Ans:SYNCHRONIZATION:
It is the process of making phase,voltage,frequency same.
PARALLELING:It is the process of sharing the load among all the generators.synchronization is done before closing the circuit breaker.after closing it paralleling starts.
Sunday, January 2, 2011
Synchronization and paralleling
What is the difference between synchronization and paralleling?
Ans:SYNCHRONIZATION:
It is the process of making phase,voltage,frequency same.
Ans:SYNCHRONIZATION:
It is the process of making phase,voltage,frequency same.
DC supply to AC motor
What will happen if DC supply is given to AC motor?
Ans:AC motor works on the principle of induction.The windings in the AC machine are wound either in star or in delta.(AC machine windings).Only if there is a rotating magnetic field,we have an EMF being induced and hence current.so, only when these current carrying conductors are placed in the magnetic field, torque will be produced.so, if we give DC supply,no emf,no current, and hence no motion!!moreover,when DC is given,impedance is very low(bcoz,the effect of inductance of coil is getting neglected in DC).So, the winding will be burnt.
Ans:AC motor works on the principle of induction.The windings in the AC machine are wound either in star or in delta.(AC machine windings).Only if there is a rotating magnetic field,we have an EMF being induced and hence current.so, only when these current carrying conductors are placed in the magnetic field, torque will be produced.so, if we give DC supply,no emf,no current, and hence no motion!!moreover,when DC is given,impedance is very low(bcoz,the effect of inductance of coil is getting neglected in DC).So, the winding will be burnt.
Earthing and Grounding
What is the difference between earthing and grounding?
Ans:GROUNDING:
grounding means,keeping that particular terminal as common point.Ex.(take any circuitry,where a number of different voltages are used,0-12v,0-24v,0-110v etc.here all the 0v terminals are grounded and taken as a common terminal.)
EARTHING:
It means making the common point to earth.The potential of this point shall be 0v.Ex.(Equipments are earthed for safety of operator.)
Ans:GROUNDING:
grounding means,keeping that particular terminal as common point.Ex.(take any circuitry,where a number of different voltages are used,0-12v,0-24v,0-110v etc.here all the 0v terminals are grounded and taken as a common terminal.)
EARTHING:
It means making the common point to earth.The potential of this point shall be 0v.Ex.(Equipments are earthed for safety of operator.)
Oil in transformers
What is the purpose of using oil in transformer tanks?which oil is used?
Ans:the function of oil is two-fold.It is used
1)As a coolant
2)As an insulator.
The oil used is mineral oil.Trade names are ASKARELS,PYROCLOR.Good transformer oil should be absolutely free from alkalies,sulphar and particularly from moisture.Hence, the tanks are sealed air-tight.
Ans:the function of oil is two-fold.It is used
1)As a coolant
2)As an insulator.
The oil used is mineral oil.Trade names are ASKARELS,PYROCLOR.Good transformer oil should be absolutely free from alkalies,sulphar and particularly from moisture.Hence, the tanks are sealed air-tight.
Efficiency
Three phase induction motor is otherwise called as rotating transformer.but which has higher efficiency?
Ans:As a transformer is a static device,only loss in it are copper loss,core loss.Hence it's efficiency is highest among all electrical machines. It's efficiency is greater than 95%.
Since 3 phase induction motor is a rotating device, mechanical losses are also included.It's efficiency is around 70%.
Ans:As a transformer is a static device,only loss in it are copper loss,core loss.Hence it's efficiency is highest among all electrical machines. It's efficiency is greater than 95%.
Since 3 phase induction motor is a rotating device, mechanical losses are also included.It's efficiency is around 70%.
Saturday, January 1, 2011
Transformer
What will happen if DC supply is given to the transformer?
Ans:Transformers have high inductance,low resistance.When DC is given, only resistance will act.(bcoz inductors,capacitors won't work in DC).since it has low resistance, high current will flow in primary side which will damage windings and insulation.
Ans:Transformers have high inductance,low resistance.When DC is given, only resistance will act.(bcoz inductors,capacitors won't work in DC).since it has low resistance, high current will flow in primary side which will damage windings and insulation.
Electro static precipitator
What is the use of electro static precipitator?
Ans: There are two types of ash produced in thermal power plants.They are bottom ash,fly ash.electro static precipitator is used to collect the fly ash.
Ans: There are two types of ash produced in thermal power plants.They are bottom ash,fly ash.electro static precipitator is used to collect the fly ash.
Synchronous condenser
When does synchronous motor act as a synchronous condenser?
Ans;when it is over excited it will act as a synchronous condenser.Sync.condenser is like a capacitor.It can be used for power factor improvement.
Ans;when it is over excited it will act as a synchronous condenser.Sync.condenser is like a capacitor.It can be used for power factor improvement.
Interview questions
Why does humming noise occur in transformer?
Ans:It occurs due to magnetostriction effect.When a ferromagnetic material is subjected to magnetism, change in dimensions will occur in the material.Due to this humming noise occurs in the transformer.
Ans:It occurs due to magnetostriction effect.When a ferromagnetic material is subjected to magnetism, change in dimensions will occur in the material.Due to this humming noise occurs in the transformer.
Interview question
Why the earthpin of a 3point pin is bigger in diameter?
Ans: The earth pin has to send the fault current to earth.So it must have smaller resistance. to have smaller resistance, the diameter should be high.It can be understood from R=pl/A.
Ans: The earth pin has to send the fault current to earth.So it must have smaller resistance. to have smaller resistance, the diameter should be high.It can be understood from R=pl/A.
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