Electrical Machines and Transformers Using Ampere’s Law - Engineering Assignment Help

Assignment Task:

1. Using Ampere’s law and other electromagnetic relations, show that flux ∅ = ???????????????? ???????? , where N is number of turns of wire, I is the current flowing and R is the reluctance.

2. What assumptions are required to convert a real transformer into the ideal transformer? What does a large value of relative permeability ???????????????? implies?

3. A three legged magnetic structure made of material with ???????? = 3000????????0 is shown in Fig. 1. Winding of N turns is placed at the centre leg and an air gap of width ???????????????? is made in the right leg with the dimensions shown. Develop an equivalent electro-magnetic circuit and determine the flux shown in the figure. Fig. 1 10 Marks

4. What is the difference between torque-speed characteristic of dc series motor with dc shunt motor? Explain in terms of the implications on machine operation. Answer must be supported with proper circuit diagram and equations. 

5. Will the voltage build up in dc shunt generator if there is no residual flux in the machine and why? What will be the impact of decreasing the flux on the operation od dc shunt motor? 

6. Consider the equivalent circuit of DC machine in the figure below and the related equation of the torque of a DC machine. The parameters of the machine are V=200 V, Ra=1Ω, T=30 Nm, the flux constant ka? = 3. Now, answer the following: a) Derive an equation for the speed as function of the torque at a given magnetization (flux) and present it graphically. If the same DC machine is driving a torque of 30 Nm, which is the rated torque of the machine:

b) Calculate the speed. c) Calculate the armature current.

7. A 100-KVA, 8000/277-V distribution transformer has the following resistances and reactances: ???????????????? = 5 ? ???????????????? = 0.005? ???????????????? = 6 ? ???????????????? = 0.006? ???????????????? = 50 The excitation branch impedances as given are referred to the high-voltage side of the transformer. Find the equivalent circuit of this transformer referred to the low-voltage side. Also, calculate and draw the per-unit equivalent circuit of this transformer. 

8. A 25-kW, 125-V, separately-excited dc machine is operated at a constant speed of 3000 rpm with a constant field current such that the open-circuit armature voltage is 127 V. The armature resistance is 0.02 ?. Compute the armature current, terminal power, electromagnetic power and torque when the terminal voltage is (a) 128 V and 124 V. Support your calculations with proper circuit diagrams.

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