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Technical Manual
KVGC202
Measurement is based on the Fourier derived value of the fundamental component of line
I
(
L), circulating current (
system voltage input (Vbc). The diagram above shows the frequency response that
results from this filtering. The "1" on the horizontal scale relates to the selected rated
frequency of the relay and the figures "2", "3", "4" etc. are the second, third and fourth
harmonic frequencies respectively. It can be seen that harmonics up to and including the
6th are suppressed, giving no output. The 7th is the first predominant harmonic and this
is attenuated to approximately 30% by the anti-aliasing filter. For power frequencies that
are not equal to the selected rated frequency. i.e. the frequency does not coincide with
"1" on the horizontal scale, the harmonics will not be of zero amplitude. For small
frequency deviations of ±1Hz, this is not a problem but to allow for larger deviations, an
improvement is obtained by the addition of frequency tracking.
With frequency tracking the sampling rate of the analogue/digital conversion is
automatically adjusted to match the applied signal. In the absence of a signal of suitable
amplitude to track, the sample rate defaults to that to suit the selected rated frequency
(Fn) for the relay. In presence of a signal within the tracking range (45 to 65Hz), the relay
will lock on to the signal and the "1" on the horizontal axis in diagram above will coincide
with the measured frequency of the measured signal. The resulting output for 2nd, 3rd,
4th, 5th and 6th harmonics will be zero. Thus this diagram applies when the relay is not
frequency tracking the signal and also if it is tracking a frequency within the range 45 to
65Hz.
I
c), Tap position indication voltage (VTPI) and low accuracy
KVCG202/EN M/H11
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