A particular area of the plant has a high rate of motor failure. The repair techs have noted problems such as burned windings or the grease baked into a fairly hard cake. The plant engineer says heat is the common denominator in most of these motor failures. He wants you to determine the root cause and identify a means to monitor and prevent it in the future.
He said he suspected voltage imbalance, and sent the electrical drawings to an engineering firm; this outside firm confirmed the loads are correctly balanced.
Where do you start?
The plant engineer correctly looked at a prime suspect. But how things look on the drawings and how they look after years of service can differ greatly.
Here’s an important question to ask. Are the drawings even current?
If the loads are correctly distributed, you could still have voltage imbalance. Check several branch circuits to see what you have. If voltage imbalance is present, you need to find the “phantom loads.”
Perhaps you have insulation failure or perhaps you have high-resistance connections. Look through the relevant maintenance procedures; if any call for tightening connections, you probably have bad connections. Check connections with an AC resistance meter or use thermography to see which ones are hot.
