
3.64
SEL-387-0, -5, -6 Relay
Instruction Manual
Date Code 20170601
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Overcurrent Element
Time-Overcurrent Curve and Time-Dial
Select the element curve and time-dial settings individually to coordinate with
downstream phase, negative-sequence, and residual time-overcurrent
elements. Refer to the time-overcurrent equations and curves at the end of this
section for the specific time-overcurrent characteristic equations.
Time-Overcurrent Element Reset Characteristic
You can set the relay time-overcurrent element to emulate an induction disk
relay reset characteristic by setting the 51
xn
RS (
x
= P, Q, or N;
n
= winding
number) setting equal to Y. With this setting, the relay emulates the spring-
torque-governed disk reset action of an induction time-overcurrent element.
Make this setting when the SEL-387 time-overcurrent element must
coordinate with upstream electromechanical time-overcurrent relays during
trip-reclose cycles.
When you set 51
xn
RS = N, the relay fully resets the time-overcurrent element
one cycle after current drops below the element pickup setting. Make this
setting when the relay time-overcurrent element must coordinate with
upstream static or microprocessor-based time-overcurrent elements that have
fast reset characteristics.
Instantaneous and Definite-Time Overcurrent Elements
The SEL-387 includes instantaneous and definite-time overcurrent elements
for phase, negative-sequence and residual current. There are three separate
phase instantaneous elements, which can be used for various tripping or
supervisory functions defined by the user. Each element operates using
measured current, a pickup setting and, for the definite-time elements, a time
delay setting.
Instantaneous and Definite-Time Element Pickup and Time Delay Settings
Use the instantaneous overcurrent elements to provide fast tripping for heavy
internal transformer faults. Set the element pickup settings high enough to
prevent tripping for faults outside the protection zone. Both definite-time and
instantaneous phase overcurrent elements are sensitive to load, but should,
based on other setting constraints, be set well above the maximum expected
loading.
Use the definite-time delayed overcurrent elements to provide fast backup
protection for downstream instantaneous elements. Allow sufficient time
delay to coordinate with downstream breakers, reclosers, or other protection.
Overcurrent Element External Torque-Control
The SEL-387 allows you to either enable or block selected overcurrent
elements using a SEL
OGIC
control equation. You may want, for example, to
control an overcurrent element using an external contact from a toggle switch,
control switch, external directional relay, or recloser. Or, you may want to use
some combination of relay elements to enable or block the overcurrent
element. These choices are easily accomplished by creating a SEL
OGIC
control equation that describes what is needed, and storing the equation as the
setting for the torque-control variable of the specific overcurrent element. For
Содержание SEL-387-0
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