The SVC is not used in a severe undervoltage conditions (less than 0.6 pu), since leaving the capacitors on can worsen the transient overvoltage once the fault is cleared, while STATCOM can operate until 0.2-0.3 pu (this limit is due to possible loss of synchronicity and cooling).
The STATCOM also provides better reactive power support at low AC voltages than an SVC, since the reactive power from a STATCOM decreases linearly with the AC voltage (the current can be maintained at the rated value even down to low AC voltage), as opposed to power being a function of a square of voltage for SVC. As a result, the reaction time of a STATCOM is one to two cycles vs. The response time of a STATCOM is shorter than that of a static VAR compensator (SVC), mainly due to the fast switching times provided by the IGBTs of the voltage source converter ( thyristors cannot be switched off in a controlled fashion). As a result, the two technologies coexist. STATCOM is costlier than an SVC (in part due to higher cost of the GTO thyristors) and exhibit higher losses, but has few technical advantages. SVC Ī static var compensator (SVC) can also be used to maintain the voltage stability. Ī voltage droop of 1-10% (usually 3%) is built into STATCOMs. For example, if the terminal voltage of the VSC is higher than the AC voltage at the point of connection, the STATCOM generates reactive current (appears as a capacitor) conversely, when the amplitude of the voltage source is lower than the AC voltage, it absorbs reactive power (appears as an inductor). The reactive power at the terminals of the STATCOM depends on the amplitude of the voltage source. However, its active power capability can be increased if a suitable energy storage device is connected across the DC capacitor. The voltage source is created from a DC capacitor and therefore a STATCOM has very little active power capability. STATCOM as a voltage source (in red) connected to a transmission lineĪ STATCOM is a voltage source converter (VSC)-based device, with the voltage source behind a reactor (STATCOM is connected to the utility grid via a transformer).
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