Damper Interbar Current Analysis Of Hydro-Generators

This paper reviews the research on the interbar currents in cage induction machines,including the mechanism of interbar currents,the electromagnetic modeling of interbar currents,the effects of interbar currents on the electromagnetic and mechanical behavior,and the measurement of bar-iron contact resistance.The similarities and differences between the operating conditions and the damper/cage winding topology of the hydro-generators and the cage induction machines are pointed out.The paper also proposes to extend the analysis method for the interbar currents in cage induction machines to hydro-generators.Through the electromagnetic theory and analytical method,the mechanism and characteristics of the damper currents in hydro-generators under different operation conditions are analyzed and summarized.A salient-pole synchronous machine with reverted magnetic pole and armature winding is used to emulate a hydro-generator.The bar-iron contact resistances between the damper bars are measured on this model generator,and the damper bar current is measured in unbalanced load tests and no-load 3-phase sudden short circuit tests.A multislice 2-dimensional(2-D)time-stepping finite-element model with interbar circuit is developed for salient-pole synchronous machines considering the damper interbar currents.This model takes into account both the accuracy and the speed of calculation.By comparing the calculation results with the experimental results,the correctness of the model is verified.By using this model,the mechanism,distribution,influential factors of interbar current and the related damper winding loss,etc,under unbalanced load and no-load 3-phase sudden short circuit of hydro-generators are calculated and analyzed.The characteristics of interbar currents in the end and the middle of the poles are summarized,and the reasons for these characteristics are analyzed theoretically.Based on the analysis of the characteristics of interbar current under different operation conditions,the paper proposes some problems worthy of attention in the design of hydro-generators,and proposes some aspects on interbar current for future research.