Circuit and method to compensate the fault current during a ground fault

The arrangement has a compensation device for partial compensation of harmonics of fundamental frequency of fault current. The device has three controllable electronic switches (7.L1, 7.L2, 7.L3) connected with conductors (L1, L2, L3) of a three phase system (1), respectively. The switches are connected with a filter circuit (6), which is connected with an earth point (5.3). The circuit is alternatively connected with the conductors. Each switch is manually and/or automatically actuated by an earth fault detecting relay, which detects the fault, where the circuit is designed as a rectifier. Independent claims are also included for the following: (1) a method for compensation of fault current in a single-pole earth fault in an electrical three-phase system (2) a method for locating an earth fault in a three-phase system (3) a method for compensation of idle power in a three phase system.