Woodward HighPROTEC - Wide Frequency Range

Wide Frequency Range
Wide Frequency Range
The frequency will be calculated based on the three phase voltages as well as the fourth voltage measuring input.
Some protective elements are using Discrete Fourier Transformation (DFT) in order to extract the fundamentals and
phase angles from the measured values. Other protective elements are using True RMS values. For some
protective elements, the User can specify if they should work based on DFT or True RMS values.
The calculation of measuring quantities via DFT is very fast. The values are calculated several times per cycle. For
some technical reasons, the calculation of DFT values is only possible if the frequency is close to the nominal
frequency (± 10% f
N
). If the frequency is out of the nominal frequency range, the DFT values are no longer precise.
That is why protective elements (and directional features), that work based on DFT values, will be blocked either
because they are set fixed to DFT or they are set by the User to DFT, as soon as the frequency leaves the nominal
range (± 10% f
N
).
Protective elements, that are working based on True RMS values are able to work in a wide frequency range (5‒
70 Hz). For technical reasons, the True RMS based calculation of measured values will be done once per cycle.
The lower the frequency, the longer the cycle, the slower the calculation will become. That means that the True
RMS based calculations will have longer settling times (< 2 cycles). This especially applies the lower the
frequency is.
The duration of a cycle will be calculated based on the voltage measuring channels. The duration of a cycle for True
RMS is possible if the voltage magnitudes exceeds 10 V. In case the cycle duration cannot be determined, the rated
frequency will be assumed for DFT and True RMS calculations. As soon as a sufficient magnitude is fed to the
relay, the wide frequency range will be activated a few cycles later (after the settling time) if the frequency is out of
the nominal range.
|f − f
N
| < 10% ⋅ f
N
|f − f
N
| > 10% ⋅ f
N
DFT available:
The measured values are calculated several times per cycle.
DFT imprecise:
Protective elements will be blocked.
True RMS available:
The measured values are calculated several times per cycle.
True RMS available 5-70 Hz:
Measured values are updated after each cycle.
The dropout ratio is 1 Hz below 5 Hz.
231 MCDGV4 DOK-HB-MCDGV4-2E