Harmonic Distortion
Harmonic Distortion
(OP)
I am a facilityt engineer in Newtown, Pa. After moving into our NEW building, many 277v, T8 electronic ballasts were found to be bad, about 15 out of 300. Since September, about 20 more have gone bad. It's a commercial office building, 30,000 sq. ft., with about 50 computers. There is a separate server room on a K-rated transformer. There are 2 TVSS surge suppressors installed, one on the feed to the server room and one at the MDP. Several personal UPS devices have failed or malfunctioned. I had a survey of the Main Distribution Panel conducted, but it only found about 2% THD, and about 25% current distortion, the only construction issue was bonding in the service entrance to MDP. We also have 4 air handling units each with it's own VFD, 2-10 hp and 2-15 hp motors. They are experiencing about 110% harmonic current, most 5th and 7th. Wondering what to do next?
Dan
Dan





RE: Harmonic Distortion
Attach a Dranitz voltage/current/power/THD recording
device at each power panel, and make a recording of what
is happening.
My hunch is the lighting ballasts are bad due to infant
mortality (poor quality). If there is any problems caused
by harmonics, the source of damaging harmonics is most likely caused by the VFD's. The UPS's may either be bad due to infant mortality, or poor quality. We have
had defective out-of-the-box equipment many times.
It's too early to tell w/o the Dranitz readout.
You may have a periodic, slow rise overvoltage from your utility....the Dranitz will uncover this as well, and can
be used as evidence for corrective action (the utility will
install or adjust voltage regulating equipment).
RE: Harmonic Distortion
Good Luck.
RE: Harmonic Distortion
RE: Harmonic Distortion
You might check the voltage on each phase of the 480/277V system. If possible, leave a meter connected to check min/max readings. High voltage could be a factor. Also, make sure you have 277V ballasts.
The ballast manufacturer should be asked to explain the failure mode. I agree that you could just have a bad batch of ballasts. There is a lot of price competition on these and sometimes QC can suffer.
I'd be surprised if your harmonic distortion is the cause of the failure, but keep in mind that these electronic ballasts create plenty of harmonics all by themselves.
RE: Harmonic Distortion