I am upgrading building service from 240/1/60, 400A to 480/3/60, 600A for my machine building business. The local utility committed to the installation, I put in the conduit, transformer base, etc. One month later, the utility wants to change to an open wye delta 480 system instead of the standard method to save money. I am not a utility engineer, so I have a feeling that I'm going to get the shaft somehow. They are pressuring me to keep the current service and add the open wye service through a second meter. Can someone give me some guidance whether I'm asking for trouble with PLC's and other control devices or trouble shooting ground faults or something if I accept their changes? I can't find a lot of information about open wye delta after the utility's connection.
Open wye delta 480 vs "std" 480/3/60 from utility
- Thread starter wiseericj
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ibew501ed
Senior Member
- Location
- danbury ct/work in white plains ny
It sound like you mean open delta/ wye service. secondary would be 277v/480v
if thats the case than the open delta just reduces the availably kva and would be easily increased in the future with the 3rd winding to close the delta connection IMO
if thats the case than the open delta just reduces the availably kva and would be easily increased in the future with the 3rd winding to close the delta connection IMO
I don't see a problem, they are aware of the actual increase in load, right ? It will save you
from getting a larger KVA transformer for the 240v loads. JMO
It is my understanding that the delta system will have a 240 secondary, not 277v. I have been reading all the threads I can find in this forum. It seems that there is a larger voltage fluxuation on at least one leg? The utility says that the system would be fully grounded, so it's safe. I'm very concerned that I'm going to have voltage trouble down the road after the dust is settled.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Do not get hung up over terms like open wye or open delta. This is simply a description of of how the utility will be connecting their transformers. There are very few reasons that most custoers should be concerned with utility transformer connections.
What you need to be concerned with are the voltages that will be delivered to you, both line-line and line-neutral.
Are you are being promised 480Y/277V or only 480V?
What you need to be concerned with are the voltages that will be delivered to you, both line-line and line-neutral.
Are you are being promised 480Y/277V or only 480V?
charlie
Senior Member
- Location
- Indianapolis
Find out for sure what they are wanting to give you! At 480 volts in an open delta configuration, they can provide:
Unless there is a great need to retain the 400 ampere service, I would tell the serving electric utility that I wanted the two services totalized or you can provide your own dry type transformer to do your lower voltage. You don't need to go through the rate steps twice. :smile:
- 480 volts, corner grounded delta, 3 wire
- 480 volts, un-grounded delta (this requires a ground detector), 3 wire
- 480/240 volts, center tap grounded delta, 4 wire
Unless there is a great need to retain the 400 ampere service, I would tell the serving electric utility that I wanted the two services totalized or you can provide your own dry type transformer to do your lower voltage. You don't need to go through the rate steps twice. :smile:
charlie
Senior Member
- Location
- Indianapolis
Jim, you can't get a wye output from an open delta configuration. :smile:
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
For sure.
But when I hear that a customer is getting an "open wye delta' as a service, I wonder if they really know what they are getting.
My point was intended to be: many people talk about utility transformer connections as if that is sufficient enough information to describe the voltage system they are getting, when in reality it is not normally important.
There is an open-wye to 4-wire 208. Some people call it an open-wye to open wye but it is really an open-wye to partial zig-zag.
add:
You can also input three lines (Δ) to that configuration and get a 4-wire wye output.
Say you had the full boat of the wye supply you depict, where A-N-B is 120?. On the same system, A-C/B-A is also 120?. A to C is -210? and B to A is -330?—a difference of 120?. Of course you'd then need the primary rated at the higher Line-to-Line voltage.
mivey
Senior Member
How true. Did not think of that, just had had the open wye on the brain. Then we must say that this:
is wrong.
charlie
Senior Member
- Location
- Indianapolis
The reason to use an open delta bank is to only use two primary phases and two transformers. To cobble together the configuration you are describing, you need three primary phases and the transformers rated for phase to phase voltage instead of phase to neutral voltage.
So, to make my statement more correct, "Jim, you can't get a wye output from an open delta configuration from any electric utility that I know of." :smile:
So, to make my statement more correct, "Jim, you can't get a wye output from an open delta configuration from any electric utility that I know of." :smile:
Not the original configuration Mivey posted... it uses Line to Neutral connections. The practicality of such a configuration in use, I believe, is mostly dependent on the transformer configurations stocked by the utilities (i.e. they'd need dual secondary windings rather than center-tapped ones).
We're mixing terminology here. What an open delta configuration is depends on the reference material.
For instance, Cooper Power Systems R201-90-2 publication on Distribution Transformers calls an Open Delta for Power configuration as one which has two transformers, a three-line delta primary (A,B,C), and a delta secondary (a,b,c).
What you describe is likened to what is called, in the Cooper publication, "Y-Delta With One Unit Missing", which has two transformers, an "open wye" primary (A,N,B), and a delta 4-wire secondary (a,b,n,c)?for light and power.
Regardless of such, your revised statement is correct TTBOMK :grin:
mivey
Senior Member
True.
So for those playing along at home:
Open-Wye primary needs two primary phases
Open-Delta primary needs three phases
Either one can supply a Wye secondary
Open-Wye to Delta is probably the most common configuration of the "opens"
I am only familiar with the Open-Wye to Wye. Neither Charlie nor I have ever seen an Open-Delta to Wye, but have to admit that it is possible per Smart$'s diagram.
Thank you for the feedback. It appears the utility is pushing an open wye/open delta design. They are definately feeding the transformers with two hot legs of single phase. The comments indicate there is some practical limit to the size of service that can be provided by this design. Any ideas what it might be? Again, I am a novice but I don't want to find out in five years that I should have resisted the lower grade service - if it really is lower grade.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is not a question of 'grade' or quality.
The utility must size their transformers correctly to provide you with your contracted voltage regulation and service capacity. They can do this regardless of the method they use to connect the transformers.
The question is: Is the utility providing the voltage, L-L and L-N, you need/want?
mivey
Senior Member
And relatively speaking, your service is not huge. What size pots are they hanging?
We would normally hang up to about 250 kVA pots on a pole before going to a platform or fencing them in on the ground or combining single phase pads. With two 250's you would get 433 kVA for the open bank, which is probably more than you need.
So size-wise, this would not be beyond what we might do. The other issue is what are the loads? We usually go to a 3-pot bank for above about a single 25-30 HP motor.
You could put in two 500's to get up to 867 kVA for the open bank, but the type load would be the determining factor.
All of this is feedback from folks who are hundreds of miles away from you. It would be best to discuss your concerns with the utility.
We would normally hang up to about 250 kVA pots on a pole before going to a platform or fencing them in on the ground or combining single phase pads. With two 250's you would get 433 kVA for the open bank, which is probably more than you need.
So size-wise, this would not be beyond what we might do. The other issue is what are the loads? We usually go to a 3-pot bank for above about a single 25-30 HP motor.
You could put in two 500's to get up to 867 kVA for the open bank, but the type load would be the determining factor.
All of this is feedback from folks who are hundreds of miles away from you. It would be best to discuss your concerns with the utility.
They tell me that I don't have a say in what they provide. They will supply 480v. There is no discussion about L-L or L-N voltage. I have a customer with an open Y/open delta system. There was a ground fault on a conveyor and people were getting poked. Turns out, the breaker wouldn't trip because of the phantom leg and parallel path feature of the system. That really scares me to know it can happen.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If the utility is suppling a delta system of 480V, you will need to 'ground' one corner or provide ground detection.
The fact that the transformer connection is "open" or "closed" does not impact the ability of a breaker to trip.
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