Operating Instructions

Chapter 4 - Parameters and Menu Structure
Parameters (M3)
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Siemens Industry, Inc.
Siemens BT300 HVAC Drive
DPD01809
Smart Infrastructure
2019-05-29
motor is reduced as well as its capacity. If the motor is equipped with an external fan, the load reduction at low
speeds is small.
The motor thermal protection is based on a calculated model and uses the output current of the drive to
determine the load on the motor. The motor thermal protection can be adjusted with parameters. The thermal
current IT specifies the load current above which the motor is overloaded. This current limit is a function of the
output frequency.
The thermal stage of the motor can be monitored on the keypad display.
NOTE:
The calculated model does not protect the motor if the airflow to the motor is
reduced by a blocked air intake grill. The model starts from zero if the control
board is powered off
Motor thermal zero speed cooling (P3.9.8)
Defines the cooling factor at zero speed in relation to the point where the motor is running at nominal speed
without external cooling. See the Table Protections Settings in the Protections (M3.9) section.
The default value is set assuming that there is no external fan cooling the motor. If an external fan is used this
parameter can be set to 90% (or even higher).
If you change Motor nominal current (P3.1.1.4), this parameter is automatically restored to the default value.
Setting this parameter does not affect the maximum output current of the drive which is determined by
Current Limit (P3.1.1.7) alone.
The corner frequency for the thermal protection is 70% of the Motor nominal frequency (P3.1.1.2).
Figure 18: Motor thermal current IT curve.
Motor thermal time constant (P3.9.9)
The time constant is the time within which the calculated thermal stage has reached 63% of its final
value. The bigger the frame and/or the slower the speed of the motor, the longer the time constant.
The motor thermal time is specific to the motor design and it varies between different motor
manufacturers. The default value of the parameter varies from size to size.
If the motor's t6-time (t6 is the time in seconds the motor can safely operate at six times the rated current) is
known (given by the motor manufacturer), the time constant parameter can be set based on it. As a rule of
thumb, the motor thermal time constant in minutes is equal to 2*t6. If the drive is in stop stage, the time
constant is internally increased to three times the set parameter value. The cooling in stop stage is based on
convection and the time constant is increased. See Figure Motor Temperature Calculation .