220 Three Phase to 220 Single Phase

[albert0510]

TL;DR Summary

I want to convert 220vac in a Wye configuration to 220vac single phase. So now I have L1, L2, L3 and N. Where Lx-N = 127 and Lx-Lx = 225. I want to transform to Lx-N = 225 3000W. Will an isolation transformer do this?

I want to convert 220vac in a Wye configuration to 220vac single phase. So now I have L1, L2, L3 and N. Where Lx-N = 127 and Lx-Lx = 225. I want to transform to Lx-N = 225 3000W. Will an isolation transformer do this?

 

[Windadct]

Hello Albert - you seem to be mixing terminology. Split phase would be 120VAC L-N and 240VAC L-L.

For a true 3 phase ( not split phase) these are kind of odd or unusual voltages. Yes - 240VAC L-L 3 Ph - will give 127VAC L-N.

So ... 127VAC for 3000 W is only ~ 24 A, for 240 VAC, 12.5 A.

It really is not clear what you are trying to do.

L-N can provide 3000W

L-L can provide 3000W

 

[albert0510]

Hello Windadct,
Thank you for your email. Let me clarify. The location is a Caribbean island where the power is not reliable. It’s indeed a 3-phase Wye configuration. That’s said the power between any of the load (Lx-Lx) is around 225 VAC, it can vary +/- 5 VAC or more. The power between Lx-N is anything between 117 VAC to 135 VAC. Today is 116.8 VAC. I have a single phase 11 Amps, 2 HP motor rated as 220VAC that is wired between L1-L2 with N and the case is grounded. This is a pool pump motor.

I have two issues. I control the motor remotely via WIFI 220 VAC smart plug rated at 16A. I have burned two of these and always happens when we are not there. Also, a motor burned 4 years ago. The other issue, that maybe related is that the pool Stainless Steel handle, builds up like soot below the salt water line. Some sort of galvanic interaction between ?

My thinking is that one leg been live all the time is perhaps the source of both issues. Thus the idea of inserting an isolation transformer. If I look at each phase when the motor is running I measured ~13A in L1 and ~10A in L2 with start up spikes of up to 30A. In the mean time I’m planning to use a 2-phase relay rated at 40A.

I hope this long explanation gives a better idea of what I’m trying to do.

 

[Windadct]

If the motor is connected L1 and L2 then the current should be equal.

A typical pool pump motor will not be connected L1 N and L2... Just L1 L2 240VAC. The Panel feeding the motor I am sure has the neutral run to it, but I doubt the motor does.

A 16A "smart" outlet for a continuous 11 A load is not so good - also if this is a regular "plug-receptacle" combo - and outside, the reliability of the the connection will be poor, so excessive heat on the "smart-plug" will kill it.

 

[Baluncore]

The other issue, that maybe related is that the pool Stainless Steel handle, builds up like soot below the salt water line. Some sort of galvanic interaction between ?

There is no need for stray electrical currents to explain the sooty appearance.
Stainless steel is only stainless in the presence of oxygen. If the pool water is chemically treated to eliminate oxygen, then the protective chromium oxide layer will be etched away and the stainless steel will corrode to become a black crumb.

 

[DaveE]

Of course you have a good ground connection to everything in your pool, right? Good, then I think @Baluncore is right about the corrosion stuff. Pool chemicals are nasty. If you want to try something anyway you could put a zinc anode on that handle. Your nearby marine store has them. It will fix galvanic corrosion issues, but I think it's a waste of time.

I think you motor should be fine running L-L. But, I really don't know what's in your smart wi-fi gizmo. Sometimes smart and rugged don't come together, especially when combined with cheap. If this was my system, I'd have a good old-fashion contactor switching the motor and then your control stuff would only operate the contactor coil. Turning motors on and off is a tough application; contactors are also tough (actually designed for this application).

A one time motor failure 4 years ago doesn't mean much to me. Motors do fail sometimes.

 

[Guineafowl]

Can you take a picture of, or otherwise post here, details of the motor rating plate? I can’t quite square the motor power with the quoted current.

Running it between L-L of a wye supply, or with an isolation transformer supplying 230V, should make no difference. L-L or L-N are essentially interchangeable as far as a load is concerned. If your motor is wired L-L, where does the neutral go?

As suggested above, use the wifi switch to activate a contactor, then it only has to run the coil of that contactor. Smart plugs are significantly derated for inductive loads like motors.

 

[Tom.G]

The "relay" type needed would be called either "Motor Contactor" or "Motor Starter." These are designed and rated to handle the high starting current and the arcing at turn-off. As it happens, 5HP is a common size for air compressors so they are readily available.

Since the incoming power has both lines above ground, that is both are Hot, the starter must control both of them. The lowest cost and readily available approach would be a 3-phase, 5HP, 240v starter. I strongly recommend a starter with built-in thermal overloads. The thermal overloads function as an automatically- reset circuit breaker that senses current on each phase.

If you are buying from an Authorized Distributor or a large industrial supplier, you can specify the coil voltage you want, usually from 24V up to line voltage. As the devices are designed for industrial usage, they are designed for easy field repair and parts are readily available.

Both manually operated and electrically operated versions are made. The one you need, with a coil, is called a Magnetic Starter.
Try a Google search for: magnetic starter 5hp 230v 3ph

Cheers,
Tom

 

[Baluncore]

Will an isolation transformer do this?

Yes.
But it may be more flexible, and lower cost ($150), to employ a 3 kW VFD = variable frequency drive.