Practical detailed model for generators

The Parks equation is currently used for mathematical expressions of the state of synchronous generators connected to power systems. The calculation results using the Parks equation, however, differ greatly from the results of measurement on the real generator when the Parks equation is applied to an event where the flux linking the generator undergoes a very large change as when the generator is suddenly disconnected from a load during normal operation. The difference between the field test result and the calculation result is larger for a turbogenerator with a solid iron rotor than for a salient synchronous machine. To deal with this problem, this paper introduces a mathematical expression of generating machines, which is an extension of the Parks equation and which is practically applicable to an event in which the flux within the generating unit changes sharply as when it experiences a load rejection. The newly introduced expression takes the following considerations: (1) a magnetic flux saturation coefficient k is applied to d- and q-axis; and (2) T´_q0 that corresponds to T´_d0 of d-axis is introduced to q-axis. A generator model incorporating the magnetic flux saturation coefficient k and another parameter T´_q0 has proved capable of providing a good simulation representing a load rejection whose calculation results coincide satisfactorily with the measurements of actual generators