DC Power Supply System in an Electrical Substation

Let’s see, the DC supply system in the electrical substation.

Primarily we will see applications & main components of the DC supply system that is Battery bank, Charger, & D-C-D -B called DC distribution board, and their working.

So let’s start with the application of DC supply. DC supply system in an electrical substation has a very important role in keeping the substation’s brains on. Meaning all modern numerical protection relays, closing tripping coils, alarms, hooters, Indications & communications devices are powered by DC. Also, some energy meters are powered by DC. Hence DC supply system keeps all the protection, communication, control, and measurement devices running in the substation.

Now let’s see the main components of the DC Supply system.
1. Battery bank.

 As we know battery bank is required as a backup DC supply in case the auxiliary AC supply breaks down and hence AC to DC converter fails to supply, Battery bank continues to supply uninterrupted DC.

In the battery bank, individual battery cells are connected in series to get the required DC voltage. For example, if the required voltage is 220 volt, and each battery cell is 2 Volt. Then 110 battery cells are connected in series. Please note that the example is just to get an idea. Practically battery bank calculations include other points such as ampere-hour capacity, charging and discharging rate of battery set, etc. 

Here we can see 3 steps 2 tier rack. Battery cells are placed one after the other and are connected in series. At the end, we can see cable connections. These cables connect to the Battery charger and DCDB.

2. Battery Charger

A battery charger is nothing but AC to DC converter and as the name says its function is to trickle charge the battery bank and to supply load. Trickle charging means charging a fully charged battery at a rate equal to its self-discharge rate, hence keeping the battery at its fully charged level. In normal conditions, the charger provides DC supply to the load and keeps trickle charging the battery bank. The battery bank provides the DC supply to load only in case the Battery charger breaks down or the AC supply to the battery charger breaks down. So in normal conditions, it is the charger that supplies DC power to protection, communication, control, and measurement devices running in the Electrical substation & not the battery bank.

3. D-C-D-B: DC Distribution Board

As the name says DCDB is used for DC Distribution to different load points. DC is distributed to different load points through their respective MCCBs. There are battery earth fault relays, DC under-voltage or over-voltage relays for protection purposes, installed in DCDB.