annual cost of electric motor
annual cost of electric motor
(OP)
I'm trying to justify energy savings on an electric motor that runs 3 hydraulic pumps. The motor is 125 hp, 480 VAC and amp load will vary according to how many of the pumps are loaded ( amp draw is approx. 50 amps with no pumps loaded and increases to approx 140 as work is done)probably averaging 75 amps. This is in a cotton gin so it is very seasonal about 600-8oo hours a year. Can anyone help me calculate the annual kilowatt hours?
thanks,
Maytag
thanks,
Maytag





RE: annual cost of electric motor
RE: annual cost of electric motor
The best way is to connect a portable power meter and monitor the actual POWER (not amps) being used.
kW x time = energy (in kWh, generally). But if you need a calculation accurate enough to compare energy usage of two different motors, you'll really need the power factor or an actual kW measurement.
RE: annual cost of electric motor
Maytag
RE: annual cost of electric motor
An interesting and independant tool is:
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NB: Big download (approx 25MB) for the tool itself and I would read the pdf first.
RE: annual cost of electric motor
I just spent 1/2 hour running assumed power factors and getting unrealistic answers.
It appears that your motor may have power factor correction installed. That makes the numbers realistic.
That makes it easy.
50 Amps x 480 Volts x 1.73 / 1000 = 41.6 kW
75 Amps x 480 Volts x 1.73 / 1000 = 62.4 kW
140 Amps x 480 Volts x 1.73 / 1000 = 116 kW
Now it's back to you to estimate the number of hours at each loading level and simply multiply and add.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: annual cost of electric motor
We really need to see the load profile.
You may benefit from an RMS horsepower survey, if your maximum loading is not more than about 80% over the nominal capacity of one motor/pump set and there are intervening periods of light loading.
For more information on RMS horsepower loading see the Cowern papers.
RMS HORSEPOWER LOADING
There are a great many applications especially in hydraulics and hydraulically-driven machines that have
greatly fluctuating load requirements. In some cases, the peak loads last for relatively short periods
during the normal cycle of the machine. At first glance, it might seem that a motor would have to be
sized to handle the worst part of the load cycle. For example, if a cycle included a period of time where
18 HP is required, then the natural approach would be to utilize a 20 HP motor. A more practical
approach to these types of "duty cycle loads" takes advantage of an electric motor's ability to handle
substantial overload conditions as long as the period of overload is relatively short compared to the total
time involved in the cycle.
The method of calculating whether or not the motor will be suitable for a particular cycling application is
called the RMS (root mean squared) horsepower loading method. The calculations required to properly
size a motor for this type of application are relatively simple and are presented in this paper.
http:/
You may be able to safely overload one motor for short periods of time.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: annual cost of electric motor
no-brainer but with the "seasonal" use it is a hard sell as the capital investment for the energy recovery is the same regardless of the usage. Thank all of you for your responses.
Maytag
RE: annual cost of electric motor
RE: annual cost of electric motor
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: annual cost of electric motor
If so, the input power to the motor will just be the losses of the motor which can just be estimated as around 10% more energy.