Sunday, January 23, 2011

Electrical Interview questions Part 18

Query:Difference between megger test equipment and contact resistance meter test instruments?
Resolution: Megger test equipment used to measure cable electric resistance, conductor continuity, phase identification where as contact resistance meter test instruments used to measure low resistance like relays ,contactors.

Query:When we connect the large capacitor bank in series ?
Resolution :we connect large capacitor bank in series to improve the voltage power supply at the load end in balanced transmission line when there is considerable voltage drop along the balanced transmission line due to high impedance of the line.So in order to bring the voltage at the load terminals within its limits (i.e (+ or - %6 )of the rated high terminal voltage )the large capacitor bank is used in series.

Query:What is electrical diversity factor in electrical installations?
Resolution :Electrical diversity factor is the ratio of the sum of the individual maximum demands of the various subdivisions of a system, or part of a system, to the maximum demand of the whole system, or part of the system, under consideration. Electrical diversity factor is usually more than one.

Query:Why field rheostat is kept in minimum position while armature rheostat at maximum position?
Resolution :In motors at the time of starting the armature resistance is introduced to reduce the high starting current and the field resistance is kept minimum to have high starting

Query:Why computer humming sound occurred in HT transmission line?
Resolution :This computer humming sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.

Query:What is rated speed?
Resolution :At the time of motor taking normal current (rated current)the speed of the motor is called rated speed. It is a speed at which any system take small current and give maximum efficiency.

Query:What is different between resistance grounding system and resistance earthing system?
Resolution :Resistance grounding system means connecting the neutral point of the load to the ground to carry the residual current in case of unbalanced conditions through the neutral to the ground whereas resistance earthing system is done in an electric equipment in order to protect he equipment in occurrence of fault in the system.

Query:Why should be the frequency 50 Hz 60Hz only why not others like 45, 95 56 or anything , why should we maintain the frequency constant if so why it is only 50 Hz 60Hz?
Resolution :We can have the frequency at any frequency you like, but than you must also make your own motors,high voltage transformers or any other equipment you want to use.We maintain the frequency at 50hz or 60hz because the world maintains a standard at 50 /60hz and the equipments are are made to operate at these frequency.