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4.4
SEL-311C Relay
Instruction Manual
Date Code 20060320
Loss-of-Potential, CCVT Transient Detection, Load-Encroachment, and Directional Element Logic
CCVT Transient Detection Logic
CCVT Transient Detection Logic
The SEL-311C detects CCVT transients that may cause Zone 1 distance
overreach. If CCVT transient blocking is enabled (setting ECCVT = Y), and
the relay detects a high SIR during a Zone 1 fault, the relay delays tripping for
up to 1.5 cycles, allowing the CCVT to stabilize.
User settings are not required. The relay automatically adapts to different
system SIR conditions by monitoring voltage and current.
For close-in faults on systems with high SIRs, the SEL-311C uses distance-
calculation smoothness detection to override the tripping delay caused by low
voltage and low current. Distance elements operate without significant delay
for close-in faults.
Consider using CCVT transient detection logic when you have either of the
following conditions:
➤
CCVTs with active ferroresonance-suppression circuits
(AFSC)
➤
The possibility of a source-to-line impedance ratio (SIR)
greater than 5
CCVT transients may be aggravated when you have:
➤
A CCVT secondary with a mostly inductive burden
➤
A low C-value CCVT as defined by the manufacturer
For a description of CCVT transients and transient detection, see the
following technical paper available on the SEL website or FaxBack system:
Capacitive Voltage Transformer: Transient Overreach Concerns and
Solutions for Distance Relaying
.
q
w
to
,
, and
Figure 4.2
CCVT Transient Blocking Logic
0
1.5
CVTBL
SIR > 5 During Zone 1 Fault
ECCVT = Y
SOTFE
3PO
Distance Calculation Stable
w
q
Содержание SEL-311C
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