dc backup power

[hawkeye23]

Can someone explain how or why dc power[ batteries ]is used in switchgears and is the same dc used with generators that backup swichgear systems ? When there is a loss of utility power is dc used to switch over to generator power ?

 

[augie47]

The battery system is there to provide a reliable source of power for operating the switches.

 

[zog]

Can someone explain how or why dc power[ batteries ]is used in switchgears and is the same dc used with generators that backup swichgear systems ? When there is a loss of utility power is dc used to switch over to generator power ?

The battery is there to provide power to the trip coils, close coils, charging motors, etc in the switchgear. It is not a back up to anything (Usually), without the battery being on line (And maintained) all of that switchgear is useless.

 

[don_resqcapt19]

And there must be some means of monitoring the battery power. Without battery power the "breakers" cannot trip in the event of a fault.

 

[broadgage]

As above, large circuit breakers normally require a battery to function, unlike the small MCBs used residentialy which are self contained.
The battery may also supply other control, monitoring, or warning equipment.

If a standby diesel generator is installed then this normally has a battery to start the engine, seperate from the switchgear battery.
The engine starting battery may also power controls and instruments on the generating set.

In some places large backup batteries are installed not for switchgear operation or engine starting, but to actually power critcial loads in the event of failure of the utility supply.
In a few cases the load might use DC power direct from the battery, but it is more usuall to use an inverter to produce line voltage AC.