Electrical Systems and Construction Level 4

EXEMPLAR-1-NC(V)2009

ELECTRICAL SYSTEMS AND CONSTRUCTION LEVEL 4

ELECTRICAL SYSTEMS AND CONSTRUCTION

NQF LEVEL 4

2009

(12041032)

(X-Paper)

09:00 – 12:00

EXEMPLAR

This question paper consists 5 of pages.

TIME: 3 HOURS
MARKS: 100
______

INSTRUCTIONS AND INFORMATION

1.
2.
3.
4. / Answer ALL the questions.
Read ALL the questions carefully.
Number the answers according to the numbering system used in this question paper.
Write neatly and legibly.

QUESTION 1: ELECTRICAL INFRASTRUCTURE

1.1 / Name FIVE component parts and equipment that are required to install medium voltage overhead networks. / (5)
1.2 / There are a variety of situations that may interfere with the normal operation of a power system.
State the predominant abnormal conditions on high voltage transmission lines and also state the causes. / (13)
1.3 / Name TWO categories of distribution networks. / (2)
[20]

QUESTION 2: DESIGN AND CONSTRUCT A THREE PHASE CIRCUIT

2.1 / Draw the IEC symbol of the following components:
2.1.1 / A contactor coil with one winding / (1)
2.1.2 / A normally closed contact / (1)
2.1.3 / A normally open contact delayed / (1)
2.1.4 / An overload relay, NC (normally closed) and NO (normally open) contacts / (1)
2.2 / Choose the correct word/words from within the brackets.
2.2.1 / A rotor of a three phase induction motor will rotate because of (a rotating magnetic field / laminations). / (1)
2.2.2 / On a direct-on-line circuit, to keep the coil energised, we use a (retaining contact / an overload relay). / (1)
2.2.3 / The motor can be stopped by means of a stop button which is connected in (series / parallel) with the start button. / (1)
2.2.4 / A coil rated at 220V will (energise / burn) when put through 380V. / (1)
2.3 / Design and wire a three phase motor circuit to meet the following requirements:
Push start button 'A'; the motor starts, in one direction.
Push stop button 'A'; the motor stops.
Push start button 'B'; the motor starts, in the other direction.
Push stop button 'A'; the motor stops. / (12)
[20]

QUESTION 3: CONSTRUCT A THREE-PHASE MEDIUM VOLTAGE OVERHEAD

SUPPLY TO DOMESTIC HOUSES

3.1 / Name the parts and equipment needed for pole line construction for an overhead system. / (5)
3.2 / When poles for constructing an overhead supply have to be erected, the distance between the poles is determined by certain factors.
Choose the correct word from COLUMN B to fill-in the missing word in COLUMN A in the table below.
COLUMN A / COLUMN B
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5 / The …of the pole.
The size and strength of the …
The difference in … of adjacent poles.
The … of the line and operating conditions.
The … in which the poles are used. / A
B
C
D
E
F / terrain
class and height
change in direction
conductors
grade elevation
size and strength
(5)
3.3 / When work has to be done on a three phase medium voltage overhead supply, certain worksite procedures should be adhered to. State these procedures. / (6)
3.4 / A three-phase medium overhead system is to be repaired. Before the job is begun you must visit the site to take notes of the physical surroundings.
Briefly describe what your notes will entail. / (4)
[20]

QUESTION 4:TEST AND INSPECT A THREE-PHASE INDUSTRIAL / COMMERCIAL

INSTALLATION

4.1 / Name FIVE instruments used for testing a three-phase installation. / (5)
4.2 / After the townhouse complex installation has been completed, inspections will be done to check fulfilment of installation requirements. State FIVE inspection requirements for the installation. / (5)
4.3 / Name the electrical tests that should be conducted on a new installation before power supply is connected. / (5)
4.4 / Draw a neat, labelled, sub-circuit diagram of a stove that is wired in three-phase. / (5)
[20]

QUESTION 5: FAULT FIND, REPAIR AND MAINTAIN THREE PHASE VOLTAGE

ELECTRIC CIRCUITS.

5.1 / A direct-on-line (D-O-L) three-phase motor circuit does not start after the 'start button' has been activated. How would you find the fault? / (10)
5.2 / You are called-out to repair a fault on a motor. How would you plan and prepare to repair the circuit? / (5)
5.3 / There are principles and procedures that must be followed when doing fault finding on a three-phase system.
Briefly explain the safety principles that are necessary for the above situation. / (5)
[20]
TOTAL: / 100