DMC Sigma2N - Page 112

Simga2N Traction Advanced Manual– V1.3 Page 112 (166) ©2021 DMC GmbH Herten Germany
Cooling
Of course, cooling will have an influence in the maximum allowable operation temperature. It may happen that
with sufficient cooling the maximum allowable operation temperature is not reached. Or, in a worse case, the
temperature rises beyond the maximum allowable operation temperature. In that case, the user must make
sure there is enough cooling (e.g. increase in air flow, water cooling, etc.).
The factor time
The allowable temperature rise is thus a known value. The rise time in which the motor temperature has
increased this amount is an important factor. This time depends on the cooling characteristics (e.g. type and
amount of cooling) of the motor.
By definition, the rise time is that time in which the motor temperature rises from the reference (ambient)
temperature to the maximum allowable operation temperature when the motor is drawing a constant current
which is twice the nominal rated current of the motor.
This rise time must be measured or calculated.
Example
• Nominal rated current 90 A
• Insulation class F
• Rise time 50 s
Thus, the motor heats up 105 °C in 50 s when 180 A is drawn, the providing starting temperature is 40 °C.
Parameters
The controller will have a set of parameters with which the I
2
t feature can be set up:
• Nominal rated current of the motor.
• The temperature rise time.
• Percentage of the maximum drive current 1.
• Percentage of the maximum drive current 2.
• Percentage of the maximum drive current 3.
The location, unit, range and step size of these adjustments can be found in the “Menu 5 “Limits Setup””.
This rise time must be established by trial and error. Once this time is established, it sets a time in which the
surplus of the nominal current may flow through the motor. After that time, the I
2
t function will limit the motor
current in three steps.
There is Microsoft Excel sheet (available on request) which can be used to setup the I
2
t parameters in the
“Menu 5 “Limits Setup”” of the Sigma2 controller. In this sheet various current settings and the time can be
filled in the white boxes (see also the example below). The figures in bold in the dark green box are the actual
current limit value in percentages. These need to be configured in the “Menu 5 “Limits Setup”” of the
controller.
A limit will run from 100 % (no cut back) to 0 % (full cut back). This is displayed also in the “Status Menu” at
“Drive torque limit”.
When the I
2
t feature is actually limiting the current, the “Status menu” will show ‘T1’, ‘T2’ or ‘T3’ limit
indication, depending in which phase the I
2
t function currently is.
The reason that percentages are used instead of real currents, is that all other limit features such as low voltage limit and controller
temperature limit are also in percentages.
Note that the maximum current is specified by “Maximum motor current” (adjustable in “Menu 3
“Autotuning””).