Fault Location For Two- and Three-Ended and Mixed Lines Using Synchronized Measurements

Transmission lines are exposed to faults due to bad weather (hurricanes, lightning), insulation breakdown, short circuits by birds, and contact by tree branches and other objects. Temporary faults are cleared by tripping then autoreclosing. For permanent faults, the power supply is restored only after the maintenance crew finds and replaces the failed component. For this purpose, precise fault location should be known, else the fault location identification job turns out to be tedious and time consuming for long transmission lines spread across rugged terrains such as hilly areas, mountains, and deserts, etc. Locating faults precisely on transmission lines is therefore highly beneficial to utilities and accurate fault location can expedite the repair of the faulted components, speed-up restoration, and reduce outage time.

In this paper the adopted method for fault location calculation is presented for the following: - two-ended transmission line - three-ended transmission line - two-ended mixed transmission line, i.e. comprising overhead line section plus underground cable section - three-ended mixed transmission line, e.g. End A to End B overhead line, with underground cable in-line T-off to End C.

Present communication technology allows for the use of data from all ends of the line to calculate the location of the fault. For the fault location methods indicated above, one IED is required at each end of the line, and each IED must be connected to each other IED via a 2Mbps communication link. Each IED therefore will have available to it time aligned sampled values of the local and all remote currents and voltages. It’s from these sampled values that the during-fault positive-sequence phasors are calculated that are then used in the fault location calculations. As each IED has available to it the values of current and voltage from all ends, each IED performs the fault location calculation (from the perspective of its own line end).

For this paper, verification of the method for a two-ended transmission line is presented - verification of the method using EMTDC simulations for lines connected with conventional and inverter-based resources (renewables) - the accuracy of the calculated fault location is not affected by renewable integration- - implemented in an IED using 1kHz sampling rate (IED for 50Hz application) and then installed on two pilot installations (400kV, 233km line in India and 220kV 256.6km line in Sweden) – both lines have had faults and the IED presented fault location is compared with the actual fault location found by patrolling crews

Line parameters are entered as settings; source impedance values are not required. However, the line parameters can be estimated from the pre-fault positive-sequence phasors (i.e. no line parameter settings are then required other than line length) – the estimated parameters can then be used in the fault location calculation rather than set values which may not be known with high accuracy, and which may vary with conditions such as weather, age of the conductor, etc. The presented results for the EMTDC simulations and calculated pilot fault locations are based on the estimated parameter calculation.

The method gives average fault location error of ~ 0.1%. The method can locate the fault within two-tower span distance (~300m) which is comparable with traveling wave-based method that requires 1000 times higher sampling rate, high-cost hardware, and more complex commissioning and settings.