3 Phase Motor Energy Calculation

[PotashMechy]

Hi All,

I am not an electrical expert but am trying to calculate the energy consumption per day of a 3 phase motor. My motor is 600V, 30A. I know that the formula for calculating the power is:

kw=(V*A*PF*1.73)/1000

My question is: For a 3 phase motor, do I use the full 600V in my calculation? Or do I use the voltage of the highest leg (or line to line voltage in my understanding) which would be somewhat lower?

Any advice would be appreciated!

Renee

 

[waross]

Take your pick:
Line to line voltage x 1.73 or line to neutral voltage x 3.

Or do I use the voltage of the highest leg (or line to line voltage in my understanding) which would be somewhat lower?

This is a little unclear, but if this is a four wire delta, do not use the wild leg voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

You can use that standard formula if your motor is running at full load all the day. But that is a very rare situation. A well designed drive doesn't do that. If you need a better result, you need to find the actual load. Best is to log power.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

Does this motor exist?

Is it driven with a VFD?

What is it actually doing?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PotashMechy]

itsmoked: this is a motor that isn't installed yet but we are looking to calculate how much energy it will use. The motor will power a vacuum cleaner. The vacuum cleaner will have 4 different intakes which may or may not be used at the same time. It will not be on a VFD.

Renee

 

[waross]

The power consumption will vary with the number of intakes in use. The more intakes the more power used. (generally)
The power may also vary with the density and amount of matter being collected.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Thanks. Whoa.. That will be a bit hard to estimate.

Things to keep in mind:

Key point: A vacuum is a mass-flow device. It consumes power based on how much air runs thru it. The less air the less power demanded. If you block all air it will essentially draw nothing, only it's own windage and bearing losses. Don't be fooled by it's greatly increased howling, it increases specifically because it speeds up due to being unloaded.

This means that maximum power will be during all intakes open.
Perhaps 500W when all ports are closed.

If it's got a filter between it and the intakes the power consumption will go down as it clogs.

If the motor is cooled by the air it is sucking in the inlets you cannot block all the inlets for very long or the motor will overheat due to its own losses.

If there will be longish periods where no vacuum is needed it may save energy to use a VFD that can spool the motor up and down as needed.

Often nameplate ratings like 600V@30A are GREATLY excessive to reality.

I would strongly suggest you find someone with the same unit and have them measure the actual current with a clamp-on ammeter. You may find it's more like 2/3's the nameplate.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

OK, when I say drive - I don't necessarily mean a variable speed drive. Anything that drives something is a drive to me.

The motor doesn't speed up much and you will probably not even notice it. Universal motors do because of their series winding arrangement. But ASIMs do not.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Stop looking at the motor for now. Look at the fan and system curves to predict the airflow through the fan. Once you know what the load is doing you can infer what is happening on the motor side of the coupling.

 

[itsmoked]

Good point Gunnar. I did slip back into typical brushed vacuum motors and this would be an ASIM.

The energy angle still holds.

What I see frequently is dust collectors in wood shops. I believe that most of the time they'd save a bundle using a VFD and some sensors. They don't want to turn the DC on and off constantly but they also don't often generate saw dust constantly. Things sit idle for minutes while contemplating or measuring or analyzing or marking. That whole time the DC is wailing away at full power. If instead it slowed down to 1/2 speed the power would drop by the cube and then a simple proximity sensor or whatever is appropriate could spool the vacuum back up because a 'board-is-coming'. The same could be achieved with solenoid valves blocking the air flow and unloading the motor.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

In the UK industrial woodworking machines are frequently provided with automatic blast gates in the suction lines which open to enable the dust extraction when the machine starts. Not the case in the US?

 

[waross]

I was in a plant where we got a new 60 HP dust collection system.
It worked great, until the 500 HP gang saw started putting out gobs of sawdust.
We had to throttle the intake about 50% (area, not flow) to keep it from overloading.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

PotashMechy,
The point is, you can only guess at the MAXIMUM energy consumption of that motor, you cannot calculate it because energy consumed is based on work performed, but the motor only works as hard as it HAS TO. The 30A FLA rating only means that at FULL LOAD it will pull no more than that and above 30A the motor may burn up, not that it WILL pull 30A all of the time. In fact as Gunnar said, it’s highly unlikely that it ever will pull that much current.

If you need to know the actual energy consumption, it can only be measured, not calculated, and only once it is doing the actual work it is required to do. If you need to estimate it from an economic cost to operate standpoint in advance of the installation, it’s often possible to ask the mfr for empirical data on a similar installation to use in extrapolating something. But other than that all you can do is to SWAG it, or accept the concept of “It will never cost MORE than xxx” using the FLA.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Compositepro]

A vfd on a dust control system is not a good idea in most cases. A squirrel cage blower is similar to a centrifugal pump. Regardless of flow, the blower must turn at speed to generate adequate pressure. Flow should be controlled with dampers.

Potash, if you look at the motor name plate it has a voltage, current and power listed. So you already have the answer to your power question. However, this is only the maximum power rating of the motor and not what you want to know, which is the actual power used. The actual power is flow rate times differential pressure. That depends entirely on how the system is designed and how you operate it. Closing dampers to unused equipment will save energy.

 

[LionelHutz]

You also want to avoid pulling dust through the ducts at a slower speed because the dust will tend to settle in the ducts.

 

[jraef]

Guys (or Gals as the case may be)...

THERE IS NO VFD. That was someone's misinterpretation of the word "drive" which was meant to refer to the MOTOR. The OP stated that there is no VFD so lets not keep going down that rabbit hole...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[LionelHutz]

In this case, best you can do is calculate worst case energy usage. Then, if you decide if the project is still worth proceeding you'll know the real power usage will make everyone involved happy.

 

[Compositepro]

My VFD comment was in reply to itsmoked saying that a vfd could save a lot of money. I try to avoid making discussions personal by not naming names.

 

[itsmoked]

Yep, I said that and I stand by it too. There is no issue with spooling up and down a vacuum cleaner dust collector.

Correct, the OP didn't mention a VFD, I did and I'd do it again. I offer up suggestions and alternatives here, sometimes even on sparse data. So Jeff, there could be a VFD added to the system if the system doesn't even exist yet.

This whole question smacks of something that 'could happen', like a dust collector could or could not be installed based on how much energy it uses. That's how the question comes across to me, otherwise why wouldn't the OP measure the power it uses instead of wasting his time with theoretical numbers that will be wrong, possibly by several thousand dollars a year?


Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

When the general manager asks;
"If we buy it, how much is this thing going to cost to run?"
What are you going to do?
Ask for help with sparse data.

Bill
--------------------
"Why not the best?"
Jimmy Carter