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Reactive current measurement

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Advanced Member level 3
Apr 24, 2010
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Dhaka, Bangladesh, Bangladesh
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How can we measure the reactive current in the line? I want to measure the reactive part only so that I can decide whether the load is inductive, capacitive or resistive.

You need also to measure the voltage, in order to take the phase drift reference.


I understand. But need details information. should I use any special CT?

---------- Post added at 04:21 ---------- Previous post was at 04:17 ----------

Once I tried with a CT with phase shift of 90° within the primary and secondary coil. But unfortunately it worked not so satisfactory.


Using only microcontroller (+ A2D) to measure is complicated task

Use AD7753 from analog device to measure reactive currents.

All the best


All the best


If you only want to know the displacement angle, not the real/reactive power magnitude, processing voltage and current polarity with a comparator is sufficient.

That means I just need to measure the time difference between the voltage and current waveform? So, sensing the voltage & current and converting them into square wave. then measuring the time difference between the two waveforms?

Thanks for the idea.

Yes, exactly. There's also a simple "analog" measurement method. Apply the C and V square waves to an XOR gate and send the output to a RC filter. The averaged signal is proportional to the displacement angle (without a sign). To get the sign (inductive or capacitive displacement), you have to determine the C/V edge sequence, e.g. with a DFF.

For an exact measurement of the displacement angle with a processor timer, bandpass or lowpass filters suppressing the harmonics be helpful.

are you using sinusoidal voltage
if yes then this can be done in two ways analog modulation or DSP
the output will be the magnitude of the quadrature components i.e. In-phase part of current and 90 degree out of phase components
this can also be used for calculation of complex impedance

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