Abstract :
The severity of unsymmetrical system faults is affected by the negative sequence impedance of the connected machines. These impedances in turn depend largely upon the character of damper windings. The paper discusses the effect of amortisseur or damper windings upon both the real and reactive components of the negative sequence impedance. Machines without damper windings possess the highest negative sequence reactance and from this point of view, are the more desirable; but machines with high-resistance damper windings possess the highest negative sequence resistance. Calculations show that combining the effect of resistance and reactance, the high-resistance damper is the more desirable. In the event of system oscillations, low-resistance copper damper windings produce the greatest damping of the mechanical movement; however, this effect is unimportant during and following a system fault except in the rather rare case in which the system is so constituted that pull-out takes place as a result of compound oscillations following a disturbance. Consideration is given also to a special type of double-deck damper winding.
