Work on Synchronized Data

Abstract:

This paper presents a fault location method for multi-circuit series compensated line using phasor data from intelligent electronic devices available at both ends. In case of unavailability of synchronized data, analytical synchronization is obtained using an operator. In the formulation, the method considers untransposed line sections resulting on two sides of the fault and the distributed nature of line. For a healthy phase, currents on two sides at the fault point are equal unlike different currents on two sides in a faulted phase. This is checked over the line length and the fault location is pinpointed. The method does not require the model of the series compensation placed at any location on the line and can be used for both inter- and intra-circuit faults. It also considers reactive component of the fault impedance for accurate fault location. The method is tested using PSCAD/EMTDC simulations for a multi-circuit series-compensated line in Indian power grid. Evaluation study confirms the validity of the method for various faults.

SECTION I.Introduction

Line tripping for a fault may cause power interruption to loads. Accurate location of fault expedites repair and enables faster power restoration [1]. Therefore, fault location has been of interest to power system engineers. Solutions to fault location problem considering various line configurations and fault types are available in [2]. Depending on availability of data, fault location methods are classified into two; using measurements from one end [3]–[7] or both ends [8]–[12] of the faulted line. Fault estimation using both end data has advantage of eliminating the influence of fault resistance thereby accuracy is enhanced. In [13], a method for location of an inter-circuit fault on a double-circuit line without any series device is developed which uses one terminal data to determine the voltage at different points in the line and uses phase mutation point to determine the exact fault location. Method in [14] uses voltage phasor measurements of one or more buses in the system which may not be of the faulted line to determine the exact fault location of double-circuit line. Synchronized sampled data based methods which use modal analysis for location of fault on a line without any series device are available in [15]– [18]. Traveling waves [19] are used to determine location of fault [20]– [23]. Detection of traveling waves requires data sampled at high frequency and thus the intelligent electronic devices involved are costly.

Series capacitors are used in transmission lines to increase power transfer capability which happens to be an economically viable solution over adding another line in parallel [24]. The capacitors can improve the transient stability of a system and damp the oscillations out if designed with care [25]. To meet the growing power demand, utilities have installed series compensation on multi-circuit transmission lines as well [26], [27]. Fault location methods for series compensated lines considering single end measurements are available in [28]– [32] which require equivalent model of the series compensation. Any inaccuracies in the model would cause significant error in fault location [33] . A method employing two end measurements uses series compensation model and suffers similar challenge [34]. To avoid non-linearities caused by metal-oxide varistor (MOV), a fault location method is proposed using data following the operation of bypass switch of the capacitor bank [33]. To overcome the issue of model errors, methods in [35]–[39] use the principle that the currents at two terminals of the series compensation device are equal. Method proposed in [35] is for single-circuit series compensated line and uses synchronized measurements from both ends of the line. A series compensation model independent method using limited synchronized measurements from both ends of the line is proposed in [36]. Two terminal fault location method is proposed using analytical synchronization of the measurements from both ends of the faulted line [12]. The methods in [37] –[39] also use such synchronization approach for fault location of double circuit series compensated lines. Existing series compensation model independent methods for fault location consider intra-circuit faults only and cannot be used for inter-circuit faults. These methods also consider each faulted section to be transposed which is not true and ignore the imaginary component of the fault impedance during calculations which result in inaccuracy.

In transmission lines, transposition is carried out to balance system impedance and admittance matrices and thus enable symmetrical component analysis. The assumption of complete transposition is not true during fault [40], [41]. Each section formed (on two sides of the fault) becomes untransposed, whereas all the available methods assume it to be transposed. This simplified assumption of transposed sections during fault is done to apply symmetrical components conveniently which compromises accuracy in locating faults. Thus there is a scope to develop a fault location method for multi-circuit series compensated line without assuming complete transposition of each fault section (when symmetrical components cannot be applied) and which addresses inter-circuit faults.

Fault in a transmission line is associated with arc and are modeled with a resistive and an inductive component. Fault impedance as such is an unpredictable quantity [42] and has an inductive component in some cases [43]. For such situation, neglecting imaginary component of fault impedance would cause error in fault location estimation. This is also considered in the proposed work.

This paper presents a method for location of both inter- and intra-circuit faults on multi-circuit series compensated transmission lines which considers each fault section as untransposed and the arc is modeled with both resistance and inductance. The location of the compensation can be at one end or any other location. The method uses synchronized measurements from both ends of the line and in case data recorded are unsynchronized, a synchronization operator is calculated using both end data to establish a common time reference for the two ends. The equality constraint of the healthy phase currents in a faulted line, at the fault point, is exploited to develop a fault location index (which is zero at the correct fault location). Possible solution for fault location is determined by calculating this index over the line length. The calculated fault location index considers mutual impedance between each pair of conductors (including inter-circuit conductors) in the line and thus can detect inter-circuit faults as well.

The proposed method is tested for various faults on a multi-circuit series