Electrical Interview questions Part 16

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.

Q:What are the operation carried out in Thermal power station?

A: The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine, the turbine which is coupled with the generator generates the electricity

Q: What is the diff. btwn. Electronic regulator and ordinary rheostat regulator for fans?

A: The difference between the electronic and ordinary regulator is the fact that in electronic reg. power losses tend to be less because as we minimize the speed the electronic reg. give the power necessary for that particular speed but in case of ordinary rheostat type reg. the power wastage is same for every speed and no power is saved. In electronic regulator triac is employed for speed control. by varying the firing angle speed is controlled but in rheostatic control resistance is decreased by steps to achievespeed control.

Q: What is 2 phase motor?

A: A two phase motor is often a motor with the the starting winding and the running winding have a phase split. e. g; ac servo motor. where the auxiliary winding and the control winding have a phase split of 90 degree.

Q:What does quality factor depend on in resonance?

A:Quality factor q depends on frequency and bandwidth.

Q:What are the types of power in electrical power?

A: There are normally three types of power are counted in electrical power. They are,

· Apparent power

· Active power

· Reactive power

Q:What are the advantages of VSCF wind electrical system?

A:Advantages of VSCF wind electrical system are:

• No complex pitch changing mechanism is needed.
• Aero turbine always keeps going at maximum efficiency point.
• Extra energy in the high wind speed region of the speed – duration curve can be extracted
• Significant reduction in aerodynamic stresses, which are associated with constant – speed operation.

Q:What is slip in an induction motor?

A:Slip can be defined as the distinction between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.