G. Ramakrishna

Application of Equal Area Criterion Conditions in the Time Domain for Out-of-Step Protection

A new procedure for out-of-step protection by mapping the equal area criterion conditions to the time domain is proposed in this paper. The classification between stable and out-of-step swings is done using the accelerating and decelerating energies, which represents the area under the power-time curve. The proposed methodology is simple and overcomes some of the difficulties associated with the previous techniques. The proposed approach is based only on the local electrical quantities available at the relay location, and does not depend on the network configuration and parameters. The proposed algorithm has been tested on a single machine infinite bus and a three machine infinite bus system using software simulations. A digital prototype of the relay has also been implemented on the hardware and its performance has been assessed in a closed loop mode using a Real-Time Digital Simulator. The simulation results and the hardware testing results confirm the validity of the approach presented.

Enhancement of Power System Dynamics Using a Phase Imbalanced Series Compensation Scheme

The paper presents a new series capacitive compensation concept, which enhances power system dynamics. The idea behind the concept is a series capacitive compensation which provides balanced compensation at the power frequency while it results in phase imbalance at other frequency of oscillations. The compensation scheme is a combination of a single-phase thyristor controlled series capacitor (TCSC) and fixed series capacitors in series in one phase of the compensated transmission line and fixed capacitors on the other two phases.

Damping Inter-Area Oscillations Using Phase Imbalanced Series Compensation Schemes

The recently proposed phase imbalanced series capacitive compensation concept has been shown to be effective in enhancing power system dynamics as it has the potential of damping power swing as well as subsynchronous resonance oscillations. In this paper, a comparative effectiveness of two “hybrid” series capacitive compensation schemes in damping inter-area oscillations is evaluated. A hybrid scheme is a series capacitive compensation scheme, where two phases are compensated by fixed series capacitor (C) and the third phase is compensated by either a TCSC or SSSC in series with a fixed capacitor (Cc). The effectiveness of both schemes in damping inter-area oscillations for various network conditions, namely different system faults and tie-line power flows is evaluated using the EMTP-RV time simulation program.

An SSSC-Based Hybrid Series Compensation Scheme Capable of Damping Subsynchronous Resonance

The recently proposed phase-imbalanced series capacitive compensation concept has been shown to be effective in enhancing power system dynamics since it has the potential to damp power swings as well as subsynchronous resonance oscillations. In this paper, the series capacitive compensation concept is investigated for damping subsynchronous resonance oscillations using a static synchronous series compensator (SSSC)-based hybrid series-capacitive compensation scheme. In this scheme, the series capacitive compensation in one phase is created by using a single-phase SSSC in series with a fixed capacitor , and the other two phases are compensated by the fixed series capacitors (C). The validity and effectiveness of the proposed scheme are evaluated on the IEEE first and second benchmark models for computer simulation of subsynchronous resonance by means of time-domain simulation analysis using the Electromagnetic Transients Program-RV program.

An improved voltage phasor estimation technique to minimize the impact of CCVT transients in distance protection

This paper describes the impact of the transient response of coupling capacitor voltage transformers (CCVTs) on the performance of distance relays. Several factors that affect the frequency and time responses of CCVTs are considered. The effect of the transient response on phasor estimation is illustrated. A new least squares phasor estimation technique, which uses the knowledge of the frequency of the CCVT transients, is presented. A sample case, taken from a set of studies, is included to demonstrate the performance of the proposed approach

Damping subsynchronous resonance using a STATCOM operating in a phase imbalanced mode

This paper describes the potential usage of a STATCOM installed in the power system for damping torsional oscillations induced in turbine generators in series capacitive compensated transmission grids. This is achieved by operating the STATCOM in a phase imbalanced mode for a few seconds after a large system disturbance. The phase imbalanced operation reduces the energy exchange between the electrical and mechanical sides of the turbine generator and, therefore, damps the subsynchronous torsional oscillations resulting from series capacitive compensation. The validity and effectiveness of the proposed scheme is demonstrated using the IEEE first benchmark model for computer simulation of subsynchronous resonance by means of time domain simulation analysis using the EMTP-RV program.

Artificial neural network applications for power system protection

The most commonly used systems for protecting transmission and subtransmission lines belong to the family of distance relays. Over the past eighty years, successful designs based on electromechanical, solid-state and digital electronics technologies have been produced and marketed. These relays implement various characteristics, such as impedance, offset-impedance, admittance, reactance and blinders. The artificial neural network based designs of distance relays proposed so far work well for ideal fault conditions but are not able to maintain the integrity of the boundaries of the relay characteristics of generic designs. This paper reviews ANN models that have been proposed in the past for protecting components of power systems and presents a methodology that fully exploits the potential of ANNs in designing generic distance relays that retain the integrity of the boundaries of their characteristics

Impact of midpoint STATCOM on the coordination between generator distance phase backup protection and generator capability curves

In this paper, investigations are carried out to explore the impact of a midpoint STATCOM on the coordination between the generator distance phase backup protection (function 21) and the generator capability curve. The results of these investigations have shown that the midpoint STATCOM has an adverse effect on such coordination. Such an impact varies according to the fault type, the fault location and the generator loading. The dynamic simulations of a test benchmark have been conducted using the PSCAD/EMTDC software.

A special protection scheme for voltage stability prevention

Voltage instability is closely related to the maximum load-ability of a transmission network. The energy flows on the transmission system depend on the network topology, generation and loads, and on the availability of sources that can generate reactive power. One of the methods used for this purpose is the voltage instability predictor (VIP). This relay measures voltages at a substation bus and currents in the circuit connected to the bus. From these measurements, it estimates the Thevenins equivalent of the network feeding the substation and the impedance of the load being supplied from the substation. This paper describes an extension to the VIP technique in which measurements from adjoining system buses and anticipated change of load are taken into consideration as well

Impact of imbalanced phase operation of SSSC on damping subsynchronous resonance

The paper investigates the impact of using Static Synchronous Series Compensator (SSSC) in phase imbalanced operation modes on damping subsynchronous resonance in series capacitive compensated transmission grid. Phase imbalance has the potential of reducing the energy exchange between the electrical and mechanical sides of the turbine-generator and, therefore, damps subsynchronous oscillations. The validity and effectiveness of different proposed phase imbalanced modes have been demonstrated on the IEEE first benchmark model by means of time domain simulation analysis using the EMTP-RV program.