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Terminals for external conductors separated from each other (Form 4a, 4b) Terminals for external conductors separate from their associated functional unit (Form 4b) By interrupting device: Fuses Air Blast Circuit Breaker Minimum Oil Circuit Breaker Oil Circuit Breaker Vacuum Circuit Breaker Gas (SF6) Circuit breaker By operating method: Manually-operated Motor-operated Solenoid/stored energy operated By type of current: Alternating current Direct current By application: Transmission system Distribution By purpose Isolating switches (disconnectors ) Load-break switches Grounding (earthing) switches
A single line-up may incorporate several different types of devices, for example, airinsulated bus, vacuum circuit breakers, and manually-operated switches may all exist in the same row of cubicles. Ratings, design, specifications and details of switchgear are set by a multitude of standards. In North America mostly IEEE and ANSI standards are used, much of the rest of the world uses IEC standards, sometimes with local national derivatives or variations.
2.12
Functions
One of the basic functions of switchgear is protection, which is interruption of shortcircuit and overload fault currents while maintaining service to unaffected circuits. Switchgear also provides isolation of circuits from power supplies. Switchgear is also used to enhance system availability by allowing more than one source to feed a load. 2.13
Safety
To help ensure safe operation sequences of switchgear, trapped key interlocking provides predefined scenarios of operation. For example, if only one of two sources