Chapter 6 – Parameters
6-32
ACH 500 Programming Manual
Motor heating is calculated assuming a load curve. The load curve is defined
by the Motor Load Curve, Zero Speed Load, and Break Point parameters. If
Motor Load Curve is set to
100%
, the Motor Thermal Protection allows the
motor to be loaded to 100% of the current set by Start-up Data Parameter F
(Motor Current -FLA). The load curve level should be adjusted if the ambient
temperature differs from the nominal value.
The motor will heat above nominal temperature if it operates in the region
above the curve, and cool if operated below the curve. The rate of heating and
cooling is set by Motor Therm Time. Motor Therm Time is the time period
within which the motor temperature reaches 63 percent of the final
temperature rise. As a rule of thumb, Motor Thermal Time equals 35 times t6
(t6 in seconds is the safe operating time at locked rotor current given by the
motor manufacturer).
Because of the simple thermal model used for calculating temperature rise,
this technique of thermal protection may cause undesirable trips if the motor
is run continuously at low frequencies. If your application requires continuous
running at frequencies lower than 25 Hz, you may need to provide external
cooling.
CAUTION: Motor thermal protection will not protect the motor if the
cooling efficiency of the motor is reduced due to dust and dirt.
Figure 6-12 Motor Load Curve
50
100
150
[%]
30.1.6 Zero Speed Load
30.1.5 Motor Load Curve
30.1.7 Break Point
Motor Fla
Frequency
