using 2 legs of 208 3 ph to supply a VFD 120 vac 1ph input and 230 v output...

[PNA]

We have had motor and or vfd failures when customers use 2 legs of a 208 vac 3 phase system to supply our machines....

we state 230 single phase 4 wire

I know there are phase issues, etc but trying to explain that to my bosses is difficult....

Help?

 

[waross]

230 single phase 4 wire

Is this a typo? If you meant "230 three phase 4 wire", then:
Issue #1. You are using single phase instead of three phase. RTFM and derate the VFD for use on a single phase supply.
Issue #2. You have only 208 Volts available rather than 230 Volts available. A 230 Volt rated motor will draw more than rated current and overheat when trying to deliver rated HP at rated speed on low voltage.
Hint: 120:208 Volts three phase is very common. 230 Volts three phase or the standard 240 Volts three phase services are few and far between.
Consider equipping your machines with either 208 Volt rated motors or 200 Volt rated motors, and specifying 120:208 Volts three phase. That's what's out there. (120:208V)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[PNA]

4 wire indicates ground, neutral, 2 hots
single phase: i.e. supplied to a house

black to neutral - 115 vac > VFD in > "230 vac out" (motor is rated for 230 vac)
red to neutral - 115 vac > VFD in > "230 vac out" (motor is rated for 230 vac)

2 "separate circuits"

so from what i have read, 208 - 3 phase (pulling 2 legs only), using a neutral, to generate 2 separate 115 vac lines is a no-no because of out of phase conditions and potential that the voltages will be unbalanced, according to ansi standards, fluctuations down to 184 vac across 2 legs is acceptable....

just wanting to verify

Paul

 

[waross]

Standard rated voltages in North America:
Supply voltages- 120V, 208V, 240V, 277V, 480V. (And in Canada 347V, 600V.)
Motor rated voltages- 115V, 200V, 208V, 200/230V, 230V, 460V, and in Canada 575V.
A VFD on a 120:240 Volt circuit will normally be connected across 240 Volts. The 120 Volts may be used for control or other devices.
A VFD on a 120:208 Volt circuit will normally be connected across 208 Volts. The 120 Volts may be used for control or other devices.
120:208 Volts is very common in larger apartment buildings, in small commercial units such as strip malls and in larger buildings and malls.
Consider using double rated motors, 200-230/460 Volt rated. These will function on either voltage. These motors may draw almost 15% more current when operating on 208 Volts.
Sample;

https://www.grainger.com/category/g...Z1z0nubl?searchRedirect=electric+motors&ssf=3

3/4 HP General Purpose Motor, 3-Phase, 1725 Nameplate RPM, Voltage 200-230/460, Frame 56
Item # 44Y987
Mfr. Model # 5KS46MN4078

Price $492.75 / each


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[PNA]

Bill,

Please read carefully....
I have a VFD that is a 120 VAC 1PH input.
I have attached a spec sheet.
It provides 230 VAC 3PH output.

We have sold hundreds and hundreds of these units.

My question is not the availability of certain voltages etc.....
I have been in design for the last 15 years....

It is the question of the suitability of using 2 legs from a 208 VAC 3 PH WYE unbalanced supply, adding a neutral that being used to supply a machine that requires 2 x 120 VAC hots...
and the potential damage to a VFD by doing so over the course of 3 months, 6 months, whatever....this all concerns warranty claims, etc.

So I appreciate you answering, however I am not asking for a lecture on standard supply voltages.

Regards

Paul

 

[itsmoked]

Gotta say I've read your question(s) several times and am still confused as to what the heck you're asking. Which I find generally means you're off in the weeds so far no one can really figure out what your 'mystical theory of a problem' is.

So I'll just say this.

If your VFD can take in 120Vac and put out 230Vac because it has a voltage doubler front end then it doesn't matter one twit as to how you came up with the 120V. Your concerns about 208 verses 230 volt service is unwarranted.

Oh, and generally 4-wire means three phases with a neutral NOT two phases a neutral and a ground grounds are now assumed and not counted. This is part of what threw waross off.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[resqcapt19]

Single phase 120 volt loads are commonly supplied by 208Y/120 volt systems without problems.
I am not sure what you mean by adding a neutral. The neural should already be a part of the system.

 

[PNA]

230 single phase.....each phase is in line with other

208 three phase.....each phase is 120 degrees apart

yes you do get 120 vac from line to neutral


however:
phasing differences can cause issues in some cases....

there are still many older existing facilities that have configurations that are not typically used anymore....depends on where you are in the US and Canada

220 single
208 unbalanced wye
208 delta
460 delta
230 single
etc etc etc

In response to Keith:

If your VFD can take in 120Vac and put out 230Vac because it has a voltage doubler front end then it doesn't matter one twit as to how you came up with the 120V. Your concerns about 208 verses 230 volt service is unwarranted.


that is not how a VFD makes 3 phase power....
we have received from customers using 208 and having VFD's or give a VFD fault...we bring it to our facility and its works perfectly fine....


and yes you are correct on the 4 wire, my bad

 

[itsmoked]

that is not how a VFD makes 3 phase power....

Yes, it is how a VFD makes three phase power! The incoming power is rectified to DC and stored on a capacitor(s) from where the drive synthesizes 3 phase power. How the power gets into the capacitor doesn't really matter. It's normally via rectifiers taking the local line voltage, as I'm sure you're aware. But it can just as easily come from DC fed in thru the same rectifier bank or DC fed directly into the DC link. It can come from single phase power or three phase power,(with some physical limitations).

What this all means is the 'phase angleness' does not matter in the least because the drive knows nothing about it. It just sees the resulting DC voltage stored on a single capacitor for its raw source of working energy.

There should be no other issues relating to equipment using the 208 or 240 provided to it, even if you then use a single phase to neutral of the supplied power that is 120Vac, as all other signals are typically low voltage DC often created by the drive itself, typically opto-isolated too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Seems to me the problem appears to be some sort of misunderstanding as to how to feed a 120V drive from 2 phases of s 3 phase 208V source.

The WAY YOU DO IT IS TO GIVE THE DRIVE ONE PHASE AND A NEUTRAL. You would NOT feed THAT drive with two phases of a 208V system. As Keith correctly said, this drive has s voltage doubler circuit in the front end that pre-rectifies the AC to DC, then passes that DC through a Voltage Doubler, then feeds that to the DC bus of the VFD. So if given 120VAC, the DC Bus ends up at around 340VDC. If you feed that drive with two phases of a 3 phase 208V source, the voltage doubler will result in the DC Bus being somewhere in the area of 588VDC, likely far out of spec for all of the components inside of the drive. The VFD PWM algorithm could probably handle making sure the RMS voltage to the motor is no more than 230VAC, but internally, you are accelerating the demise of the parts in the drive to the point of rapid failure. You are also likely accelerating the demise of your motor too, because although the OAM algorithm is making it appear to be 230VAC, the pulses are still comprised of 588VDC instead of 340VDC. That will bring with it a host of other issues, all detrimental.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[PNA]

I give up....

The facility's power supply. In today's power-hungry society, it's getting hard to obtain a good source of clean non-distorted power. Over and under voltage conditions greater than plus-or-minus 10% will trip most drives. A voltage unbalance between phases of 3% to 5% can cause tripping of the drive's overload fault protection device.

 

[PNA]

someone close this thread....please....

 

[waross]

A voltage unbalance between phases of 3% to 5% can cause tripping of the drive's overload fault protection device.
If you are getting this code on a single phase VFD, then it refers to the output and is a warning of a developing issue in the driven motor.
There is no test that you can apply to just the two wires feeding the single phase VFD that will tell whether the source is from a 120:240 Volt single phase supply or from one phase of a 120:208 Volt three phase supply. (Or from a 120:240 Volt center tapped delta service.)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

120V single phase is 120V single phase no matter how it's derived. Care to explain how there can be phasing differences on the single phase 120V?

Power quality issues are power quality issues no matter what configuration of power system. A 10% drop in the power system leads to the 120V source dropping to 108V no matter what configuration of power system.

 

[jraef]

Your link to data sheets shows this is a PowerFlex 4 drive. There is no "phase imbalance" feature on the input, or output for that matter. There is a fault called "Power Loss" that, in the manual, suggest MIGHT be caused by a phase imbalance on the input. But that would only apply to a 3 phase input version. The manual is written for all possible permutations of the drive, but that fault description would not apply to a single phase input version.

What actually triggers that fault is excess DC bus ripple. Given that this drive will have the voltage doubler on the front end, which supplants the normal rectifier, the cause of excess bus ripple is going to be either a component failure on the voltage doubler circuit, or a capacitor failure on the DC bus.

So given that, and the apparent confusion as to connecting 208V to s drive rated for 120V input, I'd still think this is a secondary affect of blowing out the components on severe over voltage.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington