Fault analysis in transmission line

Fault analysis of transmission line includes fault detection and identification of the type of fault like LG fault, LLG fault etc., The time needed for fault analysis should be very less as it protects the power system equipment from the damage and enhances the power system stability. When the fault occurs in the transmission line we have to detect the fault and give a command to the circuit breaker to isolate line immediately. So, fast detection of the fault is necessary. After the occurrence of a fault, the direction of instantaneous power is changed and hence for detection of fault we use this scenario and measure the direction of instantaneous power at every instant of time. When the direction of instantaneous power is changed that means a fault has occurred.

            After detection of the fault, we will classify the fault. For that also we will use the direction of instantaneous power and we see that direction of the instantaneous power of which phase/phases is changed. According to this, we can classify the fault among 11 types of fault. To differentiate the fault between with ground or without ground, we use zero sequence current.

            Fault detection and classification is done as fast as possible but we can take some time to find the location of a fault. When a fault is permanent in nature at that time to clear the fault, we have to reach a location of a fault. At that time, we have to know accurate location of the fault to clear fault early otherwise it is difficult to restore the power within less time. To find fault location we use the samples of voltage and current at both ends of a transmission line and these samples are synchronized with time. The sampling frequency is 20 KHz so we get the samples of phase voltage and current at every 50 μsec.

            To implement fault detection scheme and fault location algorithm, a transmission line is modeled in PSCAD (Power System Computer Aided Design). The high sampling rate is not required for fault detection and classification but for fault location, the high sampling rate is required. Fault location algorithm is based on distributed parameter model so, for simulation of transmission line in PSCAD, choose frequency dependent phase model which is recommended in case of transient analysis.