Low Voltage Transformer Preventative Maintenance

[Samuraii]

Hi Guys,

Quick question for everyone, Ive got a very dusty under 1000v transformer in my plant that I am looking to clean. Is there any other safety measures that need to be taken other then locking out the upstream breaker? I was told by an engineer (mabye just to be cautious) to turn off all downstream breakers in the panel to avoid any backfeeding. He also mentioned using protective grounds on the X0 just to ensure if there was a groundfault it could not get backfed either. Thoughts?

 

[Dennis Alwon]

I believe once the breaker to the transformer is turned off there shouldn't be any question about back feed.

 

[kwired]

If there is any sort of parallel power production equipment on the load side then I suppose the risk of backfeed is much higher.

Otherwise standby sytsems that are properly installed should not backfeed, nor should interactive inverters for PV or other sources as those tend to need to sense utility power before they will put out any power to the utility side, but might not be bad idea to isolate them anyway in case of malfunction.

 

[David Castor]

Obviously, lockout or tagout, and verify no voltage. The need for shorts and grounds is site and application specific. For a small dry-type transformer like this, it's often not done. It's also pretty easy to open the secondary side main or feeder breakers. On the other hand, it wouldn't take long to install temporary grounding if there is any concern at all. I have experienced the thrill of having an on-site contractor cut a padlock off a breaker so he could close it. Fortunately, no one was injured.

Accidental backfeed of a transformer secondary has caused incidents in the past, especially control power and potential transformers.

 

[garbo]

After securing power ( LOTTO ) I would blow off dust with low air pressure first then run my fingers to feel if anything is stuck ( glued like ) onto varnish of transformer windings. If nothing is stuck you can use higher air pressure using an OSHA approved air gun that only delivers believe a maximum of 15# air pressure even if you have air hose connected to a 125# air suppply. If something is stuck to a winding and you remove it often pulls the varnish off producing a bare spot that could cause problems. I always used 1,000 volts megger to check 480 volt transformer windings.I also like to turn off the breaker if safety switch on the secondary side to take resistance readings between each winding.