Sunday, October 6, 2013

Electrical Interview questions Part 25

Q: Do you know the advantages of speed controlusing thyristor?
A: Advantages: 1. Fast Switching Characterstics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate.

Q: Name the different types of motors used in vacuum cleaners, phonographic appliances, vending machines, refrigerators, rolling mills, lathes, power factor improvement and cranes.
A: Following motors are used: -
• Vacuum cleaners- Universal motor.
• Phonographic appliances – Hysteresis motor.
• Vending machines – Shaded pole motor.
• Refrigerators – Capacitor split phase motors.
• Rolling mills – Cumulative motors.
• Lathes – DC shunt motors.
• Power factor improvement – Synchronous motors.

Q: In the motors starting purpose why the armature rheostats at maximum position while the field rheostat is kept in minimum position?
A: In the time of starting a motor the field rheostat is kept in minimum state for the high starting torque.

In the time of starting a motor the armature rheostats is used to control or reduce the high starting current. This high starting current can damage the motors starting systems.

Q: What's the other name for short circuit?
A: fault.

Q: Name power losess in rotating electrical machines.
A: Power losess in rotating electrical machines are Copper losses, core losses, mechanical losses and stray losses.

Q: What is the significance of vector grouping in Power Transformers?
A: Every power transformer carries a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.

Q:State the factors, for the choice of electrical system for an aero turbine.
A:The choice of electrical system for an aero turbine is guided by three factors:
• Type of electrical output: dc, variable- frequency ac, and constant- frequency ac.
• Aero turbine rotational speed: constant speed with variable blade pitch, nearly constant speed with simpler pitch- changing mechanism or variable speed with fixed pitch blades.
• Utilization of electrical energy output: in conjunction with battery or other form of storage, or interconnection with power grid.