Symmetrical Components

Symmetrical Components:

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 diagram of the system. It is …


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 a dot have the same polarity. …


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 not change with alteration of phase …


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 expression for its per phase inductive …


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 Ia, Ib and Ic flow in the …


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 The following KVL equations can be written down from Fig. …


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 then be expressed in terms of …