Transfer Switch Heat Imbalance - 3rd time 1

[gokulkrish2]

Hello All,

Please see the attached photo of a transfer switch which is used in a portable conveyor system. This switch is used to supply power either from a 13.8KV/480 V transformer or a 480V Generator.

The problem we have been having with this transfer switch is that it shows high temperature at its connections and high imbalance of heat ratios. The difference in the heat measured is almost 130degF.

The very first time this problem happened we thought this was just a connection issue. We retighten the bolts and the issue seem to go away. Then when we had this problem happen again, we investigated further and saw some stress/slight melt marks on the leads and hence ended up changing all the leads to the Transfer switch and the switch itself.

Now this is the 3rd time this has happent again and we now doubt the whole design. We doubt the transfer switch and or the manufacturer. Do any of one this in forum have any experience with this kind of application. Do anyone of you guys see some stuff what we are missing. What are we doing wrong here.

Any suggestions and inputs are welcomed. Appreciate all you time.

 

[wayne440]

Have you measured the current at any point? The first thing that enters my mind when 1 lead is much cooler than the other 2 is single phasing.

 

[rcw retired EE]

As Wayne said, check the current balance between phases.

Also look at the cable terminations. B&C wires seem to be bent in a tighter radius directly at the terminal. Could that stress be pulling the individual strands loose?

The cables appear to be the extra flexible cables (Type DLO?) with many small strands. This type of cable is notorious for creating loose connections when not properly terminated. Are the lugs on the switch listed for use with the cable type?

The heat appears to be coming from the cables or terminations and not the switch so it is either unbalance currents or loose connections or both.

 

[waross]

Try measuring voltage drops. Measure the voltage drop across each pole of the transfer switch. Measure the voltage drop from the connection pad on the ATS to the crimp on terminal on the cable. Measure the voltage drop from the crimp on terminal to the cable about one inch from the crimp on terminal. Measure the voltage drops from end to end of each cable. For this measurement the crimp on terminals at each end will be a good measuring point. If the other end does not have crimp on terminals then measure to the cable surface,
Also measure the current. High current is a candidate.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gokulkrish2]

Thanks for all your inputs. I will post more information once i get some voltage drop readings and current balance readings. Thanks.

gokul