Load Calculations for 400v single phase floodlighting

The total load must be 76.428 Kw, or say 76.5 Kw if avoiding excessive precision.

As the total load is said to be balanced we have 25.5 Kw per phase.

The load in KVA will be greater than the Kw loading due to imperfect power factor.


Presuming perfect power factor, the line current is about 110 amps per phase.  Allowing for a moderately imperfect power factor will increase the line current to about 125 amps per phase.


For a practical installation I would design for at least 160 amps per phase in order to allow for

power factor a little worse than stated.

Power factor getting worse as time passes and the PFC capacitors age.

Manufacturing tolerances of lamps and ballasts.

Variations in actual supply voltage.

I have to ask why not LED lighting? Do you already have the fittings? LED is much easier on the clients pocket, good for the polar bars and smaller CSA cables. I had an initial involvement for a conversion from discharge lighting to LED to give 1500 lux at night on a well known North London football club's pitch. Philips did the lighting design. 


I would check the data sheets for you discharge lighting to verify the actual PF and harmonics.

Hi Broadgage


Thanks for your response, believe it or not but your calc's below are exactly where I started out on my first assessment, total all of the 2 phase loads then treat the sum as one 3 phase load then divide back by number of fittings per phase to get the current draw for each fitting; using the power factor allowances in calc's below give us 125/12 = 10.4A per luminaire (and maybe my issue was overthinking the problem), but, apart from less volt drop, I couldn't see the advantage in the common use of 400v luminaires for stadium lighting as the current draw on a 230v luminaire with the same power rating (assuming the same Pf) would be almost identical...(2123/(230*0.9))=10.25A. This is what got me thinking the power rating for the 400v luminaires should be treated as single phase to calculate the current, then work back from the line current to calculate the total 3-phase power....I stand corrected! Thanks for your help. I'd be interested in your thoughts on pro's/cons of 400v versus 230v luminaires in this scenario, I always thought there would be a reduced current draw with the higher voltage fittings?

John,

do they serve alcohol in those polar bars? and is that North London football club one that is always losing? ?

Thanks for your response John


This project has been on the go for over a year now while the club is raising funds to get started and I'm trying to get the client to push to LED fittings but when we last budget costed it around a year ago the capital outlay for the LED equivalent was cost prohibitive. I will give an LED option again this time around as the area to be lit has reduced a bit from previous proposals but their other concern is the effect on foundation size (read cost) as the wind loading on LED fittings would be greater. Is there any other maintenance requirements for LED apart from lens cleaning? I gather the drivers for the LED are enclosed in the fittings, if so that's another big advantage over separate kiosks required for HID control gear? While I'm here...do you know if there is a maximum recommended distance from the control gear for 2000w metal halide lamp to the fitting (which has an integral ignitor)? and does this flexible cable need to be taken into account for volt drop? Looking at putting some of the kiosks about 25m away from the base of 18m poles here.

400 volt lights have two advantages if compared to 230 volt fittings.

Firstly for high wattage lamps, they are simpler and cheaper to manufacture as large discharge lamps tend to have an arc voltage too high for operation via a series choke from 230 volt circuits.

Secondly, 400 volt lights may be connected between phase and neutral on a 4 wire 400/690 volt system, use of this higher voltage system considerably reduces voltage drop and cable sizes.


For operation from a UK standard 230/400 volt system, the advantages are confined to lower price/better availability of the light fittings, and a slightly greater efficiency since a 400 volt 2000 watt discharge lamp will have a slightly greater output than a 230 volt 2000 watt lamp of similar design.


If the total loading is known to be say 76.5 Kw, balanced between 3 phases, of a 230/400 volt system then the line current has GOT to be the same* no matter if the fittings are 230 volt or 400 volt. "you can not miniaturise the watt"


*There may be minor differences if the efficiency or power factor varies, or due to manufacturing tolerances, or rounding of figures in calculation.

Thanks Broadgage - every day's a school day!

Yes, there are limits on cable length between lamp and ballast, but these are generous for lamps with internal ignitors. Details from the manufacturers of the equipment.

Yes voltage drop between lamp and control gear needs to be allowed for. Note this current will be greater than the external circuit current since it will have a poor power factor. The power factor capacitors will be near the ballasts, and the current between lamp and ballast thereby not corrected.


Voltage drop can sometimes be compensated for by selecting a tapping on the ballast that is lower than the actual voltage at the origin of the installation. Remember though that this represents an ongoing energy waste.

Thanks Broadgage