Overvoltage relay low pass filter cutoff frequency
Overvoltage relay low pass filter cutoff frequency
(OP)
Hello all,
can anybody tell me what the cutoff frequency of the input low pass filter of a voltage / frequency protection relay, such as e.g. SEG MRN3, would be?
The manual says the relay applies an analog filter to get rid of higher harmonics before it applies digital DFT filtering. I am talking about the former analog stage.
I've tried various frequencies from 50Hz to 300Hz but have no idea would a real relay would do.
Thanks in advance,
stason
can anybody tell me what the cutoff frequency of the input low pass filter of a voltage / frequency protection relay, such as e.g. SEG MRN3, would be?
The manual says the relay applies an analog filter to get rid of higher harmonics before it applies digital DFT filtering. I am talking about the former analog stage.
I've tried various frequencies from 50Hz to 300Hz but have no idea would a real relay would do.
Thanks in advance,
stason






RE: Overvoltage relay low pass filter cutoff frequency
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(2B)+(2B)' ?
RE: Overvoltage relay low pass filter cutoff frequency
But, the relay manual does not reveal the type of filter used.
Thanks, pete, that's already something to start with.
RE: Overvoltage relay low pass filter cutoff frequency
RE: Overvoltage relay low pass filter cutoff frequency
RE: Overvoltage relay low pass filter cutoff frequency
Yes. But are you trying to simulate known RC values for a filter? Or are you trying to figure out what they should be? A 1.25 ms sampling rate would require a theoretical cutoff (brick wall filter) at 400 Hz. In reality, a first order RC filter would roll off much sooner to give adequate attenuation at 400 Hz. A higher order filter could have a higher cutoff for the same attenuation. But either way, I imagine that the filter cutoff would be somewhat higher than 63 Hz for a unit designed for 60 Hz or 50 Hz operation, as there would be appreciable attenuation of the signal of interest this close. Remember, 3 db power attenuation is about 70% of actual voltage. While communications people might throw a few db around with no concern, a 30% error is pretty significant when you are trying to set a relay. Its possible for the relay mfg to correct for filter attenuation in s/w. But you'd need to know this in order to simulate that behavior properly.
This is all speculation about what the cutoff for your particular relay might be. If you have the analog filter schematic and component values, you can calculate it.