Sel SEL-421 - Series-Compensation Line Logic; CVT Transient Detection Logic; Series-Compensation Line Logic Relay Settings

R.1.41
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Series-Compensation Line Logic
Figure 1.27 CVT Transient Detection Logic
SIR is defined as follows:
Use the Zone 1 distance element reach (Z1P, Z1MG, or XG1) since the CVT
transient detection logic only supervises Zone 1 distance protection.
Series-Compensation Line Logic
NOTE: The SEL-421-1 and the
SEL-421-2 do not provide series-
compensated line protection logic.
The SEL-421 includes logic to detect when a fault is beyond a series capacitor
(a series capacitor can possibly cause Zone 1 overreach). The relay blocks the
Zone 1 elements until the series-compensation logic determines that the fault
is between the relay and the series capacitor (i.e., the fault is on the protected
line section).
The value that you enter for setting XC depends on the position of the series-
compensation capacitor(s) relative to the relay potential transformers.
Capacitors can be on either end of a line, in the middle of a line, or at both
ends of a line. Capacitors that are external to a protected line section can have
an effect if infeed conditions are present.
In applications where there is a series capacitor on an adjacent line, for any
SEL-421 relays on non-compensated lines, set ESERCMP := Y and
XC := OFF. This allows the Zone 1 element to be set to the desired sensitivity,
yet still be secure during the voltage reversal that will occur when a
neighboring compensated line experiences a fault.
For more information on setting the relay for series-compensated lines see
SEL Application Guide 2000-11: Applying the SEL-321 Relay on Series-
Compensated Systems.
where:
Z
1S
= positive-sequence source impedance
Z
R
= distance element reach
0
1.5
CYC
Distance Calculation
Smoothness
Relay
Word
Bits
3PO
CVTBL
SOTFE
ECVT := Y
SIR > 5 During
Zone 1 Fault
Setting
SIR
Z
1S
Z
R
---------=
Table 1.37 Series-Compensation Line Logic Relay Settings
Name Description Range
Default
(5 A)
ESERCMP Series-Compensation Line Logic Y, N N
XC Series Capacitor Reactance () (OFF, 0.25–320 )/I
nom
OFF