Powering a well pump

[Arambin]

I have a question regarding the electrical power to a 20hp well pump. The only power available at the street is single phase. We want the power company to run 3 phase to the site. They want to install a 120/240 delta bank that simulates 3 phase (as best I can tell). We do not want a phase convertor. Will this delta bank have any disadvantages? We think they just don't want to run the 3 phase from a few miles away, even though it is at our expense.

This may be a question for the electrical engineers, but I thought I'd try here first. Thanks in advance.

 

[semo]

I would never use delta bank on a job again. We had a sewer system out in no mans land which had large vacuum pumps and aeration blowers. The electric company recommended the delta service as it was less expensive to install.

When placed into service the motor circuits kept blowing. It was finally determined that this was because the delta bank provided such a dirty power that it would not work for this application.

The power company was then paid a second time to install 3 phase power.

I also agree that phase converters are also expensive to maintain and stay away from them.

 

[PUMPDESIGNER]

I think you are speaking of what we call either Open Delta or "High Leg" three phase where one of the phases to Neutral reads 220 volts, the other two phases show 110 volts to neutral.

Those systems are inherently unbalanced.
You are correct, the power company is trying to save money.
Some providers have rules that will not allow them to supply any pump larger than 10 hp with Open Delta, and if that be the case then remind them of that and their internal rules should require them at no charge to you to provide the true 3 phase. Many power vendors now have young inexperienced engineers on staff (having forced the old boys out to pasture, and when you tell them they cannot supply open delta to large motors they may run to daddy and find out.

If you have to use Open Delta you can overcome some mighty big troubles by oversizing the motor to 25 hp, which then allows the motor to handle the unbalance better and stay cool inside. We have seen many old installations done this way that had motors last for 20 years or more on Open Delta systems.

I hate Open Delta, but have learned to live with it. To protect myself and my company I have become sort of expert at talking to the power company and finding people upstairs that can authorize installation of wire and transformers when you properly explain the problems with larger pumps and unbalanced power supplies (Open Delta Systems are inherently unbalanced on current even if they get the voltages to look balanced).

PUMPDESIGNER

 

[Arambin]

Thanks for all the info. I finally got them to run real 3 phase to the site, now the question is how long will it take.

Thanks again!

 

[bigfoote]

pumpdesigner, in your reply you stated that the power companies rules require them to provide 3 phase at no charge. I received 3 phase to my shop on a 1 mile run at no charge. At the time Illinois Power ran 1 mile free. A couple of years ago a friend was looking into 3 phase @ 1 1/4 mile & they quoted him $2700.00. Could you give me some enlightenment on the rules or where to check them?
Thanks

 

[panelman]

certainly in the uk you can't get 3 phase installed for free...in fact there tend to be local monopolies and costs are often measured in body parts, way way more than we (electrical contractors) would charge for the same work

 

[PUMPDESIGNER]

bigfoote,
Sorry it took me so long to get back to you, we are very busy.

Rules? There are many, the most useful are the power providers own internal rules which are usually not published, but one of their older more experienced engineers will usually give them to you verbally. For instance, I know that Florida Power and Light (FPL) has an internal rule that Open Delta systems will not be provided for any system 15 hp and greater, their rule requires them to give you full three phase on 15 hp and over. I have used that knowledge to remind their planners and they never argue, they look up the rule and then comply without question.

Their own engineers usually are the best source for this stuff because they care about what they do unlike the beancounters that try to save money at our expense. I don't dislike beancounters, just do not trust them unless they are cooperating and working with the engineers as teammates and that is rare, more likely they are dictating to engineers.

PUMPDESIGNER