Schweitzer Engineering Laboratories, Inc. SEL-487E Data Sheet
7
➤Maximum filtered combined phase current:
IMAXmmF
➤Filtered positive-, negative-, and zero-sequence:
I1mFM, 3I2mFM, 3I0mFM, I1mmM, 3I2mmM,
3I0mmM
➤RMS currents: IAmRMS, IBmRMS, ICmRMS,
IMAXmR IAmmRMS, IBmmRMS, ICmmRMS,
IMAXmmR
where:
m= Relay current terminals S, T, U, W, X, Y
mm = Relay current terminals ST, TU, UW, WX
F = Filtered
M = Magnitude
MAX = Maximum magnitude A-, B-, C-phase currents
In addition to the selectable operate quantity, the 51S ele-
ment time-delay and pickup level inputs are SELOGIC-
programmable settings. This flexibility allows these inputs
to be set to fixed numerical values to operate as standard
time overcurrent elements, or the pickup and time-dial
settings can be programmed as SELOGIC math variables.
Programming the time-delay and pickup levels as math
variables allows the numeric value of the pickup and time-
delay settings to change based on system conditions with-
out the added delay of having to change relay setting groups.
For example, change pickup and time-delay settings
dynamically in a parallel transformer application based
upon single or parallel transformer configurations. Another
example would be changing feeder time-overcurrent ele-
ment pickup and coordination delays based upon distributed
generation being connected downstream of a transformer.
REF Protection
Apply the REF protection feature to provide sensitive detec-
tion of internal ground faults on grounded wye-connected
transformer windings and autotransformers. Use single-
phase neutral current inputs for providing neutral CT oper-
ating current for as many as three windings. Polarizing
current is derived from the residual current calculated for
the corresponding protected winding. A directional ele-
ment determines whether the fault is internal or external.
Zero-sequence current thresholds supervise tripping. The
relay can accommodate CT ratio mismatch as great as 35:1.
Synchronism Check
Synchronism-check elements prevent circuit breakers
from closing if the corresponding phases across the open
circuit breaker are excessively out of phase, magnitude,
or frequency. The SEL-487E synchronism-check ele-
ments selectively close circuit breaker poles under the
following criteria:
➤The systems on both sides of the open circuit
breaker are in phase (within a settable voltage
angle difference).
➤The voltages on both sides of the open circuit
breaker are healthy (within a settable voltage
magnitude window).
The synchronism-check function is available for as many
as six breakers with a user-selectable reference voltage.
Each element has a user-selectable synchronizing voltage
source and incorporates slip frequency, two levels of
maximum angle difference, and breaker close time into
the closing decision. Include the synchronism-check ele-
ment outputs in the close SELOGIC control equations to
program the relay to supervise circuit breaker closing.
Current Unbalance Elements
The current unbalance logic uses the average terminal cur-
rent to calculate the percentage difference between the
individual phase current and the terminal median current.
If the percentage difference is greater than the pickup value
setting, the phase unbalance element is asserted. To pre-
vent this element from asserting during fault conditions
and after a terminal circuit breaker has closed, the final
terminal unbalance output is supervised using current,
fault detectors, and the open-phase detection logic.
Fault Identification Logic
The purpose of the fault identification logic is to deter-
mine, on a per-terminal basis, which phase(s) was involved
in a fault for which the transformer tripped. Determining
the faulted phase is based on current inputs from wye-
connected CTs. The logic does not determine the faulted
phase for the following cases:
➤Delta-connected CTs (CTCONm= D)
➤Where only zero-sequence current flows through
the relay terminal (no negative-sequence current
and no positive-sequence current)
This logic identifies a sector in which a faulted phase(s)
can appear by comparing the angle between the negative-
and zero-sequence currents I2mand I0m(m= S, T, U, W,
X, Y).
Application Examples
The SEL-487E-5 SV Subscriber offers comprehensive
transformer protection features. Around the clock wind-
ing phase compensation simplifies setting the trans-
former protection elements. Harmonic restraint and
blocking using second and fourth harmonic quantities
