harmonics measurement 1

[electrocharge]

Looking at measuring harmonic currents and voltages in a 22kV system. The plan is to use the output of the existing CT and VT. How much will these transformers(especially the VT)suppress the individual harmonics that we are trying to measure? What options are could be explored to do the measurements without these transformers?

 

[zohar]

The C.T and V.T should suppress the individual harmonics only when they will be under saturation condition or higer then the 50th harmonics.
I would like to know if their is anther option to do it.

 

[busbar]

Very informally, with their reduced inductance, CTs have better high-frequency response than PTs.

There are passing comments on the matter in IEEE publication 90EH0327-7-PWR (1990), Nonsinusoidal Situations: Effects on the Performance of Meters and Definitions of Power

 

[scottf]

The bandwidth of instrument transformers depend a bit on design, but in general the following applies:

For CTs, you should get pretty linear response up to about 2 kHz or so.

For VTs, they can vary substantially by voltage class and design, but they generally will only be linear up to between 500 Hz and 1 kHz.

If you want to measure harmonics only, then for the voltage, you could try a resistive divider (I believe S&C makes one at 25 kV). If you need voltage for metering or relaying as well, then you probably need to use a VT for metering and relaying and a resistive divider for harmonic measurments. If you have a high-end meter (like from PML), then it should have seperate inputs for power and harmonics.

Your best bet is to ask the manufacture for the harmonic performance, because as I mentioned, there is great variation between designs and voltages classes.