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13.33
Date Code 20060320
Instruction Manual
SEL-311C Relay
Testing and Troubleshooting
Test Procedures
Phase Mho Distance
Elements
The SEL-311 includes up to four zones of mho phase distance protection.
Enable the number of phase distance zones you would like to apply through
use of the E21P setting. Zones 1 and 2 are fixed forward. Zones 3 and 4 can be
set forward or reverse. The reach and direction of each zone is independent
from the other zones. When a zone of phase distance protection is set to reach
in one direction, the ground distance elements associated with that zone must
be set to reach in the same direction. Reach is set in secondary ohms. The
phase distance element maximum reach angle is always equal to the angle of
Z1ANG.
Each zone has an instantaneous indication. For example, the M3P element
asserts without intentional time delay for A-B, B-C, or C-A faults within the
Zone 3 characteristic. All zones also include time-delayed indication through
elements M1PT, M2PT, M3PT, and M4PT. In addition, the relay provides an
instantaneous indication for each individual phase-to-phase distance element.
For example, the MAB1, MAB2, MAB3, and MAB4 elements provide
instantaneous indication of A-B phase faults in each zone.
For general testing, use the instantaneous and time-delayed elements that
respond to any phase-to-phase fault within a given zone such as M1P, M2P,
etc. You can record more detailed and specific test results through use of the
instantaneous element associated with the faulted phase pair and zone under
test.
Phase Distance Element Supervisory Conditions
There are a number of supervisory conditions that must be fulfilled before the
relay allows a phase distance element to pick up. These supervisory conditions
are described below.
Phase-to-Phase Nondirectional Overcurrent Element, 50PPn
Each phase-to-phase distance element is supervised by a nondirectional
phase-to-phase overcurrent element. For example, the relay cannot assert the
Zone 3 A-B phase-to-phase distance element if the vector difference between
A-phase current and B-phase current is less than the 50PP3 setting. You may
set 50PP
n
, but the operation of the 50PP
n
element is internal to the phase-to-
phase distance element and may not be observed directly.
Directional Elements
The phase distance protection function is supervised by the negative-sequence
directional and three-phase directional elements to provide improved
directional security. Forward-reaching phase distance elements may not assert
unless a 32QF or F32P element is asserted. Reverse-reaching phase distance
elements may not assert unless a 32QR or R32P element is asserted. Relay
Word bits F32P and R32P are internal to the relay and may not be used or
observed directly.
Loss-of-Potential Logic
If ELOP = Y or Y1, the relay supervises the phase distance element logic
through use of the Internal Loss-of-Potential condition (ILOP). When ELOP =
Y or Y1 the relay disables the phase distance elements when a loss-of-
potential is detected, regardless of other signals applied to the relay. If you test
the phase distance elements through use of low-voltage signals, set ELOP = N
to simplify the test.
Summary of Contents for SEL-311C
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