Posted: 9/5/2013 9:54:52 AM EDT
|
We have a bank of two elevators that we took for maintenance a while back that have been problematic. We recently realized that the supply voltage to the cars is 208vac 3ph, when it requires 230vac 3ph. We could see brakes drop and drive faults when the voltage dropped to around 201v
We told the building that the voltage was the problem, and they hired an electrician to install a transformer to make the change. Each elevator needs 51 amps. I expected to see the electrician wiring in a big ass 35-40kva transformer, but they wired two 7.5 kva boxes in parallel to get a total of 15kva. This was last night. Today both cars are shutting down. Am I crazy, or did they vastly undersize their transformer? Electrically, how do you think this would show up on our end? Undervoltage? I'm thinking melted wires in the long run. |
|
:Normally the kva rating of the boost is based on the boost voltage and current. So a 7.5kva boost that has a 21v increase will carry about 65A. This is dependant on the buck/boost. Why don't you post a picture of their nameplate? Would help us after you measure the voltage at the elevator drives. Posted Via AR15.Com Mobile |
|
Quoted:
We have a bank of two elevators that we took for maintenance a while back that have been problematic. We recently realized that the supply voltage to the cars is 208vac 3ph, when it requires 230vac 3ph. We could see brakes drop and drive faults when the voltage dropped to around 201v We told the building that the voltage was the problem, and they hired an electrician to install a transformer to make the change. Each elevator needs 51 amps. I expected to see the electrician wiring in a big ass 35-40kva transformer, but they wired two 7.5 kva boxes in parallel to get a total of 15kva. This was last night. Today both cars are shutting down. Am I crazy, or did they vastly undersize their transformer? Electrically, how do you think this would show up on our end? Undervoltage? I'm thinking melted wires in the long run. Lots of possible problems there. The elevator motors are controlled by VFDs. The drive needs to be properly configured for the motor load and input voltage. Usually the drive documentation will steer the electrician the right way. The motors are probably the 9 lead type, and can be wired for different input voltage. Has that been checked? Any more info on the type of transformers? |
|
Quoted:
Unless I'm misreading this, 15kva sounds almost exactly right. For one elevator.  I may not have described the layout right. Both cars are fed from these transformers through a single set of lines from the basement. They split in the elevator room to the two disconnects, so both cars are fed from the 15kva transformers. I read where buck boost can supply more than the rated kva, but every sizing chart I see agrees with my estimates. |
|
Quoted:
Lots of possible problems there. The elevator motors are controlled by VFDs. The drive needs to be properly configured for the motor load and input voltage. Usually the drive documentation will steer the electrician the right way. The motors are probably the 9 lead type, and can be wired for different input voltage. Has that been checked? Any more info on the type of transformers? They are 9 lead, and are wired for 208. The drives can fault out when the line voltage drops below 208, which we have seen. The controller was bought by another company set up for 230. The manufacturer agrees that it needs 230. |
|
Quoted:
:Normally the kva rating of the boost is based on the boost voltage and current. So a 7.5kva boost that has a 21v increase will carry about 65A. This is dependant on the buck/boost. Why don't you post a picture of their nameplate? Would help us after you measure the voltage at the elevator drives. Posted Via AR15.Com Mobile I'm not on site, so I can't get a pic. Based upon what you have above, it does sound correct... Hmmm |