Electrical power and Drive questions

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1- Explain briefly why an iterative numerical technique is required in

load-flow studies of power systems.


2- State the general form of nodal voltage equations for a network and

derive expressions for the voltage and input reactive power at any

node in the network.


3- Compare the effects of internal and external events in the generation of

over-voltage transients in h.v. power systems. Explain the, relevance of

these effects to the specification and protection of plant.


4- Using a half-wave, three-phase, controlled rectifier bridge as an example,

explain the phenomenon and effects of ‘overlap’. Draw circuit and waveform

diagrams as necessary to illustrate your answer

Derive an expression, in terms of the supply voltage, for the voltage presented to the load during the overlap period


5- Draw a circuit diagram plus voltage and current waveform to illustrate how

the speed of a permanent. magnet dc motor may be controlled from a dc supply using a chopper drive


6- lnduction motors may present an operator with difficulties when they are connected to a ‘weak’ supply and are required to start against load. Explain how a Variable Speed Drive (VSD) can provide a better solution than other ‘soft-start’ methods.


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