Two phase elevator motor on a three phase service

[zbang]

Also, if transformers are used, then the motor might die of old age, and would almost certainly be replaced with a standard 3 phase one, thereby wasting the money spent on the transformers.

Yabut... Any 2-phase motor still in use and in reasonable shape is probably going to continue running until the sun burns out, and if it's part of an elevator, it could be part of a single-unit MG set (the OP doesn't say). Also, and I'm guessing here, replacing an elevator motor with a non-OEM unit may trigger some re-certification business, and that can't be free.

 

[kwired]

Motors draw more current at lower voltages.

Just realized this thread has been idle for a little bit but the different voltages in this case also involves 2 phase four wire vs three phase. Total VA is distributed differently in each case and current levels will be different even at same voltage.

 

[conmgt]

I know that this is not answering the question, but might a new motor be cheaper ?
Remembering that if transformers are used, the customer is paying forever for the losses in the transformers.

Also, if transformers are used, then the motor might die of old age, and would almost certainly be replaced with a standard 3 phase one, thereby wasting the money spent on the transformers.

I may need more than a new motor, a whole control/relay/reversing panel would also be required. The existing panel is a thick piece of slate with fully exposed contactors and other devices. You need to be careful walking around in the little penthouse on the roof that contains all of this. Also, I would likely need a crane to get a new motor up on the roof and then find a way to couple it to the existing gearbox and line it up precisely.

 

[conmgt]

Conmgt...

For comparison, how much do two 12.5kVA, 2-winding xfmrs cost?

Regards, Phil

Probably I could get used ones for half the price but I'm yet to be convinced that your solution would work. I'm not saying it wouldn't, I just don't know enough about the subject to say either way and wonder why a Scott-T was ever designed.

 

[jim dungar]

Probably I could get used ones for half the price but I'm yet to be convinced that your solution would work. I'm not saying it wouldn't, I just don't know enough about the subject to say either way and wonder why a Scott-T was ever designed.

At one time 2-phase power was very common in the traction industry (lifts and motion), Scott connected transformers were probably the best known and most widely used method for going between 2-phase and 3-phase systems while maintaining a large degree of balance in the systems.

If you are not comfortable with the Scott arrangement, then you could consider a Taylor connection which uses (3) transformers, however you will still need transformers with 86.6% taps, but this time they will need to be on the 2-phase side.

Personally I would stick with the Scott arrangement because it was the most common, there is a lot of literature available on it.

 

[conmgt]

If you are not comfortable with the Scott arrangement, then you could consider a Taylor connection which uses (3) transformers, however you will still need transformers with 86.6% taps, but this time they will need to be on the 2-phase side.

Personally I would stick with the Scott arrangement because it was the most common, there is a lot of literature available on it.

You have it backwards. It's the Scott-T set up that I am comfortable with, it's Phils solution of two transformers...one on AB and another on CN of the primary 208/120 that I'm not comfortable with. I don't know enough to say that that will work as well as a Scott-T. Read his post.

 

[Phil Corso]

Conmgt...

If you are unsure my suggestion will work, try it with control-type 10VA transformers! Just let me know if a schematic is needed!

Phil

 

[jim dungar]

You have it backwards. It's the Scott-T set up that I am comfortable with, it's Phils solution of two transformers...one on AB and another on CN of the primary 208/120 that I'm not comfortable with. I don't know enough to say that that will work as well as a Scott-T. Read his post.

Oops, must have gotten lost in the fog.

I do not have much problem with Phil's solution, other than it also requires a somewhat non-common transformer (208:240 single phase looks to be 1.5X the cost of a standard unit). Phil's connection appears to balance the input currents, but it also creates a neutral current so the feeder needs to be 4-wire with a full sized neutral.
The Scott connection was very popular as most early 3-phase systems were delta connections, but its use on a 208V input would also entail non-common 208:240V windings.

 

[Phil Corso]

Conmgt...
Jim has a point! Is the supply 3Ph, 4-Wire, 208Y120V, or 3Ph, 3-Wire, 208V?

Jim...
No! Depending on Conmgt's reply to my question, uncommon voltages will not be required!

Phil

 

[Phil Corso]

Conmgt...
Forgot to ask, what is capacity of source?

Phil

 

[jim dungar]

No! Depending on Conmgt's reply to my question, uncommon voltages will not be required!

I do not know of very many off-the-shelf single phase power transformers with 208V inputs, hence my use of 'non-common' rather than 'special'.

 

[conmgt]

The service will be 208/120Y 4 wire. The elevator motor is 220V 2 Phase 4 WIre 44A 980RPM....my original posting said 240V but that was wrong, the motor label says 220V. The service is 800A and has plenty of capacity.

The elevator serves 3 floors and can travel the distance in well under a minute. Will it be fine on 208V and avoid the need for one of the transformers?

 

[Phil Corso]

Conmgt...
Although older motors have more material that modern ones, I question stressing it with an increase in current if the first-phase, say 'A' , is supplied at 208V! As with 3-ph motors, a 2-ph one running at reduced volage will also result in an increase in phase-current. Furthermore, starting-torque may be compormised.
Phil

 

[Phil Corso]

Conmgt...
Can you enlighten us as to why you don't want to change the motor as suggested by someone?
Phil

 

[templdl]

I've been watching this string of posts and have been quite intrigued as to where it was leading toSince I have sold quite a few 3ph-2ph both 4 and 5 wire and 2ph to 3ph transformer into the Philadelphia area, probable at lease 2 a month, if the OP asking questions in order get an answer that he wants to hear rather that face the fact that he should either purchase a 3ph to 2ph transformer or replace the motor.
In all of the customers and reps this has always been a very short conversation as to what is required for the application.
Other that that where is this all leading to?

 

[conmgt]

templdl, I started this post to have a conversation with other members to learn something not hear something. Since this appears to be a field that you work in, it's a very short conversation for you. But to me, and I'm sure many many other watchers, 3ph to 2ph is new and intriguing and this is a long conversation because I'm a curious person. I've learned a lot. Care to follow Phil and Joe's lead and contribute and enlighten?

Replacing the motor is certainly an option but not so simple. I'd need a 15hp 980rpm motor or motor/gearbox. The motor and traction sheave are in a very small mechanical room on the roof. Access to the roof is via an extension ladder or small roof hatch. A 15hp motor isn't something I can carry on my shoulder so a crane would be needed.

Then there?s the 100y.o. motor control. The control panel for the existing motor, as I mention previously, is as old as the motor...100+/- years. Will it work with a new 3ph motor? Will a code require that it gets updated?

The existing motor has a unique shaft and bolts directly to the brake. The traction gearbox bolts directly to the other side of the brake. There is no isolation coupling between the two, things have to line up perfectly and custom machined parts will certainly be needed.

A transformer on the other hand can be installed at the service panel and conductors sent up the existing conduit to the motor room.

I have a call into a local elevator shop to get their opinion and answer questions about the control panel.

 

[templdl]

templdl, I started this post to have a conversation with other members to learn something not hear something. Since this appears to be a field that you work in, it's a very short conversation for you. But to me, and I'm sure many many other watchers, 3ph to 2ph is new and intriguing and this is a long conversation because I'm a curious person. I've learned a lot. Care to follow Phil and Joe's lead and contribute and enlighten?

QUOTE]

Thanks, point well taken. I'll back off, sit back and follow the posts as it may be interesting to find how you end up solving your predicament as I may learn something new. From my point of view and the many 3ph-2ph transformers that I have supplied over the years when you're backed into a corner with 2ph you may not have much of a choice choice but to face the music. In addition, it is also important to be aware that the 2ph can be either 4 or 5w. I have gotten an "opps" from some customers when they specified 4 and actually required 5w.
As such I always ask the customer to confirm the voltage.
I would attach a copy of the configurations but I can only find one for the 4w handy.
I wish I could find where a filed a picture of a huge 3ph-2ph transfomer that I shipped to a factory in Mexico. It must have been around 1500-1750kva and 7'-8' high. A very strange looking transformer with 2 teaser coils which I think they were called that were mounted on top.

 

[Phil Corso]

Conmgt...
You certainly satisfied my curiosity! And, I was wrong in my first reply to your post, that is, I'm not older than the motor, but close enough!

I have a idea, but await cost dataI If idea turns out to be substantially lower than the $3k figure you used, I'll let you know!

Regards, Phil

 

[Phil Corso]

Conmgt...

1) Trying to determine smaller sized xfmr via load factor! How many 1-minute trips are carried out per hr? Per day?

2) How did you arrive at the 25kVA figure?

Phil

 

[kwired]

Conmgt...

1) Trying to determine smaller sized xfmr via load factor! How many 1-minute trips are carried out per hr? Per day?

2) How did you arrive at the 25kVA figure?

Phil

I like where you are going with this. And yes 25kVA is more than necessary for 15hp, but a 15kVA is a little on the light side- however figuring in the duty cycle and how it effects things can make a big difference, but is something the typical field installer can not consider but an engineer can.