Chapter 6—Motor Protection
112
Power Xpert C445 Global Motor Management Relay
MN042003EN—January 2019
www.eaton.com
Table 23. Parameters That Control the Transition Profile
Figure 109. Start Cycle and Transition Timing
Motor Thermal Overload
The Overload function models the thermal characteristics of
a motor and generates a Fault Trip event that de-energizes
the motor before motor damage will occur. This is intended
to protect the motor and power wiring from excessive
current. Trip curves are defined by applicable agency
standards. The trip class for any particular Overload class is
user adjustable. When the FLA is entered for the motor, the
thermal capacity value will be calculated to model the motor
temperature during motor operation. Thermal capacity can be
characterized by the calculated value representing the
relative position with regard to the Trip Class curve. For
example; a motor running at a thermal capacity value of 85%
is much closer to an Overload Fault Trip than the same motor
running at a thermal capacity value of 25%.
The following items are associated with the electronic
Overload function of the C445.
●
An Overload Fault Trip will occur when the calculated
thermal capacity reaches 100%.
●
An Overload Fault Trip cannot be cleared by power cycling
the device – the thermal capacity calculated value is stored
in non-volatile memory.
●
Two thermal capacity models are used. One model is
enabled while the coil is energized (motor is running) and a
second model is enabled while the coil is de-energized
(motor stopped). The second model has a longer time
constant.
●
A RESET button is located on the Base Control Module
and the User Interface. Depressing this button will clear
any Overload fault that has been latched, but is no longer
present (thermal capacity must be less than 100%).
Resets can also be initiated through the communication
port.
●
An auto-reset option is available. This provision enables the
unit to automatically reset when the fault has cleared.
CAUTION
In the Auto Reset mode, caution must be exercised to assure
that any restart occurs in a safe manner. Auto Reset mode
should not be used in environments where excessive restart
attempts may cause component damage and/or create
unsafe conditions.
Parameter
Units
Increment
Minimum
Maximum
Default
Notes
Motor Transition Threshold Percent
%
1%
25
200
115%
Modbus Register = 1086
Motor Start Threshold Percent
%
1%
1
100
30%
Modbus Register = 1084
Motor Stop Threshold Percent
%
1%
1
50
5%
Modbus Register = 1085
Start Cycle Time
s
1%
2
360
10%
Modbus Register = 1078
