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basic question about HID lamps and power issues

Discussion in 'Home Power and Microgeneration' started by danny burstein, Jan 15, 2007.

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  1. 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.
     
  2. Eeyore

    Eeyore Guest

    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
     
  3. Eeyore

    Eeyore Guest

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

    Graham
     
  4. i[ regarding a garage wit about 35 kw of HP Sodium demand ]
    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.
     
  5. Guest

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

    Nick
     
  6. Guest

    The 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 SCREEN 9:KEY OFF: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 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
     
  7. Guest

    ... 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
     
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