Method and arrangement for protecting a frequency converter

1. An arrangement for protecting a frequency converter in a system comprising a motor and a frequency converter supplying it via a bipolar or multipolar supply connection, comprising

first connecting means adapted to couple poles of the supply connection mutually substantially into short-circuit in response to a detection of a fault in the frequency converter.

2. An arrangement as claimed in claim 1 , further comprising second connecting means adapted to break the supply connection between the motor and the frequency converter for at least one pole after said poles are connected into short-circuit.

3. An arrangement as claimed in claim 2 , wherein the second connecting means are adapted to break the supply connection between the motor and the frequency converter for all poles.

4. An arrangement as claimed in claim 2 , wherein the second connecting means comprise a contactor.

5. An arrangement as claimed in claim 1 , wherein the first connecting means are connected to the supply connection between the motor and the frequency converter at a point where a section between said point and the frequency converter is longer than a section between said point and the motor.

6. An arrangement as claimed in claim 1 , wherein the first connecting means comprise a semiconductor switch.

7. An arrangement as claimed in claim 6 , wherein the first connecting means comprise a thyristor.

8. An arrangement as claimed in claim 1 , wherein the motor is a three-phase motor and the supply connection from the frequency converter to the motor is triple-pole.

9. A method of protecting a frequency converter in a system comprising a frequency converter and a motor connected thereto, the method comprising:

supplying the motor from the frequency motor via a bipolar or multipolar supply connection, and

connecting poles of the supply connection mutually substantially into short-circuit in response to a detection of a fault in the frequency converter.

10. A method as claimed in claim 9 , further comprising:

breaking the supply connection between the motor and the frequency converter for at least one pole after said poles are connected into short-circuit.

11. A method as claimed in claim 10 , further comprising:

breaking the supply connection between the motor and the frequency converter for all poles.

12. A method as claimed in claim 9 , further comprising:

connecting the poles of the supply connection into short-circuit at a point of the supply connection that is closer to the motor than to the frequency converter.

13. A method as claimed in claim 9 , further comprising:

performing said connecting into short-circuit with a switch comprising a semiconductor.

14. A method as claimed in claim 13 , further comprising:

performing said connection into short-circuit with a switch comprising a thyristor.