ENG009 UNIVERSITY OF BOLTON SCHOOL OF … · intermediate electrical principles & enabling power electronics module no: eee5003 date: 15 january 2018 time: 10.00 – 12.00

ENG009

UNIVERSITY OF BOLTON

SCHOOL OF ENGINEERING

BENG (HONS) ELECTRICAL & ELECTRONICS ENGINEERING

EXAMINATION SEMESTER 1 - 2017/2018

INTERMEDIATE ELECTRICAL PRINCIPLES & ENABLING POWER ELECTRONICS

MODULE NO: EEE5003

Date: 15 January 2018 Time: 10.00 – 12.00

INSTRUCTIONS TO CANDIDATES: There are six 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).

Page 2 of 13 UNIVERSITY OF BOLTON ENGINEERING, SPORTS AND SCIENCE ACADEMIC GROUP B.ENG (HONS) ELECTRICAL & ELECTRONICS ENGINEERING EXAMINATION SEMESTER 1 - 2017/2018 INTERMEDIATE ELECTRICAL PRINCIPLES & ENABLING POWER ELECTRONICS MODULE NO. EEE5003

Q1.

a) Explain the implementation of a unity gain buffer amplifier with the aid of a circuit

diagram.

(8 marks) b) Determine the output voltage of a differentiator circuit as shown in Fig.1. Assume

that the input voltage v1=3.5 cos (100 π t) volt and the time constant RC = 1.5 ms.

(5 marks)

Fig.1: A differentiator circuit

c) Find voltage gain Av=Vo/Vin and input impedance of the Operational amplifier circuit shown in Fig.2.

i. with the switch open

(6 marks)

ii. with the switch closed (6 marks)

Fig.2: An Operational amplifier circuit

Total 25 marks Please turn the page


Q2.

(a) A half-wave single-phase rectifier circuit is shown in Fig. 3 below. The following

are given:

Vs=230 V , f=50 Hz, diode forward voltage drop is assumed to be zero.

Determine:

i. The load mean voltage and current

(8 marks)

ii. The load current ac component and shape for

(7 marks)

1. A pure resistive load of 8 Ω resistor and

2. An inductive load of 0.1 H inductance in series with the 8 Ω resistor

Fig. 3: A half-wave rectifier circuit

(b) In the three-phase inverter shown in Fig.4 below, the following are given:

Line-to-line voltage=450 V, f=50 Hz, E=540 V, LS=0.6 mH. Ld is assumed very

large to produce id(t)=Id.

Calculate the angles:

i. 𝛼

(5 marks)

ii. 𝛾 if the power flow is 54 kW.

(5 marks)

Question 2 continues over the page

Please turn the page


Question 2 continued

Fig.4 A three phase inverter circuit

Total 25 marks

Q3.

(a) Draw a circuit diagram for a buck converter and derive an expression for 𝑉𝑜𝑢𝑡

𝑉𝑖𝑛 defining all parameters used in this circuit.

(10 marks)

(b) For a single-phase inductive load (with parallel resistance and inductance).

i. Prove that the active power is always positive, has an average value

of 𝑉.𝐼

2 𝑐𝑜𝑠𝜃 and zero average reactive power both pulsating at double

supply frequency (2𝜔𝑡) where V and I are the peak values of the

voltage and current and 𝜃 is the power factor angle of the load.

(10 marks)

ii. Draw the relevant waveforms for 𝑣, 𝑖, 𝑎𝑛𝑑 𝑝

(5 marks)

Total 25 marks



Q4.

(a) A balanced positive sequence Y-connected source with Van=18020 V is

connected to a -connected balanced load (12+j8) per phase. Calculate :

i. The load phase currents.

(7 marks)

ii. The load line currents

(5 marks)

(b) A 3-phase motor draws 20 kVA at 0.707 power factor lagging from a 380 V.,

50 Hz source. Determine:

i. The kilovolt-ampere rating of capacitors to make the combined power

factor 0.95 lagging

(5 marks)

ii. The line currents before and after the capacitors are added.

(4 marks)

iii. The capacitance value in Farads if they are connected in delta

configuration

(4 marks)

Assuming that the voltage and active power remain constant.

Total 25 marks



Q5

The datasheet of the BJT Transistor TIP2955/3055 was provided:

(a) Find the absolute maximum power rating for the given TIP2955 NPN Power transistor

(5 marks)

(b) What is the maximum power that can be dissipated without a heat sink at

ambient temperatures of +25 oC and +50 oC ?

(5 marks)

(c) Determine the junction and case temperature if the transistor dissipates 2W at an ambient temperature of 35oC. Assume that no heat sink is used.

(5 marks)

(d) Assuming that this transistor dissipates a continuous power of 20W is mounted on a heat sink with a 3 mil mica insulator with heat sink compound, where the insulator thermal resistance (θcs) is 0.36oC/W. Determine the maximum heat sink thermal resistance required if we want to keep the junction temperature at least 60°C below its absolute maximum (to extend its lifespan) and also to keep the heat sink temperature below 70 °C. Assume that the ambient temperature varies from +15°C to +40 °C and natural convection.

(10 marks)

Total 25 marks



Q6

(a) A venturi meter uses a mercury filled manometer to measure pressure

difference. Air is flowing in the main pipe, and the diameter reduces

from 25mm to 20mm. At a certain flow rate a height difference of 46mm is

measured between the two sides of the manometer. Calculate the flow

velocity in the 25mm pipe, the volumetric flow and the mass flow rate.

Given that density for the mercury is 13600 kg/m3 and air is 1.225 kg/m3 .

i. Calculate the flow velocity in the 25 mm pipe.

(7 marks)

ii. Determine the volumetric flow

(4 marks)

iii. Find the mass flow rate

(4 marks)

(b) Explain:

i. Explain the Archimedes’ principle

(4 marks)

ii. An unloaded pontoon weights 200,000N. It has a plan area of 12m long and

7m wide. It floats in sea water with a density of 1025 kg/m3.

What is the depth of immersion?

(6 marks)

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.

Converters:

𝑉𝑑 = 1.35 𝑉𝐿𝐿𝑐𝑜𝑠𝛼 − 3𝜔𝐿𝑠

𝜋𝐼𝑑

cos(𝛼 + 𝑢) = 𝑐𝑜𝑠 𝛼 − 2𝜔𝐿𝑠

√2𝑉𝐿𝐿 𝐼𝑑


𝛾 = 180 − (𝛼 + 𝑢)

𝑉𝑝ℎ =𝑉

√3 , 𝐼𝑝ℎ = 𝐼 𝑓𝑜𝑟 𝑠𝑡𝑎𝑟 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑖𝑜𝑛, 𝑉𝑝ℎ = 𝑉, 𝐼𝑝ℎ =

𝐼

√3 𝑓𝑜𝑟 𝑑𝑒𝑙𝑡𝑎 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑖𝑜𝑛

𝑆 = √3𝑉𝐼 𝑉. 𝐴, 𝑃 = √3𝑉𝐼𝑐𝑜𝑠𝜃 𝑊. , 𝑄 = √3𝑉𝐼𝑠𝑖𝑛𝜃 𝑉. 𝐴. 𝑟

𝑄𝐶 = √3𝑉𝐼𝐶 𝑉. 𝐴. 𝑟, 𝑋𝐶 =𝑉

√3𝐼𝐶 Ω


Three-phase systems

Delta to Star conversion:

Star to Delta conversion:

Gravity:

9.81 m/s

Thermal resistance of the

interface material:

Output voltage of a differentiator circuit:

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:



Datasheet

Documents

ENG009 UNIVERSITY OF BOLTON SCHOOL OF … · intermediate electrical principles & enabling power electronics module no: eee5003 date: 15 january 2018 time: 10.00 – 12.00