Elevator Motor

[Rock86]

Hello all, I have two questions...

1. I have an elevator motor with the nameplate below... I am trying to figure out what the "starts/hr" has to with the HP rating? Why would that change things? There are not two motors in this location.


2. This elevator motor is configured with two contacts in a wye-delta (star-delta) configuration. The building is connect on the generator, but when the generator kicks on and the elevator is called, the wye setup starts the motor, but the transition from the open to delta connection won't hold the delta run contactor. The generator has the capacity, but I am thinking the holding contactor is dropping out due to the inrush during at during the delta connection. Anyone have any thoughts, or advice?

Thank you!

 

[zbang]

200 volts? There's got to be more to it.

For #2, it definitely could be that there's enough voltage drop on the transition to prevent the contactor from holding.

 

[synchro]

Is the wye-delta starter using "closed transition" which has a separate contactor and resistors to keep some current in the windings instead of leaving them open during the transition? If not then it's "open transition" and that could make the peak current at the transition much higher than the LRC.

If there's too much voltage drop at the motor to hold the contactor closed, perhaps a pair of small gauge wires could be routed to the coil from an earlier point in the electrical system that would experience less drop when the motor starts.

 

[Rock86]

Is the wye-delta starter using "closed transition" which has a separate contactor and resistors to keep some current in the windings instead of leaving them open during the transition? If not then it's "open transition" and that could make the peak current at the transition much higher than the LRC.

If there's too much voltage drop at the motor to hold the contactor closed, perhaps a pair of small gauge wires could be routed to the coil from an earlier point in the electrical system that would experience less drop when the motor starts.

It is "Open Transition". And I thought the same. Do you think a soft-starter would solve that problem?

Hmmm... I may try that, but only to test it. I wouldn't leave it as a permanent fix. Thank you.

 

[Rock86]

200 volts? There's got to be more to it.

For #2, it definitely could be that there's enough voltage drop on the transition to prevent the contactor from holding.

The motor is connected 120/208 3ph, so the 200V is fine. The motor is also designed for 50Hz which causes a problem of now becoming 60Hp on the high end... which is still confusing to me.

 

[drcampbell]

... what [does the] the "starts/hr" [have] to with the HP rating? ...

I'm sure it has to do with the total amount of heat that can be dissipated out of the motor.

Each start draws more current and generates more heat than the same amount of runtime at its full rated speed.
If you use it to develop less Hp than it's capable of, its steady-state temperature will be lower and it can tolerate more higher-current operation.

 

[drcampbell]

... The motor is also designed for 50Hz which causes a problem of now becoming 60Hp on the high end... which is still confusing to me. ...

I'm confused by a 50-Hz motor developing ~3400 rev/min. Maybe it's a 1.7-pole motor?

 

[Rock86]

I'm sure it has to do with the total amount of heat that can be dissipated out of the motor.

Each start draws more current and generates more heat than the same amount of runtime at its full rated speed.
If you use it to develop less Hp than it's capable of, its steady-state temperature will be lower and it can tolerate more higher-current operation.

That is believable. By that logic, to do load calculations, would you need to know its average starts/hr to determine if you're rating it for 50HP or 40HP (60HP/48HP in terms of 60Hz)??

 

[drcampbell]

The "horsepower rating" would come from the load, not the motor. How much (mechanical) power is the load actually using -- is it, for example, suitable for a ten-story building but installed in a five?

For sizing transformers, breakers and wires, you'll need a good estimate of the average continuous current, which would incorporate the starting current, the running current, and the amount of time spent starting, running and stopped per hour. (plus the ability to handle whatever peak currents may occur)

And before I tried to calculate that, I'd try to find a more-credible source of data than a nameplate that says 50 Hz and 3400 rev/minute.

 

[Rock86]

The "horsepower rating" would come from the load, not the motor. How much (mechanical) power is the load actually using -- is it, for example, suitable for a ten-story building but installed in a five?

For sizing transformers, breakers and wires, you'll need a good estimate of the average continuous current, which would incorporate the starting current, the running current, and the amount of time spent starting, running and stopped per hour. (plus the ability to handle whatever peak currents may occur)

And before I tried to calculate that, I'd try to find a more-credible source of data than a nameplate that says 50 Hz and 3400 rev/minute.

Thanks. Doing some research, I a credible article which stated that Less than 1% of Standard 60Hz NEMA-style motors are wired wye-delta, where as 80% of standard IEC-style 6-lead motor are 50Hz motors. This might explain the 50Hz rating, but I don't have an answer for the RPM differential.

Unfortunately I have to contend with an elevator contractor who is not giving up specifications on anything at the moment. Lots of figure pointing, but no work on a solution.

 

[LarryFine]

The "horsepower rating" would come from the load, not the motor. How much (mechanical) power is the load actually using -- is it, for example, suitable for a ten-story building but installed in a five?

Wouldn't HP affect the load limit more than the travel distance?

 

[synchro]

2. This elevator motor is configured with two contacts in a wye-delta (star-delta) configuration. The building is connect on the generator, but when the generator kicks on and the elevator is called, the wye setup starts the motor, but the transition from the open to delta connection won't hold the delta run contactor. The generator has the capacity, but I am thinking the holding contactor is dropping out due to the inrush during at during the delta connection.

If the contactor is designed for 50 Hz, then at 60 Hz the coil will be drawing 50/60 = 0.83 or 83% of the design current at the specified voltage. Using 208V instead of the spec'd 200V utilization voltage will bring the current back up to 0.83 x (208/200) = 0.86 or 86% of the design value. This remaining shortfall reduces the amount of voltage drop allowable at the contactor before it goes below its spec'd drop-out voltage (typically 65% of nominal).
Using 240V 60Hz for the contactor should bring the coil current right to the design value because (50/60) x (240/200) = 1.

Even though the generator may have an ample kVA rating, generators typically have significantly higher impedance than the POCO supply. So there can be relatively large voltage drops when starting large motors.
One possible option to reduce voltage dips that could cause contactor dropout would be to use a ferroresonant constant-voltage transformer for the contactor control circuit. Some of the ones listed below can also provide 240V as well as 208V with a 208V input.
https://solahevidutysales.com/mcr_hardwired_power_line_conditioner.htm.

The regulation performance of these transformers can be seen here:

https://www.emerson.com/documents/automation/technical-note-operating-characteristics-of-cvs-mcr-series-solahd-en-us-163812.pdf

 

[Rock86]

If the contactor is designed for 50 Hz, then at 60 Hz the coil will be drawing 50/60 = 0.83 or 83% of the design current at the specified voltage. Using 208V instead of the spec'd 200V utilization voltage will bring the current back up to 0.83 x (208/200) = 0.86 or 86% of the design value. This remaining shortfall reduces the amount of voltage drop allowable at the contactor before it goes below its spec'd drop-out voltage (typically 65% of nominal).
Using 240V 60Hz for the contactor should bring the coil current right to the design value because (50/60) x (240/200) = 1.

Even though the generator may have an ample kVA rating, generators typically have significantly higher impedance than the POCO supply. So there can be relatively large voltage drops when starting large motors.
One possible option to reduce voltage dips that could cause contactor dropout would be to use a ferroresonant constant-voltage transformer for the contactor control circuit. Some of the ones listed below can also provide 240V as well as 208V with a 208V input.
https://solahevidutysales.com/mcr_hardwired_power_line_conditioner.htm.

The regulation performance of these transformers can be seen here:

https://www.emerson.com/documents/automation/technical-note-operating-characteristics-of-cvs-mcr-series-solahd-en-us-163812.pdf

This is actually a huge help in understanding the system. Thank you!

 

[synchro]

The bottom of page 7 in the brochure below lists the motor in your picture, part number 217EAS050C001.
It specifies 60Hz operation under "Features," which makes more sense for the RPMs listed as drcampbell pointed out. In your picture the number stamped for Hz looks like 50, but it's not very distinct and could be 60.

http://www.imperialelectric.com/products/IEBrochure_Motors_121117(LR-SINGLES).pdf

You might want to see if there are any specs shown on the contactors themselves if there is access.

 

[Jraef]

The Starts/Hour affects the HP rating because in order toget the higher S/Hr rating, you are required to de-rate the motor. So the motor is designed as a 50HP motor and from a torque / speed perspective, it remains a 50HP motor. But from a CAPACITY to withstand the rigors of the duty cycle, if you take it to 120 S/Hr, it has the thermal capacity of a 40HP motor. This is all laid out in NEMA MG-1 design specifications, it's just that very few applications have the possibility of having a motor turn on and off every 10 seconds (120 S/Hr would mean Start, run for 15 seconds, Stop, rest for 15 seconds, Start again). If you DO have a machine like that, hopefully the machine designer too that into account when selecting the motor. Bt for elevators, they KNOW it can be used that way, so they put it right on the nameplate.

 

[drcampbell]

Wouldn't HP affect the load limit more than the travel distance?

The hoisting cables are a significant fraction of the total weight.

 

[zbang]

That total mass applies to the momentum but not to the lifting load; modern elevator manufacturers try really hard to balance all the mass that isn't cargo.

 

[Rock86]

Met with the elevator contractor today. He said (without citation) it was against code to change the motor controls from the current wye-delta open transition set-up to anything else. He claims if the components goes bad, then they have to replace the components with the exact same setup as what it was otherwise the whole system needs to be revamped. Anyone every hear of that??

 

[drcampbell]

Yes, it's very common that mandates are narrowly written, don't leave any room for improvement, and become ridiculous as they age.

 

[zbang]

It's probably elevator code that prevents modifications that aren't approved by the manufacturer (although at the building I manage, the elevator company offered to replace the star-delta starter with a soft-start; for the amount of usage, it's not worth the cost).