Plc Required

Hello,
I am still freshman in the PLC Controls, your kind help is highly appreciated.Could you tell me what PLC can be used for operating a DEG automatically when the commercial power goes OFF, and turn OFF the Engine when the commercial power is restored to the site.
Thanks

I believe the answer to your question is - 'any PLC you like'.

I use a Siemens S7 212 to automatically switch our supplies from mains to back-up generator in the event of a power failure.

You should only need a small brick type PLC, it would be uneconomical to use a rack type PLC just for controlling a 'stand-by genny'.

That's my view, I am sure other people will have their own.

Paul

Sometimes I wish I could use a brick for stand-by generators. Life would be simple - and probably boring.

Job just recently - 1 PLC per gen (3 of them), 1 master PLC, 1 PLC to monitor switchboards and control changeovers.

I/O count on the master PLC
3 x 96 bit input cards
3 x 96 bit output cards
1 x Device Net scanner
2 x 8 point analogue cards
1 x network card
2 x AB Powermonitors

I/O count on the switchboard monitoring PLC
2 x 64 bit input cards
2 x 64 bit output cards
6 x Device Net scanners reading 96 digital blocks and 2 AB Powermonitors

Then we start on the generator PLCs with Device Net to AB Powermonitors, Modbus RTU to generator controllers and Schneider ACB protection relays.

And the SCADA, BACnet interface to the BMS, Modbus RTU interface to the fire panel, Omron Controller Link interface to the 5 PLCs.

Got 6 weeks work out of it anyway.

BobB

What you have described there is the other end of the generator control spectrum from what I did.

Granted, these controls can be as complicated or as simple as the situation requires. My situation was a fairly simple one:-

We monitor incoming voltage (from sub-station) for voltage level and phase rotation and loss using a relay made by broyce control ltd (Link). This relay inputs to the PLC, if we loose this input the PLC will open the Mains motorised breaker (supply from sub station) and also open our bus-coupling breaker (seperates essential circuits from non-essential circuits). When both theses MCCB's are open a signal is then sent from the PLC to the generator to start up, (engine control management is contained within the generator panel), the generator voltage is also monitored using the relays described earlier, when the voltage has settled the PLC then closes the generator supply motorised breaker to put the generator onto the essential circuits only. When the mains has been restored (on the suppliers side) the mains monitor relay picks up and the PLC does the reverse switching already described.

That is a simplified description of our system, from that you can see that I only needed a few inputs and a few outputs to control this particular genny.

Inputs -

Mains voltage monitoring relay
Mains MCCB open
Mains MCCB closed
Bus-coupling MCCB open
Bus-coupling MCCB closed
Generator voltage monitoring relay
Generator MCCB open
Generator MCCB closed.

Outputs -

Mains MCCB open
Mains MCCB close
Bus-coupler MCCB open
Bus-coupler MCCB close
Generator MCCB open
Generator MCCB closed
Generator start signal
Generator failed to start alarm.

That is why I only used a 'brick' type PLC, I used this as the example to hafiznaim to keep it simple as he stated he is a PLC 'freshman'

Paul

i used micro 1 for many of generators the we build
it has enough input and output to control basic genset,
such as overspeed, shutdown for low oil press, water temp
and even for changes over contactor
i used ladder programing for this

hafiznaim said:

thanks for your answer regarding the stand by generator,
could you send me the logic lader for this circuit with some description.
your help is highly appreciated
Best Regards
hafiz

Click to expand...

I received this this morning by private message.

hafiz, as we like to keep things out in the open, so I have chosen to post a reply here rather than reply via private message. There might be someone else who comes by this forum that will find the information that you require helpful.


First of all, the logic that I have written to control our generator might not be suitable for your application, so I am very reluctant to send you this logic as this might encourage you to copy it exactly as I have written it, which could be dangerous as your system could work differently from ours.

If you want ideas on the best way to tackle your problem, then post as much information on your system as possible, together with a flow chart (that will help us understand how you would like your system to work) and any logic that you have written so far, then, I am sure all the experts here will give you all the help you need!

Paul