Schweitzer Engineering Laboratories SEL-787 - Figure 4.2 Winding 1 Compensated Currents; Figure 4.3 Differential Element (87-1) Quantities

4.7
Date Code 20081022 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
currents for Winding 1. The fourth-harmonic and fifth-harmonic compensated
currents use similar names. The I1 compensated currents are used with
differential element 87-1, I2 with element 87-2, and I3 with element 87-3.
Figure 4.2 Winding 1 Compensated Currents
Figure 4.3 illustrates how the IOP1 (operate), IRT1 (restraint), I1H24
(harmonic restraint), I1H2 (second harmonic), and I1H4 (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.
Figure 4.3 Differential Element (87-1) Quantities
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
E87
I1W1C1
I1W2C1
Σ
⏐ΣI1W
n
C1⏐
I1W1C2
I1W2C2
I1W1C4
I1W2C4
IRT1
I1H24
I1H2
I1H4
Σ
h
⏐I1W1C1⏐
⏐I1W2C1⏐
100/PCT2
100/PCT4
E87
Σ
⏐ΣI1W
n
C4⏐
⏐ΣI1W
n
C2⏐
E87
Σ
I1F2
I1F4
Σ