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Fault Calculations and Power System Protection
Published in Syed A. Nasar, F.C. Trutt, Electric Power Systems, 2018
Unsymmetrical faults such as line-to-line and line-to-ground faults (which occur more frequently than three-phase short circuits) cannot be analyzed on a per-phase basis, as we were able to do for symmetrical faults. For unsymmetrical faults, the method of symmetrical components is used. This method is based on the fact that a set of three-phase unbalanced phasors can be resolved into three sets of symmetrical components, which are termed the positive-sequence, negative-sequence, and zero-sequence components. The phasors of the set of positive-sequence components have equal magnitude and a counterclockwise rotation (or phase sequence abc); the negative-sequence components have equal magnitudes and counterclockwise rotation but have the reverse phase sequence acb; and the equal magnitude zero-sequence components are all in phase with each other. These sequence components are represented geometrically in Figure 5.12. The positive-sequence components are designated with the subscript 1, and the subscripts 2 and 0 are used for negative- and zero-sequence components, respectively.
Impedance Characteristics
Published in S.V. Kulkarni, S.A. Khaparde, Transformer Engineering, 2017
The theory of symmetrical components is commonly used in power system analyses. Unlike in rotating machines, the positive-sequence and negative-sequence reactances are equal in static devices such as transformers. Under symmetrical loading conditions, only positive-sequence reactances need to be considered. During asymmetrical loadings/disturbances or single-phase faults, the response of the system is mainly decided by zero-sequence reactances in the resultant network. It is relatively easy to understand and calculate positive-sequence reactances as compared to zero-sequence reactances in transformers. The zero-sequence reactance of a transformer may differ considerably from its positive-sequence reactance depending upon the type of its magnetic circuit and winding connections.
Power System Fault Analysis
Published in A. P. Sakis Meliopoulos, Power System Grounding and Transients, 2017
In this chapter we discuss the problem of power system fault analysis. Two distinct approaches will be presented. First, fault analysis of three-phase systems is approached in the conventional way through the use of symmetrical components. The basic assumptions and limitations of the method of symmetrical components are explicitly stated. The method of symmetrical components is extended to analyze current distribution among sky wires, neutrals, and earth. This extension of the method provides the basis for the computation of ground potential rise. Second, a general approach to the problem of fault analysis is presented. This method is applicable to symmetrical three-phase systems as well as asymmetrical three-phase systems and non-three-phase systems. The method provides the current distribution among overhead circuits and earth as well as the ground potential rise of the system neutrals.
High Impedance Fault Detection Using Multi-Domain Feature with Artificial Neural Network
Published in Electric Power Components and Systems, 2023
Suppose a single line to ground fault is occur at phase A of the feeder with no load. Due to fault, the phase A voltage will fall to near zero and the magnitude of the phase current will shoot up. Also, the fault current can be expressed as combination of symmetrical components. The negative sequence current and zero sequence current in the unbalanced system should aid the positive sequence current and also aligned in the same phase as that of Therefore considerable change is happened in the negative and positive current phasor after the fault. Moreover the positive sequence current phasor after the fault is not deviated much. Therefore, the angle difference between negative and zero sequence current is selected as a prominent feature to identify the ground faults. The magnitude and phase of the positive component negative component and zero component currents are found by using 2.
Angular symmetrical components-based anti-islanding method for solar photovoltaic-integrated microgrid
Published in Automatika, 2023
V. Arivumani, Sujatha Balaraman
Symmetrical components are mainly used for unbalanced fault analysis. So the proposed method is tested to various unsymmetrical faults. Single line to ground fault is initiated in phase “A” at 0.5 s. Phase “A” Voltage will be reduced nearly to zero for a single line to ground fault. Line voltage between B and C is not affected and the rms value is measured as 400.5 V. Line Voltage between phases “A” and “B” is reduced to 187.2 V (rms). LARMS Voltage and PSI are decreased to 285 V and 20.34%. Phase angle is increase to 169°. The tangent angle of unbalance is increased to 39.13°. All signals with respect to a single line to ground fault are displayed in Figure 14. All relays respond to this fault and generate the trip signals which are displayed in Figure 14. Detection times of various relays are displayed in Table 4.
Digital Application of Second Order Generalized Integrator Based Grid Estimator Under Unbalanced and Distorted Voltage Conditions
Published in Electric Power Components and Systems, 2019
Emre Ozsoy, Sanjeevikumar Padmanaban, Frede Blaabjerg, Pierluigi Siano, Fiaz Ahmad, Rasool Akhtar, Asif Sabanovic
Analysis of symmetrical components [18, 19] is a very important task in detecting unbalanced voltage conditions of electrical networks. It decomposes unbalanced voltage components into a set of balanced positive, negative and zero sequence voltage components by using 120° phase shift operators in the frequency domain. This method is also widely used for constructing robust controller structures for grid connected inverters under unbalanced voltage conditions [15, 20]. A simple and robust real-time calculation of symmetrical components by allowing the use of the orthogonal component of the original voltage signal is given in [19]. A different symmetrical component generation technique is given in [20] which directly shift the voltage 120° in time domain.