Sel 751A, Instruction Manual

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5.8
SEL-751A Relay Instruction Manual Date Code 20100129
Metering and Monitoring
Metering
RMS Metering
The SEL-751A includes Root Mean Squared (rms) metering. Use rms
metering to measure the entire signal (including harmonics). You can measure
the rms quantities shown in
Table 5.5 .
RMS quantities contain the total signal energy including harmonics. This
differs from the fundamental meter (
METER command) in that the
fundamental meter quantities only contain the fundamental frequency (60 Hz
for a 60-Hz system).
Figure 5.9 shows the METER RMS command.
=>>
MET RMS <Enter>
SEL-751A Date: 12/02/2008 Time: 15:45:49
FEEDER RELAY Time Source: External
IA IB IC IN
RMS (A pri.) 998.3 1080.5 963.2 0.0
VAB VBC VCA VS
RMS (V pri.) 6648 6707 7502 6741
=>>
Figure 5.9 Device Response to the METER RMS Command
Analog Input
Metering
The SEL-751A can monitor analog (transducer) quantities that it is measuring
if equipped with optional analog inputs. Analog input metering shows
transducer values from standard voltage and current transducers. These values
can then be used for automation and control applications within an industrial
plant or application.
Through the global settings, you can set each type of analog input to the type
of transducer that drives that analog input. You also set the range of the
transducer output. Analog inputs can accept both current and voltage
transducer outputs. Ranges for the current transducers are ±20 mA and ranges
for the voltage transducers are ±10 V. You also set the corresponding output of
the analog inputs in engineering units. See
Section 4: Protection and Logic
Functions for an explanation of how to set up analog inputs for reading
transducers. Figure 5.10 shows an example of analog input metering.
=>
MET AI <Enter>
SEL-751A Date: 11/28/2007 Time: 16:22:22
FEEDER RELAY Time Source: Internal
Input Card 4
AI401 (psi) 99.97
AI402 (mA) 2.013
AI403 (Volts) -0.0027
AI404 (ft-lbs) 993
AI405 (HP) 1423
AI406 (mA) 9.013
AI407 (mA) -3.014
AI408 (mA) -0.013
=>
Figure 5.10 Device Response to the METER AI Command
Table 5.5 RMS Meter Values
Relay Option RMS Meter Values
Base Model RMS current IA, IB, IC, and IN magnitudes (A)
With Voltage Option VAB, VBC, VCA or VAN, VBN, VCN, and VS (if ordered) mag-
nitudes (V)