Why AC systems are preferred over DC systems?

Due to following reasons, AC systems are preferred over DC systems:

a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution.

b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission

c. From power stations, AC is produced so it is better to use AC then DC instead of converting it.

d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.

State the difference between generator and alternator

Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.

Why star delta starter is preferred with induction motor?

Star delta starter is preferred with induction motor due to following reasons:
• Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses.
• Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused.
• In addition, starting torque is increased and it prevents the damage of motor winding.

Why don't birds sitting on a high voltage wire get a shock?

Electricity travels from a place of high voltage to low voltage, just like water travels naturally from high elevation to low elevation. If the bird sits on a wire and also touches the ground, a path is created that allows electricity to travel through the body and to the place with no voltage. When electricity travels through the body of a bird in this fashion, electrocution takes place  and the bird dies. However, if the bird touches a single wire it do not get a shock because electric current passes through the wire instead of the bird.

What is a Substation ?

In India Power plants generates power at voltage 11 KV . Since, this voltage do not suffice to cover the large distance from power plant to our homes. To do this voltage raised from 11 KV to 220 KV / 400 KV and then these voltages should bring to 440 V or 230 V to use in our homes or industries. To do this we use Substations. In substations their is a Transformer which transmits the power from one voltage to another voltage. The is also some protecting devices like Breakers, Lightening Arresters which protect those lines from faults. 

How does electricity get to our homes?

Power plant converts the energy from the raw materials of the Earth into electric current.This is done with the help of huge generators, Which are driven by water, steam or wind. Electricity is transmitted at very high voltages through transmission towers to near the point of requirement of electricity and by the use of substations the voltage brings down to 230 V or 115 V to use at our homes or to use in industries at 440 V or above.

IE Rules 1956

IE Rules 1956