Method and arrangement in connection with slip-ring machine

An arrangement for starting a slip-ring machine, the arrangement comprising:

• a frequency converter arranged to be connected between a supply network and a rotor of slip-ring machine for controlling the slip-ring machine, and
• starting means for starting the slip-ring machine, wherein the starting means are arranged between the frequency converter and the rotor of the slip-ring machine, whereby the frequency converter is arranged to control the magnitude of the current of the rotor of the slip-ring machine in connection with starting the slip-ring machine, wherein said starting means comprise:
• a three-phase auto-transformer, first ends of primary windings thereof being coupled to phase outputs of the frequency converter and second ends of the primary windings thereof being coupled to a common star point and tapping points of a secondary winding being coupled to a three-phase rotor circuit of the slip-ring machine, and
• first coupling means for connecting the first ends of the primary windings of the auto-transformer to first ends of the secondary windings, and second coupling means for separating phases of the auto-transformer from the common star point.