Out Of 3 Logic - Siemens 7SR17 Rho Manual

Lag (point C)
Pick-up
MTA MTA-85
Phase A
Phase B
Phase C
Figure 2-1
5. With the instrument reading 'Fwd' or 'Rev', reduce the voltage until the element resets. Record the minimum
phase-phase operate voltage.
Minimum Voltage Setting
2.6.1

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.
1 phase current
No 50/51-n Operation
©2014 Siemens Protection Devices Limited
Forward
Lead (point A)
Drop-off Pick-up Drop-off
MTA+85
Directional Phase Fault Boundary System Angles
Chapter 6) 7SR17 Commissioning and Maintenance Guide
Lead(point B)
Pick-up Drop-off
MTA-85
Measured
2 phase current
50/51-n operation
Reverse
Lag (point D)
Pick-up Drop-off
MTA-85
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