balancing a 240V 3 phase delta

[morbones]

I am trying to determine whether there would be any significant savings in kWhrs in balancing a 3 phase 240V delta system. Load is concentrated on A @115A and C @55A, B(hi leg) current is minimal. The facility lighting is 400W Metal Halide wired @ 120V, neutrals are imbalanced-overloaded in some cases. Considering wiring fixtures for 240V to balance.

 

[SG-1]

Welcome to the Forum !

How is your delta deriving a neutral ?

 

[morbones]

I must plead ignorance, how would I differentiate? What is the significance?

 

[SG-1]

Welcome to the Forum !

How is your delta deriving a neutral ?

You have one winding center tapped. You did say high leg.

I think it would help if only to reduce the I squared R losses in the overloaded neutrals. Also if you rewire for 240 there will be less I squared R losses in all the conductors supplying the lights, because the current will be reduced.

 

[morbones]

I did say high leg. So the only significant saving in power usage would be the resulting decrease in power loss due to reduced current?

 

[SG-1]

I am not an expert in this field. More members will post if they have something to contribute. Watch your thread for a couple of days.

I would also think that balencing the transformer would result in reduced heat loss there, but it may be insignificent.

What size transformer do you have ?

 

[LarryFine]

Bones, welcome to the forum!


There's probably no benefit to balancing as far as the power meter is concerned, but balancing the A and C currents would allow more overhead for future additions.

For high-leg Deltas, it's common for the high leg to be more lightly loaded, because it doesn't have any line-to-neutral loads, only 1ph and 3ph line-to-line loads.

 

[Smart $]

Bones, welcome to the forum!

There's probably no benefit to balancing as far as the power meter is concerned, but balancing the A and C currents would allow more overhead for future additions.

For high-leg Deltas, it's common for the high leg to be more lightly loaded, because it doesn't have any line-to-neutral loads, only 1ph and 3ph line-to-line loads.

Ditto on the welcome...

If he converts his lighting to 240, he could balance loads across 3 phases as appropriate for the system. This would further reduce I?R losses. Also, if the transformer is on the load side of the meter, the transformer (heat) contributes to the I?R losses.

 

[morbones]

Thanks everyone for your heartfelt welcome! I do not know what size the transformer is, 350kVA? Parallel 500's feed into tangle box from service mast split to 400A MDP and 200A fusible disc. I am assuming that the ct's are on the load side of the transformer. The 200A disconnect is feeding 2 QO subpanels: 1 20ckt 125A 3 phase, 1 20ckt 125A 1 phase. This is the area of the greatest concern, where I derived my current readings. I am not intentionally neglecting the big picture but the customer is experiencing equipment failure at this subpanel location. The lighting load is concentrated to circuits 7-19(all120V) ranging from 12A to 20A. There are only 4-5 #12 neutrals, only 1 carrying any significant load at 25-26A. The plastic retainer plate in the back of the panel has crumbled apart due to the heat and the breakers are just hanging on the bus. The feeder trough below the 2 panels has a hole torched in the end cap and wiremold boxes butted against it; 12-14 #12's stuffed through this tiny hole to 6-7 single pole switches to control lighting. Experiencing voltage drop on A phase; 118-120V at 200A disc., 110-112V at "dim" string of lights. Would like to replace both panels with 1 200A 3phase 48 circuit bolt-in breaker style panel, strip old wiring and pull new, reconfigure lighting to 240V and switch through contactors. That's the situation, thanks for your input!

 

[jim dungar]

Any 2-pole breaker you connect to the high leg will need to be a 'special' breaker' that is fully rated for 240V (i.e. QO2xxH) instead of a standard breaker.

I always recommend (2) panels, one for single-phase and the other for three-phase (no neutral conductor installed). I find, this arrangement seems to provide the fewest problems with future accidental high leg connections.

 

[nakulak]

sounds like a nice fix. post some pics of the burnt up panel.

 

[morbones]

Understood. The 3 phase panel currently has a neutral, contains some of the lighting load, a few other 1 phase circuits as well as 3 phase. Both panels have conduit runs that feed to a common trough so I don't know what is sharing a neutral with what; circumstances didn't allow for me to access at the time. The physical space at the panel location is limited which is the main reason I want to consolidate. The facility underwent major renovation in the early 90's and the lighting was just tied in wherever they could pick up a neutral and a hot. The location is supervised and the panel voltage would be clearly identified. Thanks

 

[LarryFine]

The facility underwent major renovation in the early 90's and the lighting was just tied in wherever they could pick up a neutral and a hot.

As made evident by the overloaded neutral.

(Presuming #12 wire, of course.)

 

[morbones]

Yes, that assumption is correct - #12 was used. It is definitely showing signs of abuse. It's in the hands of the customer; it'll either be rectified or it will fail. I appreciate everybody's input.