(1) A Your Line manager has asked you to investigate the following aspects of Power Distribution System

a) Explain the difference between a balanced polyphase system and unbalanced polyphase system. What conditions typically cause a polyphase system to become unbalanced?

b) Explain the difference between three and four wire three phase distribution systems identifying the difference between balanced star and delta connections

c) Calculate all voltages, currents, and total power in the following balanced three phase system:

(a) Balanced Delta-Delta System:

(b) balanced Y-Y system:

(c) balanced Y-Delta system:

(2) (Distinction) Identify the different voltages obtained from this coil configuration, and which connection points each voltage is measured between

(3) Discuss the difference between real and reactive power flows in distribution systems and the methods used to limit the reactive power loads in distribution systems.

a) Identify how real reactive power is measured in Power Transmission and Distribution Systems.

b) (Merit) A 20Kw electric motor Connected to 240V, 50Hz single phase AC supply takes 100Amp determine the reactive power of the load and the size of capacitor required to reduce the reactive power to zero

c) Investigate what will happen in each of these systems to the phase voltages of the load, if one of the source phases fails open?

(4) Discuss the operation of 3 phase induction motors clearly identifying the following.

a) What is meant by the synchronous speed of the induction motor?

b) What is meant the slip speed of the induction motor?

c) The methods used to start induction motors

d) The torque speed characteristics of induction motor

e) What is meant by dynamic stability?

TASK 2

Harmonics in Power Systems

(5) Harmonics are multiples of the fundamental frequency you have been asked to investigate

(a) Demonstrate how distort the supply wave form

(b) Illustrate how harmonic components adversely the RMS value of distorted wave form

(c) How harmonics effect quality of supply in distribution systems

(d) Sources of harmonics in distribution systems

(6) Discuss the methods to suppress harmonics in three phase system the following

(a) What is meant by K factor and how relates to transformers

(b) How reactors can be used to reduce harmonics in 3 phase motor drives and UPS devices

(c) How 3 phase passive and active filters may be used to reduce harmonics

(d) (Merit) One of the conductors connecting the secondary of a three-phase power distribution transformer to a large office building fails open. Upon inspection, the source of the failure is obvious: the wire overheated at a point of contact with a terminal block, until it physically separated from the terminal.

What is strange, though, is that the overheated wire is the neutral conductor, not any one of the "line" conductors. Based on this observation, what do you think caused the failure? After repairing the wire, what would you do to verify the cause of the failure?

(7) (Distinction) A periodic, sinusoidal voltage of instantaneous value is applied to a nonlinear load, and the resulting instantaneous current is given by

Calculate-

a) The P,Q,D components of the apparent Volt-amperes

b) The displacement factor

c) The distortion factor

d) The power factor

TASK 3

Understand methods of power distribution

Your line manager has asked you to report on the topological arrangement of power distribution systems. Your report should include a discussion of the following:

(a) The effect of load density on the design topology of 11KV High Voltage and 415v supply systems including a discussion on the importance and methods of earthing both Urban and rural distribution networks (L3.a)

(b) A discussion on how the topological layout of distribution interacts with security of supply constrains (L3.b)

(c) A discussion of the voltage regulation requirements of power distribution systems along with the use of transformer tap changers (M2)

(d) The importance of the short circuit ratings of switch gear on the design of distribution substations and power distribution networks, along with its effects on Safety, Voltage Regulation and protection (L3c)

(e) A general discussion on the protection devices used for both HV and L V distribution systems and how the topological design and fault level effects the types of protection used on power distribution systems. (M2)

(f) The Figure below shows the layout of a proposed substation calculate

(a) The short circuit MVA on the Low voltage side of the transformer.

(b) The short circuit rating of the switchgear on Low Voltage side of the transformer.

(c) In order to improve the reliability of the systems it is proposed that second identical transformer be installed how does this affect the short circuit rating of the LV switch gear (d1)

TASK 4

Understand the economics of components, power systems and alternative energy

The company has been asked to provide a report on the economics of power distribution systems and your line manager has asked you to prepare a report on the following:

(1) The economics of power distribution and how the following influence the cost of power distribution.

(a) Why 3 phase supplies are preferred for large customers along with a discussion of the advantages of three phase systems over single phase systems.

(b) Load factor and how it affects the economics of power distribution

(c) A discussion of the use High and low efficiency along with the need for power factor correction equipment

(d) The use of power factor correction equipment in small industrial applications to reduce the Mvar requirements.

(e) The efficiency saving achieved by using fluorescent compact lighting

(2) In order to reduce his load the customer has asked you to investigate the use of embedded generation and its effect on the costs of supply and the implications for the power distribution system note your report should include a description of the various alternative energy sources (i.e. wind, solar, small hydro generation etc.).

(3) The customer has also requested a report on the operation of power systems along with a discussion of both the capital and operating costs and how the use of pump storage equipment can be used to reduce the overall running costs of the system.