Two Marks Questions with Answers

Two Marks Questions with Answers

Q.1 What is mean by corona effect ?

Ans. : It can be noticed that near the overhead lines there exists a hissing noise and sometimes a faint violet glow. The effect due to which such phenomenon exists surrounding the overhead lines is called corona effect.

Q.2 Define visual critical voltage.

Ans. : Minimum phase to neutral voltage at which corona glow appears and visible all along the conductors is called visual critical voltage.

Q.3 Define critical disruptive voltage.

Ans. : The minimum phase to neutral voltage at which corona effect occurs is called critical disruptive voltage. It is not visible at this voltage.

Q.4 What is mean by corona power loss ?

Ans. : The ions produced in the air due to corona are moving. The energy required to keep them moving is derived from the supply system. This additional power required which is dissipated in the form of heat, sound and light in case of corona, is called corona loss. 

Q.5 What are the factors affecting corona ?

Ans. : i) Electrical factors such as supply frequency ii) Line voltages iii) Atmospheric conditions like pressure, temperature etc. iv) Size of the conductor v) Surface conditions whether rough, smooth, dirty or wet. vi) Shape of conductor vii) Spacing between conductors viii) Number of conductors per phase ix) Clearance from ground x) Load current

Q.6 What are the advantages of corona ?

Ans. : 1. Due to corona the air surrounding the conductor is ionized and becomes conducting. This increasing the virtual diameter of the corona.

2. Corona reduces the effect produced by the surges and conductor is saved from possibilities of lightning. It acts as a safety device.

Q.7 What are the disadvantages of corona loss ?

Ans. : 1. The corona power loss is the biggest disadvantage which reduces the transmission efficiency.

2. The third harmonic components produced due to corona makes the current nonsinusoidal. This increases the corona loss

3. The ozone gas formed due to corona chemically reacts with the conductor and can cause corrosion.

Q.8 Write down the methods to reduce the corona effect.

Ans. : 1. Increasing the conductor size

2. Increasing the conductor spacing

3. Using hollow and bundled conductors

Q.9 Define radio interference.

Ans. : The corona discharge produces the radiations which may introduce noise signals in the communication lines, carrier signal, radio and television receivers, navigation signals etc.. Such noise signals which adversely affect the wireless signals, produced by corona is called radio interference.

Q.10 How is corona loss related with the diameter of the conductor ?

Ans. : Corona loss is inversely proportional to the diameter of the conductor. Hence lower the diameter of the conductor, higher is the loss.

Q.11 What is local corona ?

Ans. : The corona does not start simultaneously on the whole surface, but it takes place at different points of the conductor which are pointed in nature. This known as local corona.