Why Grounded Delta?

[ptonsparky]

At a customers today looking at a project the well driller wired up. (Topic for another thread.) POCO supplied 480v
Grounded Delta. Primary looks to me like three phases coming in along with what I would call a primary neutral. Why not a provide a wye?

 

[Hv&Lv]

At a customers today looking at a project the well driller wired up. (Topic for another thread.) POCO supplied 480v
Grounded Delta. Primary looks to me like three phases coming in along with what I would call a primary neutral. Why not a provide a wye?

What did the customer ask for? Many times I have a customer that specifically wants a delta configuration.

 

[ptonsparky]

What did the customer ask for? Many times I have a customer that specifically wants a delta configuration.

Neither the well digger nor the customer would know why one vs the other.Well. maybe WD but there is no reason to spec grounded delta.

 

[Hv&Lv]

Neither the well digger nor the customer would know why one vs the other.Well. maybe WD but there is no reason to spec grounded delta.

Someone had to ask for it. I feel sure the POCO didn't just build it for no reason. They either told the POCO 480 motor in which case the POCO assumed a 480 power bank, which is required in some places to be corner grounded, and didn't specify 277 or wye.
The customer sends the power requirements to the POCO. I you want a wye, just tell them. It is really simple to convert the bank.

 

[templdl]

Neither the well digger nor the customer would know why one vs the other.Well. maybe WD but there is no reason to spec grounded delta.

I would strongly suggest that if in fact you needed 480v 3ph3w that you opted for a 480v 3ph4w wye. You ground the neutral (X0) connect your EGC at that point and bring it along with your (3) lines to the load. No need for a neutral. The benefit of this arrangement is instead of 480v to ground you no have reduced that to 277v which is a big difference.

It is not uncommon for it to be assumed that just because your 3ph load does not require a neutral and only 3 line conductors it can be mistakenly called a delta.

So you understand what I'm referring to this is a brief explanation of the used for a delta configuration which is not applicable in your application:

With a delta it is not uncommon for a plant that has a continuous process that can't be interrupted to be supplied by an ungrounded delta because of an OCPD tripping as a result of a ground fault incident and causing thousands of dollars in damaged material and equipment. With this type of system it is imperative to have ground fault detectors an alarms as well as being supervised a qualified person who would be able to address the grounding issue promptly. This is not applicable in your situation.
Otherwise the delta would be corner grounded (grounded 'B' phase). Grounding is important as it provides a current path back to the source should an ungrounded conductor fault to ground. As such it allows the OCPD to trip and clear the fault. But guess what, any line to ground fault will be 480v. Being that a GF would amount to 480v this would not be the best thing either if you had the option for 277v.

 

[petersonra]

I have been told that unless you can get special permission from ComEd that around here ComEd is only supplying 480 Wye services now.

 

[Hv&Lv]

I have been told that unless you can get special permission from ComEd that around here ComEd is only supplying 480 Wye services now.

We try to talk everyone into a 480 wye also. we really don't like to build a 480 delta bank because of the problems with lightning and imbalance. Even when we do (which is rare), we ground one winding at the midpoint.

 

[kwired]

At a customers today looking at a project the well driller wired up. (Topic for another thread.) POCO supplied 480v
Grounded Delta. Primary looks to me like three phases coming in along with what I would call a primary neutral. Why not a provide a wye?

New service or upgrade of an existing open delta maybe?

POCO around me typically only use 480 volt delta when it is open delta, if all three phases are used it is almost always a wye secondary. Customer gets more choice when selecting 120/208Y vs 120/240D but not at 480 volts.

 

[ptonsparky]

New service or upgrade of an existing open delta maybe?

POCO around me typically only use 480 volt delta when it is open delta, if all three phases are used it is almost always a wye secondary. Customer gets more choice when selecting 120/208Y vs 120/240D but not at 480 volts.

It was a 240v grounded delta from years ago that served a couple small wells from one set of pole top transformers. Primary in the whole area was upgraded several years ago due to an ice storm so reasons for limitations to power that had existed are no longer valid.

 

[kwired]

It was a 240v grounded delta from years ago that served a couple small wells from one set of pole top transformers. Primary in the whole area was upgraded several years ago due to an ice storm so reasons for limitations to power that had existed are no longer valid.

The only person that really knows why it was done the way it was likely works for the POCO.:happyyes:

 

[petersonra]

We try to talk everyone into a 480 wye also. we really don't like to build a 480 delta bank because of the problems with lightning and imbalance. Even when we do (which is rare), we ground one winding at the midpoint.

I can't imagine a customer that wanted an ungrounded system would like that very much. What is the benefit to a customer in grounding a midpoint versus a Wye system when they really want ungrounded?

In any case, why not just corner ground it? Why a midpoint ground?

 

[kwired]

I can't imagine a customer that wanted an ungrounded system would like that very much. What is the benefit to a customer in grounding a midpoint versus a Wye system when they really want ungrounded?

In any case, why not just corner ground it? Why a midpoint ground?

Around here in the irrigation capital of the US you used to see a lot of corner ground systems. Now they are all gone, and POCO doesn't even offer such thing. They may do so for some industrial plant if it were for some reason requested but not for irrigation services. Too many unqualified persons were working on them and there were too many incidents of unsafe practices going on.

Corner ground systems are safe, but only when qualified persons are working on them. Same with 120/208 or 120/240, but 120 volts to ground is a little more forgiving than 480 volts to ground when something is wrong.

 

[ggunn]

The only person that really knows why it was done the way it was likely works for the POCO.:happyyes:

Or more likely, retired from working for the POCO and is now deceased.

 

[Hv&Lv]

I can't imagine a customer that wanted an ungrounded system would like that very much. What is the benefit to a customer in grounding a midpoint versus a Wye system when they really want ungrounded?

In any case, why not just corner ground it? Why a midpoint ground?

Stops some of the confusion on the part of some electricians, and some lineman do not like the idea of connecting a hot secondary leg to a ground wire and throwing a fuse in.

 

[kwired]

Stops some of the confusion on the part of some electricians, and some lineman do not like the idea of connecting a hot secondary leg to a ground wire and throwing a fuse in.

Not so sure about that. Some are confused if it is anything but single phase or wye.

Lineman should not be too concerned about what point is grounded as long as there is only one point grounded, for the purposes of what happens when throwing in a fuse anyway.

 

[sdbob]

A corner grounded delta with a neutral?? I suspect it's a redundant grounding conductor.

 

[sdbob]

I'm pretty sure the poco is supplying a redundant grounding leg to prevent the possibility of someone putting a fuse (and subsequently blowing it) on the grounded corner. If I remember right, the grounded corner should be B phase, should be identified white or grey, and should NOT be fused.

 

[sdbob]

And out here in San Diego county we see this in rural areas to supply small three phase loads such as well pumps and irrigation pumps. They use two single phase transformers to create the open delta.

 

[Hv&Lv]

Not so sure about that. Some are confused if it is anything but single phase or wye.

Lineman should not be too concerned about what point is grounded as long as there is only one point grounded, for the purposes of what happens when throwing in a fuse anyway.

Not to put down lineman as a whole, I am one myself in my main job. Lineman usually get a job starting at the bottom just like any trade. Some view it as more of a construction trade than as an electrical trade. Many lineman have made it through their career without knowing anything about ohms law. They just know what they have seen. They put a secondary to ground and it goes boom. That is the extent of what some lineman care to know.

 

[kwired]

Not to put down lineman as a whole, I am one myself in my main job. Lineman usually get a job starting at the bottom just like any trade. Some view it as more of a construction trade than as an electrical trade. Many lineman have made it through their career without knowing anything about ohms law. They just know what they have seen. They put a secondary to ground and it goes boom. That is the extent of what some lineman care to know.

I guess I am used to most of the linemen in this area that would likely have more theory knowledge than maybe some other areas. There is a community college near here that has a very good utility line program. They do learn a lot of electrical theory. Not many POCO employees around this area that have not attended this school, and if they haven't they are either older or not originally from the area.