Electrical Engineering interview questions: part 1 1. Why star delta beginner is recommended with induction motor? An induction motor is referred with star delta starter for the following reason:
• The power is saved because of voltage drops as the starting current is reduced 3-4 times. • The motor is saved because of the star delta circuit comes along with circuit during start of motor and thus voltage is reduced by three units.
• Damage of motor winding is prevented because of the increase in starting torque. 2. Comparison between generator and alternator Generator and alternator are two devices, which converts mechanical power into electrical power. The basic principle followed by both of them is electro-magnetic induction, the only distinction is their construction. A fixed magnetic field and a rotating conductor is available on the generator that comes on the armature connected with slip rings and brushes colliding against each other, hence it transforms the emf induced into the dc current for external load whereas an alternator has a fixed armature and a rotating magnetic field for higher voltages but for reduced voltage outcome both rotating armature and stationary magnetic field is used. 3. Benefits of AC systems over DC systems Due to the following factors, AC systems are recommended over DC systems: a. Maintenance is easy and can change the voltage of AC power for transmission and distribution. b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission c. AC is produced from the power stations so AC is better for usage than DC instead of converting it. d. If a big fault occurs in a network, it is simpler to get rid of in an AC system, as the sine wave current will automatically become zero at some point making the current interruption easier.