SERVICE MANUAL R5888C
QUADRAMHO Chapter 6
Page 6 of 12
and for reverse reach ground faults is:
(K1 + K2 + K4 + K5 + K6) (K35 + K36) K33 x K37
ohms
I
n
The phase fault loop impedances required are for forward faults:
2 x (K1 + K2) (K31 + K32) K33
ohms
I
n
and for reverse phase faults:
2 x (K1 + K2) (K35 + K36) K33 x K37
ohms
I
n
The reach checks should be carried out for each element of the relay as in
Section 4.5.1.
Note: For the reverse reach an additional tolerance of ±15% is allowed.
4.6 Check Z3 lenticular polar plot (lenticular versions only).
To check the lenticular shape, note the relay settings and return to them after
this test.
Set a/b = 0.41 and the forward and reverse reaches to the same, ie.
(K31 + K32) K33 = (K35 + K36) (K37 + K33)
Also set Ø
Ph
= Ø
N
= 80°
Figure 6 shows the normalised theoretical shape for Zone 3 for these conditions.
From this diagram the theoretical reach ZT, for off angle faults can be determined
for both forward and reverse faults. Using this information the ground fault loop
impedance required is:
(K1 + K2 + K4 + K5 + K6) (K31 + K32) K33 x Z
T
ohms
I
n
at the particular angle of Z
T
.
The phase fault loop impedance required is:
2 x (K1 + K2) (K31 + K32) K33 x Z
T
ohms
Check the reach as in Section 4.5 allowing the same tolerances.
4.7 Resistive reach check (if quadrilateral characteristic is fitted)
Checks are done using resistive faults, thus in the forward direction all zones will
be seen to operate at the same loop impedance.
The required loop fault resistance is:
K3
ohms
I
n
When the fault is reversed, only Zone 3 should operate due to the slope on the
bottom line of the characteristic for Zones 1 and 2.
The checks should be carried out for all phase to ground faults and results should
be within ±10% of the selected setting.
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