Abstract
In order to enable a simulated fault current in the region of 4000 A to produce a pulsating magnetisation in the stator coil, an arrangement of a parallel tuned-circuit was constructed. The performance characteristics of the tuned-circuit were assessed from an analytical solution (Transient response method) and modelling on an Apollo computer using the transient response package.
The inrush current which is associated with the starting of the tuned-circuit was controlled with a soft-start, which increased the input voltage across the coil from zero to full preset value in 50 cycles. The soft-start circuit consisted of two anti-parallel thyristors, current-limiting resistor, phase-angle trigger unit and its control circuitry.
Spurious triggering of the thyristor was greatly reduced by placing the current-limiting resistor in between the supply and the thyristor. The possible causes are discussed.
A detailed comparison of the measured flux for the fault current of 4000A at an air-gap of 75 mm, for conditions with and without the endbell, at the end of the rotor suggests that the conduction current is dependent on the contact resistance at the endbell and rotor interface.
Get full access to this article
View all access options for this article.