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

and these factors cause the change of internal key state parameters in FOCT

thus reduce the accuracy and reliability of the product. To solve this problem

we proposed five key state parameters of FOCT

namely

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 photo detector. Analyzing the experimental results of these parameters

we quantitatively proposed the impact of the key state parameters on FOCT accuracy for the first time.Furthermore

we put forward the methods for monitoring and controlling each key state parameters respectively with experimental verification. The test results show that the ratio error and phase error of the FOCT product by state monitoring is lower than 0.1% and 3′

respectively

over a temperature range of-40 ℃

7

0 ℃. The results provide a technical guidance for the key parameter design and performance optimization of FOCT products

supplys basic model and data support for the inline monitoring and early warning to FOCT operation state

which will be helpful to improving the stability and reliability of FOCT products in long-term operation.