Construction of Sequence Networks of a Power System: Construction of Sequence Networks of a Power System – Before sections the sequence networks for various power system elements synchronous machines, transformers and lines have been given. Using these, complete sequence networks of a power system can be easily constructed. To start with, the positive sequence network is […]

### SYMMETRICAL COMPONENTS

## Sequence Impedance and Networks of Transformers

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 […]

## Sequence Impedance of Transmission Lines

Sequence Impedance of Transmission Lines: Sequence Impedance of Transmission Lines – 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 impedances offered by it to positive and negative sequence currents are […]

## 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: Phase Shift in Star Delta Transformers – Positive and negative sequence voltages and currents undergo a phase shift in passing through a star-delta transformer 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 […]

## Symmetrical Component Transformation

Symmetrical Component Transformation: Symmetrical Component Transformation – 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 […]