9. Explain advantages of storage batteries
Few advantages of storage batteries are mentioned below:
• Most efficient form of storing energy portably.
• Stored energy is available immediately because there is no lag of time for
delivering the stored energy.
• Reliable source for supply of energy.
• The energy can be drawn at a fairly constant rate.
10. What are the different methods for the starting of a synchronous motor.
Starting methods: Synchronous motor can be started by the following two methods:
• By means of an auxiliary motor: The rotor of a synchronous motor is rotated
by auxiliary motor. Then rotor poles are excited due to which the rotor field
is locked with the stator-revolving field and continuous rotation is obtained.
• By providing damper winding: Here, bar conductors are embedded in the outer
periphery of the rotor poles and are short-circuited with the short-circuiting
rings at both sides. The machine is started as a squirrel cage induction motor
first. When it picks up speed, excitation is given to the rotor and the rotor
starts rotating continuously as the rotor field is locked with stator revolving
11. Name the types of motors used in vacuum cleaners, phonographic appliances,
vending machines, refrigerators, rolling mills, lathes, power factor
improvement and cranes.
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.
12. State Thevenin’s Theorem:
According to thevenin’s theorem, the current flowing through a load resistance
Connected across any two terminals of a linear active bilateral network is the
ratio open circuit voltage (i.e. the voltage across the two terminals when RL
is removed) and sum of load resistance and internal resistance of the network.
It is given by Voc / (Ri + RL).
13. State Norton’s Theorem
The Norton’s theorem explains the fact that there are two terminals and they are
• One is terminal active network containing voltage sources
• Another is the resistance that is viewed from the output terminals. The
output terminals are equivalent to the constant source of current and it allows
giving the parallel resistance.
The Norton’s theorem also explains about the constant current that is equal to
the current of the short circuit placed across the terminals. The parallel
resistance of the network can be viewed from the open circuit terminals when
all the voltage and current sources are removed and replaced by the internal
14. State Maximum power transfer theorem
The Maximum power transfer theorem explains about the load that a resistance
will extract from the network. This includes the maximum power from the network
and in this case the load resistance is being is equal to the resistance of the
network and it also allows the resistance to be equal to the resistance of the
network. This resistance can be viewed by the output terminals and the energy
sources can be removed by leaving the internal resistance behind.