Power Transformers Blog – Expert Safety and Usage Info

MIDWEST performed an Infrared Scan of the electrical system for a new customer.  They had two old outdoor oil filled transformers with load tap changers that had not been used in some time.  So when we scanned these old transformers, we made certain we scanned the load tap changer compartments.  Each tap changer was dangerously over heating. The electrician with us wondered why, since they hadn’t operated the tap changers in 20 years.  But tap changer contacts can cause coking, especially if they are not operated.  Later, during a scheduled maintenance outage, MIDWEST found both load tap changer compartments completely coked, full of black sludge.  The sludge had to be removed by hand, like scooping out sticky black mud.  Since they would never use the transformer tap changers again, MIDWEST removed the entire interior operating mechanisms and bussed the terminals. The old transformers were very lucky the tap changers didn’t fault. If they had, it would not have been cost effective to repair them.  It was just a matter of time before a catastrophic fault in a tap changer would have cost them a transformer.  We have seen this problem before in old transformers.  In this case, certain failure was avoided, and they reused the transformer after the repair. Infrared Scanning is very important, even on old, obsolete transformers and switchgear. 

Customers can be skeptical of purchasing a transformer used compared to buying a new one.  It is understandable since a transformer is an electrical device, there is always the possibility that the unit is on its last legs and could fail and then the buyer is faced with the costly disposal of a cumbersome item that has little or no value.  But look at the cost savings if you can find a quality unit on the secondary market that will do the job compared to a new one priced at full retail or wholesale from a supply house.  There are many ways to obtain a transformer that is not ‘new’.  The secondary market can include demolition companies, scrap yards, friends, closeouts, new surplus, scratched and dented etc.  You can also find reconditioned units that have been tested and carry a warranty that is usually as long as the one offered when the unit was new.  Shopping for a transformer requires some homework to know every last detail of the transformer you want so when you stumble on a ‘non-new’ transformer, the lead time is immediate and you can snatch it up before somebody else does.  In the event you can’t find a bargain, you can always hope someone has a new one in stock.