Om Hari Gupta

An Innovative Pilot Relaying Scheme for Shunt-Compensated Line

This paper presents a fault detection and classification scheme for a shunt [static var compensator (SVC)] compensated line. The proposed relaying scheme is based on the concept of superimposed sequence components-based integrated impedance (SSCII). For an internal fault, the magnitude of SSCII is small and for an external fault, it is very large. In the SVC compensated line, a fault forces SVC to vary its impedance. Superimposed components are injected due to this impedance variation, along with the fault components. These SVC-injected components are treated as fault-injected components and, therefore, even the sound phases are detected as faulty phases. To avoid such failure, fault-injected superimposed components have been extracted by using the modified prefault data, which is estimated according to SVC impedance variations. The superimposed components measured using the modified prefault data consist of fault-injected superimposed components only. The proposed scheme has been tested for all types of faults, different values of fault resistances, and several fault locations and SVC locations. The results demonstrate that the proposed scheme successfully detects and classifies the faults. Also, the proposed scheme is robust against variations in fault resistance, source impedance, and SVC location.

An integrated impedance based pilot protection scheme for SVC compensated transmission line

This paper presents a fault detection and classification scheme, based on integrated impedance, for SVC compensated transmission line. For internal faults, integrated impedance of faulty phase is low and for healthy phase, it is high. For all external faults, integrated impedances of all phases are high. The protection scheme based on this concept is used for variable impedance shunt compensation (i.e. Static Var Compensator, SVC). Proposed scheme has been analyzed for each phase with different fault resistances, fault types and fault locations. The results demonstrate the effectiveness of the proposed scheme.

Superimposed Energy-based Fault Detection and Classification Scheme for Series-compensated Line

Abstract This article presents a fault detection and classification scheme for a series-compensated transmission line that is based on post-fault superimposed energy. The derivations of the scheme presented in this article are obtained with consideration of both the real and reactive components of the power system. However, the criterion depends only on the real components of the power system. For a forward fault, superimposed energy is negative, whereas it is positive for a reverse fault. If the relays of both ends detect forward fault, it is an internal fault; else, it is an external fault. The magnitude of superimposed energy depends on the fault type, location, and resistance, which makes it difficult to classify the type of fault as a fixed threshold cannot be set. Therefore, to classify the type of fault, energy coefficients have been introduced that depend on the superimposed energy measured at the relay. To test the capability of the superimposed energy based scheme, the test system has been simulated in PSCAD/EMTDC (Manitoba HVDC Research Centre) and an algorithm has been implemented in MATLAB (The MathWorks, Natick, Massachusetts, USA). Results proved that the scheme is accurate and robust against different system conditions and uncertainties.

Directional relaying scheme for TCSC compensated line

This paper presents an improved directional relaying scheme for thyristor-controlled series capacitor (TCSC) compensated transmission line, which is based on the initial slope of the Fault Component Energy (FCE). The initial change in FCE is negative for forward faults and it is positive for reverse faults. The performance of the scheme is tested using PSCAD/EMTDC simulations and algorithm implemented in MATLAB. It is found that proposed scheme is unaffected by voltage and current inversion phenomena, which may occur in the presence of TCSC. Further, the proposed scheme is found accurate for high resistance faults.

Relaying scheme for STATCOM compensated transmission line

Static Synchronous Compensator (STATCOM) is a high speed controllable reactive power compensator used to improve the voltage profile. STATCOM can inject/draw the reactive power by shifting the phase of its voltage relative to the bus voltage. The challenges in the presence of STATCOM have been reported in the existing literatures such as under/over-reaching of distance relays etc. In this study, a directional based internal fault detection scheme (based on superimposed energy) is presented. Along with fault injected superimposed components, there are STATCOM injected superimposed components also. However, it is found that STATCOM injected superimposed components are smaller than that of fault injected components. A relay detects forward fault if superimposed energy is negative and it detects reverse fault if superimposed energy is positive. For internal fault, both the relays detect forward fault whereas for external fault, one of the relays detects reverse fault. The developed criterion is independent of the dynamics and degree of compensation, and is adaptive to the system changes. The criterion works accurately for different types of fault and different locations of the STATCOM. Further, the scheme is fast enough to detect the fault within one cycle.

Energy based relaying scheme for series compensated line

This paper presents a directional relaying scheme for series compensated transmission line, which is based on initial change in the Fault Component Energy (FCE). During pre-fault condition, FCE is zero and after the inception of forward fault, FCE is negative and for reverse faults, it is positive. If FCE remains negative or positive for consecutive 15 samples, the direction of the fault is detected. The performance of the relaying scheme has been investigated using PSCAD/EMTDC simulations. It is found that scheme presented in this paper is robust against voltage and current inversion phenomena, TCSC impedance variation, MOV conduction, fault location variation, high resistance faults etc.

EC-based relaying scheme for the protection of shunt-compensated transmission line

Static Var Compensator (SVC) is used to enhance the power flow in the transmission line by improving the voltage profile. SVC injects/draws the reactive power by varying its susceptance. This variation in susceptance offers new challenges to the ordinary protection techniques. The direction of superimposed energy (SE) can be used to discriminate between forward and reverse faults. However, SE depends on various parameters such as the fault location, fault type, and fault resistance. This dependency makes it difficult to select proper threshold value to identify the faulty phase. Therefore, energy coefficients (ECs) are proposed and are utilized to identify the fault direction and to further classify the type of fault. If both the relays sense the forward fault, it is identified as a fault in the protected line else it is a fault outside protected zone. As the energy is dependent on the real line parameters only, this EC-based scheme is reliable for variable shunt reactive compensation. The EC-based algorithm magnificently senses the faults in the protected zone and identifies the fault type under varying system conditions i.e. different fault locations, types, and resistances. The proposed scheme is unaffected by the SVC dynamics, modes and changes in system configuration.

Positive sequence phasor estimation-based pilot relaying scheme for shunt-compensated line

Although the shunt Flexible AC Transmission System (FACTS) devices improve voltage profile, Shunt FACTS Devices (SFDs) may mal-operate the protection schemes due to reactive power injection. This study presents a phasor estimation-based pilot relaying for the SFD-compensated line. For a loaded line, the phase difference between the shunt FACTS device voltage and current is close to −90° as it injects the reactive power. However, it also draws small active power to meet the losses which deviates the working angle of SFD towards positive direction by some angle. Hence, the working angle of SFD depends on active and reactive power. During normal operation, this working angle can be estimated at both the relay locations. However, it is not possible to estimate exact working angle of shunt FACTS device at both the relay locations during an internal fault. The analysis reveals that estimated phase angle will largely tend towards positive direction during an internal fault. This criterion has been used to distinguish internal and external faults. The proposed relaying is robust against all real conditions and fast enough to detect a fault within desired time limits. Furthermore, the scheme is unaffected by the dynamics of SFD.