Power Factor: Q&A on Measurement & Waveforms

In summary, the original power factor of a compressor motor was measured to be 0.78 and after installing PFC caps, it increased to 0.91. However, when using an oscilloscope to measure the voltage and current waveforms, it was found that for the corrected load, the current and voltage were 163 degrees out of phase instead of the expected 17 degrees, and for the uncorrected load, they were 146 degrees out of phase instead of 34 degrees. This suggests that there may be an inverted CT winding or backwards polarity in one of the measurement probes, causing the unexpected results. Further information is needed to determine the exact cause of this issue.
  • #1
krw
5
0
Hi everyone! This is my first post here, and I will start with a question:

I used the wattmeter-voltmeter-ammeter method to measure both the original power factor of a compressor motor and its power factor after installing PFC caps. The values, respectively, were 0.78 and 0.91. I am 100% confident in these values because they correspond with an independent analysis someone else did.

Just for the hell of it, I also used an oscilloscope to take voltage and current waveforms of each phase to see how they differed. What I found was that for the corrected load, the current and voltage waveforms were 163 degrees out of phase rather than 17 degrees out of phase. For the uncorrected load, the current and voltage waveforms were 146 degrees out of phase rather than 34 degrees out of phase.

Essentially, the current waveform was just inverted from what I expected to see. Can anyone explain why this might be happening?
 
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  • #2
krw said:
Hi everyone! This is my first post here, and I will start with a question:

I used the wattmeter-voltmeter-ammeter method to measure both the original power factor of a compressor motor and its power factor after installing PFC caps. The values, respectively, were 0.78 and 0.91. I am 100% confident in these values because they correspond with an independent analysis someone else did.

Just for the hell of it, I also used an oscilloscope to take voltage and current waveforms of each phase to see how they differed. What I found was that for the corrected load, the current and voltage waveforms were 163 degrees out of phase rather than 17 degrees out of phase. For the uncorrected load, the current and voltage waveforms were 146 degrees out of phase rather than 34 degrees out of phase.

Essentially, the current waveform was just inverted from what I expected to see. Can anyone explain why this might be happening?

You've got a CT winding inverted. (Guess of course, but without more info what can we do. It's a measurement error but you'd have to detail you're complete measurement set up before anyone can tell you for sure what's wrong.)
 
  • #3
Yes. When you have an extra 180 degrees, that's backwards polarity in one of the measurement probes.
 

Related to Power Factor: Q&A on Measurement & Waveforms

What is power factor?

Power factor is a measure of the efficiency of an electrical system and is defined as the ratio of the real power (in watts) to the apparent power (in volt-amperes). It represents the percentage of electricity that is being used effectively to do work.

Why is power factor important?

A low power factor can result in wasted energy, increased electricity costs, and potential damage to electrical equipment. It is important to maintain a high power factor to ensure efficient use of electricity and reduce utility expenses.

How is power factor measured?

Power factor can be measured using a power analyzer or a digital multimeter with a power factor function. The instrument measures the voltage and current in an electrical system and calculates the power factor using the phase difference between them.

What is leading and lagging power factor?

Leading power factor occurs when the current leads the voltage in an electrical system, while lagging power factor occurs when the current lags behind the voltage. Leading power factor is desirable as it indicates a more efficient use of electricity, while lagging power factor can result in wasted energy.

How can power factor be improved?

Power factor can be improved by installing power factor correction devices, such as capacitors, in the electrical system. These devices help to reduce the reactive power and improve the power factor, resulting in more efficient use of electricity and cost savings.

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