Prototype NGH Subsynchronous Resonance Damping Scheme Part II - Switching and Short Circuit Tests

Abstract

This paper reports on the switching and sort-circuit field tests which have been performed on a 500-kV prototype subsynchronous resonance (SSR) damping scheme. This SSR damping scheme was developed by SCE, EPRI, and seven other southwest utilities in response to solving a subsynchronous resonance problem, or the Mohave Generating Station and others in the southwest. The details of this damping scheme are covered in Part I of this paper. The basic scheme consists of a low-ohmic resistor in parallel with the series capacitor element. The resistor is switched by thyristor switches controlled by the control system. The device is designated as the NGH scheme after its inventor, N. G. Hingorani of EPRI. The NGH scheme was installed on one segment of a 500-kV series capacitor for tests and field evaluation purposes. The capacitor bank is rated 282, 500 kvar, 3-phase, and 36.7 ohms/phase, 1600 amperes, 58.7 kV per phase. Each phase consists of four segments, one of which is permanently bypassed to prevent any hazardous subsynchronous resonance torques on the two 790-MW units at Mohave Generating Station. Each capacitor segment is rated 9.18 ohms. The NGH scheme is installed across the series capacitor segment No. 4 and forms a parallel circuit to the existing series capacitor protection.