17-03-2014, 11:16 AM
Electrical interview questions full details
Electrical interview questions.docx (Size: 52.7 KB / Downloads: 25)
Electrical interview questions: Different between merger and contact resistance meter?
Answers: merger used to measure cable resistance, conductor continuity, and phase identification where as contact resistance meter used to measure low resistance like relays, contactors.
Electrical interview questions: When we connect the capacitor bank in series?
Answers: we connect capacitor bank in series to improve the voltage profile at the load end in transmission line there is considerable voltage drop along the transmission line due to 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 terminal voltage the capacitor bank is used in series
Electrical interview questions: What is Diversity factor in electrical installations?
Answers: 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. Diversity factor is usually more than one.
Electrical interview questions: Why field rheostat is kept in minimum position while armature rheostat at maximum position?
Answers: 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
torque.
Electrical interview questions: Why humming sound occurred in h HT transmission line?
Answers: This 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.
Electrical interview questions :what is rated speed?
Answers: 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.
Electrical interview questions: What is different between grounding and earthlings?
Answers: Grounding 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 earthing is done in electric equipment in order to protect he equipment in occurrence of fault in the system.
Electrical interview questions: Why should be the frequency is 50 Hz only why not others like 45, 95 56 or anything, why should we maintain the frequency constant if so why it is only 50?
Answers: We can have the frequency at any frequency you like, but then you must also make your own motors, transformers or any other equipment you want to use. We maintain the frequency at 50 Hz or 60 Hz cos the world maintains a standard at 50 /60hz and the equipments are made to operate at these frequency.
Electrical interview questions: Which type of oil is used as transformer oil?
Answers: Transformer oil, or insulating oil, is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage switches and circuit breakers. Its functions are to insulate, suppress corona and arcing, and to serve as a coolant.
Well into the 1970s, polychlorinated biphenyls (PCB)s were often used as a dielectric fluid since they are not flammable. They are toxic, and under incomplete combustion, can form highly toxic products such as furan. Starting in the early 1970s, concerns about the toxicity of PCBs have led to their banning in many countries.
Today, non-toxic, stable silicon-based or fluoridated hydrocarbons are used, where the added expense of a fire-resistant liquid offsets additional building cost for a transformer vault. Combustion-resistant vegetable oil-based dielectric coolants and synthetic pentaerythritol tetra fatty acid (C7, C8) esters are also becoming increasingly common as alternatives to naphthenic mineral oil. Esters are non-toxic to aquatic life, readily biodegradable, and have a lower volatility and higher flash points than mineral oil.
Electrical interview questions: If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?
Answers: As we know the Voltage & current relation for transformer-V1/V2 = I2/I1
We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps.
By putting these value on Relation-
540/11000= I2/2334
So,I2 = 114.5 Amps