Why aren't ordinary motors directly applicable as inverter motors?

Here are more detailed explanations of why ordinary motors can't be used directly as inverter motors:

Insulation Breakdown from Voltage Stress:Inverter motors face rapid voltage changes (high dV/dt) and high-frequency pulses from the inverter’s switching. These voltage surges can cause stress on the insulation system of ordinary motors. Over time, the insulation in ordinary motors may degrade, leading to premature failure. Inverter motors, however, have enhanced insulation materials and designs to handle these high voltage peaks.

Cooling Problems at Low Speeds:Most ordinary motors rely on a shaft-mounted fan for cooling, which is designed to work effectively at the motor's rated speed (usually 50 or 60 Hz). When driven by an inverter, the motor speed can be reduced significantly, lowering the fan speed and impairing cooling. This can lead to overheating, especially at low speeds. Inverter-duty motors are designed with additional cooling measures, such as external fans or advanced thermal management systems, to handle a wider range of speeds without overheating.

Operation at Variable Speeds and Frequencies:Inverter motors are built to withstand varying speeds, and they can operate efficiently over a wide frequency range, unlike ordinary motors that are optimized for a fixed speed at a specific frequency (50 Hz or 60 Hz). Running ordinary motors at variable speeds can lead to imbalances, inefficiencies, and stress on mechanical components such as bearings and shafts. Inverter motors are built with reinforced structures to handle frequent speed variations and reversals.

Harmonic Distortion and Electromagnetic Interference (EMI):Inverters produce non-sinusoidal waveforms (usually PWM, or pulse-width modulation) that introduce harmonics in the motor's electrical supply. These harmonics can cause increased eddy currents, higher core losses, and additional heat in ordinary motors. Furthermore, the electromagnetic interference (EMI) generated by inverters can affect nearby sensitive equipment. Inverter-duty motors are designed with proper shielding, insulation, and grounding techniques to minimize these effects.

Torque and Load Variations:Inverter motors are optimized to provide smooth torque performance across a wide speed range. Ordinary motors may experience torque ripple at low speeds or when the load varies, leading to performance issues like jerky motion or mechanical stress. Inverter motors use special winding designs and rotor configurations to maintain consistent torque output, even under varying load and speed conditions.

Bearing Currents:High-frequency switching from the inverter can induce voltage in the rotor shaft, leading to current discharge through the motor bearings, a phenomenon called bearing currents. This can cause pitting and eventual failure of the bearings in ordinary motors. Inverter-duty motors often include insulated bearings or grounding brushes to protect against bearing currents and extend motor life.

Overvoltage and Underfrequency Protection:Inverters can cause overvoltage conditions or operate the motor at frequencies outside its designed range. Ordinary motors are not equipped to handle these extremes, which can lead to mechanical resonance, insulation failure, and operational inefficiency. Inverter motors include overvoltage protection and are designed to operate across a wider frequency spectrum without sacrificing performance or durability.

Thermal Stress from Rapid Switching:Ordinary motors may not be able to handle the thermal stress caused by rapid on/off switching, common in inverter-controlled applications. Frequent switching can lead to hotspots in the motor’s windings, damaging the insulation and reducing its lifespan. Inverter-duty motors are built to endure these rapid thermal cycles, thanks to reinforced insulation systems and advanced thermal management designs.

In summary, inverter-duty motors are specifically engineered to manage the electrical, thermal, and mechanical stresses introduced by inverter drives, whereas ordinary motors may face performance, durability, and safety issues when used in such applications without proper modifications.

At Germana, we not only supply standard electric motors but also inverter motors. 

Whatever your motor requirements, feel free to contact us for all your needs.