Circuit-breaker

The circuit-breaker/disconnector fulfills all of the basic switchgear functions, while, by means of accessories, numerous other possibilities exist

As shown in Figure H20 the circuit-breaker/ disconnector is the only item of switchgear capable of simultaneously satisfying all the basic functions necessary in an electrical installation.

Moreover, it can, by means of auxiliary units, provide a wide range of other functions, for example: indication (on-off - tripped on fault); undervoltage tripping; remote control… etc. These features make a circuit-breaker/ disconnector the basic unit of switchgear for any electrical installation.

Functions		Possible Conditions
Isolation		[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\blacksquare }[/math]
Control	Functional	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\blacksquare }[/math]
	Emergency switching	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\square }[/math]	(With the possibility of a tripping coil for remote control)
	Switching-off for mechanical maintenance	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\blacksquare }[/math]
Protection	Overload	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\blacksquare }[/math]
	Short-circuit	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\blacksquare }[/math]
	Insulation fault	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\square }[/math]	(With differential-current relay)
	Undervoltage	[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\square }[/math]	(With undervoltage-trip coil)
Remote control		[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\square }[/math]	Added or incorporated
Indication and measurement		[math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\definecolor{myblue}{rgb}{0.26,0.71,0.9}\color{myblue}\square }[/math]	(Generally optional with an electronic tripping device)

Fig. H20 – Functions performed by a circuit-breaker/disconnector

Contents

Standards and description of circuit-breakers Fundamental characteristics of a circuit-breaker Other characteristics of a circuit-breaker Selection of a circuit-breaker Coordination between circuit-breakers Discrimination MV/LV in a consumer’s substation Circuit-breakers suitable for IT systems Ultra-rapid circuit breaker