Chapter 27. Selection of power reactors
Types of power reactors
Design criterion and I f characteristics of different
types of reactors
Maintaining quality of power in terms of voltage and current waveforms (having low harmonic distortions and a stable voltage) is not only obligatory on the part of utility companies to provide quality power to their users, it is also mandatory on the part of utility companies as well as the users to meet the norms of EMC/EMI as discussed in Section 23.18. Power reactor is a simple and a handy tool to tackle these problems as discussed at different places in this book. Like for electronic circuits in Section 6.13 by way of smoothing current and voltage over-shoots (di/dt and dv/dt controls respectively), suppressing harmonics at source using harmonic filters (Section 23.9) or providing reactive support to a power network (Section 24.8) etc.
Power reactors are similar to transformers. However, they have only one winding per phase and can be represented as shown in Figure 27.1. They are employed to perform a number of functions, primarily to control and regulate the reactive power of a power system by supplying the inductive and absorbing the capacitive power. Control can be achieved in different ways as noted later. The reactors, depending upon their design and I-f characteristics, can be classified as follows:
1. Single- or three-phase Single-phase reactors are used in the neutral circuit either to limit the ground fault currents or as arc-suppression coils (Section 20.5). Similarly, three-phase reactors are used for three-phase applications.
2. Air-cooled dry type and oil-immersed type This will depend upon the size of the reactor and the design of the manufacturer. The latest practice is to use air-cooled dry type, which calls for lesser maintenance and is free from any fire hazards.
3. Indoor or outdoor types These may be designed indoor or outdoor depending upon the application.
4. Tap-changing facility Where necessary such as in reactive power management, the reactance of the coil can be varied by providing an on- or off-load tap changing gear with the reactor, similar to a power transformer.