basic question about HID lamps and power issues

 
I've seen lots of discussion about the
harmonics and other issues from HID lamps (or
more properly, tehir power supplies).

When I was working at an ISP I noticed some very
headachey readings when looking at the supply
and neutrals for the racks, but we were well
below the current ratings so left things as is.

Anyway... I know just enough about this to realize
I don't know enough, so I figured I'd better ask
a couple of questions even if they sound foolish.

In my residential building complex we've got
about 1,000 apartments, and I doubt there's
enough usage of CFLs or HIDs or switching power
supplies to be a major issue.

However, we have a standalone muliti-story garage, which is
illuminated 24 hrs/day by about 35 kw of high pressure
sodium luminaires (with another 5 kw or so at night) getting
fed via 3 phase AC. There's perhaps one or two addiotional
kw of demand for some office equipment and (fluorescent)
lighting. And a short occassional kw when opening/closing
the garage doors.

This building is separately metered.

If I ask the utilty if the wave forms are screwing
up the meter readings, would they laugh me out
of the room? Is there any valid issue here?

Thanks.
 
--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

  No, they wouldn't but unless they are a rather large utility they
probably won't have harmonic analysis equipment.

Do you fear some weird electrical stuff going on with third harmonics?

Some background information. Third harmonics will pass through three
pahse transformers and end up on all phases excatly the same. Some say
they exist in the neutral but only if you measure using the neutral,
as a reference to a phase conductor. This appears as being in the
neutral by measurement. To prove this further, if you measure a
voltage between phases and do not involved the neutral they usually do
not appear as they are common mode. The clue in this is to connect
critical loads phase to phase if possible. Power Factor correction
capacitors can help absorb some of the harmonics.

In a three phase system there are three waveform starts per cycle.
Assume the first at 0 degrees, the second a 120 degrees and the third
at 240 degree (equi-distance). Consider each phase to have third
harmonics starting at the same time (0,120,240) as their respective
cycle crosses zero. The next third harmonic waveform will now cross
zero at exactly the same time as the other two phase (fundamental)
voltages. This makes them all in phase with each other and looks like
it is in the neutral because of measurement techniques as discussed
above.

 

Solar Flare wrote:


It can also give them problems with overheating due to the high current in a cap
at 150/180 Hz instead of the intended 50/60.

Graahm

 

Solar Flare wrote:


It's not a phantom, it does really exist as can be seen with a clamp meter on
the neutral.

Graham

 

How does that work? I thought they could only reduce IV phase angles.

Nick