Customer needs 30 Hp 3 phase Specialty compressor system. - Page 2 - Electrician Talk - Professional Electrical Contractors Forum
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Old 02-14-2017, 11:10 AM   #21
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Changing a single phase service to a 240∆ or a 208Y is not all that difficult. Often, all that needs to be done is change the meter base, the panel (sometimes just the interior) and add another wire.

If it's overhead, it's likely 2" already and if the mast is straight, shoving another wire down it is easy. If it's underground, it's the POCOs problem.
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Old 02-14-2017, 06:19 PM   #22
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Originally Posted by micromind View Post
Changing a single phase service to a 240∆ or a 208Y is not all that difficult. Often, all that needs to be done is change the meter base, the panel (sometimes just the interior) and add another wire.

If it's overhead, it's likely 2" already and if the mast is straight, shoving another wire down it is easy. If it's underground, it's the POCOs problem.
In some places that's true, in other places it's not that easy. It's not that uncommon for PoCos to use a SWER (Single Wire Earth Return) system to save money on running power to users that will only need single phase. Or they will run a phase and a neutral rather than two phases, because they will reduce the size of the neutral to save money. In either of those cases if you ask for even an open delta 3 phase drop, they will make you pay for running the extra wire out from the nearest true three phase connection, then they ding you for the cost of the transformers.
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Old 02-14-2017, 08:02 PM   #23
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Originally Posted by micromind View Post
Changing a single phase service to a 240∆ or a 208Y is not all that difficult. Often, all that needs to be done is change the meter base, the panel (sometimes just the interior) and add another wire.

If it's overhead, it's likely 2" already and if the mast is straight, shoving another wire down it is easy. If it's underground, it's the POCOs problem.
I think people would prefer a WYE system but can only get a Delta due to the POCO not wanting to bring in a 3rd phase.
They would have to set a third pig too.
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Old 02-15-2017, 08:38 AM   #24
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Using a VFD for a power source is bad practice. In this case, the compressor already has a VFD to drive the prime mover. You would probably experience significant problems with the conflicting carrier frequencies of the two VFD's, not to mention problems associated with using the replicated AC waveform of the VFD powering the electronic controller. This is probably why JRaef recommended separating control power.

If your customer is only operating with 200A at 120/240 V single phase, their power consumption is not that great. The main reason for using screw compressors is for energy savings. I would discuss this situation with your customer's Ingersoll Rand representative and ask him why he is recommending this piece of equipment. It seems to me that they would most likely not do that at all. Screw compressors are high ticket items, and the I-R rep's I have dealt with always make a site visit to confirm power availability in order to specify the compressor to meet the customer's needs. I am pretty sure that someone cannot buy a compressor like this new without I-R's help. If your customer bought one on the used market, that a the sign that this customer is somewhat short-sighted.

What is your customers reasoning for the installation? Your realistic options are four-fold. You can either have a second service of the appropriate voltage system installed. All of his current 240 V equipment will function adequately at 208 V single phase. You could recommend them finding a building with the appropriate power. You could recommend against the purchase of this compressor; and if they need more volume, solve the problem by installing an additional piston compressor in parallel with the existing compressor which feeds into a holding tank. You will need the help of someone with a fair amount of experience in pneumatics for this. You could back off altogether and protect yourself from liability.
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Old 02-15-2017, 08:46 AM   #25
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It is easy to lose sight of the long term implications of working with "good" customers. There are times when helping to solve a customer's self-imposed technical problems only work against you. I have dealt with this kind of situation, where someone absolutely has to install a piece of equipment, and is not willing to invest adequately in the infrastructure to make it work properly. In this case, the purchase of a screw compressor to provide air to a small shop (200A 120/240V?) is like buying a Case Magnum tractor to plow a backyard garden because it will save time. I do not see this ending well.
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Old 02-15-2017, 09:20 AM   #26
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It is easy to lose sight of the long term implications of working with "good" customers. There are times when helping to solve a customer's self-imposed technical problems only work against you. I have dealt with this kind of situation, where someone absolutely has to install a piece of equipment, and is not willing to invest adequately in the infrastructure to make it work properly. In this case, the purchase of a screw compressor to provide air to a small shop (200A 120/240V?) is like buying a Case Magnum tractor to plow a backyard garden because it will save time. I do not see this ending well.
I think it either fell off of the back of a truck or the shop owner shops on Ebay after a few Drinks.

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Old 02-15-2017, 02:41 PM   #27
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... In this case, the compressor already has a VFD to drive the prime mover. ...
I looked at the data sheets, I didn't see that. Other than that, I agree with everything else you said. A VFD is not meant to be a power source for an entire system, it is ONLY for running a 3 phase motor.
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Old 02-16-2017, 08:14 AM   #28
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I looked at the data sheets, I didn't see that.
Thanks for pointing that out. I did not initially look at the spec.'s. I am not a compressor expert, but I have not yet seen a screw compressor without a VFD. You gave me pause to consider, though. I looked at the spec.'s and they showed it to be belt driven, which raised an eyebrow. They did not state that the controller was not a VFD, however. I tried to cross reference the model number from the sales website to I-R's website with no luck. The closest I could come was I-R advertising some compressors as VSD compressors. This is not conclusive, but certainly allows for other control means. Point well taken, it pays to look at the details and be specific.

That said, I have concerns about the proposed installation concerning necessity. How did the customer arrive at the conclusion that this was the compressor for them? Pneumatic system applications are very analogous to electrical system applications. More is better, but too much is still too much. It is very common now to forego the expense of expert advice from an engineer when designing electrical systems and the EC is used instead to save cost. This is often adequate, but not always and problems result. Even the EC (hopefully) approaches the system based on current customer needs (which includes equipment purchased but not yet installed) and projected future demands. How does this customer know his volume requirements?
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