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If rotor of motor is standstill then value of slip is
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In an induction motor, slip is defined as the relative speed between the synchronous speed (NsтАЛ) and the actual rotor speed (NrтАЛ) expressed as a fraction of the synchronous speed. When the rotor is at standstill, the rotor speed (NrтАЛ) is zero, which leads to a slip value of 1 (or 100%).
In an induction motor, slip is defined as the relative speed between the synchronous speed (NsтАЛ) and the actual rotor speed (NrтАЛ) expressed as a fraction of the synchronous speed. When the rotor is at standstill, the rotor speed (NrтАЛ) is zero, which leads to a slip value of 1 (or 100%).
s=NsтАЛNsтАЛтИТNrтАЛтАЛ тАФ General formula for slip in an induction motor
NsтАЛ=P120fтАЛ тАФ Formula for synchronous speed where f is frequency and P is poles
The slip is calculated as s=NsтАЛNsтАЛтИТNrтАЛтАЛ. At starting, since the rotor is mechanically locked or not yet rotating, NrтАЛ=0. Substituting this into the formula gives s=NsтАЛNsтАЛтИТ0тАЛ=1. This condition ensures the maximum relative velocity between the stator rotating magnetic field and the rotor conductors, inducing the highest possible rotor current during startup.
At standstill (NrтАЛ=0), the slip is 1, representing the maximum torque state.
At synchronous speed (NrтАЛ=NsтАЛ), the slip is 0, implying the motor cannot produce torque.
Induction motors typically operate at very low slip values (usually 2-5%) under full load.
High slip at starting results in high induced EMF and high starting current.
High starting slip allows for high starting torque development.
Standardizes motor performance parameters for industrial load calculations.
High slip at start induces massive inrush currents, often requiring starters.
High slip operation during running is inefficient due to increased rotor copper losses.
Starting induction motors for industrial machinery.
Calculation of rotor frequency (frтАЛ=sтЛЕf).
The range of slip for a standard induction motor is 0<s<1.
Option A (0) corresponds to the rotor running at synchronous speed (ideal condition).
Option B and C are intermediate values representing partial speeds between standstill and synchronous speed.
D is correct тАФ At standstill, the rotor speed is zero, resulting in a slip value of 1 as derived from the slip formula.
Remember that rotor frequency frтАЛ=sтЛЕf; at standstill (s=1), the rotor frequency is equal to the supply frequency, which is why the rotor acts like the secondary of a transformer at start.