why Batteries & Battery chargers are used in substation?
what is the different between UPS & battery charger?

Answer Posted / tarun aggarwal ymca

In AC substations if AC power fails, for tripping of Switchgear an alternative supply is needed. This supply is DC supply from Batteries. AC supply can not be stored where as DC can be stored in batteries. Hence all circuit breakers are with DC voltage coils. In case of a line to line fault or line to earth fault the incoming / remote breaker needs to be tripped. At this point AC is not available and hence DC is used. 
While AC over voltage or Under voltage are abnormal conditions and hence AC supply is present hence AC coil can be used. 
For charging of battery, battery charger is used. Charger takes AC voltage, steps down and rectifies in to DC voltage and supplies charging current to battery. 




UPS (Uninterrupted Power Supply), consists of a rectifier, battery and inverter and its output is AC supply. During utility power supply fails, this UPS supplies AC voltage to instruments for monitoring important parameters. But this also depends on Battery. Hence efficiency of UPS is low, as well as reliability is low due to more components. Hence using battery is better for tripping functions in protection circuits. In case AC power fails for longer duration standby DG set is started for charging battery.

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