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

Switching and short-circuit field tests have been performed on a 500 kV prototype NGH subsynchronous resonance damping scheme. Ihis damping scheme was developed in response to solving a subsynchronous resonance (SSR) problem on the eastern portion of the Southern California Edison Company's 500 kV transmission system. The present solution to the SSR problem is to reduce the series capacitor compensation from 70 percent to 26 percent but this limits the transmission capability of the system. It is desirable to return to the 70 percent compensation level and various schemes, including this damping scheme, have been investigated. Ihe details of this damping scheme are covered in Part 1 of this paper but 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 [1-4]. The NGH device was installed on one segment of the 500 kV series capacitor for tests and field evaluation purposes. This paper describes the results of the field tests, which included line switching and short-circuit tests.