In industrial and commercial applications, most pumps and fans are driven by AC induction motors. An "AC induction motor" is an asynchronous motor that relies on electrical current to turn the rotor. Torque is produced by the current in the rotor, which is produced by the stator. The magnetic field of the windings is generated by electromagnetic induction, and the rotor always rotates at a lower speed than the magnetic field. A "permanent magnet synchronous motor" relies on magnets to turn the rotor, which rotates at the same speed as the permanent magnet synchronous motor's internal rotating magnetic field.
Permanent magnet motors must use a drive
An AC induction motor can drive a pump or fan without a variable frequency drive, which is usually installed in a pump system or fan system to improve system efficiency. Permanent magnet synchronous motors require a drive to work and cannot operate without a drive. In order to precisely control the speed of a permanent magnet synchronous motor to meet application requirements such as pressure, flow, volume, etc., a frequency converter is required. Some new frequency converters are already equipped with a permanent magnet motor control option as a standard feature, allowing the operator to control the permanent magnet motor to drive the fan and/or pump with greater efficiency.
Permanent magnet motors offer significant efficiency gains compared to AC induction motors. The full load efficiency of permanent magnet motors is higher than that of AC induction motors. The efficiency range between the two standards, AC induction motors and permanent magnet motors, is shown below.
Variable frequency drives do not improve motor efficiency, variable frequency drives help improve system efficiency in the operating speed range, as most systems will not run at top speed all the time. A variable frequency drive helps improve system efficiency because of its ability to slow down a motor, fan, or pump, rather than turning a valve to throttle a pump or closing a damper to stop air flow.
The graph above compares the 10 hp 1800 rpm permanent magnet synchronous motor PMAC with the advanced AC induction motor NEMA which operates with variable torque loads in the 100 to 500 speed range, in both cases both motors efficiency will decrease. At 600 rpm, NEMA premium motor efficiency drops from about 90% to about 72% and PMAC from about 94% to 83%. Permanent magnet motors have been shown to be more efficient than AC induction motors when operating systems affect equipment efficiency. higher efficiency.
Advantages and disadvantages of permanent magnet motors
While AC induction motors are more commonly found in motor drive systems, they are generally larger and less efficient than permanent magnet motor solutions. While PM motor solutions tend to have a higher initial cost, they can provide a smaller size for a more compact mechanical package and, more importantly, higher efficiency. Permanent magnet motors tend to be more expensive than AC induction motors and more difficult to start than AC induction motors. However, the advantages of permanent magnet motors include higher efficiency, smaller size (permanent magnet motors can be one-third the size of most AC motors, which makes installation and maintenance much easier), and the ability to maintain full torque.
The trend is turning
The use of permanent magnet motors in combination with variable frequency drives is not entirely new, design engineers and equipment owners are beginning to choose more permanent magnet motor solutions for fan and pump application installations because of their smaller size and higher efficiency, variable frequency drives require There is a special algorithm to drive the permanent magnet motor. Now, there are some new variable frequency drives on the market that have a built-in standard feature to control permanent magnet motors at no extra cost. As more and more variable frequency drive manufacturers begin to add the high-performance control capabilities of permanent magnet motors, users will tend to install motor systems that operate more efficiently, in smaller packages, and at lower cost.
Is the exhaust fan motor hot?
Exhaust fans can help ventilation and ventilation. For example, in rooms with poor ventilation, such as bathrooms, etc., we can use exhaust fans to promote air flow, so that the room is not easy to get wet, and it can also remove odors. The exhaust fan is driven by a motor, so it will inevitably heat up for a period of time, but if the temperature is too high, it is best to turn it off for a period of time, which can save power and extend the service life.
There will be heat when the exhaust fan is running, but also pay attention to whether there are these faults. If the kitchen exhaust fan is hot, this is because the thermal protection has acted, causing the thermal motor to lose power to protect the motor from burning out. This is often caused by the leaves of the kitchen exhaust fan becoming hot due to friction and clogging. You can manually move the leaves back to their original positions. If there is a problem with the coil of the kitchen exhaust fan, it can also cause heat. Typically, the coils are made of all copper. If it contains impurities, such as aluminum wires, it is more likely to get hot during operation, and the overall heat dissipation rate is relatively high. The bearing housings at both ends of the motor are also an aspect that cannot be ignored. If the wear is severe and the bearing sinks, it will also cause friction and heat between the rotor and the stator. Therefore, we can dismantle the inside, check whether the position of the bearing housings at both ends of the motor has changed, and repair and fix it.
Products like fans work the same way. When the exhaust fan is working, it will pass a large current. When current passes through the fan, most of the electrical energy becomes mechanical energy that drives the rotation of the fan blades, and part of the electrical energy is consumed in the motor of the electric fan as thermal energy. Therefore, if the fan continues to work for a long time, it will cause the case to heat up and even burn your hands. If it is heated for a long time, it will burn out the motor. Therefore, after the fan has been working for a period of time, it should be stopped to allow it to dissipate heat.
This is generally not the case. The household exhaust fan itself has low power and low power consumption. The design of this exhaust fan motor can run continuously for 24 hours. The temperature rise of the exhaust fan motor is normal during operation, and there is a thermal fuse protection device inside the exhaust fan for protection. If it is often opened for a long time, it will mainly consume power. The automatic damage rate will be higher and the service life will be much shorter after a long time. Usually only public toilets will keep running, not at home.
