Rockwell Automation 825-P Modular Protection System for Motors User Manual - Manual (Page 68)

68 Rockwell Automation Publication 825-UM004D-EN-P - November 2012
Chapter 6 Configuring Protection & Logic Functions
Current Transformer (CT) Configuration, Full Load Current Settings
Table 9 - CT Configuration and Full Load Current Settings
Note the following:
• Motor FLA settings are in Primary Amperes.
• The allowed setting range is dependent on the MCM module that is
connected to the relay. The MOTOR FLA and PHASE CT RATIO
setting ranges will be a subset of the full ranges shown in Table 9.
• When Two Speed Enable = Y and a Speed 2 control input is specified,
the relay uses CT Ratio-2nd and Motor FLA-2nd for the overload
thermal model.
• CTs with a 1 or 5 A rated secondary current can be used with the
Converter Module MCM2, MCM5 or MCM20, respectively. If another
MCM module is used, the relay automatically sets CT Ratios = 1.
The CT ratio and full-load current settings, along with the connected MCM
module, configure the relay to accurately scale measured values and report the
primary quantities. Calculate the phase and neutral CT ratios by dividing the
primary rating by the secondary rating.
The relay runs interdependency checks on the FLA and CT ratios based upon
the ratings of the MCM module that is connected. If a value is set that violates
the interdependency rules, then the user will be prompted to adjust settings
to eliminate conflicts.
Setting Prompt Setting Range Factory Default
PHASE CT RATIO 1…5000 1
MOTOR FLA ( I
e ) 0.5…5000 A 0.5
TWO SPEED ENABLE Y, N N
CT RATIO–2nd 1…5000 1
MOTOR FLA–2nd 0.5…5000 A 0.5
CORE B. CT RATIO 1…2000 100
EXAMPLE Phase CT Ratio Setting Calculation:
Consider an application where
Phase CT Rating=100:5A.
Set the CT Ratio =100/5 := 20