Auto Mains Failure PLC Program Using Omron PLC

Auto start up of the DG when the Mains Supply fails . This is a very common system and is the first step in DG synchronization.
Here we will see that what is the basic concept in AMF? What hardware is required to set up AMF and how PLC Programming is done.

First of all let us understand what is AMF?
Generally all the major industries/companies/institution have the DG for power back up , but when when main power is cut off , someone has to go to start the DG and this takes time and also a man has to be kept for this purpose. So to eliminate this process PLC panel is installed to Auto start the DG when main power fails.

Working is as follows:- when main power goes , a signal is received to PLC and after 2 minutes DG starts . When the Main supply fail signal is received by PLC then after a delay time (can be from 1 to 2 minute) , output for ACB/Contactor of DG is ON and DG starts automatically. Also the ACB/Contractor of main transformer if sent OFF Command. When main power comes then the signal is again sent to PLC and PLC off the ACB/Contactor of DG and after 2 seconds it on the ACB/Contactor of main transformer and after 30 seconds it off the DG. DG is sent OFF command a little late so that the load beared by DG for a long time can be compensated by running at no load for some time.

NOTE :- In no Condition the ACB/Contactor of both DG and Main transformer should be ON.

So this is the main concept in DG AMF system.
In a simple system there are generally 4 inputs and 4 outputs.

Inputs :- 1. DG ACB/Contactor close feedback.
2. Transformer ACB/Contactor close feedback.
3. Transformer Voltage Available.
4. DG Voltage Availaible.

Outputs :- 1. DG start.
2. DG Stop
3. DG ACB/Contactor close.
4. Transformer ACB/Contactor close.

Basic PLC Program

Input signal from Input device will entrance to PLC by Input module. After that PLC will process Input signal with Processor memory. Then PLC will transfer Output signal to Output device by Output module.

Basic componant of PLC Programs .

1. CPU ( Central Processor Module )
Process software application in ROM/RAM. Some application depend on Brand or Type.

2. Memory Unit
- ROM : Storage functions of the PLC Programs, Have battery to back up.
- RAM : Can be divided into EPROM, which will require special equipment to write and delete
3. I/O Unit
- Digital input module : Receive digital signal from Input device. ( 24VDC/VAC, 110V, 220V )
- Digital output module : Send digital signal to Output device. ( 24VDC/VAC, 110V, 220V )
- Analog input modle : Receive analog signal from Input device. ( 0-10VDC, 4-20Ma )
- Analog output module : Send analog signal to Output device. ( 0-10VDC, 4-20Ma )

4. Power supply
To supply electricity to PLC Program device.

5. Base module
To connect all PLC Programs device.