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3-34
Differential, Restricted Earth Fault,
Date Code 20020129
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
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 is one set 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, 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 3.1: Overcurrent Element Summary
Definite-Time
Elements
Instantaneous
Elements
Inverse-Time
Elements
Phase (Ia, Ib, and Ic)
Winding
1
Winding
2
Winding
3
Combined (Windings 1 and 2)
50P11
50P21
50P31
50P12, 50P13, 50P14
50P22, 50P23, 50P24
50P32, 50P33, 50P34
51P1
51P2
51P3
51PC1
Negative-Sequence (IQ = 3 • I
2
)
Winding
1
Winding
2
Winding
3
50Q11
50Q21
50Q31
50Q12
50Q22
50Q32
51Q1
51Q2
51Q3
Residual (IR = Ia + Ib +Ic)
Winding
1
Winding
2
Winding
3
Combined (Windings 1 and 2)
50N11
50N21
50N31
50N12
50N22
50N32
51N1
51N2
51N3
51NC1
50Pn1 – Phase Definite-Time Element
Figure 3.15 shows the logic for the 50Pn1 element. The logic compares the magnitudes of phase
input currents IAWn, IBWn, and ICWn to pickup setting 50Pn1P. 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 50Pn1TC determines the other AND input. If
50Pn1TC is true, Relay Word bit 50Pn1 asserts and starts the timer. After the time specified by
delay setting 50Pn1D expires, a second Relay Word bit, 50Pn1T, asserts. This bit asserts only if
the 50Pn1 bit remains asserted for the duration of 50Pn1D. When 50Pn1 deasserts, the timer
resets without delay, along with 50Pn1T if it has asserted.
Содержание SEL-387E
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