Directional relays provide differential-type protection on large industrial plant power system

SEVERAL years ago it became necessary to revise the primary distribution system in a large chemical plant. This plant was approximately 25 years old and had undergone a rapid expansion during this entire period. The type of electric distribution system which had developed is typical of many other large chemical plants which have expanded over comparable periods of time. The original plant electric system consisted of 2,300-volt generation and primary distribution. Load increases associated with later plant expansions resulted in the introduction of 11,000-volt generation and primary distribution and the installation of an 11,000-volt interconnection with the local public utility. Bus tie reactors had been installed to keep the generator bus fault levels down as additional power capacity was added to the system.