Gopal Gajjar

Development and application of vacuum circuit breaker model in electromagnetic transient simulation

Vacuum circuit breakers (VCB) have excellent interruption and dielectric recovery characteristics, and can interrupt the high frequency currents, which result from arc instability. The interruption of these high frequency currents leads to multiple reignitions when the breakers are opening and severe voltage escalations under certain network conditions. The main aim of the paper is to model the vacuum circuit breaker in PSCAD that replicates the original breaker characteristics. The model developed simulates the occurrence of these transients. The model incorporates the random nature of arcing time, current chopping, dielectric strength and the quenching capability of the breaker. The developed breaker model for 3-Phi VCB is implemented in a practical circuit employing switching off an arc furnace transformer and the results are presented

Power System Oscillation Modes Identifications: Guidelines for Applying TLS-ESPRIT Method

Abstract Fast measurements of power system quantities available through wide-area measurement systems enables direct observations for power system electromechanical oscillations. But the raw observations data need to be processed to obtain the quantitative measures required to make any inference regarding the power system state. A detailed discussion is presented for the theory behind the general problem of oscillatory mode indentification. This paper presents some results on oscillation mode identification applied to a wide-area frequency measurements system. Guidelines for selection of parametes for obtaining most reliable results from the applied method are provided. Finally, some results on real measurements are presented with our inference on them.

Implementation and applications of a Wide Area Frequency Measurement System synchronized using Network Time Protocol

A Wide Area Frequency Measurement System synchronized using Network Time Protocol (NTP) has been implemented at several locations in the Indian grid. Although the synchronization accuracy of a NTP-synchronized system cannot match that of a GPS system, it is adequate to accurately capture electro-mechanical transients like inter-area power swings. This system has been successfully used to monitor events occuring in the grid, including the loss-of-synchronism during the partial blackout of 30th July 2012 in India. It has also been possible to apply power swing damping estimation algortithms to the data. The results match well with those obtained from GPS synchonized PMU data. For these applications, the NTP based system is a viable, low-cost and easy-to-deploy alternative to a PMU system.

Auto detection of power system events using wide area frequency measurements

The wide area frequency measurement system has been installed at several locations in power system. There are plans to install phasor measurements units (PMU) at almost all high voltage substations. The volume of data obtained from such systems is very large. While most of the time the power system is in ambient condition, however there are always several events per day occurring in the system. This paper presents a method to automatically detect such events from wide area frequency measurement data. The PMUs measure bus voltage frequency communicate them to a central location in real time at rate of one sample per power system cycle. These measurements are be fed to the auto event detection algorithm. The method of detection of event occurrence identification, event classification and exact instance of event occurrence identification is presented. The issues encountered in implementing such scheme is discussed in the paper.

A proposal for distributed architecture for synchronized phasor measurement unit

This paper provides initial justification for adopting a distributed architecture for phasor measurement unit. The characteristics of synchronized phasor measurement is studied in detail. The benefits and short comings of phasor measurements are highlighted from the point of view of their different applications. The need for extension of phasor measurement unit functionality is brought out through analysis of the application and synchronized phasor measurement characteristic compatibility. The concept of phasor measurement unit is extended to a distributed system with several small functions working independently to provide a complete functionality of a phasor measurement unit. The proposed substation automation works on the framework of IEC 61850 process bus.

Circuit Breaker Transient Recovery Voltage in Presence of Source Side Shunt Capacitor Bank

Reactive power compensation through connection of shunt capacitor banks is a common practice in medium voltage systems. But the presence of capacitor bank leads to some interesting phenomena in switching transients. Clearing of a fault on line side of breaker in the presence of a source side capacitor bank is one such phenomenon. While clearing the fault if there is any re-ignition, presence of capacitor bank will develop high frequency discharge current that is superimposed on the power frequency fault current. Interruption of this high frequency current would cause considerable increase in the TRV magnitude. This paper describes the above phenomenon with PSCAD simulation results of a practical system. It also explains the effect of various parameters on the breaker TRV magnitude.

Application of actor-critic learning algorithm for optimal bidding problem of a Genco

The optimal bidding for Genco in deregulated power market is an involved task. The problem is formulated in the framework of Markov Decision Process (MDP) a discrete stochastic optimization method. When the time span considered is twenty four hours, the temporal difference method becomes attractive for application. The cumulative profit over the span is the objective function to be optimized. The temporal difference technique and actor-critic learning algorithm is employed. An optimal strategy is devised to maximize the profit. Market clearing system is included in the formulation. Simulation cases of three, seven, and ten participants are considered and the results obtained are discussed.

Detection and Correction of Systematic Errors in Instrument Transformers Along With Line Parameter Estimation Using PMU Data

We consider the following two estimation problems from synchrophasor measurements: first, estimation of positive sequence transmission line parameters and second, estimation of ratio correction factors for instrument transformers (ITs), also known as remote meter calibration (RMC). These two seemingly distinct problems are actually interrelated because incorrect parameters of any one set adversely affects the results of another. Hence, a simultaneous line parameter and RMC approach is proposed. Following extensions and adaptions viz., implicit RMC, explicit RMC, solving an individual line problem, and solving a network level problem are proposed. Open-circuit tests on transmission lines are proposed to improve accuracy in RMC. A decibel-scale-based statistical score is introduced for detection of ITs which require calibration. Extensive simulation results are presented to justify the claims.

Simulation of power systems for WAMS applications

Wide variety of power phenomena can be captured by monitoring power systems through WAMS. It is observed that the signals obtained by WAMS are most useful for longer term phenomena which affect large part of power systems. This paper addresses the problem of generating similar data through simulations. Problem of obtaining large amount of reliable simulation data for synchrophasor measurement is identified. A method to obtain long term system wide multiscenario synchrophasor data with reasonable accuracy through simulation is proposed. Such a data would be useful in developing advanced analytic around WAMS.

A combined model and measurement based scheme for assessment of poorly damped power swings

Despite the use of power swing damping controllers in FACTS, HVDC and generator excitation systems, poorly damped or undamped swings are occasionally seen in many power systems due to the inability of the controllers to cater to a large variety of operating conditions and swing modes. In such situations, the intervention of system operators is required to steer the system to a stable condition. Online eigen-analysis of the linearized system model may be used to suggest corrective actions, but the results need to be correlated with the actual observations, to correctly identify the critical modes and gain confidence in the proposed actions. Therefore, a combination of model based analysis and wide-area measurement based identification of critical swing modes is essential to provide decision support during actual operation. This paper proposes such a scheme and demonstrates it feasibility by presenting case studies on a realistic large power system.