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63230-300-212 Chapter 6—Alarms
April 2001 Scale Factors
91
© 2001 Schneider Electric All Rights Reserved
A scale factor is the multiplier expressed as a power of 10. For example, a
multiplier of 10 is represented as a scale factor of 1, since 10
1
=10; a multiplier
of 100 is represented as a scale factor of 2, since 10
2
=100. This allows you
to make larger values fit into the register. Normally, you do not need to
change scale factors. If you are creating custom alarms, you need to
understand how scale factors work so that you do not overflow the register
with a number larger than what the register can hold. When
SMS is used to
set up alarms, it automatically handles the scaling of pickup and dropout
setpoints. When creating a custom alarm using the circuit monitor’s display,
do the following:
• Determine how the corresponding metering value is scaled, and
• Take the scale factor into account when entering alarm pickup and dropout
settings.
Pickup and dropout settings must be integer values in the range of -32,767
to +32,767. For example, to set up an under voltage alarm for a 138 kV
nominal system, decide upon a setpoint value and then convert it into an
integer between -32,767 and +32,767. If the under voltage setpoint were
125,000 V, this would typically be converted to 12500 x 10 and entered as a
setpoint of 12500.
Six scale groups are defined (A through F). The scale factor is preset for all
factory-configured alarms. Table 6–1 lists the available scale factors for each
of the scale groups. If you need either an extended range or more resolution,
select any of the available scale factors to suit your need. Refer to “Changing
Scale Factors” on page 191 in Appendix B—Using the Command
Interface.
Table 6–1: Scale Groups
Scale Group Measurement Range
Scale
Factor
Scale Group A—Phase Current Amperes
0–327.67 A –2
0–3,276.7 A –1
0–32,767 A 0 (default)
0–327.67 kA 1
Scale Group B—Neutral Current Amperes
0–327.67 A –2
0–3,276.7 A –1
0–32,767 A 0 (default)
0–327.67 kA 1
Scale Group C—Ground Current Amperes
0–327.67 A –2
0–3,276.7 A –1
0–32,767 A 0 (default)
0–327.67 kA 1
SCALE FACTORS