Question
Download Solution PDFA three-phase, 60 Hz, 25 HP, wye-connected induction motor operates at a shaft speed of almost 1800 r.p.m. at no load and 1650 r.p.m. at full load. The number of poles of the motor is
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
In a three-phase induction motor, synchronous speed is
\({N_s} = \frac{{120f}}{P}\)
Where,
Ns = Synchronous Speed in rpm
f = supply frequency in Hz
P = number of poles
⇒ Synchronous speed (Ns) ∝ (1 / P)
Therefore, the synchronous speed of the induction motor is inversely proportional to number of poles
Rotor full load speed, Nr = Ns (1 – s)
Where, s = full load slip
Calculation:
Given,
Ns = Synchronous Speed in rpm = 1800 rpm
f = supply frequency in Hz = 60 Hz
P = number of poles
1800 = (120 × 60)/P
⇒ P = 4
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