Street light power consumption question. 1

[Rob1984]

Hi guys,

Case: just an ordinary street light, 400w HPS bulb.

What will be total consumption?

Is this right true?

Lamp 400w
Electrical disribution(rectifier) 100w
Comprehensive Cable Loss 6%, 400x6%= 24w
Transformer loss 3%, 400x3%=12w
Reactive Power Compensation, power factor 0.85

Total: (400+100+24+12)/0.85 = 630W

Please point out where do you disagree, any comments welcome.

 

[gobblerhuntr]

I think our street lights are figured on 165 kWH per month and I believe that is figured on about a 10 hour average night.

 

[dpc]

A 400 W lamp will draw something over 400 W due to ballast losses. You can get this info by looking at ballast specifications.

The power factor relates to the phase angle between the current and voltage, so you do not divide all the power losses by the power factor. The power factor will cause somewhat higher current that results in some additional resistance losses in the wiring to the light. But nothing close to what your calculation implies. Lower power factor means higher kVA, not higher kW.

I'm not sure what recifier losses are, unless you are referring to the ballast at the lamp. Cable losses look on the high side.

 

[Rob1984]

DPC,

Can you please write all the calculations, what and how much will be consumed. This calculation was done by company who is offering some products to me, I just want to check if they are telling truth.

Thanks,
Rob

 

[dpc]

Maybe someone else has time to do that, but I really don't.

If someone gave you that equation, they definitely have no idea what they are talking about, or are deliberately misleading you.

 

[Skogsgurra]

One of those "technical reps" probably, where "technical" is no more than a word on his businees card.

I may have missed a point, but is there a rectifier in the distribution? Where? And how in the world can it have a 100 W power loss? If that is the case, it must be a common rectifier for several lamps. You shall not add that loss to each and every lamp.

Just ignore this guy. And, above all, do not divide with PF to get total power!



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[dpc]

I think they must have been talking about the lamp ballast which is not really a rectifier.

 

[Skogsgurra]

I think so too. And then, 100 W loss is way off the mark.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DonPhillips]

I read somewhere that a 400W MH lamp is a nominal wattage and the lamps actually draw more like 440 to 480W. I had to look that up to issue an adjudication order for a space proposed to be lighted with 8-400W MH luminaires (it was only like 1600 sf) and did not comply with 2006 IECC or 2004 90.1.

Don Phillips

http://worthingtonengineering.com

 

[dpc]

Don,

I think that is what I said already. There are losses in the ballasts, so the power draw will be somewhat greater than 400W.

 

[DonPhillips]

I did not know if there were large differences between high pressure sodium systems and metal halide systems. I was giving the OP my experience based on MH. His number for ballast loses was around 12W and I was finding some MH manufacturers had losses from 10% to 20% for indoor use, and, of course, differed based on the cost of the luminaire.

Don Phillips

http://worthingtonengineering.com