Synchronizing out of Phase

Synchronous-machine torques due to out-of-phase synchronizing may be quite large; larger in fact than those encountered during a 3-phase short circuit. Previous works have presented various forms of equations to calculate these torques.1-3,6 With the advent of the widespread use of systems analyzers and computers, it becomes convenient to use more exact equations to calculate synchronous machine transient performance. The objectives of this paper are to present the derivation of the equations for the currents and electrical torques which occur when turbine generators are synchronized out of phase; to show how these electrical torques arise; to illustrate the application of these equations to the problem of calculating the transient mechanical torques in a large, multiunit turbine-generator set under these conditions.