Schweitzer Engineering SEL-387-0, Instruction Manual

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3.49
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Overcurrent Element
and, through an OR gate, assert a Relay Word bit if any one of the three phases
asserts. These two elements primarily provide level detection, for applications
such as trip unlatch logic or phase identification.
In addition to the 11 overcurrent elements, there are two sets of inverse-time
overcurrent elements that use combined currents from two windings. These
phase and residual current elements, one each for Windings 1 and 2 and
Windings 3 and 4, remove circulating current components from two breakers
that connect to the same physical transformer winding but whose CT inputs go
to separate relay input terminals. These combined overcurrent elements permit
more sensitive tripping in ring-bus or breaker-and-a-half schemes. These
elements are not torque controlled.
50Pn1–Phase Definite-Time Element
Figure 3.18 shows the logic for the 50P n 1 element. The logic compares the
magnitudes of phase input currents IAW n , IBW n , and ICW n to pickup setting
50P n 1P. If one or more current magnitudes exceed the pickup level, a logic 1
asserts at one input to the AND gate at the center. The torque-control
SEL
OGIC
control equation 50P n 1TC determines the other AND input. If
50P n 1TC is true, Relay Word bit 50P n 1 asserts and starts the timer. After the
time specified by delay setting 50P n 1D expires, a second Relay Word bit,
50P n 1T, asserts. This bit asserts only if the 50P n 1 bit remains asserted for the
duration of 50P n 1D. When 50P n 1 deasserts, the timer resets without delay,
along with 50P n 1T if it has asserted.
Table 3.4 Overcurrent Element Summary
Definite-Time
Elements
Instantaneous
Elements
Inverse-
Time
Elements
Phase (Ia, Ib, and Ic)
Winding 1
Winding 2
Winding 3
Winding 4
Combined (Windings 1 and 2)
50P11
50P21
50P31
50P41
50P12, 50P13, 50P14
50P22, 50P23, 50P24
50P32, 50P33, 50P34
50P42, 50P43, 50P44
51P1
51P2
51P3
51P4
51PC1
Negative-Sequence (IQ = 3 • I
2
)
Winding 1
Winding 2
Winding 3
Winding 4
50Q11
50Q21
50Q31
50Q41
50Q12
50Q22
50Q32
50Q42
51Q1
51Q2
51Q3
51Q4
Residual (IR = Ia + Ib +Ic)
Winding 1
Winding 2
Winding 3
Winding 4
Combined (Windings 1 and 2)
Combined (Windings 3 and 4)
50N11
50N21
50N31
50N41
50N12
50N22
50N32
50N42
51N1
51N2
51N3
51N4
51NC1
51NC2