Power Automation and Protection Division
I.L. 40-201.9
REL 352 Version 1.00
5-3
5
• Enabling of Transmitted IKEY for ON-OFF Power Line Carrier Applications (see fig-
ure 3-6).
The Change Detector function is illustrated in figure 3-9.
All relay current inputs (I
A
, I
B
, I
C
and I
G
) and voltage inputs (V
A
, V
B
and V
C
) are sampled (con-
verted to numbers) 12 times per Power Line Cycle. The present samples are compared to the
corresponding samples taken 1 cycle “ago”.
The change detector is asserted if the absolute difference of present and old sample exceeds
12.5% of the old sample and the difference is greater than:
• 1 pu for current - 0.1 x 5 = 0.5A
• 7V for voltage
The CD can be generated either by using the current change detectors (
∆
I) or the current and
voltage change detectors (
∆
I and
∆
V).
The user can select the generation of change detector on:
•
∆
I
— Current change detectors only. This setting provides more security.
•
∆
I
∆
V — Current and voltage change detectors if the system has voltage inputs.
This setting provides more sensitivity and should always be used for
weak-feed applications, where the change in current may not be signifi-
cant to start the relaying system.
4.2
Fault Detector (FD2)
The Fault Detector FD2 supervises trip function as illustrated on figure 3-7. It is computed by
converting symmetrical component filter output waveform IT to its rms equivalent, and compar-
ing it versus setting FD2 (see figure 3-8).
4.3
Symmetrical Component Coefficients (C0, C1, C2)
The reader is reminded that the
IT = C0 • I0 + C1 • I1 + C2 • I2.
As seen from the above equation the coefficients are:
C0 – Zero Sequence
C1 – Positive Sequence
C2 – Negative Sequence
Typical relative values of these coefficients are:
C0 – 0.7
C1 – 0.1
C2 – 0.2
Thus providing the greatest sensitivity to phase-to-ground faults (zero sequence), and the low-
est sensitivity to normal load currents and 3-phase faults (positive sequence). The phase-to-
phase faults (negative sequence) provide moderate contribution to the resulting IT.
4.4
Number of Line Terminals (TERM)
This setting determines the number of line terminals.
For normal 2-terminal line TERM = 2.
For 3-terminal line TERM = 3
As seen on figure 3-6 the setting for TERM = 3 enables comparison of received signals S2 and
M2 from the third terminal with local signals LN2 and LP2 respectively.
