8.31
Date Code 20080213
Instruction Manual
SEL-351A Relay
Breaker Monitor and Metering
Small Signal Cutoff for Metering
Small Signal Cutoff for Metering
The relay applies a threshold to the voltage and current metering quantities to
force a reading to zero when the measurement is near zero.
lists the
thresholds for nominal current and voltage values. These thresholds are above
the noise level for analog measurement by a digital system.
Without these thresholds, if a bus is deenergized or a circuit breaker is open,
noise-level values would cause erroneous energy accumulation.
These thresholds affect the metering functions for power and energy on a per-
phase basis. For example, if a load-side single-phase disconnect is open on
C-phase, the relay will force the IC metering value to 0.00, and the resulting
power and energy values for C-phase will be 0.00. In this example, the
A-phase and B-phase values are still calculated, provided the current and
voltage exceed the threshold values.
Table 8.5
Metering Thresholds (Secondary Units)
Current Channels:
Nominal Current Input Rating
5 A
1 A
0.2 A
a
a
Not available in SEL-351A-1.
0.05 A
IA, IB, IC
0.05 A
0.01 A
N/A
N/A
IN
0.05 A
0.01 A
0.002 A
0.0005 A
Voltage Channels:
All Models
VA, VB, VC, VS
b
b
VS channel not present in SEL-351A-1.
0.1 V
Содержание SEL-351A
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