3.54
SEL-387-0, -5, -6 Relay
Instruction Manual
Date Code 20050919
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Overcurrent Element
Overcurrent Element
Application
Description
The SEL-387 provides numerous overcurrent elements, as many as 11 per
winding, 44 total. Four levels of phase instantaneous/definite-time elements
are available for single- or three pole feeder protection, breaker failure
protection, overcurrent phase selection for targeting, transformer backup
protection, etc. Two levels of negative-sequence and residual instantaneous
elements provide protection against unbalanced conditions and ground faults.
A phase, negative-sequence, and residual time-overcurrent element are
available for system backup protection.
Operating
Characteristic
Each winding input of the SEL-387 has 11 overcurrent elements (see
). Nine of these 11 are torque-controlled elements, of which there are
one definite-time element, one instantaneous element, and one inverse-time
element per each of three categories. These categories are phase, negative-
sequence, and residual current. Two of the 11 overcurrent elements, 50P
n
3
and 50P
n
4, are not torque controlled. These two elements are phase
instantaneous overcurrent elements that provide output information per phase
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.
Table 3.4
Overcurrent Element Summary
Definite-Time
Elements
Instananeous
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
Содержание SEL-387-0
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