ELECTRICAL DRAFTING AND DESIGN – PAST QUESTIONS & ANSWERS (HND 2)

This Article shows Past Questions and Answer workings in Electrical Drafting and Design for Higher National Diploma (HND) Students of Electrical/ Electronics Engineering Auchi Polytechnic, Auchi.

This Past Questions and Answers is helpful to all students in the Department of Electrical/ Electronics Engineering offering this general course; Electrical Drafting and Design (EEP 438). For those currently writing their on going exams in Electrical Engineering HND 2 Power Option. This is the past questions and answers for you to study.

N.B – These questions and answers are uploaded only as a guide and ease for your studies.

Below are the Questions:

AUCHI POLYTECHNIC, AUCHI

SCHOOL OF ENGINEERING TECHNOLOGY

DEPARTMENT OF ELECTRICAL/ ELECTRONICS ENGINEERING

FIRST SEMESTER EXAMINATION 2023/2024 SESSION

COURSE: ELECTRICAL DESIGN AND DRAFTING II

COURSE CODE: EEP 438 

CLASS: HNDII

EXAMINER NAME: ENGR F. IZUAGIE

INSTRUCTION: ANSWER ANY FOUR (4) QUESTIONS

TIME: 2 HOURS

QUESTION 1

(a) Describe a ladder diagram and state three (3) application scenario of a ladder diagram.

b) Draw a simple ladder diagram and explain why a ladder diagram is used for programmable logic controller programming (plc)

c). Draft at least five (5) symbols used in ladder diagrams and identify them.

QUESTION 2

(a) (i) Explain the NSE cap regulation

(ii) State the IEE regulations and state three standard factors considered in the design and manufacture of switchgears

(b) A 1.5mn twin and earth P.C.V sheathed copper cable is used to feed a 240v, 3kw heater. The length of run from the supply to the heater is 25metres and the resistivity of copper is 0.0172 uΩm what is the volt drop in the circuit conductors and what is the power dissipated in the heater.  

QUESTION 3

(a) Describe the following electrical devices:

(i) Switch board, (ii) Switch gear (iii) Busbars

b. State three (3) advantages of electrical symbols

C. State the three(3) methods of starting an electric motor

d. State three criteria used in classifying a circuit breaker

QUESTION 4

(a) Describe an electric power substation and state its purpose

ii) State two (2) factors to be considered while determining a substation location

(b) Four zones below planning electrification of its area represented as A,B,C,D which are approximately located at the four points assume that the area can be divided into corners of a rectangle as shown in the figure below

For supplying the area, it is proposed to locate a high voltage substation operating at 132kV. Determine a suitable location for this substation.

QUESTION 5

(a) Explain the following

i. Unit rate

ii. Cost on site

iii. Cost of installation

(b) Explain the various steps taken for preparing estimate for electrical projects

(c) Diagrammatically show a simple table of bill of quantities that covers an electrical project.

QUESTION 6

(a) Explain the uses of the following

i. Site diary

ii. Accident book; show a sample of an accident book format

(b) State four (4) electrical safety requirements when carrying out electrical installation

(c) State three (3) protective safeguarding methods against direct contact with live during electrical insulation

(d) State three (3) ways in which fire outbreak can be prevented or avoided in electrical installation.

Study the Answers Available!

ANSWER 1

(a) Ladder diagram definition and it’s application scenario.

A ladder diagram, also known as a ladder logic diagram, is a graphical representation of a control system or electrical circuit using standard symbols and notation.

Ladder Diagram Application Scenario

I. Design

II. Programming

III. Operation

IV. Maintenance

b) Draw a simple ladder diagram and explain why a ladder diagram is used for programmable logic controller programming (plc)

c). Draft at least five (5) symbols used in ladder diagrams and identify them.

ANSWER 2

(a) (i) Explaining the NSE cap regulation

The NSE cap regulation is a regulation in Nigeria set by the Nigeria society of engineers which provide guidelines for the electrical engineering practice including design, installation and maintenance of electrical system.

(ii) The IEE regulations and it three standard factors considered in the design and manufacture of switchgears.

IEE regulations refer to the guidelines and standards set by the Institution of Electrical Engineers for electrical installations and equipment. The IEE regulation requires that where an item of switcher is required by the regulation to disconnect all live conductors of a circuit, it shall be of a type such that the neutral conductor cannot be disconnected before the phase conductors and is reconnected at the same time as all before the phase conductors.

I. Breaking capacity

II. Type of enclosure.

III. Ambient temperature

IV. Type of monitoring and fixing

(b) A 1.5mn twin and earth P.C.V sheathed copper cable is uscd to feed a 240v, 3kw heater. The length of run from the supply to the heater is 25metres and the resistivity of copper is 0.0172 uΩm what is the volt drop in the circuit conductors and what is the power dissipated in the heater.  

Solution
Since R = pL/a
(0.0172) x (25.2) x 10-⁶ / 1.5 X106 Ω = 0.573Ω
R= 0.5732Ω
This is the total resistance of the circuit conductor. The resistance of the immersion heater to provide lull operation is:
(P= I²R = V²/R) R = V² / P = 240² / 3000 = 19.2Ω
The current taken from the supply by the circuit
I = V/R = 240 / 19.773 = 12.14 A
The volt drops in the cables feeding the heater is V = IR
= 12.14 x 0.573 = 6.96V
Terminal voltage at the heater is: Supply Voltage – Volt drop = 240V – 6.96V = 233.04V
The power dissIpated by the heater is I²R = 12.14² x 19.2 = 2839.68W
The Regulation state that the volt drop in the length of cable should not exceed 2.5% of the nominal voltage when the conductor is carrying a full load current, disregarding staring current.

ANSWER 3

(a) Describing the following electrical devices

(i) Switchboard: A switchboard is a electrical panel that houses electrical switches, circuit breakers, and fuses to control and distribute electrical power to various circuits in a building or installation. It is essentially a central hub that connects and manages electrical power distribution, allowing for safe and efficient control of electrical circuits.

(ii) Switchgear: Switchgear refers to a collection of electrical devices that are used to control, protect, and isolate electrical circuits. It includes devices such as circuit breakers, switches, fuses, and transformers, which are used to manage electrical power distribution and protection. Switchgears are typically used in high-voltage applications.

(iii) Busbars: Busbars are electrical conductors that serve as a common connection point for multiple electrical circuits. They are typically made of copper or aluminum and are used to distribute electrical power to various parts of a switchboard, switchgear, or electrical panel. Busbars are designed to carry large currents and are often used in high-voltage applications.

b. Three (3) advantages of electrical symbols 

I. It is ease to understand

II. It can be represented in symbols

III. Electrical symbols enable quick and efficient communication among electrical professionals, IV. It saves time and reduces errors

C. Three (3) methods of starting an electric motor

I. Direct-On-Line (DOL) Starting

II. Star-Delta Starting

III. Liquid Rotor Starter (LRS)

d. Three criteria used in classifying a circuit breaker 

I. Arc extinguishing medium

II. Operating mechanism

III. Installation location

ANSWER 4

(a) An electric power substation and its purpose

An electric power substation is a facility that plays a crucial role in the transmission and distribution of electrical energy. It is essentially a collection of electrical equipment and structures that work together to achieve distinct functions.

ii) Two (2) factors to be considered while determining a substation location

— Closeness to Load centre

— Availability of Suitable Land

— Proximity to Road

— Environmental factor

(b) Four zones below planning electrification of its area represented as A,B,C,D which are approximately located at the four points assume that the area can be divided into corners of a rectangle as shown in the figure below

For supplying the area, it is proposed to locate a high voltage substation operating at 132kV. Determine a suitable location for this substation.

Solution
Total load ill zone A
5000 + 2000 + 500 + 400 + 200 = 8100KW
Total Load in zone B
500 + 200 + 500 + 2000 + 15000 = 18200KW
Total Load in zone C
2000+ 500 + 200 + 100 + 5000 = 7800KW
Total Load in zone D
1000 + 100 + 100 + 200 = 1400KW
Let the total load be PKW
8100 + 18200 + 7800 + 1400 = 35500KW
Location of Substation: Since in the problem no restrictive is mentioned about the location and direction of the incoming line, so it is presumed that the location of substation obtained from the center of gravity load point of View is quite feasible. So take moments about YOX.

Px = 18200 x 6 + 7800 x 6 – 8100 × 6 – 1400 x 6
X = 6(18200 + 7800 – 8100 – 1400) / 35,500 = 2.788km

Similarly,
Y = 1.75 (17100)/35500 = 29925 = 0.843km
So the location is in S
X = 2.788km
Y= 0.843km
From the calculation above the best location is S near B zone.

ANSWER 5

(a) Explaining the following:

i. Unit Rate: The unit rate refers to the cost of electricity per unit (kWh) consumed by a customer. It is the rate at which a customer is charged for their electricity usage, usually measured in cents or dollars per kilowatt-hour (kWh).

ii. Cost on Site: Cost on site refers to the cost of delivering electricity to a specific location, including the cost of transmission, distribution, and delivery infrastructure.

iii. Cost of Installation: The cost of installation refers to the expenses incurred when setting up a new electrical connection or upgrading an existing one.

(b) Explaining the various steps taken for preparing estimate for electrical projects.

I. Project Scope Definition: Clearly define the project’s scope, including the specific electrical work to be done, materials required, and any special requirements or regulations.

II. Site Visit and Inspection: Conduct a site visit to gather information about the existing electrical infrastructure, identify potential challenges, and determine the feasibility of the project.

III. Quantification of Materials: Estimate the quantities of materials required, including cables, conduits, switches, outlets, and other electrical components.

IV. Labor Estimation: Estimate the labor hours required for each task, considering factors like complexity, skill level, and productivity.

V. Material and Labor Cost Estimation: Determine the costs of materials and labor based on market rates, vendor quotes, or historical data.

(c) Diagrammatically show a simple table of bill of quantities that covers an electrical project.

ANSWER 6

(a) Explaining the uses of the following

i. Site Diary: A site diary is a daily record of events, activities, and observations on a construction or project site. It serves as a historical record of the project’s progress, issues, and decisions.

ii. Accident Book: An accident book is a formal record of workplace accidents, incidents, or near misses. It helps monitor and manage workplace safety, identify trends, and implement preventive measures.

(b) Four (4) electrical safety requirements when carrying out electrical installation

I. Only authorized and trained electricians with the necessary qualifications and experience should perform electrical installations.

II. Ensure you use the right equipment and tools for the right job

III. Conduct regular inspections and testing of electrical installations.

IV. Ensure electrical circuits are safely isolated before starting work, to prevent electrical shock or injury.

(c) Three (3) protective safeguarding methods against direct contact with live during electrical insulation

I. Use appropriate PPE such as insulating gloves, sleeves, and masks to prevent direct contact with live parts.

II. Use insulated tools and equipment.

III. Avoid working on unsafe conditions i.e working in a wet environment

(d) Three (3) ways in which fire outbreak can be prevented or avoided in electrical installation. 

I. Ensure that electrical installations are designed and installed by qualified professionals, following relevant codes and standards (e.g., NEC, IEEE).

II. Perform maintenance tasks, such as cleaning, tightening connections, and replacing worn or damaged components, to prevent electrical faults that can lead to fires.

III. Overcurrent Protection: Install overcurrent protection devices (OCPDs), such as fuses or circuit breakers, to detect and interrupt excessive currents that can cause electrical fires.