Transmission interconnection: Lessons learned from a recent event at an acquired Generating plant

摘要

Transmission and Distribution (T&D) Companies tie to several generation plants and other utilities to make an electric transmission grid. Each of the interconnection facilities is governed by the Guidelines that ensure smooth operation of the Power System. However, the Interconnection guidelines are generally limited to equipment at the Point of Interconnection (POI), therefore a thorough investigation of protection schemes may not be carried out by the interconnecting Transmission Operator. North American Electric Reliability Corporation (NERC) PRC-001 requires review of the settings among interconnecting entities to ensure protection coordination. However, it does not cover a thorough review of settings that include oscillography requirements and other protective settings that may be critical to the operation of the interconnection but do not affect the protection coordination. Design standards and protection philosophies vary among generation and transmission operators. This variation in design standards makes it difficult for protection engineers to perform root cause analysis in an emergency event. In addition, testing procedures may be different from one facility to another and smaller interconnection parties may not have experienced staff to conduct maintenance testing or proper startup commissioning. A recent event at one of the combined cycle power plants recently acquired by PG&E is an example that points out some of the inadequacies of the existing interconnection guidelines. Lessons learned by PG&E have resulted in closer co-operation between the Transmission Operator and Generation Operator and is making us re-think about the way we interconnect to other customers. The policies and guidelines that govern third party interconnections are going to play even more important role in the future as the number of Interconnections are likely to increase due to the competitive bidding policy being pursued for new substations by the California Independent System Operator (CAISO) under FERC Rule 1000. As a result of CAISO's policy to bring competition to California electric transmission projects, there will be electric substations designed, owned and operated by a third party that would be surrounded by local utility grid. We as protection engineers need to re-think about how we review/analyze the third party protection schemes. The failure to do so can affect the whole electric grid. Protection Engineers should be more pro-active so that protection schemes and relay settings ensure the reliability of the Power System. Protective relays are the silent sentinels of the electric system, rules and policies need to be in place to allow the protection schemes to safeguard the power system.