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Date Code 20011112
Line Current Differential, Distance, Out-of-Step, Overcurrent,
3-31
Voltage, Synchronism Check, and Frequency Elements
SEL-311L Instruction Manual
Figure 3.25: Negative-Sequence Time-Overcurrent Elements
D
ISTANCE
E
LEMENTS
Mho Phase Distance Elements
The SEL-311L Relay has four independent zones of mho phase distance protection. All zones are
independently set. Zone 1 and 2 are fixed to operate in the forward direction only. Zones 3 and 4
can be set to operate in either the forward or reverse direction. The phase distance elements use
positive-sequence voltage polarization for security and to create an expanded mho characteristic.
The phase distance elements operate on phase-to-phase, phase-to-phase to ground, and
three-phase faults.
Compensator distance elements are included for distance relaying through wye-delta transformer
banks and for users who desire a different operating principle for backup relaying. Compensator
distance phase-elements implemented in the SEL-311L Relay detect phase-to-phase, phase-to-
phase-to-ground and three-phase faults.
Operating Principles of Phase Distance Elements
A digital relay mho element tests the angle between a line drop-compensated voltage and a
polarizing (reference) voltage using the following concepts:
Sampled currents and voltages are represented in the relay as vectors by using the most recent
sample as the real vector component and the sample taken one quarter cycle earlier as the
imaginary vector component. See Figures 12.6 and 12.7 in
Chapter 12: Standard Event Reports
and SER
for a description of this process.
Содержание SEL-311L
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