The EC-C1200 and 1700 inverters allow the connection of up to 3 external temperature sensors, which can be used to reduce the motor current automatically based on the measured winding temperature in order to protect the motor from overheating.
How to enable and configure the motor thermal derating
First, enable the temperature sensors that are used. In firmware version 7, the measurements have to be enabled separately in parameter group measurement_external before enabling them for the motor derating. When multiple sensors are enabled, the highest measured temperature value is used for derating.
Firmware 11:
2.9 Motor thermal derating -> Use temperature measurement 1/2/3 (2.9.2, 2.9.3, 2.9.4)
Firmware 7:
motprot -> use_temp_meas_mot1/2/3 (11015.11, 11015.12, 11015.13)
Temperature measurements 4 and 5 are not present in a EC-C1200 inverter so they should be disabled in devices with firmware version 7.
The time constant for the estimation of the rotor temperature is used also for filtering the measured stator winding temperature. For small motors that are run at highly cyclic loads above the nominal values, the time constant can be lowered to ensure that the measurement reacts quickly to the increase of temperature.
Firmware 11:
2.9 Motor thermal derating -> Rotor thermal time constant (2.9.20)
Firmware 7:
motprot -> time_const_temp_rotor (11015.20)
Enable the derating function.
Firmware 11:
2.9 Motor thermal derating -> Enable motor thermal derating (2.9.1)
Firmware 7:
motprot -> motor_current_temp_derating_ena (11015.50 )
Set the derating curve start and end points. It is best to use at least 15 degrees ramp to ensure smooth operation of the derating curve. The heat transfers slowly from the windings to the temperature sensors, so the longer ramp ensures that the winding temperature does not have time to rise too high. The default values are recommended for a motor with a maximum temperature of 155 degrees Celsius.
Firmware 11:
2.9 Motor thermal derating -> Begin derating temperature (2.9.10)
2.9 Motor thermal derating -> Full derating temperature (2.9.10)
Firmware 7:
motprot -> temp_motor_no_derating (11015.55)
motprot -> temp_motor_full_derating 11015.57
The last parameter determines the maximum current when the highest measured temperature is at or above the value of the parameter 2.9.10 Full derating temperature (temp_motor_full_derating). The derated current is calculated by multiplying the motor nominal current with this value.
Firmware 11:
2.9 Motor thermal derating -> Maximum current at full derating (2.9.12)
Firmware 7:
motprot -> current_full_derating (11015.60)
When the highest measured temperature is at or below the value of the parameter 2.9.10 Begin derating temperature (temp_motor_no_derating), the maximum current is the inverter's rated current.
Example:
Let's assume the following:
The maximum current of the inverter is 300 A
The nominal current of the motor is 120 A
Derate start temperature 130 C
Full derate temperature 150 C
Current at full derate 0.5 pu
The resulting derating curve will be as shown in the picture below: