tw34 university of bolton school of engineering, …

TW34

UNIVERSITY OF BOLTON

SCHOOL OF ENGINEERING, SPORTS and SCIENCES

BENG (HONS) ELECTRICAL & ELECTRONICS ENGINEERING

EXAMINATION SEMESTER 1 - 2015/2016

INTERMEDIATE ELECTRICAL PRINCIPLES & ENABLING POWER ELECTRONICS

MODULE NO: EEE5003

Date: Tuesday 12 January 2016 Time: 10.00 – 12.00

INSTRUCTIONS TO CANDIDATES: There are five questions.

Answer ANY FOUR questions.

All questions carry equal marks.

Marks for parts of questions are shown in brackets.

Electronic calculators may be used provided that data and program storage memory is cleared prior to the examination.

CANDIDATES REQUIRE: Formula Sheet (attached).

of 12 School of Engineering BEng (Hons) Electrical & Electronics Engineering Examination Semester 1 - 2015/2016 Electrical Principles and Enabling Power Electronics Module No: EEE5003

Q1

a) An operational amplifier can be considered to have certain ideal characteristics which are used in the analysis of amplifier circuits containing such devices.

i) Describe the characteristics of an ideal operational amplifier.

(4 marks)

ii) Identify the key rules used when analysing operational amplifier circuits.

(4 marks)

b) One of the standard circuits for an operational amplifier is in the non-inverting mode.

i) Draw the circuit for an operational amplifier in non-inverting mode and derive from first principles an equation describing the operation of the circuit.

(10 marks)

ii) Design a non-inverting amplifier having a gain of 21. Use resistor values

between 1k Ohm and 100 k Ohm in your design.

(2 marks)

c) Define the term Common Mode Rejection Ratio (CMMR). (5 marks)

Total 25 marks

Please turn the page


Q2

a) State three advantages of the three-phase systems over single-phase systems for the transmission of power. (3 marks)

b) Use network conversion to find the equivalent or total resistance RT between a and d in a bridge circuit consisting of two deltas as shown in Figure 1. (5 marks)

Figure 1: Mesh network circuit

c) A balanced positive sequence Y-connected source with Van=10010 V is connected to a -connected balanced load (8+j4) per phase. Calculate the phase and line currents.

(8 marks)

Question 2 continued over the page

5 Ω

5 Ω 5 Ω

10 Ω 10 Ω

5 Ω


Question 2 continued

d) Figure 2 shows two balanced three phase loads are supplied by 1000 V rms, 60 Hz line. Load 1 is Y connected with 20+ j40 Ω per line. Load 2 is a three phase motor drawing 50 kW with a pf=0.75 lagging. (i) Calculate the total complex power of the combined load.

(6 marks)

(ii) Calculate the kVAR rating of the three Delta connected capacitors connected in parallel with the load to raise the pf to unity.

(3 marks)

(a) (b)

Figure 2: Three phase star-to-star (Y-Y) circuit

Total 25 marks



Q3.

a) Calculate vo and io in the operational amplifier circuit shown in Figure 3.

(5 marks)

Figure 3: Operational amplifier circuit

b) Determine the common-mode gain of an op amp that has a differential voltage

gain of 150 x 103 and a CMRR 0f 90 dB.

(5 marks)

c) As shown in Figure 4, determine the cut-off frequency of an op amp having a

unit gain frequency f1 = 10 MHz and voltage differential gain Gd = 20V/mV.

(5 marks)

Figure 4: Voltage gain verse frequency




d) Find the line currents and the real power absorbed by the load in the

unbalanced three-phase circuit as shown in Figure 5.

(10 marks)

Figure 5: Three-phase delta-to-delta unbalanced circuit.

Total 25 marks



Q4

a) Describe the construction of an SCR with sketch and explain the I-V

Characteristics.

(5 marks)

b) Draw a circuit diagram of Buck converter and explain the operation.

(10 marks)

c) What is the difference between analogue and digital PWM generator? Explain

with the help of circuit diagrams.

(5 marks)

d) Briefly explain the use of PWM technique in inverters and how duty cycle of a

PWM signal is calculated.

(5 marks)

Total 25 marks



Q5

a) Describe the three modes of the heat transfer from an electronic device.

(6 marks) b) Figure 6 shows a power transistor with a heat sink. By using this diagram,

draw a thermal equivalent circuit to describe the relationship between the transistor and heat sink.

(4 marks)

Figure 6: Power transistor with a heat sink

c) A To-220 package outline device is dissipating 10 watts (Q), the Tj=170oc and

Ta=60oC. θjc is found to be 4.0oC/W from the data sheet. Given that the Interface material is silicon grease has thickness of 0.005 inches, 0.40 in2 contact area and density of 205. Design a heat sink for this device.

(10 marks)

d) An inverted U tube manometer, as shown in Figure 7 below, contains oil with a

density of 800 kg/m3 above the pipe liquid which is water (1000 kg/m3). The

pipeline is horizontal; what is the difference in pressure, P2-P1 ?

(5 marks)


Heat Sink

Transistor



Figure 7: An inverted U tube manometer

Total 25 marks

END OF QUESTIONS



Formula sheet

These equations are given to save short‐term memorisation of details of derived equations and are given without any explanation or definition of symbols; the student is expected to know the meanings and usage.

Delta to Star conversion:

Star to Delta conversion:

Gravity:

9.81 m/s

Thermal resistance of the

interface material:

𝜃𝑐𝑠 =(𝜌)(𝑡)

𝐴

Compressibility relationship:

General manometer:


Venturi meter:

Force on a submerged wall:

Drag coefficient:

Flow through a small hole:

Flow through a rectangular slit:

Tank draining:

Flow over a rectangular weir:

Flow over a V‐notch weir:

Poisseuille’s Law:

Darcy’s Law:

tw34 university of bolton school of engineering, …

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