So if stator emf remains constant, then rotor emf also remains constant. We define the transformation ratio as the ratio of rotor emf to that of stator emf. The supply voltage to the three phase induction motor is usually rated and remains constant, so the stator emf also remains the constant. The rotor resistance, rotor inductive reactance and synchronous speed of induction motor remain constant. Maximum Torque Condition for Three-Phase Induction Motor The starting torque is also known as standstill torque. So, the equation of starting torque is easily obtained by simply putting the value of s = 1 in the equation of torque of the three phase induction motor, We know that at the start the rotor speed, N is zero. Starting torque is the torque produced by induction motor when it starts. Substitute this value of N s in above equation and simplifying it we getĬomparing both the equations, we get, constant K = 3 / 2πn s Working Principle of Three Phase Induction Motor – Video N s is speed in revolution per minute (rpm) and n s is speed in revolution per sec (rps) and the relation between the two is Substituting this value of rotor speed in above equation we get, We know that the rotor speed N = N s(1 – s)
ELECTRIC FLUX EQUATION PC
Substitute the value of Pc in above equation we get, The ratio of P 2 : P c : P m = 1 : s : (1 – s) Substitute this value of I 2 in the equation of rotor copper losses, P c. These rotor copper losses are expressed as In case of three phase induction motor, there occur copper losses in rotor. So, finally the equation of torque becomes, Removing proportionality constant we get, Putting the value of flux φ, rotor current I 2, power factor cosθ 2 in the equation of torque we get, We know that power factor is defined as ratio of resistance to that of impedance. Putting this value in above equation we get, And total impedance Z 2 on rotor side is given by ,
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