Voltage Drop

[jokoMalong]

Hello everyone!,
just need a little help from you, I'm calculating a voltage drop of a 3 phase circuit with single phase lighting load into it. system is 220V line to line 3 phase 3 wire,pf=80%. 5 -176W floodlight with a 50 meter distance at each other.
Question:
1. Should I use single phase or 3 phase voltage drop calculation?

 

[ramsy]

If your audience is another engineer or a design competition, then a 3-phase circuit can be balanced across 2-pole luminaries in multiples of 3, with any unbalanced remainder using the single-phase calc.

However, installations are another matter. While a contractor's Responsible Managing Operator (RMO) may be licensed up with credentialed experience, jobs are routinely run by apprentices & laborers that don't speak the local language, much less read plans. To idiot proof for installers capping off one wire color, and using the same 2 wires for all luminaries, a single-phase calc may be more realistic for field plans.

 

[paradox413]

The voltage drop you're calculating is for a single phase branch circuit which is definitely a single phase calculation.

 

[jokoMalong]

The voltage drop you're calculating is for a single phase branch circuit which is definitely a single phase calculation.

Is that how will it be calculated even though the circuit is of 3 phase?

 

[winnie]

Hello everyone!,
just need a little help from you, I'm calculating a voltage drop of a 3 phase circuit with single phase lighting load into it. system is 220V line to line 3 phase 3 wire,pf=80%. 5 -176W floodlight with a 50 meter distance at each other.
Question:
1. Should I use single phase or 3 phase voltage drop calculation?

Do you have 3 phases going out to the loads, but the individual loads are single phase lamps? In other words lamp 1 is connected from A to B, lamp 2 from B to C , lamp 3 from C to A, and so on?

-Jon

 

[jokoMalong]

Do you have 3 phases going out to the loads, but the individual loads are single phase lamps? In other words lamp 1 is connected from A to B, lamp 2 from B to C , lamp 3 from C to A, and so on?

-Jon

yes Sir.

 

[winnie]

Okay. You have 5 lamps, so they cannot be divided evenly across the 3 phases. They are also at different distances. So to do an _accurate_ calculation of voltage drop you would need to do a calculation of current flow at each point and then calculate the individual voltage drop for each of the conductors on each length of the circuit, and then add it up. Neither the simple 3 phase or 1 phase calculation would apply.

However this is also a small circuit, and probably not worth doing an _accurate_ calculation. Instead you want a conservative approximation, one that lets you know that you have a sufficient wire. To do this, assume you have 6 lights (thus a balanced 3 phase load) all lumped together at the maximum distance of the circuit, and then do the 3 phase calculation. Very likely you will find that with the smallest allowed conductor you will have an acceptable voltage drop with this calculation, and the real voltage drop will be better than this approximation.

-Jon