Method and apparatus for relieving a capacitor of a controlled series compensator as a function of the load on its arrester

The invention relates to a method and to a device for unloading a capacitor (16) of a controlled series compensator (2) as a function of the load on its suppressor (26) when high-current line defects occur. According to the invention, the energy (w) absorbed by the suppressor (26) is determined from a current (u1) flowing through it. A temperature gradient ( DELTA t'A) is then determined from this energy (w) as a measure of the step-function load on the suppressor (26) and is compared with a limit value (tH). This comparison value (SK) is then processed as a function of the determined actual suppressor temperature (t'A) and the measured line current (iL) to form a control signal (Si), as a result of which the converter valve (8) of the controlled series compensator (2) is driven in such a manner that its equivalent impedance is controlled in the direction from being capacitive to being inductive. The number of necessary cut-offs in the event of high-current line defects is thus considerably reduced, as a result of which the availability is significantly increased.