480 volt delta, high leg problem

[tlorick]

I am in mexico installing equipment. I need 480 volt 3 phase. I get a very high spike on one leg and it is playing havock with my drives. I know there is a way to stablize this problem but have never had to do. Any help on this matter would be great.

Thanks
Terry

 

[Smart $]

I believe you will need to provide more detail on the 'spike' before anyone can make a suggestion...

 

[drbond24]

There is a difference between a voltage spike and a high-leg delta circuit. Which do you have?

 

[catchtwentytwo]

I am in mexico installing equipment. I need 480 volt 3 phase. I get a very high spike on one leg and it is playing havock with my drives. I know there is a way to stablize this problem but have never had to do. Any help on this matter would be great.

Thanks
Terry

A high-leg delta has 3 phases and a neutral (4-wire).

Are you reading phase to neutral or phase to ground (earth)?

Is the problem confined to one part of the building (or a specific transformer) or do you find it everywhere?

 

[beanland]

240/480v?

240/480v?

Is it a 480V 3-phase with center-side ground? That will give 416V phase to ground on oone phase and many VFD willnot tolerate that. Even though the VFD is said to be 480V delta, they use an earth reference to look at phase-ground voltages and will reject the service if they are not balanced. I saw this happen on an ungrounded 480V delta system that developed a corner ground. The VFD refused to work until the corner ground was fixed.

 

[infinity]

Do they really use a 4 wire, 480 volt Delta system? Something sounds wrong.

 

[drbond24]

Do they really use a 4 wire, 480 volt Delta system? Something sounds wrong.

Yes. We had one here until late last year when we changed out that transformer. There is a tap in the center of one of the delta windings. From that tap, the voltage to two of the phases is the same, but the voltage to the third phase is higher, thus 'high leg delta'.

I'm sure you could find a good picture with a Google search.

 

[infinity]

Yes. We had one here until late last year when we changed out that transformer. There is a tap in the center of one of the delta windings. From that tap, the voltage to two of the phases is the same, but the voltage to the third phase is higher, thus 'high leg delta'.

I'm sure you could find a good picture with a Google search.

What would you typically use the 240 volts for?

 

[drbond24]

What would you typically use the 240 volts for?

We just avoided that leg. Almost all of the loads on that circuit were single phase (i.e. receptacles and 120 V lighting). There may have been some small shop equipment like a grinder or drill press that used the 240, but not much.

 

[beanland]

240/480V Delta

240/480V Delta

240/480V delta is safer than 480V ungrounded delta. It is common on irrigation banks in rural installations. Three single-phase pole transformers are wired together. By grounding one center side, a reliable ground reference is provided to avoid surges on the primary from coupliing thru to the secondary.

 

[infinity]

We just avoided that leg. Almost all of the loads on that circuit were single phase (i.e. receptacles and 120 V lighting). There may have been some small shop equipment like a grinder or drill press that used the 240, but not much.

I'm confused. We're talking about a 4 wire 480 volt system with a center tap and 240 volts on two of the phases. Where does the 120 come into play?