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I'm the electrician for a club that builds an illuminated carnival parade float, and historically we've lit our float using around 10,000 x 40w incandesant lamps powered by a 800kVA 3 phase generator.

Times are changing, and you can no longer buy 40w incandesant lamps easily anymore, and the cost of diesel and generator hire is expensive, so I want to look at using LED lamps instead.

Due to cost, it's really only viable for me to buy very cheap LED B22 lamps from China, with a basic built-in power supply with a poor power factor.

Wiring up a purely resistive system was easy, but I'm struggling to understand and research how to do this correctly without causing a high current in the neutral.

To balance the system, I've heard that I need to either add a resistive dummy load to each phase, or use a power factor correction capacitor, but I don't know how to calculate the size/rating of these.

Can anyone point me in the right direction or explain how to do this?

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  • \$\begingroup\$ If you balance the number of LED lights on each phase, I would think that you wouldn't need anything else. Poor power factor in for LED lights would be due to harmonic distortion of the current waveform. Correcting that would require adding tuned filters rather than just capacitors. I will see if I can find specific information. \$\endgroup\$
    – user80875
    Nov 17, 2015 at 15:03
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    \$\begingroup\$ Look into a multipulse (auto)transformer. 18pulse +. This should minimise wastage due to useless harmonic current \$\endgroup\$
    – user16222
    Nov 19, 2015 at 23:32
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    \$\begingroup\$ Design your own string driver and make it 600VDC to make your job easy.Then run the string drivers which you will have heaps of 6 diodes connected in the standard 3 phase bridge .Now your harmonics will be tolerable,and if you needed perfection much easier to correct \$\endgroup\$
    – Autistic
    Nov 20, 2015 at 12:12

4 Answers 4

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I found a study that showed various brands of LED bulbs rated 3 to 8 watts with power factors ranging from .48 to .79. If you can find 8 watt LED bulbs with .5 power factor that give equivalent light as your 40 watt incandescents, you would need 16 VA per bulb vs 40 for the incandescents. If you distribute the bulbs equally among the phases, you should not have any difficulty with the neutral currents. You should still have some concern about extra heating in the generator due to harmonics. It is difficult to determine how much the generator should be oversized for harmonics. The generator manufacturer may have a recommendation.

A harmonic filter would both reduce the harmonics and increase the power factor. I don't believe that you should purchase a 3-phase choke and harmonic filter separately. You should be able to get the most effective filter if it is purchased as a package.

Estimating Harmonic Distortion

For estimation purposes, it can be assumed that the power factor of the fundamental current of an LED bulb is 1.0. It can also be assumed that the source voltage is not significantly distorted. Total power factor = Watts / (Voltage X Total RMS current). Total or “true” RMS current is the RMS value of the distorted current waveform. It calculated as the square root of the sum of the squares of the fundamental current plus each of the harmonic currents. You can break that down as Irms = (If^2 + Ih^2)^.5 where If is the fundamental current and Ih is the square root of the sum of the squares of the individual harmonics.

If the voltage, total RMS current and power is known for an LED bulb, the harmonic current and total harmonic current distortion can be calculated as follows:

Only the fundamental current (If) produces power (W). W = V X If X pf. Assuming pf for the fundamental = 1, If = W / V

From Irms = (If^2 + Ih^2)^.5, Ih = (Irms^2 – If^2)^.5

Total harmonic current distortion, THDi = (Ih^2 / If^2)^.5 = Ih / If

The total RMS current and power may be marked on the bulb. If it is not marked it can be measured with an inexpensive power meter like a Kill-A-Watt.

Here is a link to the study mentioned above.

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  • \$\begingroup\$ I think harmonics is certainly the issue here after reading up on it, although I think I'm a bit out of my depth in trying to mitigate the problem. So you are saying that the company I hire the generator from should be able to also supply me with a harmonic filter? \$\endgroup\$
    – BG100
    Nov 19, 2015 at 13:04
  • \$\begingroup\$ If you explain to them that led and cfl lighting as well as every kind of electronic device down to the smallest adapter and charger that anyone might plug in may add up to pose a risk to the equipment, they should at least find out from the manufacturer how much the generator needs to be oversized to avoid overheating. They may also be willing to purchase harmonic filters and offer them for hire along with the generators. \$\endgroup\$
    – user80875
    Nov 19, 2015 at 15:04
  • \$\begingroup\$ If you work as an electrician full-time, you might want to consider educating yourself to a greater extent in this area. You could also find local suppliers that can supply harmonic filters and offer assistance. There may also be local consulting engineers that perform harmonic analysis and recommend mitigation equipment. This has been an issue for a long time with variable speed electronic motor controls used in industries and for HVAC in large buildings. \$\endgroup\$
    – user80875
    Nov 19, 2015 at 15:16
  • \$\begingroup\$ I'm not a full time electrician... I do this as a hobby in my spare time with limited funds. Anything that would cost a lot would not be viable. \$\endgroup\$
    – BG100
    Nov 19, 2015 at 16:32
  • \$\begingroup\$ You should be able to save money with LED lighting, a smaller generator and a filter. If the generator supplier won't supply the filter, contact industrial electrical suppliers and see if you can get some assistance. \$\endgroup\$
    – user80875
    Nov 19, 2015 at 16:59
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A LED itself is resitance load, while the problem is the rectifier and step down circuit. The cheapest LED lamps use a series capacitor that uses its reactance to increase overall impedance, which means that such lamp will have a cap. phase lag not the inductive as motors or lamps with ballasts.

http://www.ebay.com/gds/LED-Lamps-using-5050-LED-chips-/10000000177064387/g.html

Or the LED lamp can have a small SMPS inside with a transformer, in this situation you will get more a harmonic distortion rather than phase lagging. You should buy one of these first, then see with power meter.

Lastly, LED lamps consume less power than incandescent lamps, so you will have extra current reserve for feeding also the reactive power.
IMO you don't need nothing at all, perhaps a choke or sinusfilter.

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  • \$\begingroup\$ Thanks, these are interesting points... but I do want to reduce the size of the generator also to save money. This has been attempted before and resulted in a very costly burnt out alternator in the generator, which I want to avoid! \$\endgroup\$
    – BG100
    Nov 17, 2015 at 15:44
  • \$\begingroup\$ Also, thanks for the link... I'll use the info here to check the safety of a sample of the lamps before I order a load of them. \$\endgroup\$
    – BG100
    Nov 17, 2015 at 15:49
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    \$\begingroup\$ The presence of HF harmonics lead to additional power looses in iron and increment the equivalent resistance in copper due to skin effect. This was the reason why Nikola Tesla burned the first generator plant at Niagara using his HF transmitter, he learned that series chokes prevent HF from sinking into the generator. Therefore I suggest you, no matter what to install a three phase choke and then optionaly one another LC circuit for sinus filter (see a harmonic filter), that needs to be tuned to your specific need. \$\endgroup\$
    – Marko Buršič
    Nov 17, 2015 at 16:12
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We are having the same issues with the harmonics. I calculated total load of 170 kva last year at the start of the year, we had 17,000 lamps on board we pulled 110 kva total on circuit. it wasn't pushing the generator at all as we had a 250kva set.

The only way I managed to improve power factor was by using motors and variable load heater which I ran constantly and I left it on when I started the set every time. I based the 3w led at 0.4 pf. The set readings came out 0.85pf. We found as led are linear loads as well as flourescents, we need non linear loads such as heaters and motors to balance this. But also balancing the phase current as best possible helps. We also used par cans to balance the phases as they only produce resistive loads this way you can protect the generator.

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You could make it a 1000 bulb, 24 volt DC system, using 4ea 6vdc golf cart batteries wired in series. This would feed 10 branch circuits of 16.7amps with 20amp circuit breakers. Each branch circuit would power 100ea 4watt 500lumen 24vdc LED bulbs, for a total load of 24vdc, 167 amps, 4kW, and a run time of 1 hour.

Make 10ea of these circuits for 10,000 bulbs total. No noisy, smelly generator required. No power factor correction. Just 40kW smooth DC providing the LED equivalent light of 10,000 40watt incandescent bulbs.

Here is one such bulb:

4 watt LED globe bulb

Example product and original source for bulb image above:

4W E26/E27 LED Globe Bulbs G60 27 SMD 5730 500lm Warm White 3000～3500K DC 12 AC 12 AC 24 DC 24V 1pc

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