The Shielding Effect of the Built in Damper Cage in a Synchronous Machine.

Abstract

Because of the cost efficiency of modern machines, the design of a damper winding in a synchronous machine must be met the following both subjects. One criterion is a functional design, and a second one is an as cheap as possible design. Normally, the complete damper cage is substituted by the slot wedges of the rotor. But this replacement cage isn’t as effective as the original cage [1]. Furthermore the damping moments of the eddy currents in the massive rotor and in massive parts of a synchronous machine don’t changed. So in the case of an absent damper winding the sum of the damping moments decreases. In order to answer the question of the aims of a built in complete damper cage it must be differentiated between synchronous generators and motors. Generators have to produce sinusoidal voltages. As a result, the damping of higher harmonics in the generator is important. Furthermore, the damping of the negative sequence caused by an increased asymmetric load must be defined by the consumer. Normally, a five percent asymmetric load is acceptable. In the case of synchronous motors the damping of load impulses are important. One result is the difference between the damping moment of a complete built in damper cage and an incomplete built in damper cage. In addition this paper treats about the damping of higher harmonics and the damping of the negative sequence rotating field.