Important Diploma Electrical Questions 2

Important Diploma Electrical Questions 2

Q: What is the permissible value of earth resistance.??
Answer: Earth resistance should be as small as possible . It depands on voltage level of the system to be grounded . As voltage level increases the earth resistance required to be nearer to zeero as far as possible....
For large power station = 0.5
for small substation = 2.0
for domestic wiring = 5.0

Q: whay we used silica gel in Transformer ?
Answer: it absorbs the moiosture content of the air and send dry air inside the transformer.....

Q: a 50hz motor to give 60hz whats happening in motor.what happen the motor?
Answer: If we increase only frequency of motor and keep voltage constant as a rated voltage then speed of motor will increase but maximum torque capacity of motor will reduce.....

Q: what is ferranti effect?
Answer: Under no-load or light load condition the receiving end voltage is grater than sending end voltage this effect is called ferranti effect. this is due to because of the capacitance effect in the long transmission lines only, this is not applicable for medium and short transmission lines...

Q: what is corona ?
Answer :corona is a one type of phenomenon, mainly occurs in transmission line, some electric charge act with surrounding air moisture. A violet glow mainly seems Also produce vibration in transmission line, produce ozone gas And odor....It calculating as loss of energy.

Q: what is bausbar?
Answer: it is metalic bar or hollow rod in which potential is same everywhere........ it receive electrical power to one or many incoming circuits and deliver this power to one or many outgoing circuits....

Q: what is the difference between ACTIVE POWER and REACTIVE POWER?
Answer: POWER SUPPLIED BY EXT. SOURCE IS CONSUMED IN 2 PARTS
1-ACTIVE POWER-which actually does the useful work in the machine and overcome losses.
2-REACTIVE POWER-which the system needs to produce magnetic field in the machine.
Understsnding of active power and reactive power is very 
much related to our life.What we eat gives power to us is
acive (power for doing any work) but power required to our mind to do a job is a reactive power......

Q: what r the types of transmission line?
Answer: Transmission lines are classified according to their span and working voltage.Usually, the following nomenclature is adopted to classify lies:
1. Short Lines: Less than 20kV and less than 80km
2. Medium Lines: Lengthe between 80-200km and Voltage between 20-100kV
3. Large Lines: More than 100kV voltage and more than 200km span.

Q: super position theorem is applicable to..........
answer: linear and lumped networks

Q: Current chopping mainly occurs in air blast circuit breaker.why?
Answer: In an air blast breaker a high velocity jet of air is made to flow through the arcing contacts that extinguishes the arc much before natural ac current 0 is reached , the air blast breaker retains the same extinguishing power irrespective of the nature of the fault , onsequently theblast of air sweeps out the ionised particles in between the contacts thereby buiding the rsistance and hence ultimately extnguishing the arc.

Q: what is main difference between electrical and electronics??
Answer: electrical is works on conductor materials and electronic works on semiconductor materials.

Q: What is meant by regenerative braking?
Answer: The Regerating braking is the speed of a motor is increased upto or above to the top speed. And suddenly disconnect the supply to motor. So, the motor is act as a generator and the generated supply opposing the main supply. So, the motor is tried to rotate in opposite direction. So it will
be stopped suddenly......
isme motor ko supply disconnect kiya jata h or motor apne inertia k karan lgtar run krta rhta h or field ko cut krke generator ki tarh behave krti h....

Q: Why frequency fix in 50 Hz?

Answer: We know that syn speed=120f/p The turbines are designed such that they will give max efficiency at 3000rpm. for good performence a generator should have 2field poles. hence giving f=50hz

Q:what is name of transformer oil ?
answer: The chemical name of transformer oil name is "Dicloro di-floro ethyle benzene" and brand name is Askarel, pyroclor (naphtheline base), etc

Q: why the generating voltage in India is 11kV or why is it be transmitted as multiples of 11..???

Answer: In India the generating voltage is 11kv.b,coz we,all know the formfactor value is 1.11.due to this the power is generated in 11kv & transmitted as multiples of 1.11