3.3
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Differential Element
Figure 3.2 Winding 1 Compensated Currents
Figure 3.3 and Figure 3.4 illustrate how the IOP1 (operate), IRT1 (restraint),
IHRT1 (harmonic restraint, all but SEL-387-0 Relay), I1HB2 (second
harmonic), and I1HB4 (fourth harmonic, all but SEL-387-0) quantities are
calculated for the 87-1 element. IOP1 is generated by summing the winding
currents in a phasor addition. IRT1 is generated by summing the magnitudes
of the winding currents in a simple scalar addition and dividing by two. The
87-2 and 87-3 quantities are calculated in a similar manner.
For each restraint element (87R-1, 87R-2, 87R-3), the quantities are summed
as phasors and the magnitude becomes the Operate quantity (IOPn). For a
through-current condition, IOPn should calculate to about 1 + (–1) = 0, at
rated load. Calculation of the Restraint quantity (IRTn) occurs through a
summation of all current magnitudes and then division by two. For a through-
current condition, this will calculate to about (| 1 | + | –1 |) / 2 = 2 / 2 = 1, at
rated load.
Figure 3.3 Differential Element (87-1) Quantities (SEL-387-0)
Data
Acquisition
Fundamental
Frequency
Filter
TAP1
Scaling
Connection
Compensation
(CTC1)
Second-
Harmonic
Filter
TAP1
Scaling
Connection
Compensation
(CTC1)
Fourth-
Harmonic
Filter
TAP1
Scaling
Connection
Compensation
(CTC1)
I1W1C2
I2W1C2
I3W1C2
I1W1C4
I2W1C4
I3W1C4
I1W1C1
I2W1C1
I3W1C1
IAW1
IBW1
ICW1
IOP1
E87W1
I1W1C1
I1W3C1
I1W2C1
I1W4C1
E87W2
E87W3
E87W4
Σ
| ΣI1W
n
C1 |
E87W1
I1W1C2
I1W3C2
I1W2C2
I1W4C2
E87W2
E87W3
E87W4
IRT1
I1HB2
Σ
Σ
| ΣI1W
n
C2 |
| I1W4C1 |
| I1W3C1 |
| I1W2C1 |
| I1W1C1 |
100/PCT2
÷2
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