Past Question Papers in Electrical Power Engineering

These Questions have been Obtained with the Express Permission of the Lecturer Teaching the Course

ENUGU STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ESUT

DEPARTMENT OF ELECTRICAL/ELECTRONICS ENGINEERING

SECOND SEMESTER EXAMINATION 2011/2012 SESSION            MASTERS CLASS

ELECTROMAGNETIC FIELD THEORY AND ELECTRICAL MACHINE DYNAMICS (EEE 770)

TIME: 1Hr 30Min (Answer All Questions)

NB: IF you have not done any continuous assessment, write down what you have learnt in about 120 words first.

BASIC CONCEPTS

Explain the characteristics and behavior of the Electrical Frequency on the Rotor of an induction motor. What are the main types of induction motors and how are they constructed? What is an Induction Motor? How does it Work? What is the difference between an induction motor and a synchronous machine? Explain the concept of slip. What is slip speed? How is torque developed in an induction motor? Compare the principle of operation of the transformer and the induction Motor. Explain the concept of rotating transformer. What happens as the induction motor approaches synchronous speed? What is the maximum possible speed of an induction Motor and why? Explain the Power flow in an induction motor. What is the efficiency of an induction motor? How does a thyristor work? What is Maxwell's equation? What is the relevance of Maxwell's equation in the study and investigation of fields and waves? Show that the continuity equation is imbedded in the Maxwell's equation. What is directional derivative? What is the curl? What is the gradient of a scalar function? What is the del? What is the divergence of a vector?

APPLICATION

You are responsible for setting up a new Vehicle assembly plant in Nigeria. What motors would you recommend for the various drives and why? How would you control the various drive systems and why? What kind of switches would you use and why? What would be the switching response of the entire assembly and why? What kind of load would this present to the Electrical Power System and how would you make provision for it? What are the applications of Power Electronics in Machine dynamics? Illustrate an induction motor equivalent circuit.

CALCULATIONS

A 200V 10hp four-pole 50Hz Y- connected induction motor has a full-load slip of 4 percent. Answer the following questions about this machine and explain your work:

a)      What is the synchronous speed of the motor?

b)      What is the rotor speed of the motor?

c)       What is the rotor frequency of this motor at the rated load?

d)      What is the shaft torque of the motor at the rated load?

A 450V 50hp three phase induction motor is drawing 50A at 0.8 p.f. lagging. The Stator copper losses are 1.82kW, and the rotor copper losses are 500W, the core losses are 1500W, and the stray losses are negligible. Find the following quantities and explain your work.  Explain in some considerable detail, how the induction motor converts Electrical energy to Mechanical energy. 

a)      The air-gap Power P(AG)

b)       The Power Converted P(conv)

c)       The output Power P(out)

d)      The efficiency of the motor