3 phase Screw Compressor on an Add-A-Phase.

[electrofelon]

If that’s the only piece of three phase equipment, why not have the poco quote.adding only one line brought in instead of two? Two is all that is required for an open delta three phase bank with one additional transformer.

Just for completeness, it depend on what the distribution system is. Your comment assumes an mgn with an existing phase and neutral conductor. Most areas here are ungrounded Delta so you would already have two line conductors for a single phase service.

 

[11bgrunt]

This POCO is Y-Y. The existing service is single phase primary. The three phase is 1400' away. Whether adding one wire or two, the cost is the same. Poles would change, framing would change, and all would require a line crew to get a pole where an Open or Closed bank can be decided.
If no overhead construction was needed, this story would be different.

 

[ramsy]

this (540A) starting current is the root of all his power quality complaints over the last five years.

Dim lights may be preferred to VFD noise.

On the other hand, the motor in the compressor may not be happy with the switching noise from a VFD. The switching can create voltage spikes that damage old insulation. Also the compressor may have mechanical limitations (lubrication issues, resonances, etc.) that prevent changing speed.

Finally the input rectifier to the VFD may cause power quality issues for other loads on the transformer.

Constant VFD radio noise may be worse for LED lights, smoke or security alarms, energy efficient appliances, big screen TV’s, AFCI, and GFCI devices.

 

[hillbilly1]

Just for completeness, it depend on what the distribution system is. Your comment assumes an mgn with an existing phase and neutral conductor. Most areas here are ungrounded Delta so you would already have two line conductors for a single phase service.

In my area, there usually is not two line conductors with a neutral, mostly either a single phase line, or complete three phase lines. They add a second line, and use only two transformers for substantial savings on small three phase service's.

 

[kwired]

This POCO is Y-Y. The existing service is single phase primary. The three phase is 1400' away. Whether adding one wire or two, the cost is the same. Poles would change, framing would change, and all would require a line crew to get a pole where an Open or Closed bank can be decided.
If no overhead construction was needed, this story would be different.

That is the thing, single phase often is one wire at top of the pole and other one (usually the grounded conductor) a little lower. To go with three phase they need to add cross arms, whether adding one or two conductors and possibly use heavier pole than the existing one. The third conductor doesn't add all that much cost especially on only 1400' but all the other work needs done either way.

If they had to run several miles, that third conductor maybe a bigger factor, but the structures are going to still cost about the same whether adding one or two conductors.

 

[electrofelon]

That is the thing, single phase often is one wire at top of the pole and other one (usually the grounded conductor) a little lower. To go with three phase they need to add cross arms, whether adding one or two conductors and possibly use heavier pole than the existing one. The third conductor doesn't add all that much cost especially on only 1400' but all the other work needs done either way.

If they had to run several miles, that third conductor maybe a bigger factor, but the structures are going to still cost about the same whether adding one or two conductors.

Around here, with most distribution being delta as i mentioned, the poles would already have crossarms, and I think to add the third phase they would just add an insulator to the middle. IF they were converting it to a wye then they would likely add the neutral down below the crossarms. But even without having to add crossarms and/ or replace poles, Im sure it still wouldnt be cheap to add the 3rd conductor. Adding a conductor to an energized and in use line has got to be a pain. I hear what they do is install a special certified non conductive rope and then pull the conductor in under tension.