy and reliability of the product. To solve this problem, five key state parameters of FOCT, which are junction temperature of SLDs, transmitting optical power of SLD, half-wave voltage of phase modulator, working temperature of fiber sensing coil and the received optical power of photodetector, were proposed in this paper, the analysis and experiment of these parameters were given, the impact of key state parameters on FOCT accuracy is descripted quantitatively for the first time, further, the methods for monitoring and controlling each key state parameters were proposed respectively with experimental verification. The test results show that the ratio error and phase error of the FOCT product used state monitoring is small than 0.1% and 3 min respectively over a temperature range −40 °C–+70 °C The study provides a technical guidance for the key parameter design and performance optimization of FOCT products, supplied basic model and data support for the inline monitoring and early warning to FOCT operation state, it will be helpful to improve the stability and reliability of FOCT products in long-term operation.