★The principle of the motor: The principle of the motor is very simple. Simply put, it is a device that uses electrical energy to generate a rotating magnetic field on the coil and drives the rotor to rotate. Those who have learned the law of electromagnetic induction know that the energized coil will be forced to rotate in the magnetic field. This is the basic principle of the motor. This is the knowledge of junior high school physics.
★Motor structure: Anyone who has disassembled a motor knows that the motor is mainly composed of two parts, the fixed stator part and the rotating rotor part, as follows: 1. Stator (stationary part) Stator core: an important part of the motor magnetic circuit, and the stator winding is placed on it; stator winding: the coil, the circuit part of the motor, connected to the power supply, used to generate a rotating magnetic field; base: fix the stator core and the motor end cover, and play a role in protection and heat dissipation; 2. Rotor (rotating part) Rotor core: an important part of the motor magnetic circuit, the rotor winding is placed in the core slot; rotor winding: cutting the stator rotating magnetic field to generate induced electromotive force and current, and form electromagnetic torque to rotate the motor;
1. Stator (stationary part) Stator core: an important part of the motor magnetic circuit, on which the stator winding is placed; stator winding: the coil, the circuit part of the motor, connected to the power supply, used to generate a rotating magnetic field; base: fix the stator core and the motor end cover, and play a role in protection and heat dissipation; 2. Rotor (rotating part) Rotor core: an important part of the motor magnetic circuit, with the rotor winding placed in the core slot; rotor winding: cutting the stator rotating magnetic field to generate induced electromotive force and current, and form electromagnetic torque to rotate the motor;
★Several calculation formulas for motors: 1. Electromagnetic related 1) The formula for the induced electromotive force of the motor: E=4.44*f*N*Φ, where E is the coil electromotive force, f is the frequency, S is the cross-sectional area of the conductor (such as the iron core) that is wound around, N is the number of turns, and Φ is the magnetic flux. We will not delve into how the formula is derived, but mainly look at how to use it. Induced electromotive force is the essence of electromagnetic induction. When the conductor with induced electromotive force is closed, an induced current will be generated. The induced current will be subjected to the Ampere force in the magnetic field, generating a magnetic moment, thereby driving the coil to rotate. From the above formula, we know that the magnitude of the electromotive force is proportional to the power supply frequency, the number of coil turns, and the magnetic flux. The formula for calculating magnetic flux is Φ=B*S*COSθ. When the plane with an area of S is perpendicular to the direction of the magnetic field, the angle θ is 0, COSθ is equal to 1, and the formula becomes Φ=B*S.
Combining the above two formulas, we can get the formula for calculating the magnetic flux intensity of the motor: B=E/(4.44*f*N*S). 2) The other is the Ampere force formula. If we want to know how much force the coil is subjected to, we need this formula F=I*L*B*sinα, where I is the current intensity, L is the conductor length, B is the magnetic field intensity, and α is the angle between the current direction and the magnetic field direction. When the wire is perpendicular to the magnetic field, the formula becomes F=I*L*B (if it is an N-turn coil, the magnetic flux B is the total magnetic flux of the N-turn coil, and there is no need to multiply N again). Knowing the force, we know the torque. The torque is equal to the torque multiplied by the radius of action, T=r*F=r*I*B*L (vector product). Through the two formulas of power=force*speed (P=F*V) and linear speed V=2πR*speed per second (n seconds), we can establish a relationship with the power and get the formula of No. 3 below. However, it should be noted that the actual output torque is used at this time, so the calculated power is the output power. 2. The formula for calculating the speed of an AC asynchronous motor is: n=60f/P. This is very simple. The speed is proportional to the power supply frequency and inversely proportional to the number of motor pole pairs (remember, it is a pair). Just apply the formula directly. However, this formula actually calculates the synchronous speed (rotating magnetic field speed). The actual speed of the asynchronous motor will be slightly lower than the synchronous speed, so we often see that the 4-pole motor is generally more than 1400 revolutions, not reaching 1500 revolutions. 3. The relationship between the motor torque and the power meter speed: T=9550P/n (P is the motor power, n is the motor speed), which can be derived from the content of No. 1 above, but we don’t need to learn how to derive it, just remember this calculation formula. But again, the power P in the formula is not the input power, but the output power. Because the motor has losses, the input power is not equal to the output power. However, books are often idealized, and the input power is equal to the output power.
4. Motor power (input power): 1) Single-phase motor power calculation formula: P=U*I*cosφ. If the power factor is 0.8, the voltage is 220V, and the current is 2A, then the power P=0.22×2×0.8=0.352KW. 2) Three-phase motor power calculation formula: P=1.732*U*I*cosφ (cosφ is the power factor, U is the load line voltage, and I is the load line current). However, this type of U and I is related to the connection method of the motor. When the star connection is used, since the common ends of the three coils with voltages 120° apart are connected together to form a 0 point, the voltage loaded on the load coil is actually the phase voltage; and when the triangle connection is used, each coil is connected to a power line at both ends, so the voltage loaded on the load coil is the line voltage. If we use the commonly used 3-phase 380V voltage, the coil is 220V in star connection and 380V in triangle connection, P=U*I=U^2/R, so the power in triangle connection is 3 times that of star connection, which is why high-power motors use star-delta step-down starting. Mastering the above formula and understanding it thoroughly, you will no longer be confused about the principle of the motor, and you will not be afraid of learning a difficult course like motor drag. ★Other parts of the motor.
1) Fan: usually installed at the tail of the motor to dissipate heat for the motor; 2) Junction box: used to connect to the power supply, such as AC three-phase asynchronous motor, and can also be connected in star or triangle as needed; 3) Bearing: connects the rotating and stationary parts of the motor; 4. End cover: the front and rear covers on the outside of the motor, which play a supporting role.
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