Pole Lights Calculation

[ishaq]

Dear member,
i have a project based on a highway pole lights.
so now i have to calculate how many poles will be on one transformer,details are ....Trnsrfmr rating is 200 kVA, Lamp rating is 1.5 kW, and we have to fix 12 no of lamps in one pole.so one pole rating is 18 kW.so how many poles will be on one transformer.?

 

[Dennis Alwon]

You can load a transformer 100%

 

[ishaq]

Question??

Question??

You can load a transformer 100%

Dear Sir,
Can you tell me how much poles of the same rating i.e 18 kW will facilitate a 200 kVA transformer???

 

[Dennis Alwon]

Is the transformer 3 phase? What is the voltage of the lighting, ie 120 or 240 etc.

 

[mivey]

8 poles per transformer, maybe 9 depending on fixture type

 

[Smart $]

If these are ballasted fixtures, you have to calculate using ballast rating instead of lamp rating.

 

[Dennis Alwon]

8 poles per transformer, maybe 9 depending on fixture type

Wouldn't that depend on whether or not they are using dp or single pole breakers? or whether the trany is 3 phase?

 

[Smart $]

Wouldn't that depend on whether or not they are using dp or single pole breakers? or whether the trany is 3 phase?

Not really... and you left out 3P breakers.

With 12 fixtures per pole, they could be wired almost any way you want to balance the load, regardless of number of poles.

BTW, it appears he is assuming there is power factor and/or ballast losses involved, because 200kVA ? 18kVA = 11.1

 

[Dennis Alwon]

Not really... and you left out 3P breakers.

With 12 fixtures per pole, they could be wired almost any way you want to balance the load, regardless of number of poles.

BTW, it appears he is assuming there is power factor and/or ballast losses involved, because 200kVA ? 18kVA = 11.1

Can't you have 11 fixtures per phase if they were say 120v units-- I am sure they are not. In this case there would be 33 fixtures. NO

 

[Smart $]

Can't you have 11 fixtures per phase if they were say 120v units-- I am sure they are not. In this case there would be 33 fixtures. NO

Not sure where you are coming up with 11 fixtures per phase. There's 12 fixtures per pole. Each pole is 18kW (lamps only?) and can be split wired to balance the load, so number of poles is irrelevant to balancing.

 

[mivey]

BTW, it appears he is assuming there is power factor and/or ballast losses involved, because 200kVA ? 18kVA = 11.1

Correct. I used 80%. Could be in the 70's or closer to 90's but 80 is a reasonable guess if you don't have better info.

 

[mivey]

Can't you have 11 fixtures per phase if they were say 120v units-- I am sure they are not. In this case there would be 33 fixtures. NO

You would have multiples of 12 fixtures.

Some of the possibilities:
200/8=25 kVA per pole. 8 poles gives 96 fixtures. Single-phase means 48 or 96 fixtures per phase. 3-phase is 32 fixtures per phase. 72% ballast/power factor allowance. Plenty of allowance for poor factors and phase loading. Higher factors might not require fixture balancing for 3-phase supply (see 81% for 9 poles so we could have 8=3+3+2 poles).

200/9=22.2 kVA per pole. 9 poles gives 108 fixtures. Single-phase means 54 or 108 fixtures per phase. 3-phase is 36 fixtures per phase. 81% ballast/power factor allowance. Possible but might require careful balancing for poor ballast/poor factors. Higher factors might not require fixture balancing for single-phase supply.

200/10=20 kVA per pole. 10 poles gives 120 fixtures. Single-phase means 60 or 120 fixtures per phase. 3-phase is 40 fixtures per phase. 90% ballast/power factor allowance. Maybe, but not conservative enough for a guess.

200/11=18.2 kVA per pole. 11 poles gives 132 fixtures. Single-phase means 66 or 132 fixtures per phase. 3-phase is 44 fixtures per phase. 99% ballast/power factor allowance. Not likely.

I picked 8 poles and said maybe 9 poles. Better data would yield a better answer.

 

[weressl]

Dear member,
i have a project based on a highway pole lights.
so now i have to calculate how many poles will be on one transformer,details are ....Trnsrfmr rating is 200 kVA, Lamp rating is 1.5 kW, and we have to fix 12 no of lamps in one pole.so one pole rating is 18 kW.so how many poles will be on one transformer.?

Have to find out the operating power factor of the lights and see how many kVA of each light is. Simple multiplication/division from that point on.

 

[ishaq]

Voltage=400 v, 3 phase, freq=60 Hz

 

[weressl]

Voltage=400 v, 3 phase, freq=60 Hz

If you did not understand my question about the power factor, then you have no business asking the original question, regardless of what you call yourself in your profile.

 

[ishaq]

Have to find out the operating power factor of the lights and see how many kVA of each light is. Simple multiplication/division from that point on.

"one pole rating = 18 kW so 18kW/.9 = 20 kVA
now no of poles = 200 / 20 = 10..???

 

[weressl]

"one pole rating = 18 kW so 18kW/.9 = 20 kVA
now no of poles = 200 / 20 = 10..???

So the power factor is exactly 0.9? I would not load up a transformer to it's full capacity and since you have to deal with 20kVA increments, I would suggest 9 poles or 180kVA.

 

[Sahib]

You may dispense with power factor. Simply find out the ballast power loss in watts from manufacturer cataloge (For simple inductive magnetic core chokes it is around 25% and it may not exceed 10% for electronic chokes) and add to the lamp watts per pole. Taking the transformer capacity as 160 KW,(20%reduction for adverse environmental conditions) divide it by the total arrived to get an estimate of the number of poles (an estimate, because the power loss in the connecting power cables not taken into account!).

 

[weressl]

You may dispense with power factor. Simply find out the ballast power loss in watts from manufacturer cataloge (For simple inductive magnetic core chokes it is around 25% and it may not exceed 10% for electronic chokes) and add to the lamp watts per pole. Taking the transformer capacity as 160 KW,(20%reduction for adverse environmental conditions) divide it by the total arrived to get an estimate of the number of poles (an estimate, because the power loss in the connecting power cables not taken into account!).

You should not, if you are an engineer. Those folks rely on DATA, not WAG's and approximations. A 200kVA transformer can deliver 160kW onto a load with a power factor of 0.8, not because of 'adverse environmental conditions'.

 

[Sahib]

You should not, if you are an engineer. Those folks rely on DATA, not WAG's and approximations. A 200kVA transformer can deliver 160kW onto a load with a power factor of 0.8, not because of 'adverse environmental conditions'.

Without a knowledge of data on the power cable connecting the highway pole lights, those folks are making only an approximation.