SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 4 of 74
Section 4. MODULE DESCRIPTIONS
To provide the user with a thorough understanding of the operating principle of the
relay and the function of the individual modules within the relay, the following sub-
sections describe the operating functions of each module. Where necessary,
references to more detailed descriptions in Section 5 are given.
4.1 Relay block diagram
Figure 3 shows the relative positions of the modules within the relay case and
Figure 4 shows the overall relay block diagram.
4.2 The voltage input module RFV 04
The voltage input module isolates and filters the ac inputs from the transmission line
voltage transformers. Reference to Figure 5 reveals that the module has three
phase-neutral connected isolating transformers insulated to 5kV peak. These have
interwinding screens to attenuate common-mode high frequency interference.
The output from each transformer is passed through an overvoltage surge
protection circuit which limits overvoltages due to lightning strikes, cross country
faults and other high voltage transients, to within limits which are safe for the
electronic circuitry contained within the relay.
The signals are then filtered by low-pass filters with cut-off frequencies of 300Hz.
The purpose of the filters is to remove unwanted high frequency signals such as
line reflections following the incidence of a fault and also interference induced on
substation wiring by switching operations. Each output is then passed to a
calibrated attenuator and a band pass filter. The filters are of second order with
centre frequencies equal to the nominal supply frequency and Q values of 0.5.
This type of filter is very effective in eliminating unwanted exponential and high
frequency components of the input voltage.
Under normal conditions the distance measuring elements use the voltage signal
produced by the attenuator. However, the measuring elements are automatically
switched to the filtered output of the band-pass circuits after a predetermined
interval from the incidence of a fault. This ensures that, if the comparator operating
time has been slowed by abnormally severe exponential or high frequency
components of the voltage signal, the comparators have the opportunity of
remeasuring on a relatively uncontaminated voltage signal.
This arrangement prevents any possibility of excessively long comparator operating
times which might otherwise occur under certain extreme conditions, such as (a)
severe CVT transient errors with high SIR and high fault position, (b) severe
travelling wave distortion on a long line at high fault position (c) large mismatch
between source and line time constants with high SIR and high fault position.
An example is shown in Figure 6.
The voltage level detectors are used as fault detectors for the purpose of controlling
the transfer from normal to band pass filtered voltage signal. Solid state switches
are used under the control of input “ENF” for the signal transfer circuits. The reset
time of the voltage level detectors is approximately 12 to 22ms depending on
point-on-wave of fault incidence and a further delay of 14ms is introduced by a
software timer. Resetting of any voltage level detector causes all three phases of
voltage signal to be transferred to the band pass filter outputs.
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