# Assignment Electromagnetics

Assignment 3

(1) Define :

(a) The Scalar and Vector Magnetic Potential
(b) Magnetic flux density
(c) Current Density
(d) Surface Current density

(2) An infinitely long coaxial cable is carrying current I by the inner conductor of radius ‘a’
and – I by the outer conductor of radius ‘b’ and ‘c’. where c > b.
Deduce the expressions for H at
(i)  < a (ii) a <  < b (iii) b <  < c (iv)  > c.
Sketch plot of H as a function of radius.

(3) Justify:
a. The curl of the gradient of any scalar field is always the zero vector.
b. The divergence of the curl of any vector field A is always zero.
c. The Laplacian of a scalar field is the divergence of the gradient.

(4) State and explain Ampere’s circuital law. Find the magnetic field intensity due to
Long straight conductor using Ampere’s circuital law.

(5) State and explain Stokes’ Theorem.

(6) What is curl? Explain the physical interpretation of curl and state its application.

(7) A filamentry current of 20 A is directed in from infinity to origin on the positive Y axis,
and then back out to infinity along the positive X axis. Use Biot-savart law
to find H at P (0, 2, 0 )

(8) Find the magnetic field intensity at P(1, 2, 3) caused by curernt filament of 15 A in the ax
direction on X axis and extending from x=0 to 5.

# Assignment Three Phase Induction motor

Assignment 3: Three phase induction motor

1. Explain the equivalent circuit and Phasor diagram of three phase induction motor.
2. Discuss the procedure of no-load and blocked rotor test with test setup arrangement.
3. List out the basic steps of drawing the circle diagram with any one example.
4. Explain the unbalanced operation of the induction motor. Also discuss the case of single phasing.
5. Explain in brief about the cogging and crawling phenomena.
6. What are the desirable starting conditions for a three phase IM? Discuss all the starting methods with the circuit diagram.
7. Explain the construction, operation and equivalent circuit of double cage induction motor.
8. Discuss the methods of speed control of three phase induction motor.

Using circle diagram method, solve the followings:

1. Motor data: 3 phase, 20 HP, 440 Volt, 50Hz, 4 pole
2. No load test: 440 V, 10 A, 1.5 kW
3. Blocked rotor test: 120 V, 30 A, 2.25 kW
4. Determine   Full load current and PF & Maximum possible output power

1.  Motor data: 3 phase, 10 HP, 200 Volt, 50Hz, Slip ring IM, Rs = 0.38Ω and Rr = 0.24Ω  per phase, winding turns ratio unity
2. No load test: 200 V, 7.7 A, 0.195 pf
3. Blocked rotor test: 100 V, 47.6 A, 0.454 pf
4. Determine,   Starting & Maximum torque, Slip at maximum output and maximum output

1. Motor data: 3 phase, 40 HP, 440 Volt, 50Hz, 4 pole
2. No load test: 440 V, 16 A, 0.15 pf
3. Blocked rotor test: 100 V, 55 A, 0.225 pf
4. Ratio of rotor to stator copper losses is 0.9
5. Determine,   Full load current and PF & Maximum possible output power

1. Motor data: 3 phase, 15 HP, 230 Volt, 50Hz,Slip ring, Rs = 0.42 Ω and Rr = 0.3 Ω  per phase, winding turns ratio unity
2. No load test: 230 V, 9 A, 0.2143 pf
3. Blocked rotor test: 115 V, 45 A, 0.454 pf
4. Determine   Starting & Maximum torque & maximum output.

# Assignment Three Phase Transformer

Electrical and Electronics Engineering

Electrical Machines II

Assignment 2: Three Phase Transformers

1. Explain in brief about the construction of three phase transformer.
2. Draw all the vector group of transformer connection.
3. Discuss in brief about the application of the four basic types of connections of three phase transformer.
4. Discuss about the open delta connection and derive that the power transfer capacity is reduced by two third.
5. Explain about the scott connection. How three phase to two phase transformation is done?
6. Explain the parallel operation of the three phase transformers.
7. Discuss the harmonic phenomenon for three phase transformer.

Example:

Three 1100/110 V transformers connected in delta-delta supply a lighting load of 100kW. If one of the transformer is out of service, determine the following:

1. Current of each transformer in healthy condition.
2. Current of each transformer when one transformer is out of order.
3. kVA rating of each transformer if it supplies full load in open delta connection.

A 400 kVA load at 0.7 power factor lagging is supplied by three single phase transformers connected in ∆-∆ each. Each transformer is rated at 200 kVA, 2300/230 V. If one defective transformer is removed from service, calculate for the V-V connection,

1. kVA load carried by each transformer.
2.  Percent rated load carried by each transformer.
3.  Total kVA ratings of transformer bank in V-V.
4. Ratio of V-V bank to  ∆-∆ bank transformer ratings.
5. Percent increase in load on each transformer when one transformer is removed.