Comparison Between Statcom and SVC – It may be noted that in the normal linear operating range of the V-I characteristic and functional compensation capability of the STATCOM and the SVC are similar. However, the basic operating principles of the STATCOM, which, with a converter based var generator, functions as a shunt-connected synchronous voltage source, are basically different from those of the SVC, since SVC functions as a shunt-connected, controlled reactive admittance. This basic operational difference renders the STATCOM to have overall superior functional characteristics, better performance, and greater application flexibility as compared to SVC. The ability of the STATCOM to maintain full capacitive output current at low system voltage also makes it more effective than the SVC in improving the transient (first swing) stability.
Comparison between series and shunt compensation:
Advantages of series compensation:
- Series capacitors are inherently self regulating and a control system is not
- For the same performance, series capacitors are often less costly than SVCs and losses are very low.
- For voltage stability, series capacitors lower the critical or collapse
- Series capacitors possess adequate time-overload capability.
- Series capacitors and switched series capacitors can be used to control loading of paralled lines to minimise active and reactive losses.
Disadvantages of series compensation:
- Series capacitors are line connected and compensation is removed for outages and capacitors in parallel lines may be overloaded.
- During heavy loading, the voltage on one side of the series capacitor may be out-of range.
- Shunt reactors may be needed for light load compensation.
- Subsynchronous resonance may call for expensive countermeasures. Advantages of SVC
- SVCs control voltage directly.
- SVCs control temporary overvoltages rapidly.
Disadvantages of SVC:
- SVCs have limited overload capability.
- SVCs are expensive.
The best design perhaps is a combination of series and shunt compensation. Because of higher initial and operating costs, synchronous condensers are normally not competitive with SVCs. Technically, synchronous condensers are better than SVCs in voltage-weak networks. Following a drop in network voltage, the increase in condenser reactive power output is instantaneous. Most synchronous condenser applications are now associated with HVDC installations.