Ordinary motors are regulated using frequency converters
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Many of the motors in our factory are ordinary motors, but an inverter is added to enable frequency conversion control. What problems might this cause? The upper limit of the frequency converter is the power frequency. I hope everyone can discuss this and share their experiences more. Thank you
Does no one know? ? Could it cause things like magnetic deflection? ?
What the original poster is suggesting is the most dangerous approach – ordinary motors cannot be used with frequency converters, as this can lead to shutdown due to under-voltage protection or even damage to the motor. If a frequency converter is to be used, then only frequency-driven motors should be employed.
The most direct effect of installing a frequency converter on a regular motor is poor heat dissipation, which makes it very easy for the motor to burn out!
Actually, if the requirement is that the speed change not much, there should be no problem! If the change is too large, since the motor is cooled by its fan, a low rotation speed results in poor cooling, which may cause the motor to burn out! Variable-frequency motors have an additional strong cooling fan
Thank you all for your help; it’s been very educational
If the requirement is that the speed change not be significant, for example from 50HZ to 30HZ, there should be no problem!
This post was last edited by liuxc on 2011-3-26 at 16:21. For centrifugal pumps, since the torque output by the motor is proportional to the operating frequency, the motor’s output decreases when operating at low frequencies; as a result, the current is lower and heat generation is reduced as well. However, since the inverter is driven by high-frequency voltage, it generates abundant harmonics, which leads to increased iron loss in the motor. Therefore, it is generally believed that for centrifugal pumps coupled with ordinary motors, the recommended operating frequency should not be lower than 30 Hz. Yet even within this operating range of 30 to 50 Hz, it is possible for companies to save 10–20% on electricity costs. The power-saving effect is quite noticeable. However, it is necessary to conduct regular checks on motor temperature. For piston pumps, the situation is somewhat worse than that of centrifugal pumps. Ordinary motors are more likely to overheat. Small motors generally have a high degree of thermal redundancy, so there is no major issue. Large motors use voltage levels of 6000V or higher; in such cases, the cooling fans are separate, so there are no major issues. Medium-sized motors are actually a bit more troublesome; it’s necessary to analyze each case on its own. For project implementation, set up inspection points for logistics; if things don’t work well, install separate air-cooling facilities, which isn’t too troublesome either. Previously, with the centrifugal pump + conventional motor setup, we reached a capacity of 240 KW, and switching to variable frequency drive didn’t present any issues. For piston pumps, 30 Hz is acceptable for long-term operation at 160 KW, but for capacities over 200 KW, it’s recommended to use a frequency of no less than 35 Hz; an independent air cooling system is preferable in such cases.
It’s possible, but it’s better to use a dedicated variable-frequency motor. At least in my usage scenarios, there’s no problem with directly connecting ordinary motors with a power rating of 30KW or less to an inverter. But is it really necessary? People keep saying that using variable frequency drives can save electricity; well, both the variable frequency drives and the cabinets are quite expensive.