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Date Code 20020129
Differential, Restricted Earth Fault,
3-3
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
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Figure 3.2: Winding 1 Compensated Currents
Figure 3.3 illustrates how the IOP1 (operate), IRT1 (restraint), IHRT1 (harmonic restraint),
I1HB2 (second harmonic), and I1HB4 (fourth harmonic) 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.
Содержание SEL-387E
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