Model Question II

Model Question Paper-II

Part A

1. State the ohm’s law.
2. Define energy.
3. Define impedance and admittance.
4. Define bandwidth.
5. Define efficiency of the transformer.
6. Define regulation of transformer.
7. What is meant by voltmeter sensitivity?
8. State any two uses of maxwells bridge.
9. What is meant by transducer?
10. State differences between XY recorder and strip chart recorder..
    
    Part B
11. State the KVL and KCL and explain.
12. Define susceptance and conductance and impedance.
13. Explain various losses in transformer?
14. Explain various forces required in indicating instruments?
15. What is meant by strain gauge and load cell?

Part C

16. (a) State and explain Thevenin’s theorem.
           (or)
     (b) State and explain maximum power transfer theorem.

17. (a) Derive the relation between line and phase voltage in star connection.
          (or)
     (b) Derive an expression for the impedance of an RLC series circuit.

18. (a) Explain the working principle of a transformer.
         (or)
     (b) Explain the principle of operation of a single phase induction motor.

19. (a) Draw the block diagram of CRO and explain its operation.
        (or)
    (b) Explain wheatstone’s bridge circuit and list out the applications.

20. (a) With a diagram, explain the working principle of stripchart recorder.
        (or)
      (b) With the block diagram, explain the working of successive approximation type DVM

Answer will be posted very soon

Model Question I

Model Question Paper-I

Part A

1. State Kirchhoff’s laws.
2. Define power.
3. What is meant by Resonance?
4. Define quality factor.
5. What are the losses in transformer?
6. State any two application of Dc shunt generator
7. List out the types of damping.
8. State any two application of Hays bridge.
9. What is meant by LVDT?
10. State any two application of load cell.
    
    Part B
11. Find the value of current in circuit with resistance 2 Ohm and 1 Ohm connected in parallel.
12. Explain star and delta connection.
13. List out the types of DC generator mention its application.
14. Draw the diagram of Hay’s Bridge, and explains its feature.
15. What is meant by thermo couple? And explain.

Part C

16. (a) State and explain Super position theorem.
           (or)
      (b) State and explain Norton’s theorem.

17. (a) Find out the impedance and Admittance of RL & RC parallel circuit.
           (or)
      (b) Explain the condition for resonance and compare series and parallel resonance circuits.

18. (a) Explain in details of OC & SC test on transformer.
           (or)
      (b) Explain the principle of operation of capacitor start induction motor.

19. (a) With a diagram, explain the construction features and working of PMMC instrument.
          (or)
     (b) Explain the operation of vertical deflection system and mention the applications of CRO.

20. (a) Explain the operation of LVDT and mention its applications.
         (or)
     (b) Explain the principle of operation of digital frequency counter.

Answer will be posted very soon

Homemade wind generators are becoming an increasingly popular way to reduce reliance on fossil fuels and reduce increasing utility bills by generating electricity for direct use in the home or other properties.A wind generator needs to be supported by a tower, which will raise it to a level where its blades can be rotated by the wind most efficiently.

Instructions

Make the body of the wind generator with a piece of 2 by 4, approximately one yard in length. To one end of the 2 by 4, attach a rectangular piece of plastic or metal to act as a sail, swiveling the blades towards the wind.To the other end of the 2 by 4, attach the motor. Cover the motor with some plastic sheeting to protect it from the weather. Drill a hole in the wood behind the motor for the wires to run through. To the motor at this end of the 2 by 4, attach the blade section of the wind turbine.All of these components together will sit on top of the tower; the tower raises the turbine above obstructions and allows it to generate electricity from the power of the wind.

Construct the tower for the wind generator using a pipe; the wires from the motor can run through a hollow pipe.The size and strength of the pipe required for the tower will vary depending on the height of the tower; taller wind generators will require a wider pipe to support it, wind generators installed on a roof will only require a narrower and shorter pipe.

The tower for the wind turbine both raises the turbine above other obstructions, so making it more efficient, and with this design, allows the wind turbine to turn to face the wind. This tower also protects the wires running from the main body of the wind generator to the battery.

Attach the tower to the tail of the wind generator. Secure a pipe bracket, slightly larger than the pipe used for the tower, underneath the hole drilled in the 2 by 4 for the wires. Slot the tower pipe into this bracket; the smaller pipe will allow the tail of the wind generator to pivot the blades towards the wind.

Secure the other end of the tower pipe to a large piece of wood acting as the base to the wind generator. The wood used for the base should be large in order to securely anchor the wind generator. If possible, screw the base into the ground or surface that the wind generator is on for extra stability.

Run the wires from the tower to the battery. House the battery in a place where it will be protected from the weather, for example in a shed. Connect the positive and negative wires to the corresponding electrodes on the battery. The electricity generated by the wind generator will be stored in the battery until use.

An alternator uses a rotating magnetic field to turn kinetic energy into electrical power. A functional, used alternator from a car can be used with a small engine and AC-DC converter to provide power. For an alternator to work properly, the magnetic field must rotate at a very fast speed, which is why alternators need to be connected to a quickly rotating engine rather than a wind turbine or water wheel. An engine that runs at least 2,100 rpm or greater is best for solid results.

Instructions

1. •  1.Place the alternator on the corner of a full sheet of 3/4-inch plywood so that the pulley hangs over the edge of the sheet. Mark the mounting bolt holes with a marker.2.Remove the alternator and drill holes through the marks with a drill. Return the alternator to the board and slide lag bolts through the mounting holes. Place a washer on the bottom and thread a nut onto the bolt by hand as far as possible. Hold the nut in place with a crescent wrench and tighten it with a socket wrench.
     
     
     
   • 3.Set a small gas-powered engine with a mounted pulley parallel to the alternator. Wrap the alternator belt around the engine pulley and the alternator pulley. Pull the engine away from the alternator until the belt is tight.4.Line the pulleys up so that they are exactly parallel. Move the belt by hand to make sure there isn't any wobble in the movement. Mark the engine mounting holes with a marker, then slide the engine out of the way and drill the holes with a drill.5.Slide the engine back in place with the belt still on. Drop lag bolts into the mounting holes. Fit washers and nuts on the back of the bolts and tighten them down with a socket wrench.6.Attach an AC-DC converter to the alternator. Tighten the retaining nuts by hand until they're snug.7.Turn the engine on. Plug an appliance or battery into the AC-DC converter.
     
     
     

Ia = (Vln –CEMF)/Ra.

Ia = armature current
Vln = line voltage to the motor
Ra = armature resistance
CEMF = voltage generated within the motor

Equation tells us that the armature current is a function of the applied voltage minus the CEMF. Because CEMF increases with motor speed, the faster the motor runs, the less current the motor will draw, and consequently its torque will diminish. This explains why most DC motors have a finite maximum speed; eventually, if the motor keeps going faster, the CEMF will nearly cancel out the line voltage, and the armature current will approach zero.

Speed regulation is the ability of a motor to maintain its speed when the load is applied. The basis of this self-regulation is the CEMF. When the motor’s load is increased, the speed tends to decrease, but the lower speed reduces the CEMF, which allows more current into the armature. The increased current results in increased torque, which prevents the motor from slowing further.
Courtesy : eblogbd.com

Lenz’s law of motor-

Principle theory of motor 
A current carrying conductor will experience a force when placed in a magnetic field. The conductor can be any metal—iron, copper, aluminum, and so on.

F = IBL sin θ

where
F = force on the conductor (in Newtons)
I = current through the conductor (in amperes)
B = magnetic flux density (in gauss)
L = length of the wire (in meters)
θ = angle between the magnetic field and current

The direction of the force is perpendicular to both the magnetic field and the current.

Picture: Action of force on a wire in a magnetic field.

Electric motor torque is directly proportional to the force on the armature wires.

T = Kt Ia φ

where
T = motor torque
Kt = a constant based on the motor construction
Ia = armature current
φ = magnetic flux

As the armature of motor is rotating in the magnetic field of field winding, according Faraday’s laws of electromagnetic induction a certain voltage also induced in the armature winding.
EMF = KeφS

where
EMF = voltage generated by the turning motor
Ke = a constant based on motor construction
φ = magnetic flux
S = speed of motor (rpm)

This induced voltage will try to cancel out the line voltage, that is it will be of opposite polarity.
The actual voltage available to the armature is the line voltage
minus the CEMF:

VA = Vln – CEMF
where
Va = actual voltage available to the armature
Vln = line voltage supplied to the motor
CEMF = voltage generated within the motor

We can not directly measure Va with a voltmeter because it is an effective voltage inside the armature. However, there is physical evidence that the CEMF exists because the armature current is also reduced

Ia = ( Vln – CEMF)/Ra
where
Ia = armature current
Vln = line voltage to the motor
Ra = armature resistance
CEMF = voltage generated within the motor

The actual relationship between motor speed and CEMF follows
S = CEMF/(Kφ)
where
S = speed of the motor (rpm)
CEMF = voltage generated within the motor
KE = a motor constant
φ = magnetic flux

P = TS
where
P = power
T = torque
S = motor speed

1 hp = 33,000 (ft.lb/min)

Courtesy: eblogbd.com

Ques-17: Can 4-Winding Single Phase Transformer be auto-connected? 
Ans: Yes. There are occasions where 480 volts single phase can be stepped down to 240 volts single phase by auto connecting a standard 4-winding isolating transformer as shown in Figure-1. If connected in this manner, the nameplate KVA is doubled. For example: A 10 KVA load can be applied to a 5 KVA 4-winding transformer if connected per Figure-1.

Ques-18: How is magnetic leakage reduced?

Ans: Magnetic leakage is reduced to a minimum by sectionalizing and interleaving the primary and secondary windings.

Ques-19: Why are iron cores in transformers made laminated?

Ans: Iron cores are made laminated to reduce eddy current loss.

Ques-20: What is meant by “impedance” in transformers? 

Ans: Impedance is the current limiting characteristic of a transformer and is expressed in percentage.

Ques-21: What is the power factor of a transformer?

Ans: At no load, the power factor of a transformer is very low and lagging, whereas the power factor on load is nearly equal to the power factor of the load, which it is carrying.

Ques-22: What are the advantages of using a transformer in an AC supply?

Ans: The transformer has the following advantages:

1. Voltage can be transformed from low voltage to high voltage for transmission and high voltage to low voltage for distribution without changing the frequency.
2. As the transformer has no rotating parts, there is no factional loss and wear and tear is minimum.
3. A high voltage or an extra high voltage can be transformed easily by providing good insulation.
4. Its maintenance cost is low.
5. Practically it requires very little attention for its operation.

Ques-23: What do you mean by power transformer?

Ans: Transformers that are used on transmission lines for the transmission and distribution of relatively large quantities of energy are called power transformers.

Ques-24: What do you mean by distribution transformers?

Ans: When transformers are used for distributing the energy from transmission lines as well as net-works for local consumption and the secondaries are directly connected to the consumer's load, they are called distribution transformers.

Ques-25: What do you mean by lighting transformer?

Ans: A transformer used to supply a distribution circuit having no motors connected to it is called lighting transformer.