Question

• A three-phase 440 V, 6 pole, 50 Hz, squirrel cage induction motor is running at a slip of 5%. The speed of stator magnetic field with respect to rotor magnetic field and speed of rotor with respect to stator magnetic field are (a) zero, -50 rpm a (b) zero, 950 rpm (c) 1,000 rpm, -50 rpm (d) 1,000 rpm, 950 rpm
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Answer 1

The speed of rotor with respect to stator magnetic field are $zero,-50rpm$.

Explanation:

$N_{S}=\frac{120*f}{p}$

$=\frac{120*50}{6}$

$=1000rpm$

Rotor speed=$N_{s}-SN_{s}=950rpm$

Stator magnetic filed speed,$N_{s}=1000r.p.m.$

Relative speed between stator and rotor magnetic fields is zero

Rotor speed with respect to stator magnetic field $=950-1000$

$=-50r.p.m.$

Answer 2

The speed of rotor with respect to stator magnetic field are $zero,-50rpm.$

Explanation:

$N{S}=\frac{120*f}{p}$

$=\frac{120*50}{6}$

$=1000rpm$

Rotor speed = $N{s} - SN{a}=950rpm$

Stator magnetic filed speed,$N{s}=1000r.p.m.$

Relative speed between stator and rotor magnetic fields is zero

Rotor speed with respect to stator magnetic filed$=950-1000$

$= -50r.p.m.$