Humming Noise

[patweldon]

I would like to know if
you or your members might be able to help me one more time.
I am the Manager of a large Data Center electrical infrastructure, we
are in the process of installing a new UPS system. As a temporary feed
to the data center we are using a Cutler- Hammer 800A molded case switch
in a motor control center configuration. Since we cut over to this
switch I have noticed a vibration and hum very similar to a 60 cycle
transformer, coming from this switch and enclosure. We have contacted
the vendor and have taken infrared pictures and vibration analysis, to
no avail. The load is evenly balanced across all three phases at about
300 amps. We have current harmonics averaging 20% and voltage harmonics
averaging 6% across the phases. I wondered if you or any of your readers
have ever experienced this.

 

[wanderer20001us]

Re: Humming Noise

The breakers usually hum when they don't know the words....

There could be multiple causes for the noise. If the breakers use solid state trips, the CT's internal to the breaker could be loose. There could be dozens of parts that could be loose. Was the breaker tested per NETA acceptance testing standards before energized. This testing can find most problems before things go on-line.

Does the breaker have an undervoltage coil? These will cause noise occassionally.

You are probably going to have to shut it down to find and correct the problem.

 

[brian john]

Re: Humming Noise

Have you isolated the hum to the CB? It may well be the enclosure or CB mounts vibrating...Or as mentioned was this CB tested. Some CB's will vibrate/hum as they approach the long time pick-up trip point.

What is the current draw per phase?

 

[catchtwentytwo]

Re: Humming Noise

We had a buzzing noise on an I-Line Breaker(also in a major Data Center). In our case, Square D determined that it was related to the internal solid state electronics of the breaker. What Cutler-Hammer model do you have and does it have any internal electronic circuitry such as a trip unit?