Schweitzer Engineering Laboratories SEL-311B, Instruction Manual

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13-36 Testing and Troubleshooting Date Code 20011205
SEL-311B Instruction Manual
Each zone has an instantaneous indication. For example, the Z3G element asserts without
intentional time delay for A-G, B-G, and C-G faults within the Zone 3 mho or quadrilateral
characteristic. All zones include time delayed indication through elements Z1GT, Z2GT, Z3GT,
and Z4GT. In addition, each individual phase-ground distance element provides an instantaneous
indication for each zone. For example, the MAG1, MAG2, MAG3, and MAG4 elements provide
instantaneous indication of A-G ground faults in each zone.
For general testing, use the instantaneous and time delayed elements that respond to any phase-
ground fault within a given zone such as Z1G, Z2G, etc. You can record more detailed and
specific test results using the instantaneous element associated with the faulted phase and zone
under test.
There are a number of supervisory conditions that must be fulfilled before the relay allows a
ground distance element to pick up. These supervisory conditions are described below.
Ground Distance Element Supervisory Conditions
Note: Unless otherwise indicated, all of the supervisory conditions listed below apply to the
ground mho and ground quadrilateral distance elements.
Phase and Ground Nondirectional Overcurrent Elements, 50Ln and 50GZn
Each zone ground distance element is supervised by two nondirectional overcurrent elements,
50GZn and 50Ln, where n indicates the zone associated with the overcurrent element. For
example, the relay may assert the Zone 3 A-ground distance element only if the A-phase current
is greater than the 50L3 setting and the residual current is greater than the 50GZ3 setting.
Ground Directional Element
The ground distance protection function is supervised by the ground directional element to
provide improved directional security. Forward-reaching distance elements may not assert unless
the 32GF element is asserted. Reverse-reaching distance elements may not assert unless the
32GR element is asserted. See
Directional Control for Ground Distance and Residual
Ground Overcurrent Elements in Section 4: Loss-of-Potential, CCVT Transient Detection,
Load-Encroachment, and Directional Element Logic for a complete description of ground
directional elements.
Loss-of-Potential Logic
If ELOP = Y or Y1, the relay supervises the ground distance element logic using the Internal
Loss-of-Potential condition (ILOP). When ELOP = Y or Y1, the relay disables the ground
distance elements when a loss-of-potential is detected, regardless of other signals applied to the
relay. If you test the ground distance elements using low voltage signals, set ELOP = N to
simplify the test.