basic question about HID lamps and power issues

[danny burstein]

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.

 

[Eeyore]

Power Factor correction
capacitors can help absorb some of the harmonics.

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

 

[Eeyore]

This makes them all in phase with each other and looks like
it is in the neutral because of measurement techniques as discussed
above.

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

Graham

 

[danny burstein]

i[ regarding a garage wit about 35 kw of HP Sodium demand ]

No, they won't laugh but there isn't an issue here. That kind of
service is demand metered and if an electronic meter is involved, also
power factor metered. If it's a mechanical meter then most likely the
utility either measured the power factor or was involved in approving
the building's electrical design. Utilities charge a penalty for low
PF. Harmonic energy shows up as out of phase current and registers as
low PF. If there was a significant problem it would show up on your
power bill.

Given that the fixtures were installed over ten years ago,
and were probably lowest bidder.... I'd guess they'd probably
be lower PF than today's stuff.

Unfortunately, while I could physically do a bit of
checking myself, the facility would frown on my clipping
apart wires. (I'm going to try to get a look at the
bill and see what the demand and the kw-hr numbers
are... since I can visually count the fixtures and
calculate what the numbers should be, I'd be able to
at leasst catch a gross difference).

So... is there any downside to politely asking the
utility to take a look?

Thanks again for your help.

 

[[email protected]]

Power Factor correction capacitors can help absorb some of the harmonics.

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

Nick

 

[[email protected]]

The R in these series RLC circuits broadens the notch and uses real

Man, you're pushing my math skills here. I used to gobble this stuff
for breakfast nut now I'm not even sure I could do it with a Geritol
injection...LOL

In general, the power factor is the real power (add up the IV products
for a number of samples) divided by the rms of the sample voltages and
the rms of the sample currents.

10 SCREEN 9:KEY OFFI=4*ATN(1)
20 VPEAK=120*SQR(2)'peak voltage
30 R=100'load impedance (ohms)
40 IPEAK3=.1*VPEAK/R'peak 3rd harmonic ripple current
50 TCYC=1/60'cycle time (s)
60 NSAMP=60'samples per cycle
70 DT=TCYC/NSAMP'time step (s)
80 FOR N=0 TO NSAMP-1
90 T=N*DT'time into cycle
100 V=VPEAK*SIN(2*PI*T/TCYC)'applied voltage
110 I=V/R'current (amps)
120 I3=IPEAK3*SIN(3*2*PI*T/TCYC)'ripple current
130 I=I+I3'add ripple current
140 E=E+V*I*DT'energy (joules)
150 VS=VS+V^2'sum of squared voltages
160 IS=IS+I^2'sum of squared currents
170 NEXT N
180 REALPOW=E/TCYC'real power (watts)
190 VRMS=SQR(VS/NSAMP)'root mean square voltage
200 IRMS=SQR(IS/NSAMP)'root mean square current
210 PF=REALPOW/(VRMS*IRMS)'power factor
220 PRINT REALPOW,VRMS,IRMS,PF

Watts RMS volts RMS amps PF

144 120 1.2 1 with no ripple current
144 120 1.205985 .9950372 with 10% ripple current

But if I'm doing this right, a 10% 3rd harmonic ripple current makes little
difference in the power factor, and my EE prof friend says these harmonics
tend to cancel out in a building...

Nick

 

[[email protected]]

... R in these series RLC circuits broadens the notch and uses real
In general, the power factor is the real power (add up the IV products
for a number of samples) divided by the rms of the sample voltages and
the rms of the sample currents.

10 PI=4*ATN(1)
20 VPEAK=120*SQR(2)'peak voltage
30 R=100'load impedance (ohms)
40 IPEAK3=.1*VPEAK/R'peak 3rd harmonic ripple current
50 TCYC=1/60'cycle time (s)
60 NSAMP=60'samples per cycle
70 DT=TCYC/NSAMP'time step (s)
80 FOR N=0 TO NSAMP-1
90 T=N*DT'time into cycle
100 V=VPEAK*SIN(2*PI*T/TCYC)'applied voltage
110 I=V/R'current (amps)
120 'I3=IPEAK3*SIN(3*2*PI*T/TCYC)'ripple current
130 'I=I+I3'add ripple current
140 'I=SQR(2)*VPEAK*SIN(2*PI*T/TCYC+PI/4)/R'current with phase delay
150 IF ABS(I)<1.6 THEN I=0 ELSE I=3.7176*SGN(I)'use only full-wave peaks
160 E=E+V*I*DT'energy (joules)
170 VS=VS+V^2'sum of squared voltages
180 IS=IS+I^2'sum of squared currents
190 NEXT N
200 REALPOW=E/TCYC'real power (watts)
210 VRMS=SQR(VS/NSAMP)'root mean square voltage
220 IRMS=SQR(IS/NSAMP)'root mean square current
230 PF=REALPOW/(VRMS*IRMS)'power factor
240 PRINT REALPOW,VRMS,IRMS,PF

Watts RMS volts RMS amps PF

144 120 1.2 1 with no ripple current
144 120 1.205985 .9950372 with 10% 3rd harmonic
144 120 1.697056 .7071067 with a phase delay
144 120 1.795772 .6682429 only peaks

But if I'm doing this right, a 10% 3rd harmonic ripple current makes little
difference in the power factor, and my EE prof friend says multiple sources
of 3rd harmonics tend to cancel each other out in a building. Rewiring might
help with that.

He also questions whether a YMCA can have a low power factor, especially if
they also have voltage surges, and suggests the utility may be mismeasuring,
having uncovered this in the past. When he checked a warehouse with his own
power line monitor, it showed a unity power factor, which PECO later verified,
before refunding tariff penalties paid.

Nick