Instruction Manual

Application Notes Appendix D-3
Motor Overload
For single motor applications the drive can be programmed to protect the motor from
overload conditions. An electronic thermal overload I
2
T function emulates a thermal
overload relay. This operation is based on three parameters; Motor NP FLA (42),
Motor OL Factor (48) and Motor OL Hertz (47).
Motor NP FLA (42) is multiplied by Motor OL Factor (48) to allow the user to define the
continuous level of current allowed by the motor thermal overload. Motor OL Hertz
(47) is used to allow the user to adjust the frequency below which the motor overload
is derated.
The motor can operate up to 102% of FLA continuously. If the drive had just been
activated, it will run at 150% of FLA for 180 seconds. If the motor had been operating
at 100% for over 30 minutes, the drive will run at 150% of FLA for 60 seconds. These
values assume the drive is operating above Motor OL Hertz (47), and that Motor OL
Factor (48) is set to 1.00.
Operation below 100% current causes the temperature calculation to account for
motor cooling.
Motor OL Hertz (47) defines the frequency where motor overload capacity derate
should begin. The motor overload capacity is reduced when operating below Motor OL
Hertz (47). For all settings of Motor OL Hertz (47) other than zero, the overload
capacity is reduced to 70% at an output frequency of zero.
Figure D.2 – Motor Overload Curve
Figure D.3 – Changing Overload Hz
Motor Overload Curve
100 125 150 175 200 225 250
Full Load Amps (%)
Trip Time (Sec)
Cold
Hot
10
100
1000
10000
100000
Changing Overload Hz
0102030405060708090100
% of Base Speed
Continuous Rating
OL Hz = 10
OL Hz = 25
OL Hz = 50
0
20
40
60
80
100
120