Schweitzer Engineering Laboratories SEL-387E - Metering Functions

Date Code 20080110 Protection Functions 3-3
SEL-387E Instruction Manual
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
DWG: M3871108
I1W1C1
I2W1C1
I3W1C1
IAW1
IBW1
ICW1
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.