Induction Motors Objectives Part 01
1) The difference between synchronous speed and actual speed of induction motor is known as Slip.
2) In an induction motor, if P is the power delivered to a rotor and s is the slip, then the power lost in rotor as copper loss, will be sP.
3) Copper loss in rotor of an induction motor is appears as heat.
4) Slip rings for induction motors are made of Phosphor Bronze.
5) For an induction motor, the power factor on short circuit can be determined by Blocked Rotor Test.
6) As the load on an induction motor increases, its power factor goes on increasing up to full load then it falls again.
7) The phenomenon of crawling occurs in induction motors due to Harmonics developed in the motor.
8) Starting torque of an induction motor is proportional to (𝐒𝐮𝐩𝐩𝐥𝐲 𝐕𝐨𝐥𝐭𝐚𝐠𝐞)𝟐.
9) The data required for drawing complete circle diagram of induction motor is No Load Test, Blocked Rotor test and State Resistance test Data.
10) A 3-phase slip ring induction motor has wound rotor.
11) The slip in actual induction motor is generally 3% to 5%.
12) The maximum speed of an induction motor cannot be 3000rpm.
13) In a squirrel cage induction motor, the starting current is 5 to 7 times the rated current.
14) In a squirrel cage induction motor, the rotor slots are usually given a slight skew in order to reduce the magnetic hum and locking tendency of the rotor.
15) When ‘N1’ is the synchronous speed, and ‘N2’ is the actual speed of rotor, the slip is given by (𝟏−𝑵𝟐𝑵𝟏).
16) When ‘f’ is the supply frequency, and ‘s’ is the slip, the frequency of rotor current is given by f.s.
17) When a motor is switched on, the rotor frequency is same as supply frequency.
18) In an induction motor the rotor reactance per phase is proportional to slip.
19) A 7.5HP, 3 Phase, 400V, induction motor will draw a full load current of 11A.
20) An induction motor is Self-starting with small torque as compared to rated torque.