and dips transients these double switches can also be provided in the embodiments shown in fig3 and 4 it should be noted that the application of the disturbance component can also be controlled directly from the inverter 37 without switches 23 24 via rapid regulation at the inverter 37 fig6 shows a further circuit arrangement which can be used selectively to produce overvoltage or undervoltage this is based on the circuit variant shown in fig4 a multi switching unit 4 is additionally provided and comprises two changeover switches 41 42 which selectively connect the input 26 to the connection of the primary winding 31 or of the secondary winding 32 or the second switch 24 to the connection of the secondary winding 32 or of the primary winding 31 when the multi switching unit 4 is in its rest position as is illustrated in fig6 a then this results in a circuit arrangement corresponding to that shown in fig4 when the first and the second switches 23 24 are operated the wind energy installation 1 therefore has an overvoltage applied to it in contrast when the switching system is in the second position as illustrated in fig6 b a circuit arrangement is thus formed in which.