Electrical World

Hello and wellcome. Do you know what is corona effect?              First consider a conductor system to which voltage is applied. If the potential applied is raised, gradually, beyond a limit, a pale voilet glow will appear. This will be accompanied by a hissing noise indicating the ionization of surrounding air of the conductor surface with characterstic smell of ozone. This phenomenon is known as corona.             Simply we can say, phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as corona effect.            High electric field at conductor surface provides enough energy to the molecules of surrounding air that causes breakdown of air.        In case of a.c. Transmission ionized particles get attracted and repelled to conductor once du...

Hello. Q.1 Corona is- A. Partial breakdown of air B. Complete breakdown of air C. Sparking between lines D. None of these Ans: B Q.2 Which of the following statements is true regarding corona- A. Corona takes place at a voltage lower than breakdown voltage B. Corona takes place at a voltage higher than breakdown voltage C. Corona is a current phenomenon D. Corona increases the transmission line efficiency Ans: A Q.3 Corona is accompanied by- A.Violet visible discharge in darkness B. Hissing sound C. Vibration D. Power loss E. Radio interference F. Ozone G. All of the above Ans: G   Q.4 Ozone effect can be detected by A. Presence of ozone detected by odour B. Hissing sound C. Faint luminous glow of bluish colour D. All of the above Ans: D Q.5 Corona loss increases with A. Decrease in conductor size and increase in supply frequency B. Increase in conductor size and decrease in supply frequency C. Increase in both conductor size and supply frequency D. Decrease in ...

In case of D.C., current density is uniform over cross section of conductors. On the other hand, in a conductor carrying A C there is a tendency of current to crowd near the surface of conductor that means alternating current flowing through a conductor doesn't distribute uniformly and concentrate near the surface of conductor. In AC System no current flows through the core and entire current is concentrate on surface regions. Due to this effective area of conductor is reduced so ac resistance of conductor increases. This phenomenon is known as Skin Effect as it causes concentration of current at the skin of conductor. To explain skin effect, we assume conductor which is made up of a number of concentric cylinders. Magnetic flux linking a cylindrical  element near the centre of conductors is greater than that linking another element near the surface of conductor. It is due to the fact that former elements is surrounded by internal as well as external flux, while latter element by ...

Q. What is meant by knee point voltage? A. Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.(CT-current transformer). Query:What is reverse power relay? Resolution:Reverse Power flow relay are used in generating stations's protection. A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay. Q:What is the difference between Isolator and Circuit Breaker? A:Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. it is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load. first the load on it must be...