Circuit for monitoring the current distribution in parallel-connected converted branches

A circuit arrangement for monitoring current in two parallel-connected converter branches each of which comprises at least two series-connected converter valves comprising:

• a differential current transformer for measuring the difference between the levels of currents flowing in the two branches at a junction point of the branches,
• cross-connections, each containing the primary winding of a current transformer, for connecting the anodes and cathodes of corresponding converter valves in both branches, and
• threshold detection means associated with each transformer for triggering protective measures in response to current imbalance comprising an amplifier connected to the output of the differential current transformer for supplying a signal to a threshold detector and a summing amplifier in each cross-connection for supplying a signal to a threshold detector,
• the summing amplifier having one summing input connected to the current transformer and another summing input connected to the output of the respective preceding amplifier,
• the gains of the circuits containing the amplifier and the summing amplifiers being in the ratio of 0.5 to 1, respectively.