Implementation of reliable high-speed islanding detection, zone interlocking, and source selection schemes using smart algorithms

The Valero Bill Greehey Refineries West Plant houses on-site generation and is interconnected to the utility via a looped power system. With the on-site generators not having the capacity to carry the entire plant load, this plant relies on importing power from the utility. Valero upgraded their medium-voltage protection system and was looking for a fast, deterministic, reliable, and cost-effective solution to protect their medium-voltage busbars as well as a local-area measurement-based generator islanding detection system to protect their generator equipment. An economical solution was proposed and implemented using automation controllers, which receive information from the new relays using a fiber-optic link and a protection-speed protocol. Multiple techniques on redundant hardware are used to detect the islanding condition and help improve the dependability of the islanding detection scheme, regardless of generation-load mismatch. A unique voting scheme was developed to improve security. The zone interlocked bus protection scheme programmed in the controllers uses directional information to provide high-speed selectivity during bus faults. An intelligent source selection algorithm automatically modifies the bus protection logic depending on the topology of the power system. The protection-speed processing capabilities of the automation controllers enable the high-speed operation of the schemes. This paper describes the solution implemented at Valero and introduces the algorithms developed to provide a robust integrated protection system that operates with dependability, selectivity, and security.