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Air Conditioner Motor Contribution
https://brainfiller.com/arcflashforum/viewtopic.php?f=15&t=4249		 Page 1 of 1
Author:  jessman1340 [ Mon Sep 19, 2016 12:41 pm ]
Post subject:  Air Conditioner Motor Contribution
I'd like to hear how some of you are handling Air Conditioner motor contributions in your models. I'm working off a one-line to build the model (while the site is under construction!). I'm wondering if most people model the various motors separately (compressor, fan, other?), or do you leave them modeled as one.
Also, as some of the motors may be buried in the equipment, do you always verify RPM, service factor, FLA, and other motor nameplate data?
I'm not sure some of this data will even be available as these motors may or may not be NEMA standard motors...

Thanks!
Author:  JBD [ Mon Sep 19, 2016 3:18 pm ]
Post subject:  Re: Air Conditioner Motor Contribution
This sounds like way too much work with little, if any, gain.

What is the purpose behind the model you are creating?
How big are the motors you are considering?

In my experience;
Short Circuit Current Rating evaluation pretty much only depends on if all of the motors are running.
Time Current Coordination should be concerned with the branch/feeder, the internal component coordination should have been done by the manufacturer.
Arc Flash incident energy is probably worse with either all motors on or all motors off.
Author:  matt_engr [ Fri Feb 17, 2017 5:34 pm ]
Post subject:  Re: Air Conditioner Motor Contribution
Section 4.2 of IEEE 1584 mentions including motors 37kW (50hp) and larger during the system data collection process. This is a rule of thumb. It does not hurt to model all your motors for the sake of showing them on the single lines, future load flow analysis, etc. If you have the time, model your entire system.

I recommend you look into the VFD specifications regarding line-side and load-side short circuit contributions. Most modern drives are designed to not allow let-through on either side. This is not the same for starter applications.

As JBD mentioned, motor diversity might play a factor depending on your system. From my experience, small motors won't have any significant effect. I have seen cases with large motors where their SC contributions were more impactful in terms of incident energy results.
Author:  bbaumer [ Mon Feb 20, 2017 4:24 am ]
Post subject:  Re: Air Conditioner Motor Contribution
matt_engr wrote:
Section 4.2 of IEEE 1584 mentions including motors 37kW (50hp) and larger during the system data collection process. This is a rule of thumb. It does not hurt to model all your motors for the sake of showing them on the single lines, future load flow analysis, etc. If you have the time, model your entire system.

I recommend you look into the VFD specifications regarding line-side and load-side short circuit contributions. Most modern drives are designed to not allow let-through on either side. This is not the same for starter applications.

As JBD mentioned, motor diversity might play a factor depending on your system. From my experience, small motors won't have any significant effect. I have seen cases with large motors where their SC contributions were more impactful in terms of incident energy results.


^^^^ this.
Author:  PaulEngr [ Mon Feb 20, 2017 6:50 pm ]
Post subject:  Re: Air Conditioner Motor Contribution
Depends on size. A plant that I regularly service has 600-1000 HP chillers. Those obviously get modeled individually.

The only HVAC motors I can recall that are definitely not NEMA that I run into frequently are the brushless DC kind. In this case you model the drive...the motor doesn't matter a whole lot because the drive limits current.
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