Electric System Seismic Safety & Reliability

Earthquake damage to substation equipmentIn California, it is not a matter of “if” an earthquake will happen, but “when.”. In the event of a major earthquake, those who are called upon as first responders will be critical to determining how emergencies are handled, including police officers, emergency operators, hospital staff, and fire fighters. But before these emergency personnel can even begin to do their job properly, there is one thing that they need: — electric power.

Thanks to research sponsored by the California Energy Commission’s PIER program and Pacific Gas and Electric Company (PG&E), and conducted by the Pacific Earthquake Engineering Research Center, new tools and methods are being developed to make electric power transmission more reliable in the event of a major seismic event in California. When it comes to construction standards, California is first in the nation and in the world in preparing for an earthquake. When it comes to predicting what will happen to the electric power grid during the course of an earthquake, energy leaders in California continue to strive to make the system perform the best it possibly can.

Among the areas under study are the substations that receive and distribute electricity to large areas of the state. The major causes of outages during past earthquakes were the catastrophic failures of circuit breakers, transformer bushings and disconnect switches at the substations. The following addresses the ways PEER researchers are currently working to make the power system more reliable:

Substation Porcelain Transformer Bushings

Transformer bushing during earthquake simulator testingThroughout most of California and the nation, high-voltage wires leading into substation transformers are insulated by a porcelain bushing on top of the transformer. This material is very brittle and susceptible to failure during earthquakes. Although the bushings can be replaced after an earthquake, the loss of a 500kV substation could not only disrupt electricity in California, but also possibly in surrounding states. Also, the repair of substations could involve a significant amount of time — at the very least, several hours — during the crucial time following a disaster.

PEER is testing new materials and anchorage designs for these bushings to help prevent their destruction during future earthquakes. Based on results to date, PG&E is actively upgrading and replacing older, brittle bushings before the next major earthquake strikes. This amounts to a cost avoidance of approximately $100,000/year, and a loss of service avoidance of $25,000/bushing for each of the California utilities’ service areas.

Fragility Testing — 500 and 230kV Disconnect Switches

Fragility testing of disconnect switchesLike the electric circuits in our homes, substations are equipped with disconnect switches, which are used for routing power to the desired circuit, or for shutting down power for a variety of reasons: damaged equipment, routine maintenance, or a downed line. Any time that work is done on power lines in your neighborhood, a disconnect switch is used to shut down a specific area for the safety of the workers. As you might imagine, there are thousands of these switches in the state of California. Like everything else, these switches must survive an earthquake for the system to remain functional.

PEER is currently developing a more cost-effective and resilient disconnect switch/support system to reduce the damage during a seismic event. This research has provided valuable data for the development of new industry standards that will help to reduce damage to these important substation components and other equipment in the event of a major earthquake. To date, the implementation of these new industry standards has resulted in achieving superior performance of 230 kV disconnect switches with minor modifications. The cost avoided by not having to purchase more expensive switches is estimated to be $250,000/ year to PG&E alone.

Rigid and Flexible Conductor Studies

Flexible strap conductoryThe Electric System Seismic Safety and Reliability project is also researching the effects of seismic motions on the conductors, or busses, that connect substation equipment. Rigid busses and connectors tend to transfer damaging motions to more fragile equipment such as transformer bushings during earthquakes.

New flexible connectors, such as the "S"-shaped flexible strap connector, which may "bend, but will not break during an earthquake," are being tested at this time to evaluate their effectiveness in minimizing damaging motions to substation components. This design, developed by UC Berkeley and being considered for patent, will help to improve substation performance during earthquakes.

Conclusion

Although earthquakes are inevitable, the damage caused by earthquakes is not. Through research and development, demonstration and implementation, the State of California leads the world in preparation and prevention of damage through collaborative projects such as PEER’s program on Electric System Seismic Safety and Reliability. By continuing to make our electric system even more reliable during a major seismic event, PEER, in collaboration with the California Energy Commission and PG&E, is committed to reducing the damage to the power system in an earthquake and helping emergency personnel carry on with their tasks during a potentially dangerous situation. In addition, faster post-earthquake resumption of utility services will enable a timely resumption of normal business operations, which benefits both the California and national economies.