Static switch definition

A switch having no moving part called as a static switch. Power semiconductor devices which can be turned on and off within a few microseconds can be used as fast acting static switches.

Static switches can be also used for latching, current and voltage detection, a time delay circuit, transducers etc.

A static switch is two types :
  1. AC switches
  2. DC switches 
If we are using input is ac then ac SS are used while we are using input is DC, DC SS are used. Switching speed for AC switches is governed by the supply frequency and turn off time of thyristor (SCR). 

For DC static switches, the switches speed depends on the commutation circuitry and turn off time of fast thyristor. AC switches may be single phase or three phases. 

Static switches do not change or control the power delivered to load as it is done in a single phase voltage controller In a static switch, the semiconductor switches are turned on at zero crossing of the load current, whereas it is not so single-phase voltage controller.

Static switches are now replacing mechanical and electromechanical switches because of several advantages listed below.
  • A static switch has no moving parts, It maintenance is therefore very low
  • A static switch has a long operational life
  • A static switch has no bouncing at the time of turning on
  • On time of a static switch is of the order of 3 microseconds, it has therefore very high switching speed
  • Inbuilt AC overvoltage protection
  • High-performance AC line quality monitoring

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