Best practice for large electric motors

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Discussion Overview

The discussion revolves around the operational efficiency of large electric motors in a manufacturing setting, specifically whether to shut down motors during breaks or leave them idling. Additionally, participants explore the concept of motor efficiency and the potential benefits of using phase aligners or capacitor banks to improve power factor.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the cost-effectiveness of shutting down electric motors during breaks versus leaving them idling, noting that the motors are not loaded during these times.
  • Another participant estimates potential energy savings of about $60 per lunch hour if the motors are fully loaded but doing unnecessary work.
  • Concerns are raised about the implications of a demand meter and whether it is better to leave motors running to avoid demand charges associated with restarting them.
  • Discussion includes the effectiveness of phase aligners, with one participant sharing a personal experience that suggested limited benefits from such products.
  • Participants mention the importance of monitoring power factor on the electric bill, indicating that a poor power factor could lead to additional charges from the electric company.
  • Clarification is sought regarding how to identify power factor issues on utility bills, with a suggestion that it should be labeled clearly.

Areas of Agreement / Disagreement

Participants express differing views on whether it is more cost-effective to shut down motors or leave them running during breaks. There is also uncertainty regarding the effectiveness of phase aligners and how to interpret power factor information on utility bills.

Contextual Notes

Participants acknowledge that the effectiveness of shutting down motors may depend on specific operational conditions and that utility bills may vary in how they present power factor information.

Who May Find This Useful

This discussion may be useful for manufacturing professionals, electrical engineers, and facility managers interested in optimizing energy consumption and understanding power factor implications in industrial settings.

justaguywa?
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This may not be the place to ask this question, but I can't seem to get a good answer anywhere else...I have a manufacturing company. I am on a 3-phase demand meter. I'm trying to figure out if it is more cost effective to shut all the electric motors down during breaks and lunch and restart or just leave them running "idling" during these times? The motors are 2 - 100 HP, 4 - 75 HP, and 4 - 50 HP.

The other question I have is about motor efficiency - I've had a salesman come by and talk to be about "phase aligners" (Don't really know what they are, but I'm guessing some sort of capacitor that "cleans up" the inbound electricity). Anyone know anything about these and if they are worth fooling with?
 
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For the first question, it depends a little on what these motors are doing, but if they are fully loaded but doing something unnecessary, they are consuming a lot of energy that could be saved. About $60 per lunch hour.

For the second, there are some products that advertise various power cleaning capabilities. I tested one once on a compressor and it didn't seem to do much. What you do really want to make sure of, though, is that your power factor isn't bad enough that the electric company charges you for it (it should be clear on your bill). If it is bad, you should have an engineer select and a contractor install a capacitor bank to correct it.

Welcome to PF - there's no better place for such a question!
 
Thanks for the response.

The motors are not loaded during these times - I thought it would be better to shut them down, but the practice has always been to leave them running - someone told a previous supervisor that because of the demand meter, it was better just to leave them running than to restart them after breaks (15 minutes X 2) and lunch (30 minutes). Each motor is started independent of the other, so it's not like they are all restarting at once.

You say that there should be something on my bill if the power factor is bad? Where should I look for that. I'm sure every power companies bill is different, but is there a certain nomenclature that would show up or stand out if I have a problem?

Again thanks for the information.
 
For power factor, it should just say power factor, followed by a number between 0.5 and 1.0. The detail of the bill shouldn't be very long...
 

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