Category: Symmetrical Components

Construction of Sequence Network in Power System

Construction of Sequence Network in Power System: Before sections the Sequence Network of various Power System elements synchronous machines, transformers and lines have been given. Using these, complete Sequence Network in a Power System can be easily constructed. To start with, the positive Sequence Network in Power System is constructed by examination of the one-line […]

Sequence Impedance and Networks of Transformers

Sequence Impedance and Networks of Transformers: It is well known that almost all present day installations have three-phase transformers since they entail lower initial cost, have smaller space require­ments and higher efficiency. The positive sequence series impedance of a transformer equals its leakage impedance. Since a transformer is a static device, the leakage impedance does […]

Sequence Impedance of Transmission Line

Sequence Impedance of Transmission Line: A fully transposed three-phase line is completely symmetrical and therefore the per phase impedance offered by it is independent of the phase sequence of a balanced set of currents. In other words, the Sequence Impedance of Transmission Line offered by it to positive and negative sequence currents are identical. The […]

Sequence Impedances and Networks of Synchronous Machine

Sequence Impedances and Networks of Synchronous Machine: Sequence Impedances and Networks of Synchronous Machine – Figure 10.11 depicts an unloaded synchronous machine (generator or motor) grounded through a reactor (impedance Zn). Ea,Eb and Ec are the induced emfs of the three phases. When a fault (not shown in the figure) takes place at machine terminals, currents […]

Sequence Impedances of Transmission Lines

Sequence Impedances of Transmission Lines: Sequence Impedances of Transmission Lines – Figure 10.9 shows the circuit of a fully transposed line carrying unbalanced currents. The return path for In is sufficiently away for the mutual effect to be ignored. Let Xs = self reactance of each line Xm = mutual reactance of any line pair […]

Phase Shift in Star Delta Transformers

Phase Shift in Star Delta Transformers: Positive and negative sequence voltages and currents undergo a Phase Shift in Star Delta Transformers which depends upon the labelling of terminals. Before considering this phase shift, we need to discuss the standard polarity marking of a single-phase transformer as shown in Fig. 10.5. The transformer ends marked with […]

Symmetrical Component Transformation

Symmetrical Component Transformation: Symmetrical Component Transformation is given by a  set of three balanced voltages (phasors) Va,Vb,Vc is characterized by equal magnitudes and interphase differences of 120°. The set is said to have a phase sequence abc (positive sequence) if Vb lags Va by 120° and Vc lags Vb by 120°. The three phasors can […]