Power Recorder Reading - 5 Elevator Bank
Power Recorder Reading - 5 Elevator Bank
(OP)
Hi,
Attached is a short (1-1/2 minutes) table of power mesurements taken at 1 sec. intervals on the main feeder (wireway) for five elevator car disconnects at an existing hospital facility.
Being a PE in the design field all my professional career, this power measurements are some what unfamiliar to me and would like to share them with you to hear your comments.
I would suspect that many of my concerns are related to the fact that all of this elevators are controlled by VFD's, but the readings are very interesting to me. I am more used to readings at non-VFD controlled building mains, etc. I would like to hear your comments on the following issues or any other observations you could make.
1.) THD for currents reaching 100%
2.) having such a large unbalance on the reactive power readings for all three phases (being a three phase elevator bank).
3.) Why such a discrepancy between the VA Sum vs. the W sum and the VAR sum.
Thanks in advance to everybody. I continually monitor the Forum to keep me up to date.
Attached is a short (1-1/2 minutes) table of power mesurements taken at 1 sec. intervals on the main feeder (wireway) for five elevator car disconnects at an existing hospital facility.
Being a PE in the design field all my professional career, this power measurements are some what unfamiliar to me and would like to share them with you to hear your comments.
I would suspect that many of my concerns are related to the fact that all of this elevators are controlled by VFD's, but the readings are very interesting to me. I am more used to readings at non-VFD controlled building mains, etc. I would like to hear your comments on the following issues or any other observations you could make.
1.) THD for currents reaching 100%
2.) having such a large unbalance on the reactive power readings for all three phases (being a three phase elevator bank).
3.) Why such a discrepancy between the VA Sum vs. the W sum and the VAR sum.
Thanks in advance to everybody. I continually monitor the Forum to keep me up to date.






RE: Power Recorder Reading - 5 Elevator Bank
While I can't shed any light on the numbers, I just wanted to post my own bafflement and wish for a look at those current waveforms...
Let's see who's got good thoughts.
Good on ya,
Goober Dave
RE: Power Recorder Reading - 5 Elevator Bank
RE: Power Recorder Reading - 5 Elevator Bank
My initial impression is that some type of filters should be provided, since all of these harmonics are being fed periodically to the system at aproximately every minute or so.
Could some one comment on the negative reactive power readings. Could this be associated with the elevator motor or with some type of capacitor bank in the elevator controller?
RE: Power Recorder Reading - 5 Elevator Bank
Keith Cress
kcress - http://www.flaminsystems.com
RE: Power Recorder Reading - 5 Elevator Bank
However, this did not make any sence to me with regards to the negative reactive power. Unless the VFD could make the elevator motor to operate like some sort of synchronous generator.
RE: Power Recorder Reading - 5 Elevator Bank
RE: Power Recorder Reading - 5 Elevator Bank
The 100% THD obviosly is a percent value of the fundemental. For example, you could have 120% THD but the fundemental current is only 3 Amps, the 120% is not a concern in this case due to low current magnitude.
If the drive is a six pulse drive, the dominant harmonics will the be the 5th and the 7th. (np-1 and np+1 ; np = number of pulses). Also, you will get some 11th and 13th
With no line reactor in place, you will get very high THD and could reach 100%. with 3 to 5% line reactor, the THD will drop to approx 35%.
RE: Power Recorder Reading - 5 Elevator Bank
I tend to discard any problems with the equipment connection, because it is usual to detect the problem based on the readings (if one ct was reversed, etc.), because the difference is persistent and can be detected on most of the sampled values.
For your reference, the connection was not changed during the 1.5 minutes of readings, therefore the negative values seen were actually recorded by the meter and not by changes in pt's or ct's connections.
Thanks for your input.