## Line Power Quality

**Question:** Can you please discuss the differences between Instantaneous Power, Apparent Power, Reactive Power and True Power? How do these all relate?

**Answer**: True Power, Apparent Power and Reactive Power are typically measured on the power line input to determine the impact of the power supply on the power source that feeds it. Instantaneous Power is the instantaneous voltage multiplied by the instantaneous current. It represents the power on the power line at any one point in time. Apparent Power is actually calculated by determining the RMS voltage of the voltage waveform for an entire waveform acquisition and multiplying it by the RMS current for the same waveform acquisition.

To determine True Power, the oscilloscope determines the phase difference between the voltage and current waveforms. True Power is then simply the Apparent Power multiplied by the cosine of the phase angle difference. Similarly, Reactive Power is the Apparent Power multiplied by the sine of the phase angle difference.

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**Tags:** line power quality

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