Delta-Wye Question

[OldSparks]

In a situation with a 480 x 240 delta-wye xfmr is used, is the 240v output across any two legs truly 60 HZ? I've seen recommendations to not run 230/240v motors from a Wye output. Any guidance will be greatly appreciated.

 

[jim dungar]

In a situation with a 480 x 240 delta-wye xfmr is used, is the 240v output across any two legs truly 60 HZ? I've seen recommendations to not run 230/240v motors from a Wye output. Any guidance will be greatly appreciated.

Transformers do not change frequency, 60 in is 60 out.

240Y/136V wye is not a common voltage outside of data centers.
208Y/120 3 phase 4 wire is the most common.
240V 3 phase 3 wire is no longer common except for dedicated machines/systems
240/120 3 phase 4 wire is common. These are often installed as open delta, and we're intended for motor loads. The delta has one winding center tapped for the 120V, so you end up with one high leg.

You were probably warned against installing 230/240V motors on 208V supplies.

 

[retirede]

A transformer cannot change the frequency.

An induction motor can’t tell if the source is wye or delta.

 

[OldSparks]

Transformers do not change frequency, 60 in is 60 out.

240Y/136V wye is not a common voltage outside of data centers.
208Y/120 3 phase 4 wire is the most common.
240V 3 phase 3 wire is no longer common except for dedicated machines/systems
240/120 3 phase 4 wire is common. These are often installed as open delta, and we're intended for motor loads. The delta has one winding center tapped for the 120V, so you end up with one high leg.

You were probably warned against installing 230/240V motors on 208V supplies.

I may be overthinking this, but because the 3-phase supply legs are 120 degrees apart, I thought that the Wye windings would in turn, be 120 degrees apart, thus causing overheating if the motor is significantly loaded.

 

[winnie]

I may be overthinking this, but because the 3-phase supply legs are 120 degrees apart, I thought that the Wye windings would in turn, be 120 degrees apart, thus causing overheating if the motor is significantly loaded.

The wye windings are 120 degrees apart, which is exactly what a the 3 phase load requires.

The motor doesn't care if the source for the 3 phase supply is delta or wye.

-Jonathan

 

[OldSparks]

The wye windings are 120 degrees apart, which is exactly what a the 3 phase load requires.

The motor doesn't care if the source for the 3 phase supply is delta or wye.

-Jonathan

Is that true even if the motor is 240V single phase? That's what I was warned about and really don't want to eat this motor. It drives a pretty pricey 4HP airless sprayer.

 

[OldSparks]

I see now that my original question is flawed, I asked about frequency when I really meant phasing and its effect on a single-phase motor winding.

 

[LarryFine]

I see now that my original question is flawed, I asked about frequency when I really meant phasing and its effect on a single-phase motor winding.

A 1ph transformer will function equally well powered line-to-line from a wye or a delta source.

 

[retirede]

I may be overthinking this, but because the 3-phase supply legs are 120 degrees apart, I thought that the Wye windings would in turn, be 120 degrees apart, thus causing overheating if the motor is significantly loaded.

The voltage between the 3 phase conductors will measure exactly the same regardless if the source is wye or delta.

 

[jim dungar]

Is that true even if the motor is 240V single phase? That's what I was warned about and really don't want to eat this motor. It drives a pretty pricey 4HP airless sprayer.

The issue is still what voltages you actually have, not what the L-N phase angle might be, unless you are running the neutral to the motor.

208Y/120V is probably the most common wye system. Many 240V motors may not like the L-L 208V regardless that it is from a wye system.

240Y/136V is a rare wye system used in data centers. 240V motors would not have a problem with the L-L 240V even though it is from a wye system

 

[TwoBlocked]

Your volt meter can't tell if 240 vac is coming from a three phase system (120 degrees apart) or a split phase system (180 degrees apart), so neither will the motor be able to tell. Both have just two hot legs.

 

[tortuga]

In a situation with a 480 x 240 delta-wye xfmr is used

By delta-wye I take that to be a a nameplate of 480 : 240/139y

I asked about frequency when I really meant phasing and its effect on a single-phase motor winding.

A single phase 240V motor will run great off any two lines (phases) from the above transformer.
A single phase 120V motor (or anything else) is not recommended off the above setup.

 

[winnie]

There is one important difference between 240V from a 480V:240/139V wye three phase transformer and 240V from a 480V:240V single phase transformer.

The L-L voltage and frequency are exactly the same. But the voltage to ground is different. This will mean greater leakage current through insulation, and may cause problems for the electronics of any electronically commutated motor.

But for a typical L-L motor the two sources are equivalent.

 

[tortuga]

There is one important difference between 240V from a 480V:240/139V wye three phase transformer and 240V from a 480V:240V single phase transformer.

The L-L voltage and frequency are exactly the same. But the voltage to ground is different. This will mean greater leakage current through insulation, and may cause problems for the electronics of any electronically commutated motor.

But for a typical L-L motor the two sources are equivalent.

Where I have seen 240/139y is as a replacement for corner grounded 240 delta.

 

[pipe_bender]

There is one important difference between 240V from a 480V:240/139V wye three phase transformer and 240V from a 480V:240V single phase transformer.

The L-L voltage and frequency are exactly the same. But the voltage to ground is different. This will mean greater leakage current through insulation, and may cause problems for the electronics of any electronically commutated motor.

But for a typical L-L motor the two sources are equivalent.

Why go thru all the hassle and not just use a standard 480d x 208/120y?

 

[winnie]

Why go thru all the hassle and not just use a standard 480d x 208/120y?

Because the load needs 240V.

 

[ggunn]

Your volt meter can't tell if 240 vac is coming from a three phase system (120 degrees apart) or a split phase system (180 degrees apart), so neither will the motor be able to tell. Both have just two hot legs.

 

[OldSparks]

My concern is that the two hot legs are only 120 degrees out of phase. Will that not cause more slippage in the motor and therefore more heat (possibly to the point of winding failure)?

 

[winnie]

My concern is that the two hot legs are only 120 degrees out of phase. Will that not cause more slippage in the motor and therefore more heat (possibly to the point of winding failure)?

Nope.

The two hit legs are 120 degrees apart relative to a voltage reference point that is not present in the motor.

As far as the motor winding is concerned you have a single 240V supply with no phase angle defined.

 

[kwired]

In a situation with a 480 x 240 delta-wye xfmr is used, is the 240v output across any two legs truly 60 HZ? I've seen recommendations to not run 230/240v motors from a Wye output. Any guidance will be greatly appreciated.

I think your real question was probably about running a motor only rated for 230 volts on a 208 supply.

It will work. It will draw roughly 10% more current for same output as it does when supplied from 240 volt supply. Closer you are to loading it to it's rated output the more likely it will be operating beyond it's designed current rating. If it runs for short periods of time, or is seldom to never fully loaded you may never really have any trouble with it. If it runs rather continuously and at/near rated load you may have shorter motor life due to extra heat in the windings.

Motors marked 208-230 volts were intentionally designed to handle the extra current when used on a 208 supply. Also if your 208 supply tends to run a little on the high end of acceptable tolerance - say around 215 volts, you are kind of near the lower acceptable tolerance range of 230 volts and that does help you out a little with how much impact you will have from operating it at a low voltage.