Transient security assessment of the China Southern Power Grid considering induction motor loads

The impacts of induction motor load models, mechanical load characteristics, motor load percentages and motor undervoltage tripping and reconnection relay on the transient security assessment (TSA) of the China Southern Power Grid after large disturbances are examined using a transient security assessment tool in this paper. The results show that the first order mechanical model gives more optimistic TSA than the third order electro-mechanical model under the specified simulation conditions. Motor mechanical load characteristics have different impacts on the TSA, which depends on network and disturbance characteristics. Transient voltage instability occurs firstly and then generator angle instability occurs after a critical motor load percentage under specified simulation conditions. The motor undervoltage tripping and reconnection relay may be propitious to transient voltage stability but not to transient angle stability after a large disturbance. Induction motor loads should be included in the composite load models if reliable results are obtained