1. Polar distance calculation formulaThe pole pitch refers to the distance occupied by each magnetic pole of the motor along the circumferential surface of the air gap, which is often expressed by the number of slots of the motor occupied by each magnetic pole.τ=Z/2p, where the Greek letter τ is the pole pitch; Z is the number of motor slots; p is the number of pole pairs of the motor. For example, the pole distance of a 4-pole 36-slot motor is τ=36/4=9.2. Air gap main flux formulaThe three-phase AC current in the three-phase winding of the stator of the motor establishes the three-phase synthetic rotating electromotive force of the stator and generates a rotating magnetic field. The magnetic flux of the rotating magnetic field flowing through the air gap is called the air gap main magnetic flux, which is the medium for energy conversion of the motor.Φ=U/4.44KNf. In the formula, Φ is the main magnetic flux of the air gap, Wb; K is a proportional constant related to the structure of the motor (air gap size, etc.); U is the power supply voltage, V; f is the frequency of the AC power supply, Hz; N is the number of turns of the stator winding.3. Synchronous speed formulaThe synchronous speed refers to the speed n 1 of the rotating magnetic field of the motor stator .n 1 =60f/P, where n 1 is the synchronous speed, r/min; f is the AC power frequency, Hz; P is the number of pole pairs of the motor.4. Slip formulaThere is a speed difference between the speed n of the rotor of the asynchronous motor and the speed n1 of the stator's rotating magnetic field. This speed difference is the speed at which the stator's rotating magnetic field cuts the rotor conductor. Its size determines the magnitude of the rotor electromotive force and its frequency, which directly affects the motor . working status. The speed difference is represented by the slip s.s=(n 1 -n)/n 1 . Where s is the slip rate; n 1 is the synchronous speed, r/min; n is the speed of the motor rotor, r/min.5. Motor speed formulaThe speed of the motor refers to the rated speed of the motor, that is, the speed of the motor at rated power.n=(1-s)n 1 =(1-s)×60f/P, where s is the slip; n 1 is the synchronous speed, r/min; f is the AC power frequency, Hz; P is the magnetic pole of the motor logarithm.6. Input power formulaThe input power of the motor refers to the active power drawn by the motor from the power supply.P 1 =√3UIcosφ. Where P 1 is the input power, W; U is the supply voltage, V; I is the stator current, A; cosφ is the power factor.7. Motor power formulaThe power of the motor is the rated power on the nameplate, which refers to the mechanical power output on the motor shaft. It is equal to the input power minus the losses in the motor itself.P=P 1 -P loss . Where P is the motor power, W; P 1 is the input power, W; P loss is the loss of the motor itself.8. Motor efficiency formulaThe efficiency of the motor refers to the efficiency of the energy conversion of the motor, which is equal to the percentage of the ratio of the mechanical power output by the motor to the active power input.η=(P/P 1 )×100%=(P/√3UIcosφ)×100%. Where η is the motor efficiency; P is the motor power, W; P 1 is the input power, W; U is the power supply voltage, V; I is the stator current, A; cosφ is the power factor.9. Motor torque formulaThe torque of a motor refers to the amount of force it drives to rotate the machine. The electromagnetic torque of the three-phase asynchronous motor comes from the electromagnetic force generated by the interaction between the rotor current and the stator rotating magnetic field, which generates electromagnetic torque on the rotor of the motor.T=9.55P/n, where T is the motor torque, N m; P is the motor power, W; n is the motor speed, r/min. Both P and n can be found directly from the nameplate of the motor, because both P and n are the rated values of the motor, so T is the rated torque of the motor. Its derivation process is:From P=Fv=(T/R)×(2πRn/60)=Tπn/30:T=30P/πn=(30÷3.14)P/n=9.55P/n.
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