Cooling Tower Fan Motor Problems

200x4???? are you sure?? your FLA should be over 500A@200v

The sub feeds a total of 5 200hp fan motors @ 33A each & 2 larger pump motors that run at about 220A each.

You may be lacking a wild leg or improperly positioned...check each leg to ground, and do the same on one of the other towers that is working...

You think that in one of the sub panels that I may have a wild leg that is improperly positioned?

Dunno. Anonymous Poster #1 may have, though.

....or it may be required and somehow not present....

AS you stated this has been happening for the last 15 plus years... has anyone checked the power quality??

Do you have anti-windmill devices, are they working?

Do you have soft starters or DOL/ATL starters for the motors?

I recently completed a project for a smaller cooling tower arrangement, new installation of Variable speed drives with generative capability so when off the motors generated power back to the gird, and as with all VSD's these drives soft started the fans. No trips on start-up!

I asked that question about power quality first & was told yes. There are no anti windmill devices or soft starts. When first presented with the issue I first wanted to go with VFD's. I'm still looking into that. I still question why I would trip another fan when I try to start another. They have said that they've played musical chairs stopping one fan before starting another with no pattern or order working.

Why in the world did they put up with this for so many years?

My first guess would something in the original wiring of the controls. This could be checked if the 2400 volt starters have a test position that could allow the controls to be operated without operating the motors. If that is not possible the motor leads could be pulled but that is time consuming but may be the only way to limit the actions to control power only unless you could supply control power to the units with the 2400 volt not energized. While most starters have an internal transformer for control power, many have a switch that can be placed in a test position to apply control power externally. If you can tell me what brand you have and whether they are normal contacts or vacuum bottles I might remember the options.

The next possibility would be the the fan was already rotating in reverse when the start is tried. You had mentioned that they did not have an anti-windmill option. Is there anyway to visually observe that? If that is the case a soft start or properly applied VFD would solve the problem. One selling point to your management is that the VFD might pay for itself in the long run, through power savings.

What trips? The starter or the transformer feed? Your numbers indicate the transformer should not trip and you didn't indicate it, but a poorly set relay could be the culprit. CT's not wired properly could also trip due to a false ground or false differential signal. The difference in current when the increase is seen trigger a relay. At the end probability is that a current transformer is failing as the current increases. There are tests for that, but it involves removal of the CT and using it as a voltage step down transformer by putting a few turns through it. You have to have the accuracy class of the CT to evaluate the results. I have seen this a couple times, but it is rare.

I have seen some really strange things around cooling towers, but the strangest I ever saw was a large LV casino where the prevailing winds did more cooling than the fans such that the cooling effect went down when the fans were activated, plus they tripped. This was found to be due to the shape and location of the cooling tower and buildings. The starters were replaced with 4 quadrant drives and damage to the cooling towers was limited, plus much of the time, the power flowed back towards the utility. Wind Power!!! It was however, microscopic compared to the total power consumed.

Sorry that it's been a while since I've updated. Other issues have been pressing. The starter has an internal current transformer for 115V power. There is a test position. It has normal contacts. I'm not sure what the brand is. When I can open a panel I will let you know.

I've had people verify that the fan was not rotating in reverse. I would like the VFDs & Soft Starts but I feel I may lose on the argument initially due to the other towers working fine. I may be able to make a future case for power savings alone but not for one tower at this time.

As for what trips, that is what I'm trying to find out. Ive been told that the 115V to the local start/stops near the motors are run in one conduit inside the tower but the others towers are run the same way. I don't know why it was run inside instead of external, probably to not have to reroute during construction or new installations in the area.

Sounds similar to reflective current problems we used to see when running motors at variable speeds, not enough reflective current would allow the motor to overdraw incoming current. Make sure your motors are actually turning at rated speeds.