Electrical electronics technology

Since we know the motor running torque is T = K1 * φ * sE2 * R2/( R2² + X2²) Where φ  - flux per status pole I₂ - rotor current E2 rotor emf per phase. So if S = 0 then T = 0 Let's start from right hand side of the curve from point 0. Let's say, motor is running near to synchronous speed. The term sX2 approximately equals to zero negligible. Therefore, T = K1 * s * φ * E2 /R2 Assuming stator flux per pole, rotor EMF per phase, rotor resistance per phase is constant. T ⇒ s  So for low value of sleep torque slip service straight line. As the load increases sleep increases. As the load further increases it touches the maximum torque point when S = R2/X2 called pull- out torque or breakdown torque. Any further increase is in load that is slip increases R2 becomes negligible.  So,  T ⇒ 1/s Hence after pull out torque or breakdown torque the curve will be rectangular hyperbola. Hence we can see that any further increases in load motor slow down and eventually stopped. If w...

When we connect three phase applied to stator winding then rotating flux will set up due to this flux rotor start rotating but it will never catch up the synchronous speed of flux Ns=120 f/p. if it did so then no relative speed between flux and rotor then no EMF will induces, no current and so no torque to maintain rotation. So motor will always rotate less than synchronous speed of magnetic flux Ns = 120 f/p. The difference between synchronous speed and actual speed Nr is known as slip.      Slip = Ns - Nr.  Unit revolution per second. Express percentage of synchronous speed  % slip S = ( (Ns -  Nr) /NS) * 100 % One more term we call it as slip speed Slip speed = sNs = Ns- Nr  when rotor is stationary then frequency of rotor current is same as supply frequency. But when rotor start rotating then frequency depend upon relative speed between the two rotating magnetic flux and rotor. Let's say at any sleep Speed the frequency of rotor current is f' . Ns ...

The torque in induction motor is proportional to the product of flux per stator pole and the rotor current one more term we will take in account is power factor of the rotor.   T →  φ  *  I₂  * cos∅₂  Where φ  - flux per status pole I₂ - rotor current cos∅₂ - rotor power factor ∅₂ phase angle  rotor current and rotorEMF. The induced rotor EMF E2 is proportional to flux per stator φ. Therefore T = K1 * E₂ *  I₂ * cos φ2  Where K1 is another constant. This is torque at standstill condition.   Under running condition induced EMF is T = K1 * Er *  Ir * cos ∅2 ---------------------- (1) Where Er = rotor induced EMF per phase under running condition. Ir = rotor current per phase under running condition. φ = flux per stator pole. rotor current, Ir = Er / Zr = sE2/  √( R2² + (sX2)²)  ----------- (2) power factor, cos∅2 = R2 / √( R2² + (sX2)²)   ----------------(3) So the rotor torque is,  After putting Ir from ...

When we supply three phase input to the rotor of the motor then voltage is induced in the rotar e2 and current I to start flowing. The frequency of rotar and voltage of rotor at stand still is equal to supply frequency. Because relative velocity is maximum at a stand still when s= 1 between status flux and rotar. Let at stand still S =1 , E2= stand still rotar induced EMF per phase f2 = rotar current frequency at stand still X2 = stand still rotor induced reactance per phase. when rotor starts rotating then relative velocity between rotor and stator flux decreases then induced voltage E2  start decrease. When  rotor speed catches rotating flux speed than relative velocity becomes zero that is S= 0 then induced voltage then become zero. let's say for a slip 's' the rotor induced EMF will be s times the induced emf at a stand still. Therefore under running condition Rotar induced EMF running condition Er = s E2 Frequency of induced EMF at running condition fr = sf2 Since freq...

The torque in induction motor is proportional to the product of flux per stator pole and the rotor current one more term we will take in account is power factor of the rotor.   T →  φ  *  I₂  * cos∅₂  Where φ  - flux per status pole I₂ - rotor current cos∅₂ - rotor power factor ∅₂ phase angle  rotor current and rotorEMF. The induced rotor EMF E2 is proportional to flux per status φ. Therefore T = K1 * E₂ *  I₂ * cos φ2  Where K1 is another constant. From the above equation it is clear that when φ2 increases cos φ2 decreases and vice versa. Due to the revolving stator flux EMF is induced in rotor conductor, and this EMI is also sinusoidal. When rotor is non inductive. φ₂=0 in this case rotor current is in phase with rotor EMF. So the instantaneous value of torque is product of instantaneous value of flux and current. It is seen that torque is always positive. When rotor is inductive load. In inductive load I₂ lags behind E₂ bY an angle φ2...

Impedance traingle of rotor circuit of induction motor. Let E2 = rotar EMF per phase at stand still  R2 = rotar resistance per phase X2 = rota reactance per per phase at stand still . Z2 = √( R2² + X2²) rotar impedance per phase at stand Still. I2 = E2 / √( R2² + X2²)  = rotar current cos∅2 = R2 / √( R2² + X2²) = power factor  T = K1 E₂ R2/( R2² + X2²)  = rotor torque = K1 * E2 / √( R2² + X2²) * E2 * R2 / √( R2² + X2²) = K1 E₂² R2 /(R2² + X2²) if we increase the resistance of rotor circuit then we can improve the power factor. Torque in squirrel cage induction motor :- The resistance of squirrel cage rotor is fixed and small as compared to reactance. Reactance of rotor is high as frequency of a current is equals to supply frequency. Hance at starting power factor is poor. starting current is although very high but lags by very large angle behind E2. So the torque is only 1.5 times the full load torque but starting current is 5 to 7 times the full load current. Hence ...