Factors affecting the commutation reactance of direct connected generator-converter units

The effect of generator subtransient reactance, rotor saliency, the number of generators in the group connection configuration and adjustable speed operation on the commutation reactance and harmonic levels of direct connected units are examined. Restriction limits for firing angles imposed by the commutation angle, generator terminal power factor, equivalent continuous negative-sequence harmonic loading are derived that permit the use of normal generators in direct connected units without the need for extra harmonic loading capacity. The generator harmonic ratings can be taken at the nominal speed and rated power output.