Single Phase Motor on 2 phase

[GoldDigger]

From what I have heard, the largest single legacy use of two phase power is elevator traction motors, where the starting torque and multiple starts are critical so single phase would not suffice and three phase power was not as common as it is now.
Conversion to three phase would be expensive and require design approval by the elevator manufacturer.

Tapatalk!

 

[kwired]

From what I have heard, the largest single legacy use of two phase power is elevator traction motors, where the starting torque and multiple starts are critical so single phase would not suffice and three phase power was not as common as it is now.
Conversion to three phase would be expensive and require design approval by the elevator manufacturer.

Tapatalk!

I don't think the OP has an elevator, but apparently a shop with some old machines.

 

[jmc679]

One other place that hasn't been mentioned is the paper industry. At least here in Maine, there is still one mill (I know for sure uses, and others I've heard have) that have hydro generators and many 2 phase motors powering machines. Some power is derived from a Scott T though. There is also 11kv 3p and 2300 in house. I believe the 2p distribution is 2300 from the hydro dam, possibly 11kv, it's been a few years since I was there and know both voltages where common. 2300 was common in 2 and 3p. Most of the motors are 440 though, and a few @ 2300. I've worked in the substations and chased out circuits through miles of tray there. Knife switches and open bus is the norm in the oldest indoor subs. The mill Has been electried for 130 years and has all kinds of artifacts that no one would touch today, while hot.

 

[hurk27]

One other place that hasn't been mentioned is the paper industry. At least here in Maine, there is still one mill (I know for sure uses, and others I've heard have) that have hydro generators and many 2 phase motors powering machines. Some power is derived from a Scott T though. There is also 11kv 3p and 2300 in house. I believe the 2p distribution is 2300 from the hydro dam, possibly 11kv, it's been a few years since I was there and know both voltages where common. 2300 was common in 2 and 3p. Most of the motors are 440 though, and a few @ 2300. I've worked in the substations and chased out circuits through miles of tray there. Knife switches and open bus is the norm in the oldest indoor subs. The mill Has been electried for 130 years and has all kinds of artifacts that no one would touch today, while hot.

Or steel mills, as in around the Pittsburgh area, the first poly-phase generator plant installed was by Tesla and Westinghouse at Niagara Falls, they used 25hz (one hz over the frame rate of motion picture to prevent the Edison lamps from strobing) and 110/220 volts or 220/440 as the customer end standard voltages, the 110 came from the fact that Edison lamps used 100 volts DC so 110 volts @ 25hz would give the lamp about the same brightness, and it would also last about the same amount of time.

Many of the old 2? 25hz motors were very large for their HP size, a 10hp would be as large as a 100hp motor today.

At the steel mill I work at today we still have allot of old switch gear no longer in use but still marked 2? 25hz, 110/220 or 220/440 volts, this is why we still hear old timers still refer to these voltages, once 3-phase made it to main stream the voltage standard was bumped up a bit.

The last 2? motor I had to work on was an old 500hp draw bridge motor, we had to install a 3? motor gen-set to produce 25hz as 25hz wasn't available and drives was non-existent back then.

 

[Tony S]

LeBlanc

LeBlanc

There is another transformer that can be used for two phase three wire from three phase.
LeBlank

 

[SG-1]

Short History of Two Phase

Short History of Two Phase

This site has a short history of two phase

http://www.3phasepower.org/2phasesystems.htm

 

[KEM]

2-phase 5 wire (4 hot 1 neutral)

2-phase 5 wire (4 hot 1 neutral)

I am installing a new compressor for a customer. His shop is 2-phase 5 wire (4 hot 1 neutral) but the new compressor is single phase. I mainly do commercial and light industrial work, but I have never come across 2 phase. Even though I sort of picked up on the basics I'm still unfamiliar with it so hopefully someone can help me out. I need to get the 2 phase supply to the single phase compressor. Can I just use one leg or is there a transformer I need?


Thanks!

2-phase 5 wire (4 hot 1 neutral) sounds like 3 phase and it seems to me that one needs to know if the source is a Delta or Wye connected secondary depending on what the voltage is being transformed into. A delta supply could have 240 volts between phases with one coil center tapped between two phase lines creating a neutral of 120 volts between the lines of the center-taped coil, but 208 volts from the neutral to the third leg. That "208 volts from the neutral to the third leg" is known as the high leg and is required by code to be marked as such. A Wye connected source with neutral could have 208 volts between phases, but in this case would have 120 volts from one of the 3 phase to neutral. The characteristic of the supply transformer is indicated by the phase to phase and phase to neutral voltages. Depending on what the single phase motor has been wired for, 120 or 240 volts, and the demand cycle determines the calculations to select conductor size, over-current device size and type, overload size, and the equipment grounding conductor size. If the motor is rated for only 120 volts, a single phase breaker would work.
A two phase systems would have a floating neutral problem with the voltages 90 degrees out which may be why they were phased out and replaced with 3 phase systems where voltages are 180 out and hence the neutral can be derived by center tapping one of the windings.

 

[GoldDigger]

Actually 2 phase 5 wire describes a true two phase system with four phase lines at a 90 degree rotation and a common neutral.
If the phase to neutral is 120V, then each pair of opposite phases provides a true 240V single phase with center tap.

Tapatalk!

 

[kwired]

2-phase 5 wire (4 hot 1 neutral) sounds like 3 phase and it seems to me that one needs to know if the source is a Delta or Wye connected secondary depending on what the voltage is being transformed into. A delta supply could have 240 volts between phases with one coil center tapped between two phase lines creating a neutral of 120 volts between the lines of the center-taped coil, but 208 volts from the neutral to the third leg. That "208 volts from the neutral to the third leg" is known as the high leg and is required by code to be marked as such. A Wye connected source with neutral could have 208 volts between phases, but in this case would have 120 volts from one of the 3 phase to neutral. The characteristic of the supply transformer is indicated by the phase to phase and phase to neutral voltages. Depending on what the single phase motor has been wired for, 120 or 240 volts, and the demand cycle determines the calculations to select conductor size, over-current device size and type, overload size, and the equipment grounding conductor size. If the motor is rated for only 120 volts, a single phase breaker would work.
A two phase systems would have a floating neutral problem with the voltages 90 degrees out which may be why they were phased out and replaced with 3 phase systems where voltages are 180 out and hence the neutral can be derived by center tapping one of the windings.

To add to what Golddigger said, there is such a thing as a two phase system, it is somewhat of a dinosaur and you will only find remaining systems for the most part in the east and northeast areas of the US. The OP is in PA which did have these systems and still has some but AFAIK there is no longer any utility distributing two phase, though they may still separately derive it from three phase sources to supply to customers that request it. Go back and read the information Smart$ submitted in post #9 it explains basics of a two phase system pretty well.

 

[PetrosA]

I don't know how many customers are still fed with two phase vs. three phase and converting power themselves. I know that there are still a lot of shop machines out there from the Philly area with two phase motors that are running fine on single phase - you just have to get a capacitor in there for starting then pull it back out. Easy to do with an ice cube relay. There are still a few motor shops around that know how to work on them too. Mostly old guys, but they know their stuff.

 

[Tony S]

This site has a short history of two phase

http://www.3phasepower.org/2phasesystems.htm

Cheers for that. Being in the UK I've not really found a great deal of reading about 2 Phase.

 

[kwired]

I don't know how many customers are still fed with two phase vs. three phase and converting power themselves. I know that there are still a lot of shop machines out there from the Philly area with two phase motors that are running fine on single phase - you just have to get a capacitor in there for starting then pull it back out. Easy to do with an ice cube relay. There are still a few motor shops around that know how to work on them too. Mostly old guys, but they know their stuff.

I would think to get full rating out of a two phase motor you would need constant supply at correct displacement of both phases. I could see it working for a motor that is relatively lightly loaded, as that is essentially exactly what a single phase capacitor start motor is, two phases until the start winding is disconnected, then it runs on single phase only, a PSC or capacitor start - capacitor run is essentially a two phase motor with the second phase created by capacitors, as well as different inductive properties between windings themselves in some cases.