I'm designing an underground 78 lot residential subdivision where only single phase power is available for almost a mile. Site plans call for a 3phase 23HP sewer pump. Boss (poco engineering manager) says "make him pay for bringing in 3 phase". Would a 400a single phase service, with a rotary phase converter for the 3phase motor loads supplied by a dedicated 50kva xfmr be more cost effective? (full 3phase = about an additional $30k)
phase adders
- Thread starter magoo66
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luke warmwater
Senior Member
Re: phase adders
I only have a limited experience with phase converters, and they were smaller than 23 HP.
One question that comes to mind is how are you going to start such phase converter, automatic or manual?
Thinking about it, $30k divided by 78 lots is less than $400 add to each lot.
I only have a limited experience with phase converters, and they were smaller than 23 HP.
One question that comes to mind is how are you going to start such phase converter, automatic or manual?
Thinking about it, $30k divided by 78 lots is less than $400 add to each lot.
charlie
Senior Member
- Location
- Indianapolis
Re: phase adders
Magoo, in my area, the government will not permit 1? motors to be used since the systems will be turned over to the city after it is completed. A 1? motor has too many things that can go wrong with it and it costs more than a 3? motor to replace. Assuming a phase converter is installed, that is an extra piece of equipment that has to be maintained and in my area, the government will not permit a phase converter to be used.
Let the developer know that you will install what he desires but this is the cost. It is now his responsibility to verify that he can use a phase converter and take 1? service or is required to put out $30k and take a full 3? service.
By the way, it sounds like you are opposed to charging for the 3? service. Keep in mind that the developer is the one making the money and should pay for what he gets or requires like this or relocating poles at the entrance. Why should your rate payers foot the bill so that the developer makes money?
Magoo, in my area, the government will not permit 1? motors to be used since the systems will be turned over to the city after it is completed. A 1? motor has too many things that can go wrong with it and it costs more than a 3? motor to replace. Assuming a phase converter is installed, that is an extra piece of equipment that has to be maintained and in my area, the government will not permit a phase converter to be used.
Let the developer know that you will install what he desires but this is the cost. It is now his responsibility to verify that he can use a phase converter and take 1? service or is required to put out $30k and take a full 3? service.
By the way, it sounds like you are opposed to charging for the 3? service. Keep in mind that the developer is the one making the money and should pay for what he gets or requires like this or relocating poles at the entrance. Why should your rate payers foot the bill so that the developer makes money?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: phase adders
I would not want a phase convertor either. Too many extra places something can fail.
Seems to me that the developer should just pay for what is needed.
I don't think I have ever seen a 23 HP motor before.
I would not want a phase convertor either. Too many extra places something can fail.
Seems to me that the developer should just pay for what is needed.
I don't think I have ever seen a 23 HP motor before.
charlie
Senior Member
- Location
- Indianapolis
Re: phase adders
I made the assumption that it was a specialty motor. It is a bit (lot?) weird though isn't it.
I made the assumption that it was a specialty motor. It is a bit (lot?) weird though isn't it.
georgeswe
Senior Member
- Location
- The Republic of Southern California
Re: phase adders
I installed a Safetronics Electronic phase converter its a neat lil piece of equipment the only downfall is it does not work on non-linear loads. I installed it on a 20 hp dive compressor and could not get it to work the control circuitry on the compressor only the motor which was a pain in the butt. www.safetronics.com
I installed a Safetronics Electronic phase converter its a neat lil piece of equipment the only downfall is it does not work on non-linear loads. I installed it on a 20 hp dive compressor and could not get it to work the control circuitry on the compressor only the motor which was a pain in the butt. www.safetronics.com
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: phase adders
I think there would be additional cost savings with the 3-phase service. You would need to put in some heavy duty copper to avoid voltage drop problems with a single phase line over the distances you are talking about. I'd suggest a quick spread-sheet comparison of 1-phase versus 3-phase. I think the difference will drop below the $30K you are looking at now.
I think there would be additional cost savings with the 3-phase service. You would need to put in some heavy duty copper to avoid voltage drop problems with a single phase line over the distances you are talking about. I'd suggest a quick spread-sheet comparison of 1-phase versus 3-phase. I think the difference will drop below the $30K you are looking at now.
charlie
Senior Member
- Location
- Indianapolis
Re: phase adders
Charlie, I am assuming that the primary conductors are #2 Al or larger and are at the 8.66 kV class. In other words, the voltage drop would not be significant under those conditions.
Charlie, I am assuming that the primary conductors are #2 Al or larger and are at the 8.66 kV class. In other words, the voltage drop would not be significant under those conditions.
rick hart
Senior Member
- Location
- Dallas Texas
Re: phase adders
I don't know for sure just asking:
If this is a development of at least 78 utility customers and more are likely in the future, wouldn't it be to the advantage for the utility to bring 3 phase into the new subdivision?
Someone has to bring sewer, water, telephone, gas and HBO. Usually the first developers in an area bring the civil engineering as part of the cost.
Forget the phase converter, more parts-more problems.....
I don't know for sure just asking:
If this is a development of at least 78 utility customers and more are likely in the future, wouldn't it be to the advantage for the utility to bring 3 phase into the new subdivision?
Someone has to bring sewer, water, telephone, gas and HBO. Usually the first developers in an area bring the civil engineering as part of the cost.
Forget the phase converter, more parts-more problems.....
charlie
Senior Member
- Location
- Indianapolis
Re: phase adders
Rick, this is a small subdivision that can easily be handled on a 1? line. This would likely be on poles with a riser (two risers if they use a loop system like we do) for underground into the subdivision. The developer will supply plans for the entire development and planning for the future will be taken into consideration.
An additional phase or two can be taken down the same pole line with the addition of cross arms and insulators in the future. This is really no big deal.
Rick, this is a small subdivision that can easily be handled on a 1? line. This would likely be on poles with a riser (two risers if they use a loop system like we do) for underground into the subdivision. The developer will supply plans for the entire development and planning for the future will be taken into consideration.
An additional phase or two can be taken down the same pole line with the addition of cross arms and insulators in the future. This is really no big deal.
Re: phase adders
23 hp seemed weird to me too. I've installed up to 10 hp phase converters before and no problems beyond trying to make them idiot proof. Still, the more complicated the system, the more stuff to go wrong.
I spoke with the developer today and managed to convince him to at least bury enough conduit to "eventually" bring in full underground 3 phase. This is a common problem in my area as the residential explosion continues. Thanks for the input guys.
23 hp seemed weird to me too. I've installed up to 10 hp phase converters before and no problems beyond trying to make them idiot proof. Still, the more complicated the system, the more stuff to go wrong.
I spoke with the developer today and managed to convince him to at least bury enough conduit to "eventually" bring in full underground 3 phase. This is a common problem in my area as the residential explosion continues. Thanks for the input guys.
bensonelectric
Senior Member
Re: phase adders
Perhaps a big single-phase input three-phase output VFD?
I wonder if Telemcanique has a higher power VFDs simmilar to the Alitivar 11, I have used one of these to drive a 208v 3phase off of 115 single-phase, and it worked quite well... I believe it worked by rectifing input single phase AC to DC, stepping the voltage up, then using SCRs to generate the waveforms. However I do not deal with motors much and do not have alot of experience with them so this could be totally worthless.
[ August 05, 2005, 03:00 AM: Message edited by: bensonelectric ]
Perhaps a big single-phase input three-phase output VFD?
I wonder if Telemcanique has a higher power VFDs simmilar to the Alitivar 11, I have used one of these to drive a 208v 3phase off of 115 single-phase, and it worked quite well... I believe it worked by rectifing input single phase AC to DC, stepping the voltage up, then using SCRs to generate the waveforms. However I do not deal with motors much and do not have alot of experience with them so this could be totally worthless.
[ August 05, 2005, 03:00 AM: Message edited by: bensonelectric ]
Re: phase adders
Charlie
The URD subdivisions that I have worked with had 3 primary cables installed but it was not classified as 3 phase. AS you know a cable failure will result in the cable termination in a pad mtd transformer to be disconnected and may be left that way or switched to another source.
Any 3 phase equipment was dealt with individually.
In a case as this a tranclosure with 2 or 3 transformers or pad mtd 3 phase were installed separately from the URD installation.
Charlie
The URD subdivisions that I have worked with had 3 primary cables installed but it was not classified as 3 phase. AS you know a cable failure will result in the cable termination in a pad mtd transformer to be disconnected and may be left that way or switched to another source.
Any 3 phase equipment was dealt with individually.
In a case as this a tranclosure with 2 or 3 transformers or pad mtd 3 phase were installed separately from the URD installation.
charlie
Senior Member
- Location
- Indianapolis
Re: phase adders
Where we have just a few customers, we will take just a single phase of primary into it and loop it back to the overhead. The larger the subdivision, the more primary phases. Even with all three primary phases into the area, if a customer needs a 3? service for a lift station or pump for a lake, we will charge him to run it and not mix the 1? with the 3? conductors.
You also don't want to lose sight of the fact that this is a really small subdivision. Also remember that an overhead line is very flexible for future growth but you can get painted into a corner very quickly if everything is buried.
Where we have just a few customers, we will take just a single phase of primary into it and loop it back to the overhead. The larger the subdivision, the more primary phases. Even with all three primary phases into the area, if a customer needs a 3? service for a lift station or pump for a lake, we will charge him to run it and not mix the 1? with the 3? conductors.
You also don't want to lose sight of the fact that this is a really small subdivision. Also remember that an overhead line is very flexible for future growth but you can get painted into a corner very quickly if everything is buried.
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