Throughout the history of power system protection, researchers have strived to increase sensitivity and speed of apparatus protection systems without compromising security. With the significant technological advances in wide-area measurement systems, for transmission system protection, current differential protection scheme outscores alternatives like overcurrent and distance protection schemes. Therefore, in this paper, we address this challenge by proposing a methodology for adaptive control of the restraining region in a current differential plane. First an error analysis of conventional phasor approach for current differential protection is provided using the concept of dynamic phasor. Subsequently, we extend the methodology for protection of series compensated transmission lines. Finally, we also evaluate the speed versus accuracy conflict using phasorlets. Electromagnetic Transient Program simulations are used to substantiate the claims. The results demonstrate the utility of the proposed approach.

Adaptive Current Differential Protection Schemes for Transmission-Line Protection

The paper presents a new approach for performing the fault analysis of multiphase distribution networks based on the symmetrical components. The multiphase distribution system is represented by an equivalent three-phase system; hence, the single-phase and two-phase line segments are represented in terms of their sequence values. The proposed technique allows the state of the art short-circuit analysis solvers to analyze unbalanced distribution networks. The fault currents calculated using the proposed technique is compared with the phase components short-circuit analysis solver. The obtained results for the IEEE radial test feeders show that the proposed technique is accurate. Based on the proposed method, the existing commercial grade short-circuit analysis solvers based on sequence networks can be utilized for performing unbalanced distribution systems.

Fault Analysis of Multiphase Distribution Systems Using Symmetrical Components

Series capacitor imposes problems to line protection and other online decisions. The directional relaying issues during voltage and current inversions in a series-compensated line are addressed in this paper. A conventional directional relaying algorithm uses fault voltage and current phasors to derive the decisions and, thus, finds its limitation at voltage or current inversion. This paper proposes a fault direction estimation technique for a series-compensated line using phase change in positive-sequence current and magnitude change in the positive-sequence voltage at fault. The technique is evaluated by using data simulated with EMTDC/PSCAD for a series-compensated line, and the dynamic performance of the algorithm is also studied.

A Positive-Sequence Directional Relaying Algorithm for Series-Compensated Line

This paper presents a new method for online determination of the Thevenin equivalent parameters of a power system at a given node using the local PMU measurements at that node. The method takes into account the measurement errors and the changes in the system side. An analysis of the effects of changes in system side is carried out on a simple two-bus system to gain an insight of the effect of system side changes on the estimated Thevenin equivalent parameters. The proposed method uses voltage and current magnitudes as well as active and reactive powers; thus avoiding the effect of phase angle drift of the PMU and the need to synchronize measurements at different instances to the same reference. Applying the method to the IEEE 30-bus test system has shown its ability to correctly determine the Thevenin equivalent even in the presence of measurement errors and/or system side changes.

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Online Thévenin Equivalent Determination Considering System Side Changes and Measurement Errors

Protection of series compensated transmission line: Issues and state of art

A capacitor in series with a transmission line is protected from overvoltage due to a large fault current by a nonlinear metal-oxide varistor (MOV) connected in parallel. Fault analysis, as well as the evaluation of performance of the transmission protection system, in the presence of MOV action becomes complex because (1) v-i characteristics of the MOV are nonlinear; (2) un- symmetrical MOV action for unsymmetrical faults will introduce coupling in sequence networks; and (3) MOV action will influence voltage or current inversion phenomenon. This paper presents a computationally efficient and simple methodology for fault analysis wherein the linear part of the network is modeled by an equivalent multiport Thevenin network. The proposed approach handles nonlinearity in fault analysis efficiently. It also provides an elegant approach to model unbalance in a network due to MOV action. The proposed approach can be used to determine relays prone to voltage or current inversion. Results on a real-life 716-bus Indian system illustrate the efficiency of the proposed approach.

P. Kulkarni

Papers

Computationally Efficient Methodology for Analysis of Faulted Power Systems With Series-Compensated Transmission Lines: A Phase Coordinate Approach