7SR11 & 7SR12 Commissioning and Maintenance Guide
©2017 Siemens Protection Devices Limited Chapter 6 Page 13 of 72
polarising reference voltage is set to 0deg and the current phase angle is measured with respect to this
reference.
Alternatively, the instrument can be checked at the 4 points marked a,b,c & d on Figure 2-1 only.
Forward Reverse
Lag (point C) Lead (point A) Lead(point B) Lag (point D)
Pick-up Drop-off Pick-up Drop-off Pick-up Drop-off Pick-up Drop-off
MTA
MTA-85
MTA+85
MTA-85
MTA-85
Phase A
Phase B
Phase C
V
C
V
B
V
A
I
A
With balanced
3-phase system quantities:
Adjust the phase angle of the currents
relative to the voltages
:
Verify directional pick
-up and drop off at
points A
, B
,
C and D
Alternatively,
Verify correct directional indication at points
a
,
b,
c and d (C.
A +
75
0
, +
95
0
,
-75
0
,
-
95
0
)
A
B
D
C
a
d
b
c
FWD
REV
+6
0
0
+
3
0
0
0
0
+270
0
+
18
0
0
+
210
0
+24
0
0
+
9
0
0
V
BC
Figure 2-1 Directional Phase Fault Boundary System Angles
5. With the instrument reading ‘Fwd’ or ‘Rev’, reduce the voltage until the element resets. Record the minimum
phase-phase operate voltage.
2.1.1 2 out of 3 logic
Ensure that at least 1 Phase Overcurrent element is set to Directional. Apply balanced nominal voltage. Apply
current at a level above the 50/51 setting on phase A only at the characteristic angle for forward operation,
normally 45º lagging. Ensure no Directional Phase Overcurrent element operation occurs. Note that non-
directional Phase Overcurrent and Non-direction Earth Fault elements may operate unless disabled.
Repeat the test with Phase A current as above but also with equal current in the B phase at 180º to that in the A
phase.
To Next Page
Loading...
