What makes electric drives superior?
We are very passionate about VFDs and electric drives in general. They have some unique features that make them outstanding compared to other types of drivers. What are some of these properties? This post lists 8 reasons that make electric drives superior to their traditional counterparts.
8 reasons for choosing electric drives
Now we are gonna present 8 good reasons why electric drives make a real difference to other drivers. We do not intend to provide an extensive list but rather highlight some of the most significant advantages. Do you have additional reasons in mind? Let us know in the comments below.
1. Long lifetime
Electric machines have long lifetime. One example (proof) may be certain hydro power plants that are in operation for decades and many of them still have the original electric generators. Another example is traction. There are plenty of locomotives being 30 to 40 years (or even more) in service and still having original electric traction motors. See example of locomotive Re 4/4 or Re 420 of Swiss Federal Railways in Figure 1a. These locomotives were built between 1964 and 1985 and most of them are still in operation. Figure 1b depicts synchronous generator manufactured by BBC of Switzerland (today ABB), constructed in 1901! The machine is not in commercial service anymore but remains fully operational. You can witness it when visiting Electropolis museum in Mulhouse, France.
The long lifetime of electric motor is also expected as major advantage in the booming e-mobility (electric cars, buses, trucks etc), especially when compared to internal combustion engines (ICE).
Next to long lifetime electric drives require minimum maintenance (see [1] making the comparison with gas turbine driver) thus increasing the availability and reducing service and maintenance cost.
2. Wide range of power and torque
Electric drives are perfectly scalable in power and torque. They range from microdrives with few watts over consumer motors to industrial drives with several MW and finally up to large generators in power plants with rated output as high as 1’500 – 2’000 MVA. Similarly, the torque goes from fraction of Nm up to several MNm. No other type of motor offers such wide range of power and torque.
3. High efficiency / Low losses
Electric machines are highly efficient. High power industrial asynchronous machines reach up to approx. 97.5% efficiency. Synchronous motors achieve even more – up to approx. 98.5%. Large generators exceed 99%.
Therefore, the electromechanical power conversion is extremely efficient with minimum associated losses. Specific directives, such as e.g. the EcoDesign directive of the European Union, set minimum standards for efficiency values of industrial motors.
Keep in mind that even relatively small improvement in efficiency will generate substantial energy and cost savings over the lifecycle (especially considering the long lifetime as per point 1).
4. Short time overloadability
Another advantage of electric motors is their inherent overload capability. As the thermal time constant is in the range of several minutes or even hours the machine can usually be overloaded. Of course, when operating at variable speed the VFD must be able to support the short time overloads (as for the VFD the thermal time constants are much shorter).
5. Four quadrant operation
Electric machines can operate in both directions of rotation and with positive or negative polarity of torque. Hence they allow operation in all four quadrants of the torque-speed plane. The VFD, if present, shall support the necessary quadrants as well (e.g. having a braking chopper or regenerative braking feature).
6. Low noise level
Noise (acoustic sound) level depends on several factors, such as the speed range, cooling type or voltage and current waveform (in case of VFD fed motors). However, in general electric motors generate less noise than diesel engines or gas turbine drivers.
7. Almost no local emissions
Obvious advantage is that electric motor drives generate practically no emissions locally (“invisible” nature of electricity). That helps to create safer workplace with lower environmental impact.
8. Excellent controlability
The unparalleled controlability of electric motor drives is what makes them outstanding. No other drive can be controlled with such a precision (best examples: servo drives, CNC machines, robotics). Also high power applications prefer electric or diesel-electric drive trains to achieve high level of controlability.
More reasons for electric drives
Do you know more reasons for electric drives than what is mentioned above? Please share them with us – either in comment section below or by using this short contact form. We love to hear from you!
References
[1] Comparison of VFD and gas turbine, https://mb-drive-services.com/comparison-of-vfd-and-gas-turbine/
[2] Power, speed and torque, https://mb-drive-services.com/power-speed-and-torque/
[3] What efficiency can you expect from your drive system? https://mb-drive-services.com/energy-efficiency-part-5/
[4] Acoustic noise level, https://mb-drive-services.com/acoustic-noise-level/
