ELECTRICAL KNOWLEDGE (7)

Q1) Can we replace a 110/220 turns transformer with a 10/20 turns? Even though the turns ratio is same i.e 1/2

Ans) No, we cannot replace it because a 110/220 turns transformer with a 10/20 turns transformer because number of turns are directly proportional to the flux and if number of turns increases then flux increases and vice versa.

Also Flux is directly proportional to emf:

 EMF= 4.44*f*phi*N

Assuming flux (phi) = 0.00901

FOR 110/220 TRANSFORMER EMF WILL BE:

 V1( primary side)= 4.44*50*0.00901*110= 220 volts

V2(secondary side)= 4.44*50*0.00901*220= 440 volts

FOR 10/20 TRANSFORMER EMF WILL BE:

V1( primary side)= 4.44*50*0.00901*10= 20 volts

V2(secondary side)= 4.44*50*0.00901*20= 40 volts

Q2) suppose a consumer consumes 1000 watt load per hour daily for one month. What will be the total energy bill of the consumer if the per unit rate is 9

ANS ) 1 unit = 1 kwh                        

Total watt hour consumed in one month = 1000*24*30= 720000watthour

We want to convert it into units hence

Total unit consumed = 720000/1000                             ( 1 kwh=1000wh)

Total unit consumed= 720 units

Cost per unit = 9

Bill = 720 *9 = 6,480 rupees

Q3) What is the operation carried out in thermal power plant?

1.  Fuel( coal, oil, gas) is burnt at high temperature and heat is produced.
2.  This heat is passed to the boiler containing water and it converts water to high temperature and high pressure steam.
3.  This steam is allowed to pass though turbine where it moves the turbine and produced rotational energy.
4. The turbine shaft is connected to a generator which converts the rotational energy to electrical energy

Q4) What is the working principle of motors and what is armature reaction?

WORKING PRINCIPLE OF MOTOR:

Whenever a current carrying conductor is placed in a magnetic field it produces a turning or twisting movement called torque

ARMATURE REACTION:

The effect of armature flux on main flux is called as armature reaction. Armature flux may suppose or oppose main flux

Q5) What is vector group in transformer?

Vector group indicates how the primary and secondary windings are connected and the phase difference between current and voltage. For eg vector group “ Dy11” indicates that HV winding will be “ delta connected”, Lv winding will be “ Y connected” and there exist 30 degrees phase difference between hv and lv side.

NOTE:

1) D = Delta winding or mesh winding

2) Y= star or y winding

3) Z= zig zag winding

4) n= it indicates that neutral is connected on LV side

5) N= it indicates that neutral is connected on HV side

HV Winding will always be indicated by a capital letter, where as LV winding will be indicated by a small letter.

EXAMPLES:

Yd11 = Hv side is y connected, Lv side is delta connected and HV sides leads LV side by 30 degrees

Q6) What is the significance of vector group?

The Determination of vector group of transformers is very important before connecting two or more transformers in parallel. If two transformers of different vector groups are connected in parallel then phase difference exist between the secondary of the transformers and large circulating current flows between the two transformers which is very detrimental.