Detection of Phase and Neutral Fault Currents by Using Noninvasive Sensing and Electromagnetic Field Modelling

Detection of fault and span is very critical from reliability and outage time reduction point of view. The power delivery to widespread geographical areas and growing cities is mostly happening through the overhead transmission and distribution lines. In a multi-grounded distribution system with a large variation of soil type there is a high probability of undetected high-impedance faults resulting in difficulty in detection of fault location. Different geographic conditions and weather conditions add up to difficulty in sensing high-impedance ground faults. These undetected faults can reoccur and can cause damage to the power system equipment as well as pose hazards to human safety. Installation of the protection relays at the substations may not always prove successful in detecting the exact location of incipient faults caused due to neutral unbalance or ground faults. Installation of current sensing instrument transformers is not a practical and economical solution for transmission and generation utilities. Moreover, the conventional core wound current transformers exhibit saturation under symmetrical and asymmetrical fault condition and thus limiting the detection capability for fault sensing. In this paper a novel approach of non-invasive sensing of the magnetic field generated by transmission or distribution overhead lines is proposed. The magnetic field is measured with the help of an array of low cost, broad frequency range Tunneling Magnetoresistive (TMR) sensors. Based on the measured magnetic field, an algorithm is developed that can estimate the fault current and the type of fault with the location span in a three-phase overhead power system. A detailed calibration process for each sensor in the sensor array is performed using the measurements from experiments to verify the modelling results and the accuracy of fault current detection.