13-30
Testing and Troubleshooting
Date Code 20011205
SEL-311A Instruction Manual
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 50PPn, but the operation of the 50PPn 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 using 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 using low voltage signals, set ELOP = N to simplify the test.
Load-Encroachment Logic
The relay includes Load-Encroachment logic to help prevent the relay phase distance elements
from operating improperly under heavy load conditions. Forward and reverse load regions are
defined using impedance and angle settings. The relay calculates the positive-sequence
impedance. If the calculated impedance falls within the set load area, the phase distance
elements are blocked from operating. This may result in a phase distance element characteristic
that appears to have a bow tie shaped section missing near the area of the resistive axis. Double-
check the relay Load-Encroachment logic settings if your test results appear incorrect near the
resistive axis.
Out-of-Step Blocking Logic
The relay includes Out-of-Step Tripping and Blocking logic that operates based on the Zone 5
and Zone 6 positive-sequence impedance zones and several timers. If you suspect that the Out-
of-Step logic is blocking operation of a phase distance element under test, check the relay
settings associated with the Out-of-Step function and review the relay event report.
Phase Distance Element Test Using Three Voltage Sources and One Current Source
Note:
This test refers directly to the Zone 2 phase distance element, but may be applied to
any other forward-reaching phase-to-phase distance element zone. To test reverse-
reaching zones, simply add 180° to the calculated test current phase angle. Verify
correct operation of the 32QR element for the test voltage and current signals using
Equation 13.1 in the Negative-Sequence Directional Element Test Procedure.
Содержание SEL-311A
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