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For a relatively weak electrical grid, let's say 20 MW (precise value is not important), I want to develop a measuring system for monitoring the voltage and save the waveform (as timeseries signal), for performing frequency analysis.

If the grid is low voltage, using a voltage divider to step-down the 400 V is tested and safe. Obviously the design needs proper spacings, and an isolation stage (optocoupler, isolation amplifier or something like this), but what about a 6.6 kV system?

Should I use a voltage or capacitor divider? Should I use a high-voltage transformer (6.6 kV to 400 V or even lower) and then integrate a voltage divider? Is there a standard for these kinds of measurements?

Edit #1: The grid is 50/60 Hz. I would like to be able to measure harmonics up to 3-4 kHz.

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  • \$\begingroup\$ Depends. Are you only interested in 50/60 Hz fundamental or do you need much more bandwidth? \$\endgroup\$ Commented Dec 6, 2024 at 9:54
  • \$\begingroup\$ @winny the grid is 50/60 Hz, no high-frequency stuff. Since the grid is weak and loads (mainly AC motors and heaters) have a big influence on the power quality and introduce higher harmonics, I would like to be able to capture frequencies up to 3-4 kHz. But these harmonics have significantly lower amplitudes. \$\endgroup\$ Commented Dec 6, 2024 at 11:01
  • \$\begingroup\$ @thece if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$ Commented Nov 19 at 12:21

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If you use an appropriate transformer you can step down voltage and provide safety isolation all in one hit. That has to be favourite in terms of safety and performance but, if you are careful (and implement other appropriate safety precautions), you can use a resistive-capacitive divider.

The resistor divider would likely contain several series elements in order to meet the individual voltage rating for each component and, because the resistance would be high (to avoid excessive power dissipation), it would be appropriate to have parallel capacitors with each series resistor.

The parallel capacitors themselves form a potential divider and, if you are only wanting to measure an AC voltage, you need not use the resistors. I don't know if there are standards that insist that such-and-such an application uses a such-and-such method.

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