Patent ID: 8228694

Claim:
A converter station connected between an AC system and an HVDC transmission line, said station comprising at least one converter having a DC-side thereof connected to a pole of said transmission line on high potential and to low potential and an AC-side connected to said AC system, a plurality of critical components comprising at least one transformer arranged on the AC-side of said converter and converter valves comprising power semiconductor devices, wherein a maximum allowed temperature of said critical components may be reached if power transmitted through the converter station be raised above a rated power of the converter station defined as the maximum power allowed to be transmitted through the converter station at continuous operation and at a maximum ambient temperature, a control device adapted to control said at least one converter for determining a level of power transmitted through the converter station, an overload limiting arrangement adapted to, based upon information about an ambient temperature prevailing, determine an overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a certain period of time without exceeding said maximum allowed temperature of said critical components and deliver this information to said control device for being used thereby upon a possible request of utilizing this overload capability, wherein said overload limiting arrangement is adapted to carry out said calculation of overload capabilities for each of said critical components and determine lowest overload capabilities so obtained as the converter station overload capabilities, an element adapted to determine a value of an actual temperature of said critical components, and an element adapted to determine a value of an actual temperature of any media used to cool said critical components, wherein said overload limiting arrangement is adapted to utilize these temperature values as well as information about actual cooling capacity of any cooling equipment present to cool said critical components and information about a thermal behavior of said critical components and said any media used to cool said critical components upon a possible change of power actually transmitted through the station in a mathematical model for calculating present overload capabilities of the converter station for use in control of the control device upon a possible said request.