3.14
SEL-587Z Instruction Manual
Date Code 20020903
Relay Elements
Overcurrent Protection
C3–Class C (Extremely Inverse)
C4–Long-Time Inverse
C5–Short-Time Inverse
Reset Characteristic Settings
Refer to
for the setting labels. Set the time-overcurrent
reset characteristic to emulate an induction disk relay reset characteristic or
linear one-cycle reset.
The induction disk selection emulates the spring-torque governed disk reset
action of an induction time-overcurrent unit. Set 51nRS = Y when the time-
overcurrent element must coordinate with upstream electromechanical time-
overcurrent relays during trip-reclose cycles.
The one-cycle reset selection fully resets the element one cycle after current
drops below the element pickup setting. Set 51nRS = N when the time-
overcurrent element must coordinate with upstream static or microprocessor-
based time-overcurrent elements, which have fast reset characteristics.
Overcurrent
Application
Guidelines
Transformer Overcurrent and REF Protection
Figure 3.16
Transformer With Grounded-Wye-Connected Winding.
Set the SEL-587Z instantaneous overcurrent elements to detect high current
faults, such as transformer bushing faults. Use time-overcurrent elements to
detect transformer faults of lower current magnitude, faults not involving
ground that the REF cannot detect, and excessive through currents caused by
slow clearing external faults. Use appropriate delays to coordinate with
upstream and downstream protection.
Thermal and mechanical damage curves should be available from the
transformer manufacturer for specific transformer designs. You can consult
several references, including the IEEE Standard C37.91: 2000,
IEEE Guide
for Protective Relay Applications to Power Transformers,
that provide generic
through-current limitations for various classes of transformers.
SEL-587Z
87
SEL-587
or SEL-387
87
50/51
REF
1
Содержание SEL-587Z
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