Patent ID: 6995994

Claim:
A converter comprising: a series connection of at least two current valves ( 2 , 3 ) arranged between two poles ( 4 , 5 ), a positive and a negative, of a direct voltage side of the converter, each of which current valves comprising at least one circuit ( 12 ) provided with a semiconductor component ( 13 a , 13 b ) of turn-off type and a rectifying component ( 14 a , 14 b ) connected in anti-parallel therewith, an alternating voltage phase line ( 11 ) being connected to a mid-point ( 10 ), denominated phase output, of the series connection between two current valves while dividing the series connection into two equal parts ( 1 a , 1 b ), a resonant circuit ( 16 ) comprising snubber capacitors ( 15 ), which are connected in parallel with a respective one of the semiconductor components ( 13 a , 13 b ) of turn-off type of the current valves, and at least one inductor ( 17 ) and an auxiliary valve ( 18 ) provided with semiconductor components ( 20 a , 20 b ) of turn-off type for recharging said snubber capacitors ( 15 ) in connection with a commutation of the phase current, and a control device ( 24 ) for controlling the turn-on and turn-off of the semiconductor components ( 13 a , 13 b ) of turn-off type of the current valves, wherein the converter comprises a device ( 31 ) for measuring the derivative (dI/dt) of the current through the current valves ( 2 , 3 ), and a detection device ( 32 ) co-operating with said measuring device ( 31 ) for detecting a short-circuit in the converter, the detection device ( 32 ) being adapted to detect a short-circuit current when the current derivative (dI/dt) measured by the measuring device ( 31 ) is equal to or exceeds a stipulated current derivative limit value (dI/dt lim ) during a length of time exceeding a stipulated time limit value (t lim ).