Chapter 23. Power capacitors: behaviour, switching phenomena
and improvement of power factor
Application of power capacitors
Effect of low PF
Other benefits of an improved power factor
Behaviour of a power capacitor in operation
Generation of triple harmonics in an inductive circuit
Generation of harmonics by a power electronic circuit
Effective magnitude of harmonic voltages and currents
When harmonics will appear in a system
Filter circuits: suppressing harmonics in a power network
Excessive charging currents (switching inrush or making currents)
Limiting the inrush currents
Capacitor panel design parameters
Capacitor rating for an induction motor
Location of capacitors
Automatic PF correction of a system
PF correction relays
In view of the considerable increase in power distribution networks and their over-utilization to meet increasing consumer and industrial demands it has become imperative to optimize the use of available power through efficient transmission and distribution.
Voltage and power factor (p.f.) are the two most important parameters in a power system that influence its utilization. The element of voltage is optimized by raising the transmission and distribution voltages as much as feasible. The more prevalent of these are 400 kV a.c. for long-distance transmissions and 33–132 kV or even higher for secondary transmissions. Figure 23.1 illustrates a typical transmission and distribution network. Continued efforts are being made to raise the transmission voltage to 765 kV a.c. or 500 kV d.c., or higher. Some countries such as the USA, Russia and Canada have already adopted such systems. A d.c. system, we recall, has no skin effect (Section 28.7) and can transmit power at unity p.f.
The element of p.f. mainly affects the secondary distribution system which serves industries, agriculture, public utilities and domestic loads. Most of them are highly inductive and result in lowering the system p.f. These loads are largely responsible for most of the distribution losses and voltage fluctuations at the consumer end. In developing countries it is estimated that useful power is lost mainly due to transmission and distribution losses. In India, for instance, it is estimated to result in a loss of about 18–20% of the total useful power, most of which occurs at the secondary distribution attributable to low p.fs.
The application of power capacitors, can tackle problems of both low p.f. and voltage fluctuations and these aspects are discussed here.
Electromagnetic compatibility (EMC) and electromagnetic interferences (EMI)
EMC/EMI is a vast subject. We have attempted to provide a brief reference of it so as to enable a reader, user or a manufacturer of electrical and electronic equipment and devices to comprehend the implications of EM interferences, their adverse influence on the performance of sensitive electrical and electronic equipment and devices operating in such environments and tackling the same at source as far as possible. We have suggested possible safeguards and certain disciplines for the user and the manufacturer to follow, to save the environment from EMI and protect the sensitive equipment and devices from the influence of the same. Since electronic circuits are affected the most, our present thrust is on electronic equipment and devices.