The Thevenin Equivalent Circuit

The one-port circuit of Figure A.1 was initially assumed to be passive, i. e consisting of R, L or C components. In contrast, active networks include energy sources. A valuable method of representing active networks by simpler equivalent circuits is based on the Thevenin theorem. This theorem states that any one – port network consisting […]

Three-phase AC

Power systems are almost universally three-phase AC. This gives a significant saving in the construction of all power system equipment from generators to transmission lines and con­sumer equipment compared to single – phase [ 1] . Even more importantly, three-phase very elegantly provides the rotating magnetic field required in synchronous and induction genera­tors, as described […]

Effects of Reactive Power Flow – Power Factor Correction

Figure A.21 represents a basic circuit of energy transportation from a generator to a consumer through a transmission line, which is simply represented by a series inductance and resistance. The consumer is represented by an inductive resistive impedance. The reason for these rep­resentations are explained in Chapter 5. The consumer ‘absorbs’ both PL and QL. […]

Conservation of Active and Reactive Power

Unlike voltage and current in AC systems, active power is a scalar quantity. If a heating element and an induction motor are connected at the terminals of a consumer, the total active power absorbed from the mains is the scalar sum of the two active powers associated with the two components. This is, of course, […]

Complex Power

The V and I phasors in Figure A.18 are shown again in Figure A.19(b) in the form of a tri­angle. With the current as reference, the voltage V applied across the circuit is equal to the Figure A.19 The complex power triangle phasorial addition of the voltage VR across the resistor (in phase with the […]

Reactive Power

Equation (A.12) gives the instantaneous power for an inductor as p = (a>L)I2sin2a>t. It is known that raL = XL and therefore the peak of the power variation is given by V2 V 12XL = — = 12Z sin в = 12— sin в = Q = VI sin в (A.26) XL 1 The quantity […]

Power in AC Circuits

The foundations have now been set for the investigation of power flows in power system networks. In Section A.2 the ideas of generators and consumers of energy were investigated. The concepts are very clear when the quantities involved are considered at one instant in time or are of a DC nature. An investigation will be […]

Reactance and Impedance

Now expressions will be developed that describe the ‘resistance’ or ‘opposition’ offered to the flow of AC currents by the three types of circuit elements. This can be found by dividing the phasor of voltage by the resulting current phasor. The voltage will be taken as the refer­ence phasor and polar notation will be used […]