A-Phase Problems

bigger picture please

Not sure what you mean...

These are part of a central plant. Boilers/chillers/towers

In my experience, and by common sense, you have a loose connection on phase A of each fan terminals, if it was an overload in the motors, or VFD's supplying more current, you would have a burnt motor by now; but you surely will if you don't correct the connections.

We checked the connections. They were not loose.

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Are you suggesting it is the motors themselves?

Maybe you got a bad batch of terminal strips/contactors? An IR scan should be real useful here.

Even though the connection on the A phase did not appear to be loose, it still could have been originally. After overheating several times, the connection has corrosion in place of a good contact. I have taken wires off lugs like you have to find this to be the case. Not a guarantee but possible.

vibration too

Of course vibration too ! that one alone is the reason of periodic re-tightening of terminals in load centers and such devices.

If you've ever felt (unwilingly) the 60Hz of a household current running thru your muscles, well, imagine those poor wires that carry it day and night.

Wow! Thank you gentlemen. I know that the field techs replaced the damaged sections of cable (otherwise we would not be running the towers). They did not replace the terminal strips however.

We did some amp measurements this morning:

1st motor:

Phase, Low speed, High Speed

A, 17.4, 60

B, 16.8, 57

C, 17.0, 57

2nd motor:

Phase, Low speed, High Speed

A, 17.5, 62

B, 17.1, 60

C, 17.2, 61

Slightly higher on A, across the board.

62 amperes of current! It does not look to me like you have 6 AWG wire in this box. My guess on the cabling I see in the picture is that this is at best 10 AWG wire. I'm also assuming that this is the ubiquitous THHN wire.

Thanks. I will look into this when I can get the bucket open. I should note that these have been in place ~10 years.

Dear Mr. jlfiegel,

I want to supplement ( in continuation to your Reply to No.2 by Mr.Yahlasit) You may feel the connections were in tact and no looseness observed. If the Strip is already got damaged in course of use, then over heating will occur, and get further damage. This is to be corrected before it dies, and cause break-down.

Pl. check up the strip condition and whether it is correctly sized. If it is not correctly sized, get it replaced with a correct size and use.

Pl. post the information what was the cause of the problem.?

DHAYANANDHAN.S

Yes. This appears to be heat damage caused by a loose connection.

This can be prevented by adapting and enforcing a regular PM program wherein all electrical connections including the switchgear buss connections are checked and adjusted to the proper torque value.

The PM results should be recorded by date to identify repetitive issues.

Hi everyone

First, let me say Thank You for the many responses. Our client is requesting a followup on this, and I am preparing a report.

It will be difficult to determine the exact cause at this point. The towers are critical to operation so the techs on duty called in a electric shop and had the problem resolved posthaste.

The 2 towers are 701 and 702. I located the old parts and took some better pictures posted here:

http://postimg.org/gallery/q4bmp5o/

http://postimg.org/gallery/drg2cbg/

If these lead to any additional insight, please let me know.

It was also brought to my attention that we have had 2 other failures of equipment for similar reasons, over the last year or so. Maybe coincidence...? One was also an A-phase issue so there's concern that the problem may be something bigger.

Based on what I'm reading, I'm thinking the problem is one of poor connection. I'll need to work on some sort of plan for regular tightening of lugs.

Best

John

Yes, you clearly have experienced a bad connection at the terminal block of your power breaker. Both power breakers show arc damage at the connection point. You can even see a melted conductor bead in the upper right picture of 701.

You should notice the other two wires on this end of the two breakers follow a curved path into the breaker. I still suspect that a part of the problem is a lack of a service loop for this wire from the tie wrap to this breaker. I assume that this chassis is not in a temperature controlled environment. This wire may shorten just enough to pull out of this connection by a small amount every cool down cycle. Add in the mechanical vibrations from operation and the taught wire slowly gets pulled out of the connection point. This is plausible but not what I think is the root of the problem of having this wire entering the connection in a straight path. Without a service loop on this wire, a pull on this wire to test the connection can easily provide a false result.