Elevator UPS Rescue System

[Pepwr2011]

Hello All,

NEC code question.

Scenario:

I am in the process of developing a Elevator UPS rescue system. Basically in the event of a building power loss I am using a UPS to run one elevator at a reduced speed to the nearest landing to let the passengers out. Under the building power loss condition the UPS requires 5kVA of power to perform this task. Under normal building power the input of the UPS is connected to a secondary of 2kVA transformer. The UPS only requires 1.5kVA under this condition (charging current, providing power to the elevator control system, etc.). Under normal power condition the UPS does not provide power to the drive/motor hence does not need the total kVA of the UPS. I have properly sized the wires for the primary and secondary of the 2kVA transformer, UPS wiring, and fuse sizing for the primary of the 2kVA transformer.

Diagram:

460VAC Building voltage(Disconnect switch) ---------> (Fused on primary of transformer), 460VAC/240VAC (2kVA Transformer) ----------> (240VAC/240VAC) 5kVA UPS -----------> Elevator system.

Is there anything in the NEC code that I need to address having a 2kVA transformer connected to a 5kVA UPS?

Thank you for your time and feedback.

 

[steve66]

So the elevator gets normal power from another path? Does the UPS power and normal power both feed a automatic transfer switch? I don't see how else you can do this.

I wouldn't reduce the UPS feed below the 5KVA. I don't know of a code violation offhand, but 5KVA is pretty small. Why not just feed the UPS with the entire 5 KVA? (Actually, I'd probably give it about a 7 KVA feed - 5KVA plus charging current plus a short term overload factor). Or just use a 2KVA UPS if that's all the elevator needs.

Have you considered motor starting current? I don't see how a UPS that small can run an elevator. Much more common to have an elevator on a generator, or to have hydraulic lowering.

 

[Pepwr2011]

Hello Steve66,

Thank you for your reply. You are correct that the elevator should be on a generator if available. Unfortunately allot of buildings do not have an emergency generator and to install one is quite cost prohibitive for this application when the building is modernizing the elevator system. When power is lost to the disconnect we are not running the elevator at its rated speed and capacity (rated voltage and current of the motor) from the UPS. The system is set-up to run the elevator at a fraction of the speed of the elevator and in the direction of the load. If the load of the elevator is lighter than its counterweight, the elevator will then move up. If the load of the elevator is heavier than its counterweight then the elevator will travel in the down direction. Why not use gravity to our advantage . I know what happens when the system is perfectly balanced??? We just need enough power to get the elevator to a floor to get the people out. We have done various tests on our elevator test tower and based on our calculations and test measurements we are able to perform the task with the kVA rating of the UPS mentioning here. The kVA of the UPS obviously will depend on the motor being used. We have hardware interface to switch the UPS power to the drive and motor when the building power is lost in addition to the elevator control system. Therefore the UPS now has to provide additional power to the drive/motor which it would not need to provide under normal building power.

I have clarified the diagram below.

460VAC Building voltage(Disconnect switch) ---------> (Fused on primary of transformer), 460VAC/240VAC (2kVA Transformer) ----------> (240VAC/240VAC) 5kVA UPS -----------> Elevator control system.
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--------------------------------------------------------------Hardware/contacts, etc. to switch from Normal power to UPS power to-------> Drive and Motor

Hope this makes somewhat more sense......

Thank you.