Prabodh Bajpai

A Fault Detection Technique for the Series-Compensated Line During Power Swing

A distance relaying scheme is susceptible to power swing. To avoid unintended trip operation during such conditions, a power swing blocking function is utilized in distance relays. However, if a fault occurs during power swing, the relay should detect the fault and trip as soon as possible. The detection of fault in a series-compensated line during the power swing is further complicated due to complex transients produced by series capacitor and the metal-oxide varistor (MOV) protecting it. This paper proposes a negative-sequence current-based technique for detecting all types of faults during the power swing in a series-compensated line. The technique is tested for different series-compensated systems including a 9-bus 3-machine power system. Different types of faults: symmetrical, asymmetrical, and high resistance occurring during the power swing are simulated through EMTDC/PSCAD to test the algorithm. The method is compared with available techniques and found to be accurate and fast.

Wide-Area Measurement-Based Backup Protection for Power Network With Series Compensation

This paper presents a synchronized phasor measurement-based wide-area backup protection scheme which compares the magnitude of sequence voltages of buses at a system protection center to identify the bus closest to the fault. Then, the sign of cosine of the angle between voltage and current at both ends of all lines connected to this bus are compared to identify the faulted branch. The technique is tested for various faults resulting in voltage/current inversion in a series-compensated line and during load encroachment and power swing conditions using data simulated through EMTDC/PSCAD for a nine-bus, three-machine power system. The scheme is found to be accurate and fast. With todays synchronized phasor measurement technology and communication system, the proposed scheme can overcome the limitations of the conventional backup protection scheme.

Secured Zone 3 Protection During Stressed Condition

Maloperation of the zone 3 element of distance relays during stressed system conditions, such as power swing, load encroachment, or voltage stressed condition is one of the main reasons for large disturbances in power systems. The improved protection technique for zone 3 can help to prevent such maloperation and, thus, more reliable power systems can be envisaged. This paper proposes an algorithm that utilizes two new criteria: (1) the maximum value of the transient monitoring function obtained from three-phase currents and (2) the phase angle of the positive-sequence impedance to support zone 3 of the distance relay. The technique is tested for various power system events, such as the three-phase fault during the power swing, load encroachment, voltage stressed conditions, and current-transformer saturation during the three-phase fault using data simulated through EMTDC/PSCAD in the IEEE 39-bus New England system. The simulation results show that the zone 3 protection scheme using the proposed technique can correctly discriminate the three-phase fault from stressed system conditions.

Sizing optimization and analysis of a stand-alone WTG system using hybrid energy storage technologies

Decentralized distributed generation technologies based on renewable energy recourses such as Solar PhotoVoltaic (SPV)/ Wind Turbine Generators (WTG) address the major issues concerned with conventional diesel generators to a large extent and are therefore considered as emerging alternate power solutions to stand alone applications. Three stand alone WTG power systems using different energy storage technologies, i.e. WTG-Battery system, WTG-Fuel Cell (FC) system and WTG-FC-Battery system are optimized and compared in this paper. The analysis of such hybrid systems feeding a standalone load of 45.6 kWh/day energy consumption with a 2.3 kW peak power demand is carried out using Hybrid Optimization Model for Electrical Renewable (HOMER) software. Based on simulation results, it was found that WTG-FC-Battery hybrid system is most economic solution compare to either single storage system. Cost sensitivity analysis with wind speed is also performed in this paper.

Sizing optimization of PV-FC-Battery system with hybrid PSO-EO algorithm

One of the most important issue in designing of renewable hybrid energy systems is to size the system components optimally to meet load requirement with minimum annualized cost of system and maximum reliability of power supply. This paper presents comparison of two approaches for calculating optimal size of hybrid energy system components with minimum annualized cost considering reliability constraint. In this paper an extremal optimization based particle swarm optimization algorithm has been proposed to determine optimal size of system components. To demonstrate the validity of proposed approach and to evaluate relative merit of this approach, a comparative study has been done with simple particle swarm optimization algorithm considering identical system configuration. The simulation results show that the optimal system components can deliver energy in a stand -alone installation with minimum system cost and maximum reliability.

Control of PV-FC-Battery-SC hybrid system for standalone DC load

This paper presents a hybrid system comprise of Photovoltaic (PV), Battery, Supercapacitor (SC), Fuel Cell (FC) to meet isolated DC load demand. The PV is the primary energy source, whereas battery and SC both are considered for their different power density to supply transient and steady load respectively. To increase the reliability of the system the fourth source FC has been chosen to keep the battery fully charged. All sources are connected to DC bus by different DC-DC converters. A power flow control strategy adapts their variable DC voltage to Bus voltage by means of these converters. In this work, FC is chosen to work for a limited period. This will avoid the over sizing of the FC and limit the operational cost of the system. The whole energy management principle has been validated in MATLAB/SIMUINK with variable load demand and solar radiation profile.

A Three-Terminal Line Protection Scheme Immune to Power Swing

Communication-assisted distance protection schemes are widely used for three-terminal line protection and are susceptible to power swings. The available differential protection scheme is also considered to be suited to protect three-terminal lines and is free from problems associated with the power swing. However, the performance of the current differential protection scheme may be affected if an outfeed condition occurs during an internal fault. This paper presents a new technique for protecting three-terminal transmission lines immune to power swing. The technique uses synchronized voltage and current measurements from three terminals for calculating voltage at the tee-point. The maximum magnitude of the superimposed component of positive-sequence voltage estimated at the tee-point is compared with the maximum magnitude of superimposed components of the positive-sequence voltage measured at three terminals of the line to discriminate a fault from power swing. The method is accurate even for an outfeed condition during the internal fault, current-transformer saturation during severe internal or external faults, large load rejection, and different prefault loading conditions occur during the power swing. The proposed algorithm is verified using data simulated through EMTDC/PSCAD for a 400-kV double-circuit three-terminal system.

Hybrid modulation technique for binary asymmetrical cascaded multilevel inverter for PV application

Performance of a binary asymmetrical cascaded H-bridge (CHB) inverter using two H-bridges is investigated in this paper. A modified hybrid modulation technique is implemented where one bridge operates at fundamental switching frequency and handles most of the power. The 2nd bridge operates at a higher switching frequency to generate a desired sinusoidal waveform at the output. Thus, the H-bridges of CHB inverter operate at different voltage levels and at different frequencies. This allows the performance to be optimized. Simulation and experimental results are produced to prove the usefulness of the proposed system configuration. A possible application in solar PV system is reported.

Effective market monitoring for surveillance of the Indian electricity market

Purpose – The purpose of this paper is to introduce a prospective market monitoring system (MMS) for surveillance of Indian power market using a set of new market monitoring indices.Design/methodology/approach – It is necessary for the system regulators and policy makers to identify the potential market power and find ways to mitigate them to improve the market efficiency. The simple way to curb market power is the capping of bidding price to several times the average price of electricity. However, this approach is not ideal as it could mask the real market trading situation. The best way for the regulator is to identify which particular generators are exercising market power and deal with them individually.Findings – Identification of major activities under MMS and effectiveness of new market indices have been established through quantitative analysis.Practical implications – The MMS will provide in‐time warning signals and identify the suppliers taking maximum unfair advantage which needs intense scruti...

New Voltage Control Strategies for VSC-Based DG Units in an Unbalanced Microgrid

This paper presents the positive-sequence, negative-sequence, and zero-sequence voltage and current control schemes in the dq frame for the voltage-source converter (VSC)-based distributed generation (DG) units in order to compensate for voltage unbalance in a microgrid. The objective of these schemes is to control the positive-, negative-, and zero-sequence components (separately and independently) of the voltage at the point of common coupling and the VSC currents to their respective reference commands. Dynamically varying limits have been proposed for the positive- and negative-sequence references for the current control schemes in order to protect the VSC from overloading (under unbalanced conditions) and unsymmetrical faults. The active power control, frequency control, and the reactive power–voltage droop control schemes decide the references of the positive-sequence voltage control scheme in order to fulfill the objective of using the same control schemes for the grid-connected and the islanded modes of operation of the microgrid, thereby eliminating the need for islanding detection. The performance of the various control schemes employed for controlling the VSC-based DG unit has been tested on two identical VSC-based DG units feeding power to the IEEE 34 node distribution network implemented in PSCAD/EMTDC.