Leonard motor, Germany Leonard model, Leonard price

Leonard motor refers to a motor that can operate continuously under standard environmental conditions at 100% rated load within the 10%~100% rated speed range, with temperature rise not exceeding the motor's specified allowable value. For asynchronous motors, when the slip variation is small, the speed is proportional to the frequency; thus, changing the power supply frequency changes the asynchronous motor speed. During variable frequency speed control, it is always desired to keep the main magnetic flux constant. If the main magnetic flux is greater than the flux during normal operation, the magnetic circuit becomes oversaturated, causing an increase in excitation current and a decrease in power factor; if the main magnetic flux is less than the flux during normal operation, the motor torque decreases.

Leonard motor operating mode

Several methods for obtaining excitation current for motors: 1, excitation method powered by a DC generator. Generators using this excitation method have a dedicated DC generator, known as a DC exciter. The exciter is generally coaxial with the generator, and the generator's excitation winding obtains DC current from the exciter via slip rings mounted on the main shaft and fixed brushes. This excitation method offers advantages such as independent excitation current, reliable operation, and reduced auxiliary power consumption. It was the main excitation method for generators in past decades and has mature operational experience. The disadvantages are slow excitation regulation speed and high maintenance workload, so it is rarely used in units above 10MW. 2, excitation method powered by an AC exciter. Some modern large-capacity generators use an AC exciter to provide excitation current. The AC exciter is also mounted on the generator's main shaft; its output AC current is rectified to supply excitation to the generator rotor. In this case, the generator's excitation method belongs to separate excitation, and due to the use of static rectification devices, it is also called separate static excitation. An AC pilot exciter provides the excitation current. The AC pilot exciter can be a permanent magnet measuring device or an AC generator with a self-excited constant voltage device. To improve excitation regulation speed, AC exciters typically use medium-frequency generators of 100——200HZ, while AC pilot exciters use medium-frequency generators of 400——500HZ. In these generators, both the DC excitation winding and the three-phase AC winding are wound in the stator slots. The rotor has only teeth and slots without windings, resembling a gear. Therefore, it has no rotating contact parts such as brushes or slip rings, offering advantages like reliable operation, simple structure, and convenient manufacturing processes. The disadvantages are higher noise and larger harmonic components in the AC electromotive force. 3, excitation method without an exciter. In this method, no dedicated exciter is installed; instead, the excitation power is obtained from the generator itself, rectified, and then supplied to the generator for excitation, known as self-excited static excitation. Self-excited static excitation can be divided into self-shunt excitation and self-compound excitation. The self-shunt excitation method obtains excitation current through a rectifier transformer connected to the generator outlet, which is then rectified to supply the generator excitation. This method has advantages such as simple structure, fewer devices, cost savings, and low maintenance workload. The self-compound excitation method, in addition to having a rectifier transformer, also includes a high-power current transformer connected in series in the generator stator circuit. The function of this transformer is to provide a larger excitation current to the generator during short circuits to compensate for the insufficient output of the rectifier transformer. This excitation method has two excitation power sources: a voltage source obtained through the rectifier transformer and a current source obtained through the series transformer.

Leonard motor advantages

The motor's magnetic field is generated by permanent magnets, thereby avoiding excitation losses (i.e., copper losses) caused by generating the magnetic field through excitation current. With no current in the rotor, the motor temperature rise is significantly reduced, being more than 20K lower under the same load conditions. Permanent magnet synchronous motors have a high power factor that is independent of the number of motor poles. At full load, the power factor approaches 1, resulting in lower motor current compared to asynchronous motors, which in turn leads to lower stator copper losses and higher efficiency. In contrast, the power factor of asynchronous motors decreases as the number of poles increases. Furthermore, due to the high power factor of permanent magnet synchronous motors, the capacity of the associated power supply (transformer) can theoretically be reduced, allowing for a reduction in the specifications of associated switchgear and cables. Permanent magnet synchronous motors also offer advantages such as high starting torque, short starting time, and high overload capability. This allows for a reduction in the installed capacity of the equipment drive motor based on the actual shaft power, saving energy and reducing fixed asset investment. Permanent magnet synchronous motors are easy to control, with constant speed that does not vary with load or voltage fluctuations but depends only on frequency, ensuring smooth and reliable operation. Due to strict speed synchronization and good dynamic response, they are suitable for variable frequency control. The installation dimensions of permanent magnet synchronous motors comply with IEC standards, allowing direct replacement of three-phase asynchronous motors. The protection rating can achieve IP54 and IP55, and some manufacturers also produce explosion-proof permanent magnet synchronous motors.

Leonard motor speed control

An impeller is added between the motor shaft and the load shaft. By adjusting the pressure of the liquid (usually oil) between the impellers, the purpose of regulating the load speed is achieved. This speed control method is essentially a slip power consumption approach. Its main disadvantages are decreasing efficiency as speed drops, the need to disconnect the motor from the load for installation, high maintenance workload, and the need to replace components such as shaft seals and bearings after a period of time. The site is generally dirty, making the equipment appear low-grade, and it is considered an obsolete technology. Manufacturers who were initially interested in speed control technology, either due to the lack of high-voltage speed control options at the time or considering cost factors, had some applications of hydraulic couplings. Examples include water pumps in water companies, boiler feed pumps and induced draft fans in power plants, and dust removal fans in steel mills. Today, some old equipment is gradually being replaced by high-voltage variable frequency drives during retrofitting. The variable frequency drive (VFD) is a low-voltage VFD, using an input step-down transformer and an output step-up transformer to interface with the high-voltage grid and the motor. This was a transitional technology when high-voltage VFD technology was not yet mature. Since the low-voltage VFD has low voltage, the current cannot increase indefinitely, limiting the capacity of this type of VFD. The presence of the output transformer reduces system efficiency and increases the footprint. Additionally, the magnetic coupling capability of the output transformer weakens at low frequencies, reducing the VFD's load-carrying capacity during startup. There is significant harmonic distortion to the grid. Using 12 pulse rectification can reduce harmonics, but it does not meet strict harmonic requirements. While the output transformer steps up the voltage, it equally amplifies the dv/dt generated by the VFD. Filters must be installed to make it suitable for ordinary motors; otherwise, corona discharge and insulation damage may occur. Using special variable frequency motors can avoid this situation, but it is not as advantageous as using high-low type VFDs.

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