Two phase elevator motor on a three phase service

[iwire]

Is it still a freight elevator? Passenger elevators have much more regulation than freight elevators and like has been said you usually must be properly licensed to even look at one if you are anything besides a passenger.

Where I am and I suspect other areas if it is called an elevator people can ride it and I can't work on it.

If it looks much like an elevator but is designed so that it cannot be operated from within it would be a material lift and I can service it.

But of course rules can be vary by location.

 

[kwired]

Where I am and I suspect other areas if it is called an elevator people can ride it and I can't work on it.

If it looks much like an elevator but is designed so that it cannot be operated from within it would be a material lift and I can service it.

But of course rules can be vary by location.

Capable of being operated from within is likely the big key most places. Don't let the wrong people find out passengers are riding "material lifts", it happens.

 

[conmgt]

Sorry to be silent for so long...

So I got a price of $1800 for a 30kVa Scott T 3ph to 2ph transformer. I like that price. It's $1k less than the other one. Probably because I asked for aluminum windings with $$$ in mind. I've yet to contact Acme and talk to the tech that Phil posted. I'll get to it. A 15kVa is available for $1100 but it provides 44A on the load side and the motor's nameplate says 44A.

The manufacturer, it's made in VA, said that the standby draw is 575W. Load draw is 1400W. 575 adds up over the course of a month. 575 x 24 x 30 = 414,000Wh = 414kWh * $0.12/kwh = $49.68. Does that calc look right?

The elevator is very rarely used and I'm thinking some way to disconnect the xfmer in between uses (as someone else mentioned I believe). Is there a specific product for that purpose? Would it be similar to a motor starter? It would be nice if say 12V or 24V could control it. I'll talk to the elevator company to see about rules regarding the ability to turn the power on and off. Probably put the control in the cab. There is an emergency ON/OFF switch in it but I'm not sure what it controls...yet.

I should have pics soon.

 

[templdl]

Good choice as I suggested back on post #36 and #37 about 2 weeks ago, a 3ph-2ph transformer. But it was fun to watch going around the block a number of times and learn some possible very interesting solutions in the process.
Yes, the suggestion of disconnecting the transformer of an elevator that is used infrequently is an excellent idea as it will certainly save on the power that is required to keep the transformer energized. Most wouldn?t have even thought about it.

Select a suitable lighting or definite purpose contactor with a 120vac coil and use a 12 or 24vac interposing relay to control the contactor and that should work just fine. When you consider the no load watts the cost of the wasted power does add up.
Get your 120vac power from a common lighting ckt, wire the contactor coil in series with a N/O contact of the interposing relay. When you energize the interposing relay with the elevator control it will close the N/O contact and close the contactor.
The nice thing about using an interposing relay is that you only require the power to close the interposing relay which will be much less than if you were trying to pull in the power required closing the contactor. In addition you can set up everything except selecting the interposing relay coil voltage when you finalize your control circuit voltage.
Anyway lighting and/or definite purpose contactors with 120vac coils are a lot more available and I don?t think there will be any availability issues with an interposing relay with a 12 or 24vac coil. If you get one with a plug on base all the wiring goes to the base and the relay can be changed quickly.

 

[kwired]

The manufacturer, it's made in VA, said that the standby draw is 575W. Load draw is 1400W. 575 adds up over the course of a month. 575 x 24 x 30 = 414,000Wh = 414kWh * $0.12/kwh = $49.68. Does that calc look right?

.

Is 575 watts or volt-amps? Power factor unloaded will be poor and actual watts may be pretty low compared to total VA. That said transformers still do use energy when idle. I have placed air compressors in same small room with transformers so that the oil in compressor will stay warm in winter months in some installations. Heat given up by 15kVA or larger transformer is often plenty of heat for this type of application.

 

[templdl]

Is 575 watts or volt-amps? Power factor unloaded will be poor and actual watts may be pretty low compared to total VA. That said transformers still do use energy when idle. I have placed air compressors in same small room with transformers so that the oil in compressor will stay warm in winter months in some installations. Heat given up by 15kVA or larger transformer is often plenty of heat for this type of application.

Using a transformer as a space heater, that's one heck of an idea. Why not?

 

[conmgt]

Here are some pics...the motor, the controls, and the brake between the motor and the gearbox.

 

[conmgt]

So, does the transformer fall under Article 450 Transformers or Article 455 Phase Converters. Article 455 defines a phase converter as "An electrical device that converts single phase power to three phase electrical power."
In this case, I'm converting 2 phase to 3 phase.

Article 450 speaks little if anything about whether or not I need secondary protection. That's a big deal when looking at Table 450.3(B). The chapter speaks a lot about autotransformers, secondary ties, and installation locations.

And since this transformer is only serving a single motor, how does that play into sizing the primary conductors and OCP if at all. Does Article 430 come into play?

 

[jim dungar]

So, does the transformer fall under Article 450 Transformers or Article 455 Phase Converters. Article 455 defines a phase converter as "An electrical device that converts single phase power to three phase electrical power."
In this case, I'm converting 2 phase to 3 phase.

it is a transformer subject to 450.

Article 450 speaks little if anything about whether or not I need secondary protection. That's a big deal when looking at Table 450.3(B). The chapter speaks a lot about autotransformers, secondary ties, and installation locations.

The secondary conductors need to be protected per 240.21(C). Based on the secondary conductor protection method and size, you may be able to take advantage of Table 450.3(B) and increase the transformer primary protection above 125%.

And since this transformer is only serving a single motor, how does that play into sizing the primary conductors and OCP if at all. Does Article 430 come into play?

Article 430 would apply only to the secondary conductors and protection.

 

[conmgt]

Let's talk about primary side conductors and protection.

The 30kVa transformer is 83A on the primary side and it solely serves a 44A motor that is a noncontinuous load (the elevator only travels 3 floors and does so in <60 secs.). The transformer is almost 200% of the load. #2 AL XHHW is rated for 90A and protect the primary with a 90A breaker.

Or could I size the primary protection to the motor load since the transformer only supplies the 44A motor? The biggest benefit of that would be the reduced size of the lighting contactor used to disconnect the transformer in between the occasional use of the elevator.
What is the load created on the 3 phase primary side of a transformer when the 2 phase secondary side is a 44A motor?

 

[kwired]

Let's talk about primary side conductors and protection.

The 30kVa transformer is 83A on the primary side and it solely serves a 44A motor that is a noncontinuous load (the elevator only travels 3 floors and does so in <60 secs.). The transformer is almost 200% of the load. #2 AL XHHW is rated for 90A and protect the primary with a 90A breaker.

Or could I size the primary protection to the motor load since the transformer only supplies the 44A motor? The biggest benefit of that would be the reduced size of the lighting contactor used to disconnect the transformer in between the occasional use of the elevator.
What is the load created on the 3 phase primary side of a transformer when the 2 phase secondary side is a 44A motor?

The protection rules in 450 are maximums, nothing says you can't use lower protection levels as long as what you choose will hold for inrush current at energization.

Now look at 240.4 (F) It does not mention two phase, but two phase is a different animal and is not really all that well included in the NEC. I think this installation is similar enough to what 240.4(F) is about it needs consideration to allowing it to use similar install for two phase.

I am in no way experienced with two phase systems, never even seen any equipment other than pictures like has been submitted in this thread. But lets think about it, it feeds a single load, that should have overload protection, the transformer primary overcurrent protection will protect it in event of short circuits or ground faults. Is this really much different than what is allowed for two wire secondaries, or delta-delta transformers used to supply an individual load?

 

[conmgt]

The protection rules in 450 are maximums, nothing says you can't use lower protection levels as long as what you choose will hold for inrush current at energization.

I agree.

Now look at 240.4 (F) It does not mention two phase, but two phase is a different animal and is not really all that well included in the NEC. I think this installation is similar enough to what 240.4(F) is about it needs consideration to allowing it to use similar install for two phase.

There is already a set of fuses protecting this motor and I won't be installing the transformer in between those fuses and the motor.

 

[conmgt]

I've settled on using the 30kVA Scott T transformer.

I could just cover my but by going 125% of the transformer's size (30kVA) on the primary conductors, OCP, and a contactor and be done with everything but I'm here to learn something.
That would be 30k / 208 / 1.732 = 84A * 1.25 = 104A

But we have a single transformer supplying only a single motor. The motor is 2ph 220V 44A for a kVA of 19.4 (2phase). The transformer to be purchased is 30kVA 3ph 208.
The 4 secondary conductors are going to see 44A in each. The 3 primary conductors are going to see...19.4k / 208 / 1.732 = 54A each. How am I doing here?

Can I go with 54A to size the primary conductors?

This load is far from continuous. Check out T430.22(E).

 

[kwired]

I agree.




There is already a set of fuses protecting this motor and I won't be installing the transformer in between those fuses and the motor.

What length of conductor between transformer secondary and these fuses? As long as you don't go beyond tap rule distances you have a transformer with primary and secondary protection and use different row in table 450.3(B) Then comes the question of whether or not your fuses are overload protection or if they are only for short circuit and ground fault protection.

I've settled on using the 30kVA Scott T transformer.

I could just cover my but by going 125% of the transformer's size (30kVA) on the primary conductors, OCP, and a contactor and be done with everything but I'm here to learn something.
That would be 30k / 208 / 1.732 = 84A * 1.25 = 104A

But we have a single transformer supplying only a single motor. The motor is 2ph 220V 44A for a kVA of 19.4 (2phase). The transformer to be purchased is 30kVA 3ph 208.
The 4 secondary conductors are going to see 44A in each. The 3 primary conductors are going to see...19.4k / 208 / 1.732 = 54A each. How am I doing here?

Can I go with 54A to size the primary conductors?

This load is far from continuous. Check out T430.22(E).

I did not look into this, but is the primary current (three phase) going to be balanced assuming balance on secondary? If it is balanced I don't see why this can't be treated any different than a two wire - two wire or delta-delta transformer and provide protection according to primary to secondary current ratio.

I will also add to that if the transformer is oversized and you apply overcurrent protection that applies to the load vs. max allowed for the transformer you still have a protected transformer as long as there is overload protection on the motor (which there is supposed to be anyway) which would protect the transformer (and motor) from any unbalance condition that may happen down the road. (Like open circuit in one phase for some reason)

 

[Phil Corso]

ConMgt...

Primary-current value depends on actual parameters of the transformer. Were they provided by the mfgr?

Regards, Phil Corso

 

[conmgt]

Primary-current value depends on actual parameters of the transformer. Were they provided by the mfgr?

Not yet. But I didn't include the 1400W that the manufacture says the transformer will consume under load and what the controller will draw so I need to add all of that.

What length of conductor between transformer secondary and these fuses? As long as you don't go beyond tap rule distances you have a transformer with primary and secondary protection and use different row in table 450.3(B) Then comes the question of whether or not your fuses are overload protection or if they are only for short circuit and ground fault protection.

They are likely to be less than 25'

I did not look into this, but is the primary current (three phase) going to be balanced assuming balance on secondary? If it is balanced I don't see why this can't be treated any different than a two wire - two wire or delta-delta transformer and provide protection according to primary to secondary current ratio.

This project is low priority...can't you tell...and the transformer hasn't been ordered yet but when the order is placed, I'll ask for their input on many of the things discussed here including that. Thanks for bringing it up.

 

[conmgt]

The elevator motor's controller draws about 8A. I compared the draw ahead the controller and beyond the controller.
So I have the 44A for the motor and 8A for the controller on the secondary side of the transformer. 52A*240V*2/1k=25kVA
And add the 1400W for the transformer on the primary side of the transformer. 59*208*sqr3/1k=22kVA
#4 XHHW should suffice as primary and secondary conductors in 1" EMT. Any thoughts?

 

[kwired]

The elevator motor's controller draws about 8A. I compared the draw ahead the controller and beyond the controller.
So I have the 44A for the motor and 8A for the controller on the secondary side of the transformer. 52A*240V*2/1k=25kVA
And add the 1400W for the transformer on the primary side of the transformer. 59*208*sqr3/1k=22kVA
#4 XHHW should suffice as primary and secondary conductors in 1" EMT. Any thoughts?

I haven't gone back to check where your numbers are coming from but something is not right, you can not have more kVA on the output than you have on the input, if you do I want to know where you are getting your transformers, I may want some of them myself. :happyyes:

Where did the 59 amps come from on your primary calculation? I think you need to work the primary calculation in reverse - take the known 25 kVA and find the corresponding amps at 208 volts three phase. I come up with around 69 amps.

I don't know that you should include the 1400 watts idle current - first is it 1400 watts or 1400 VA? And if it is VA what is power factor when loaded, as it is probably low when unloaded?

 

[conmgt]

I haven't gone back to check where your numbers are coming from but something is not right, you can not have more kVA on the output than you have on the input, if you do I want to know where you are getting your transformers, I may want some of them myself.

Yes...I see your point. And where was my head? I don't understand why with 2ph you multiply A*V*2 since Phase A and Phase B are 90 out of sync.

Where did the 59 amps come from on your primary calculation? I think you need to work the primary calculation in reverse - take the known 25 kVA and find the corresponding amps at 208 volts three phase. I come up with around 69 amps.

You're right, I should work backwards from the load...25kVA. But I need to add the 1400W for the transformer's load while under load. It's 600W when idle. Both numbers are straight from the manufacturer.

How about A=(kVA*1000)/(208*sqr3) 25000/360=69 Hey, same as your figure. And now the 1400W transformer draw under load. 1400/(208*1.732)=4A Total of 73A.

 

[kwired]

Yes...I see your point. And where was my head? I don't understand why with 2ph you multiply A*V*2 since Phase A and Phase B are 90 out of sync.


You're right, I should work backwards from the load...25kVA. But I need to add the 1400W for the transformer's load while under load. It's 600W when idle. Both numbers are straight from the manufacturer.

How about A=(kVA*1000)/(208*sqr3) 25000/360=69 Hey, same as your figure. And now the 1400W transformer draw under load. 1400/(208*1.732)=4A Total of 73A.

I really have no 2 phase experience but it would seem to me that the reason for the current x 2 multiplier is that only half your load is carried by one phase - make sense? Is not quite the same animal as three phase where current circulates between all three phases, in two phase the current in phase A is independent of the current in phase B where in a three phase system the total current in phase A is also partly flowing in phase B as well as phase C therefore the square root of three net result.