3-4
Differential, Restricted Earth Fault,
Date Code 20020129
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
S
K
3&7
S
ÌS,:
Q
&Ì
,23
ÌS,:
Q
&Ì
S
':*0
Ì,:&Ì
Ì,:&Ì
Ì,:&Ì
·
S
(:
,:&
,:&
,:&
(:
(:
(:
,:&
,:&
,:&
(:
(:
(:
,:&
,:&
,:&
(:
(:
3&7
ÌS,:
Q
&Ì
S
Q
,57
,+57
,+%
,+%
Figure 3.3: Differential Element (87-1) Quantities
Figure 3.4 shows how the differential element quantities are used to generate the unrestrained
87Un (87U1, 87U2, 87U3) and restrained 87Rn (87R1, 87R2, 87R3) elements. These elements
are combined to form differential element targets (87-1, 87-2, 87-3).
Unrestrained elements (87U1, 87U2, and 87U3) compare the IOP quantity to a setting value
(U87P), typically about 10 times TAP, and trip if this level is exceeded. Elements 87U1, 87U2,
and 87U3 are combined to form element 87U as shown in the lower right corner of Figure 3.4.
Harmonic blocking is not performed on the unrestrained elements. Use these elements to protect
your transformer bushings and end windings while maintaining security for inrush and through-
fault conditions. Operating current elements 87On (87O1, 87O2, 87O3) are provided for testing
purposes.
Restrained elements (87R1, 87R2, and 87R3) determine whether the IOP quantity is greater than
the restraint quantity using the differential characteristic shown in Figure 3.1. Set HRSTR=Y
(harmonic restraint) to modify this characteristic as a function of the second- and fourth-harmonic
content in the input currents.
In element 87Rn, for example, the IOPn and IRTn quantities determine whether the relay trips.
The logic enclosed within the dotted line of Figure 3.4 implements the Figure 3.1 characteristic.
The differential element calculates a threshold as a function of IRTn. IOPn must exceed this
threshold to produce tripping. The function uses the SLP1, SLP2, and IRS1 setting values, along
with IRTn, to calculate the IOP value. The differential element decision logic compares the
calculated value, denoted f(IRTn), to the actual IOPn. If IOPn is greater, one input of the AND
gate at the right receives a logic 1. Comparison of IOPn with the O87P setting determines the
second AND input. If IOPn is greater than O87P, Relay Word bit 87On asserts. The
AND gate
Содержание SEL-387E
Страница 8: ......
Страница 10: ......
Страница 12: ......
Страница 50: ......
Страница 124: ......
Страница 176: ......
Страница 196: ......
Страница 198: ......
Страница 242: ......
Страница 270: ......
Страница 308: ......
Страница 422: ......
Страница 428: ......
Страница 432: ......
Страница 448: ......
Страница 450: ......
Страница 462: ......