Protecting apparatus for secondary excitation type variable speed AC generator/motor

An apparatus for protecting a power converter system for use with a secondary excitation type multiphase variable speed AC generator/motor having a primary winding connected to an electric power system and a secondary winding in which each phase is AC excited, said power converter system being connected between the electric power system and said secondary winding and including a plurality of independent power converter units for AC exciting the respective phases of said secondary winding of said AC generator/motor, said apparatus comprising:

• means for detecting an electrical event which includes at least one of an overvoltage and overcurrent appearing at each of the power converter units;
• switch means associated with each of said power converter units, said switch means normally being in an opening state for enabling the associated power converter unit to operate normally, and being operative in a closing state to protect the associated power converter unit from at least one of the overvoltage and overcurrent;
• means for deciding whether the electrical event detected in each of the power converter units meets a predetermined condition;
• and
• means associated with each power converter unit for holding said switch means of a respective power converter unit in the closing state thereof in response to the deciding means deciding that the electrical event in the power converter unit associated with one phase of said secondary winding meets the predetermined condition thereby protecting the power converter unit for the one phase from at least one of the overvoltage and overcurrent and enabling the power converter units associated with other phases of said secondary winding to operate normally.