PLC - Power Supply

In our plant UPS for PLC System is down. Currently running on raw supply. Is there any problem of running PLC with Raw Supply ?

It will work but it is generally it is not a good idea as if you lose power to your plc you lose alarming and visibility of your process. I like to ensure my plc always has power so I know what is going.

Ideally all your devices should go to failsafe position on loss of signal but this is not always the case depending on your setup you may have motors that keep running or valves that stick open.

As long as you know the risk and don't let it linger it can get you through

That should not be a problem. Be sure that any PLC batteries are in good shape in case you lose ALL power, you don't want to lose programs.

a short time ago I was talking with somebody that they had a 24V power supply in a major system panel go out. The replacement was days away they needed to run. so they connected the 24VDC to a tow motor battery
It got them by until the new power supply was installed.

This is one of the reasons I make critical systems operate on DC wherever possible. Much easier to do redundancy with DC. I feed one DC supply from UPS and one from mains. If one is lost you have the other.

Just beware if you were using the UPS as a surge and line filter, you may have removed these protections too. So a separate surge and line filter may be a nice to have...