Performance of a 230 KV ATB 7 Power Circuit Breaker Mounted on GAPEC Seismic Isolators

The successful operation of each pumping plant in the California State Water Project is dependent upon the performance of its electrical equipment to supply large quantities of electrical power. Furthermore, the success of the entire Water Project depends upon the performance of each of the individual facilities (e.g., dams, reservoirs, power and pumping plants) which are a part of this water supply system. In 1971 the San Fernando Earthquake demonstrated that electrical facilities were extremely vulnerable to damage due to strong ground shaking.

The consequences of this event ultimately led to the identification of the electrical equipment in the switchyards of power and pumping plants as the "weak links" in the water supply system.

In particular, the 230 KV ATB 7 power circuit breakers represent one of the most critical components of equipment found in the switchyard facilities. For this reason, the State Department of Water Resources (DWR) sponsored a program for the dynamic testing a 230 KV ATB 7 circuit breaker modified with GAPEC seismic isolators. The dynamic testing was conducted by the John A. Blume Earthquake Engineering Center at Stanford University in July, 1979.

The circuit breaker tested is located in the switchyard of the A. D. Edmonston Pumping Plant. As a part of the Water Project, this plant is situated on the California Aqueduct, approximately 35 miles south of Bakersfield, in a highly seismic region of southern California.

The dynamic characteristics (e.g., damping, natural frequencies, mode shapes) of the modified circuit breaker structure (e.g., with GAPEC isolators) were measured and compared the dynamic characteristics of the unmodified breaker structure, which were determined from previous tests.

This report discusses the differences in structural response between the modified and unmodified circuit breaker structures, and evaluates the effectiveness of the seismic isolation system for the modified breaker.