HIGH VOLTAGE CIRCUIT BREAKERS
High voltage circuit breakers of 34.5 kV and above may be used in the switch-yard associated with the generating plant, but are rarely used in a generating plant.MEDIUM VOLTAGE SWITCHGEAR
Medium voltage breakers are 2.4 to 13.8 kV. Breakers in this range are used for large motors in the plant. The most prevalent is 4.16 kV.MEDIUM VOLTAGE AIR CIRCUIT BREAKERS
Air circuit breakers were the most common type of breaker until about 1995. Due to large size and high maintenance requirements of air circuit breakers, they have been replaced by vacuum breakers.MEDIUM VOLTAGE VACUUM CIRCUIT BREAKERS
Vacuum circuit breakers are the most common type of circuit breaker used in new installations. Vacuum circuit breakers are being used to replace air circuit breakers. Vacuum breakers are smaller and can provide additional space if the plant needs to be expanded to meet new requirements. Before using vacuum circuit breakers, a transient analysis study should be performed to determine if there is a need for surge protection. If required, surge protection can be supplied by the installation of capacitors and/or surge suppressors can be used to eliminate voltage surge problems.MEDIUM VOLTAGE SF6 CIRCUIT BREAKERS
SF6 circuit breakers have the same advantages as vacuum circuit breakers but there is some environmental concern with the SF6 gas.LOW VOLTAGE SWITCH GEAR
Low voltage is 600 V and below. The most common voltage used is 480 V.LOW VOLTAGE AIR CIRCUIT BREAKERS
Air circuit breakers are used in load centers that may include a power transformer. Air circuit breakers are used for motors greater than 200 hp and less than about 600 hp. Low-voltage circuit breakers are self-contained in that fault protection is an integral part of the breaker. Low-voltage devices, which do not contain fault protection devices, are referred to as low-voltage switches. Low-voltage breakers may be obtained with various combinations of trip elements. Long time, short time, and ground trip elements may be obtained in various combinations.Low-voltage breakers manufactured before 1970 will contain oil dashpot time delay trip elements. Breakers manufactured after the mid-1970s until about 1990 will contain solid-state analog trip elements. Breakers manufactured after 1990 will contain digital trip elements. The digital elements provide much more flexibility.
A circuit that may be large enough for a load center circuit breaker but is operated several times a day should not be put on a load center circuit breaker. The circuit breaker would be put through its useful life in a very short time. A motor starter would be a better choice.