Lutz motor Germany Lutz model Lutz price

Lutz motor refers to a motor that, under standard environmental conditions, operates continuously at 100% rated load within the 10%~100% rated speed range, with temperature rise not exceeding the motor's specified allowable value. When the slip of an asynchronous motor does not change significantly, the speed is proportional to the frequency; thus, changing the power supply frequency changes the speed of the asynchronous motor. 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 the excitation current to increase and the power factor to decrease; if the main magnetic flux is less than the flux during normal operation, the motor torque decreases.

Lutz motor speed control

The motor consists of three parts: a squirrel-cage motor, an electromagnetic slip clutch, and a DC excitation power supply (controller). The DC excitation power supply has low power and is usually composed of a single-phase half-wave or full-wave thyristor rectifier. Changing the conduction angle of the thyristor can change the magnitude of the excitation current. The electromagnetic slip clutch consists of three parts: an armature, magnetic poles, and an excitation winding. The armature and the latter have no mechanical connection and can rotate freely. The armature is coaxially connected to the motor rotor, called the driving part, which is driven by the motor; the magnetic poles are coupled to the load shaft via a coupling, called the driven part. When both the armature and the magnetic poles are stationary, if DC current is applied to the excitation winding, several pairs of N and S alternating polarity magnetic poles will form along the circumference of the air gap, with their magnetic flux passing through the armature. When the armature rotates with the driving motor, relative motion between the armature and the magnetic poles induces eddy currents in the armature. These eddy currents interact with the magnetic flux to produce torque, driving the rotor with magnetic poles to rotate in the same direction, but its speed is always lower than the armature speed N1. This is a slip speed control method. By varying the DC excitation current of the slip clutch, the output torque and speed of the clutch can be changed. A hydraulic coupling is a hydraulic transmission device, generally consisting of a pump impeller and a turbine, collectively known as working wheels, housed in a sealed casing. The casing is filled with a certain amount of working fluid. When the pump impeller rotates driven by the prime mover, the fluid inside is pushed by the blades to rotate. Under the action of centrifugal force, the fluid enters the turbine along the outer ring of the pump impeller, exerting thrust on the turbine blades in the same rotational direction, thereby driving the production machinery. The power transmission capacity of the hydraulic coupling is consistent with the relative amount of fluid filling in the casing. During operation, changing the fill rate can change the turbine speed of the coupling, achieving stepless speed control.

Lutz motor classification

Theoretically, a single-phase motor can be started if measures are taken to create a certain phase difference between the AC currents flowing through its two windings. How to create a certain phase difference between magnetomotive forces or magnetic fluxes that are already spatially offset by a certain angle is the starting point for solving the starting problem. Based on this, single-phase AC asynchronous motors can be divided into two major categories: split-phase and shaded-pole. Split-phase single-phase motors use capacitors or resistors connected in series with the inductive starting winding to achieve phase shifting, causing the current phase of the starting winding to be offset from that of the running winding, known as "split-phase." Capacitor split-phase single-phase motor principle wiring. Due to the significant phase-shifting effect of the capacitor, connecting a capacitor of appropriate capacity (generally about 20～50μF) in series with the starting winding can make the current phase difference between the two windings close to 90°. At this point, the resulting rotating magnetic field is close to a circular rotating magnetic field, resulting in high starting torque and low starting current. This type of single-phase motor is widely used. After starting, the capacitor can be retained as needed (called a capacitor-run motor) or disconnected (called a capacitor-start motor, executed by a centrifugal switch located inside the motor). If it is necessary to change the direction of rotation of the motor, simply swap the output terminals of any one winding; this reverses the current phase relationship between the two windings. Resistance split-phase single-phase motors have fewer turns and thinner wires, resulting in lower reactance and higher resistance compared to the running winding. When using resistance split-phase starting, the starting winding current leads the running winding, and the resulting magnetic field is an elliptical rotating magnetic field with high ellipticity. The starting torque is small, so it is only used for no-load or light-load applications and is less common. The starting winding of a resistance split-phase single-phase motor is generally designed for short-term operation and is disconnected by a centrifugal switch after starting, with the running winding maintaining operation. Figure (b) shows the principle wiring of a resistance split-phase single-phase motor.

Lutz motor working principle

When the stator winding of the motor is connected to the power supply, a rotating magnetic field is generated. Since the magnetic reluctance of the rotor's direct axis magnetic circuit is less than that of the quadrature axis magnetic circuit, and magnetic flux lines always close through the path of least reluctance, the stator magnetic field always attempts to align the rotor's direct axis with the direction of the stator magnetic field. When both the rotor and the stator magnetic field rotate at synchronous speed n1, if there is no load on the shaft, the rotor's direct axis remains aligned with the stator magnetic field axis. If there is a load on the shaft, the load's resisting torque causes the rotor's direct axis to lag behind the stator magnetic field axis by an angle θ. At this point, the magnetic field is distorted, and the magnetic flux lines are stretched. The stretched flux lines attempt to shorten, producing a synchronous electromagnetic torque in the same direction as the rotor's rotation. If the synchronous electromagnetic torque can balance the load torque, the rotor will continue to rotate at synchronous speed; otherwise, the motor will lose synchronism. To improve synchronous electromagnetic torque and power factor, the difference between the direct-axis and quadrature-axis magnetic reluctances should be increased, i.e., increase the ratio Xd/Xq of direct-axis synchronous reactance Xd to quadrature-axis synchronous reactance Xq. For this purpose, the rotor can have a salient-pole structure, or a non-salient pole structure with reaction slots cut into the rotor (usually filled with non-magnetic metal) to create unequal magnetic reluctances in the quadrature and direct axes, or a combination of both structures. However, Xd/Xq should not be too large, as excessive values make motor starting more difficult. The synchronous electromagnetic torque of a reluctance motor cannot start the motor, so a squirrel-cage winding must be installed on the rotor. Asynchronous electromagnetic torque is used to start the rotor, and when the speed approaches synchronous speed, the synchronous electromagnetic torque pulls the rotor into synchronism.

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