Transformer Valve Risky Replacement
Over the years MIDWEST has had to do some creative and sometimes risky work. These things typically occurred when there were very unusual or strange circumstances. And they were usually performed against our advice to customers that had no easy or inexpensive alternative. When we say risky, we are not talking about risk to life safety. This following example was a very simple task, unless something went wrong. We just needed to replace the lower main valve of a 2000 kva oil filled power transformer without draining the transformer first. The owner could de-energized the transformer for a short time, but could not tolerate an outage long enough to drain the oil, change the lower main valve, and replace the oil. They were willing to take on the risk of changing the value with the transformer full, and de-energized and grounded, of course. Actually, we have changed valves on smaller and larger power transformers, but the circumstances were always different. We knew in this case we would end up with possibly two gallons of messy waste oil, even if things went well. Our procedure was as follows. Loosen the existing lower valve from the 2000 kva power transformer lower valve stem. Prepare the replacement valve such that it could be immediately installed after the existing valve was removed. Secure the area. A large spill pan was placed under the existing transformer valve and stem. All the needed tools and the new replacement valve were placed inside a sturdy large clear plastic bag, including a pipe cap, just in case. A vacuum was pulled on the transformer. The plastic bag was secured about the pipe stem at the bottom of the old transformer. The bag was big enough to hold and manipulate the valves. Then, like two lab rats, one technician removed the old valve while a second technician held the new valve adjacent the existing valve. The old valve was removed and slide to the side just as the new valve was slide into place and screwing onto the pipe stem. Works well if you catch the threads on the first try. Either way, one ends up with a blast of old oil all over the inside of the bag. If the valve quick exchange fails, the cap is put on the stem. It is amazing what happens inside the clear plastic bag in the seconds it takes, hopefully, to change the valve. This task may sound like a good idea, but we do not recommend it. And we have a hundred years of experience working on old and new power transformers. We’re good at it and we like it. But we know old oil filled electrical power transformers are good at hiding defects until you try to work on them. Sometimes the messy work is the fun work on transformers.