Power electronic equipment

Previously the static compensators are presented. This kind of equipment belongs to the class of active compensators. Furthermore, static means that, unlike the synchronous condenser, they have no moving parts. They are used for surge-impedance compensation and for compensation by sectioning in long- distance, high-voltage transmission systems. In addition they have a variety of load-compensating applications. Their practical applications are listed in greater detail in Table 6.1. The main headings in Table 6.1 will be recognized as the fundamental requirements for operating an AC power system, as discussed in previous chapters. Other applications not listed in Table 6.1, but which may nevertheless be very beneficial, include the control of AC voltage near conventional HVDC converter terminals, the minimization of transmission losses resulting from local generation or absorption of reactive power, and the suppression of subsynchronous resonance. Some types of compensators can also be designed to assist in the limitation of dynamic overvoltages.

In later some widely used thyristor based controllers, namely the TCR, the thyristor-controlled transformer (TCT), and the TSC will be introduced. We then discuss the conventional switch-mode voltage-source converters (VSCs). Some new topologies incorporating solid-state technology to provide multilevel waveforms for high power applications are also presented. Finally, the chapter discusses applications of such technology in energy storage systems, HVDC power transmission systems and active filtering.

Table 6.1 Practical applications of static compensators in electric power systems.

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Maintain voltage at or near a constant level

1. under slowly varying conditions due to load changes
2. to correct voltage changes caused by unexpected events (e.g. load rejections, generator and line outages)
3. to reduce voltage flicker caused by rapidly fluctuating loads (e.g. arc furnaces).

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Improve power system stability

1. by supporting the voltage at key points (e.g. the mid-point of a long line)
2. by helping to improve swing damping.

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Improve power factor

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Correct phase unbalance

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