Basic 3 Phase Question

Thread Starter

WBogen

Joined Apr 30, 2015
2
I was given some two channel amp readings from a 3 phase 480 volt motor; see sample below. How do I translate this to power being consumed? Thanks.
NO.RMS/TRCH1CH2TIME
1RMS31.7A33.9A23/02/15 08:38:05
2RMS41.7A27.8A23/02/15 08:58:05
3RMS24.1A25.0A23/02/15 09:18:05
4RMS27.9A34.4A23/02/15 09:38:05
5RMS24.9A27.6A23/02/15 09:58:05
6RMS33.3A26.9A23/02/15 10:18:05
 

Reloadron

Joined Jan 15, 2015
7,446
I suggest you read this as to calculating 3 phase power. You are not recording enough data. To simply state 480 volts is not enough, each phase should be recorded and measured. Next each phase current needs measured and recorded and finally the power factor needs know. What I see looks like someone recorded some data every 20 min between 08:38:05 and 10:18:05 which included two channels of current. The data isn't even separated making it hard to interpret. If there was enough data to get the actual power then the numbers could get you to KWH but I don't see enough data.

Ron
 

Thread Starter

WBogen

Joined Apr 30, 2015
2
Sorry, I should have separated the data better to make it more understandable:
NO. RMS/TR CH1 CH2 TIME
1 RMS 31.7A 33.9A 23/02/15 08:38:05
2 RMS 41.7A 27.8A 23/02/15 08:58:05
3 RMS 24.1A 25.0A 23/02/15 09:18:05
4 RMS 27.9A 34.4A 23/02/15 09:38:05
5 RMS 24.9A 27.6A 23/02/15 09:58:05
6 RMS 33.3A 26.9A 23/02/15 10:18:05
 

Reloadron

Joined Jan 15, 2015
7,446
I was able to read the data, the problem I see is not enough data. Looks like the current of two of three phases is being measured. Take for example a three phase delta supply driving a motor. To calculate the power used by the motor with any degree of accuracy:

In order to calculate three-phase wattage, we multiply the average voltage of each phase times the average current of each phase, times the power factor, then multiply by the square root of 3. The square root of 3 is equal to 1.732, so the equation is written as shown:

  • Watt's Law: W = V avg. x A avg x p.f. x 1.732
Where:

  • W = wattage (watts)
    Vavg = average voltage of the three separate phases (volts)
    Aavg = average current of the three separate phases current (amps)
    p.f. = average power factor or the three separate phases
    1.732 = a constant necessary with 3 phase.
You can't just assume 480 Volts, each phase voltage needs measured then averaged, the same for each phase current. Those numbers are multiplied by the power factor and then 1.732 the square root of three (Three Phase). So what I am saying is there is not enough data to answer the question. You can't convert the data you have to the power being used by the 3 phase motor.

Ron
 
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