To be observed for open drive compressors
Select motor and frequency inverter in agreement with the manufacturers. Standard motors for open drive compressors may not be suitable for operation with frequency inverters – critical is e.g. a shaft height >225 mm.
Risk of motor damage due to insufficient cooling!
Ensure that the motor is sufficiently cooled at every speed! Observe the application limits provided by the motor manufacturer.
Motor protection
Besides a typical line protection switch, the use of thermistor thermal motor winding protection is additionally recommended to ensure that the motor is only operated at permissible temperatures.
Shaft coupling and seal
Select the coupling carefully (see Bitzer Software). For low speed (frequency) operation, a shaft coupling with sufficient inertia must be selected.
Phase sequence protection relay
Because an incorrect phase sequence / rotation direction is not authorized and will damage the screw compressor, a rotation direction monitoring is necessary. Most available devices, however, are not able to sense the output voltage of an inverter and thus the rotating field. If needed, please contact Bitzer.