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Distance relays are the workhorses of transmission-line protection systems. But those close to the electrical center will pickup even during transient instability. To identify them, we introduce a new coordinate system with normalized minimum magnitude of positive-sequence voltage on the line (\mathrmV{\mathrm{min}\mathrm{pu}}) as the y-coordinate and angular separation of positive-sequence voltage phasors at line terminals (\delta \text{SR}) as the x-coordinate. We show that in the \delta \text{SR}-{\mathrm{V}}{\mathrm{min}\mathrm{pu}} plane, the electrical center has a strong separation from a three-phase fault and stable disturbances. Subsequently, we propose a combined out-of-step prediction and relay blocking scheme. It uses line-end phasor measurement unit inputs for detecting vulnerable relays and blocking their zone 1 trip for a limited time interval before ingression into zone 1. We also show that it is possible to detect a line fault during the block state and consequently rescind the block decision. Extension of the proposed scheme to zone 2 and zone 3 is also described. Simulations considering noisy data and round robin delays demonstrate efficacy of the proposal. [ABSTRACT FROM PUBLISHER]

We propose a new approach to current differential protection of transmission lines. In this approach, we transform the instantaneous line current(s) by using a moving window averaging technique. If the time span of moving window is equal to one-cycle time, then the steady-state value of the transformed current is zero for a periodic signal which is composed of fundamental and harmonic frequencies. Signal distortions (e.g., a fault) cause the transformed currents to deviate from the nominal zero value. This permits the development of a sensitive, secure, fast, and yet simple current differential protection scheme. The scheme can be applied in toto to series-compensated transmission lines. Results on a four-machine ten-bus system and comparative evaluation with state-of-the-art methods brings out promise of the proposed method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Megawatt (MW) power flow tracing can assess the extent of network usage by the participants that can be effectively used for multiple objectives like transmission pricing, loss allocation, etc. MW power tracing, a post-facto analysis of power flow solution, is amenable to multiple solutions. This implies multiplicity of solution space of transmission cost and loss allocation problems. The conventional tracing methods enforce a ‘proportionate sharing rule’ to calculate the shares. These shares are sensitive to quantity and distance as against the postage stamp method, which is immune to distance. Any of these methods will result in penalizing a set of constituents, which raises a fairness issue. This is evident from the experiences of developing countries like India. In this paper, a new paradigm is suggested that attempts to capture the best of the two methodologies by exploring multiplicity of the solution space of the tracing problem, within the given constraints. We show that the tracing problem can be formulated as a linear constrained optimization problem. We propose a tracing compliant modified postage stamp allocation method that computes a traceable solution that minimizes overall deviation from the postage stamp allocation. Results on actual data of central transmission utility of Western Regional Grid of India demonstrate the claims. [ABSTRACT FROM AUTHOR]

Postfault rotor angle oscillations lead to power swings. Both unstable and stable swings can induce distance relay tripping. For unstable swings, a new computational procedure to locate all of the electrical centers is developed. It simplifies the work associated with visual screening of all the R-X plots. For stable swings, a generic three-tier hierarchy of stability-related norms defined by branch norm, fault norm, and system norm is proposed. Ranking by branch norm leads to ranking of power swings. Ranking by fault norm leads to ranking of faults or contingencies. Magnitude and rate of change of system norm can be used to detect an out-of-step condition. Results on a ten-machine system and a utility system with detailed models are also presented. [ABSTRACT FROM AUTHOR]

Instrument transformers (ITs) once installed in the field are seldom calibrated. We propose two tests to detect systematic errors in capacitive voltage transformers (CVTs) and current transformers (CTs). The first test, a direct test, compares the mid-point voltage estimated from both ends of a transmission line using PMU data. The second test, an indirect test, analyzes the deviation of the estimated positive sequence line parameter values from the design values. Subsequently, we propose a robust method to simultaneously determine the positive sequence line parameters and IT calibration factors. Special care is given to numerical sensitivity of the method to the noise in the data and we show by Monte Carlo simulations that the proposed approach is accurate and robust. A noteworthy feature of this paper are the case studies based on field PMU data for short, medium, and long length lines of 400 kV and 765 kV. It clearly demonstrates the stability of both line parameters and IT calibration factors and hence justifies the claims. [ABSTRACT FROM AUTHOR]

This paper addresses various aspects of optimal phasor measurement unit (PMU) placement problem. We propose a procedure for multistaging of PMU placement in a given time horizon using an integer linear programming (ILP) framework. Hitherto, modeling of zero injection constraints had been a challenge due to the intrinsic nonlinearity associated with it. We show that zero injection constraints can also be modeled as linear constraints in an ILP framework. Minimum PMU placement problem has multiple solutions. We propose two indices, viz, BOI and SORI, to further rank these multiple solutions, where BOI is Bus Observability Index giving a measure of number of PMUs observing a given bus and SORI is System Observability Redundancy Index giving sum of all BOI for a system. Results on IEEE 118 bus system have been presented. Results indicate that: 1) optimal phasing of PMUs can be computed efficiently; 2) proposed method of modeling zero injection constraints improve computational performance; and 3) BOI and SORI help in improving the quality of PMU placement. [ABSTRACT FROM AUTHOR]

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) unsymmetrical 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. [ABSTRACT FROM AUTHOR]