SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 10 of 74
4.8 Zone 3 module RRM 09
Introduction
This is a two board module which contains the forward and reverse reach settings,
polarising, and comparators for Zone 3 (Z3) and Zone 6 (Z6) the power swing
blocking zone. The two versions available are offset lenticular for phase and
ground faults, or offset mho for phase faults with offset quadrilateral for ground
faults. The two nameplates showing the setting details are shown in Figure 22.
4.8.1 Setting board ZH0734
The right hand board is common to both versions except the addition of a switch
labelled a/b for the lenticular version. This switch controls the aspect ratio.
A block diagram is shown in Figure 18.
The forward Z3 reach is obtained by attenuating each of the phase-neutral
voltages by switches and resistor networks. The switches labelled K31, K32 and
K33 set the forward reach. The attenuated voltages are mixed with the appropriate
IZ signals and the resultant squared and level shifted to produce the six (V – IZ)
square waves. The reverse Z3 reach is similarly obtained by switches labelled
K33, K35 and K36 and resistor networks. An additional switch K37 controls an
amplifier to give fractional settings. The six (V +
IZ) square waves required for Z3
polarising are obtained by mixing the attenuated voltages with the appropriate
IZ
signals and squaring the resultant and level shifting.
The power swing blocking zone (Z6) surrounds the Z3 A–B phase-phase element.
The forward reach is set to 130% of Z3 forward reach by attenuating the Z3
voltage and mixing with the appropriate current to give (V –
IZ)
AB
Z6. The reverse
Z6 reach is set to be Z3 reverse +30% of Z3 forward. The (V +
IZ)
AB
Z6 square
wave is obtained by scaling and mixing appropriate voltages and currents.
This requires extra switches ganged to the Z3 setting switches.
The low set neutral level detector is located on this board. It operates in
conjunction with the reference level and hysteresis circuits on the level detector
board in the same way as the high set neutral described in Section 4.4.
For this level detector t1 = 0.155 cycle and t2 = 1.1 cycles
4.8.2 Comparator board ZH0733
A block diagram for the lenticular version of this board is shown in Figure 19 and
for the quadrilateral version in Figure 20. The functions of the left hand board can
be divided into two areas:
a) The polarising circuit
The polarising signals required to produce the offset lenticular and circular
characteristics are described in Section 5.2.2. The (V +
IZ) signals are phase
shifted by the appropriate angles using digital shift registers.
Digital multiplexers are used to select the appropriate signals for the aspect
ratio selected by the switch a/b.
b) Comparator
The comparators used for Z3 and Z6 are of the same design as those described
in Section 4.7 used for Z1 and Z2. Four ULA are required for the lenticular
version and five for the quadrilateral.
The lenticular characteristic described in Section 5.4 is constructed using a main
comparator and an inhibit comparator. The quadrilateral characteristic is
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