Power System Part-I

Q.How can you relate power engineering with electrical engineering?

Ans:

Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of electrical energy. Design and maintenance of all power equipments,power grid and off grid equipments comes under power engineering.

Q. What are the main divisions of power system?

Ans:

The generating system,transmission system and distribution system are the main divisions of power system.

Q. Why AC systems are preferred over DC systems?

Ans:

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

• It is easy to maintain and change the voltage level of AC electricity for transmission and distribution using efficient transformer.
• Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission.
• In generating stations, AC is produced so it is better to use AC than DC instead of converting it.
• When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally zero at some point making the current easier to interrupt.

Q. State the difference between generator and alternator.

Ans:

Generator and alternator converts mechanical energy into electrical energy. Both have the same principle of working i.e. electromagnetic induction, the only difference is that their construction.
In Generator 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 application

but for low voltage application output, rotating armature and stationary magnetic field is used.

Q.Define the following term of Power System.

Reliability, Reserve generating capacity, Availability.

Ans:

1. Reliability: It is the capacity of the power system to serve all power demands without failure over long periods.
2. Reserve generating capacity: Extra generation capacity installed to meet the need of scheduled downtime's for preventive maintenance is called reserve-generating capacity.
3. Availability: As the percentage of the time a unit is available to produce power whether needed by the system or not.

Q.Explain the terms real power, apparent power and reactive power for ac circuits and also the units used.
Ans:

1. Real Power: It is watt full component in power system which creates losses.It is the product of voltage, current and power factor i.e. P = V I cos(Theta) and basic unit of real power is watt. i.e. expressed as W or kW.

2. Apparent power: It is the product of voltage and current. Apparent power = V I and basic unit of apparent power is volt-ampere and expressed as VA or KVA.

3. Reactive Power: It is watt less component in power system.It is the product of voltage, current and sine of angle between the voltage and current i.e. Reactive power = voltage X current X sin(Theta) expressed in VAR or KVAR.

Q.Define the following: Average demand, Maximum demand, Demand factor, Load factor.

Ans:
1. Average Demand: the average power requirement during some specified period of time of considerable duration is called the average demand of installation.
2. Maximum Demand: The maximum demand of an installation is defined as the greatest of all the demand, which have occurred during a given period. 

3. Demand Factor: It is defined as the ratio of actual maximum demand made by the load to the rating of the connected load.
4. Load Factor: It is defined as the ratio of the average power to the maximum demand.