cameroon gce A level 2024 design of electrical installation 2
cameroon gce A level 2024 design of electrical installation 2
THEME: ELECTRICAL INSTALLATION OF NEWLY CREATED TECHNICAL SCHOOL
The technical school is made lip of two workshops and an administrative block equipped with equipment. I he
administrative block is made of five offices. The line diagram of the installation is shown in figure I .
A. Presentation of the installation
Load distribution
Location Loads
02 three–phase squirrel cage induction motor of 3kW each, coscp – 0.8, q = 0.88
02 single phase drilling machines of 1.5kW each, costp = 0.75, q = 0.75
04 three–phase welding machines of 4kW each, coscp = 0.8, q = 0.8
24 single sockets 2P+T, 220V, 16A
06 three phase sockets 3P+T, 380 V, 20 A
j • 01compressorsdrivingbyamotorabsorbs32kWeachandcoscp=0.8,q= 1
01 sander of 2kW, coscp = 0.8, q = 1
20 fluorescent lamps of 40W, coscp = 0.9, q = I
01 three–phase compressor of 15kW, coscp = 0.92, q = 0.9
10 twin tube fittings compensated DUO connection for 20 fluorescent tubes of 40W,
coscp = 0.9, q = 1 , the power consumed by each ballast is evaluated as 20% of the tube
Workshop 1
power.
04 three–phase welding machines of 4kW each, coscp = 0.8, q = 0.8
07 incandescent lamps of 75W each
03 three phase oven of 25kW each
16 single phase sockets (2P+T), 220V, 16A, coscp = 0.8
08 single phase sockets (3P+T), 380V, 32A, coscp = 0.8
Workshop 2
Each office has the following equipment:
02 fluorescent lamps of 40W each, coscp = 0.9, q = 1
01 fridge of 500W, coscp = 0.9, q = 1
01 air conditions of 1.5hp each, coscp = 0.8, q = 0.9
04 single phase sockets (2P+T), 220 V, 16 A, coscp = 0.8
02 incandescent lamp of 60W each
SECTION A: (COMPULSORY)
a) Determine the power demand by completing Appendix 1.
b) Considering the apparent power demand to be equal to 248kVA and by envisaging an extension of loads of 25%,
select using appendix 2 the characteristics of the transformer to be installed.
c) With the aid of appendix 3, determine the capacitance of the bank of capacitors to correct the power factor of
workshop 2 from 0.86 to 0.96 if the installed power is 146kW.
1 .
(30 marks)
(5 marks)
(5 marks)
SECTION B (OPTIONAL)
a) The cable from BB 1 to BB2 carries a current of 276A at a p.fof 0.85. This is made up of a PVC insulated copper
three–core cable which is installed touching 3 other multi–core cables on perforated trays in an ambient
temperature of 40°C. Using appendix 4, 5 and 6, determine the cross–sectional area of this cable. ^ (15 marks)
b) The cable from BB 1 to BB2 has a resistivity of 0.0225£lmm 2/m and linear reactance of 0.08* 10 T2/m. Calculate
the relative voltage drop if the length of the cable is 55m. 00 marks)
c) Using appendix 7, determine the short circuit current at the BB2 considering the upstream short circuit current of
9kA. (5 marks)
j.
a)
| Considering the current of 375A absorbs by the whole installation, with the aid of appendix 8, select the circuit | l. | |
| breaker CKM by completing table 3. | (5 marks) | |
| Using appendix 8, what is the overload protection threshold current of a Compact NSJ600 circuit breaker | u. | |
| equipped with trip unit STR23SP? | (5 marks) Breaking capacity |
Un(V) Number of poles |
| Circuit breaker | Reference | ln(A) |
CKM
Table 3
b) One of the 3kW three–phase squirrel cage induction motor in workshop 1 is replaced with a 7.5k W motor and the
starting method of this motor is direct–on–line. Using appendix 9 and 9, give the average full–load current of this
| motor and select the various components for the control and protection of the motor. | (10 marks) | |
| 4. | ||
| a) Using the data on the additional block, reproduce and complete table 4 by obtaining a balanced | ||
| installation. | ( 12 marks) | |
| Load | Phase 1 current (A) Phase 2 current (A) Phase 3 current ( A ) | |
| 3–phase compressor Single phase drilling machines |
0 | (8 marks) |
| 2 | . 2 | |
| Table 4 | ||
| b) I. |
||
| For each of the area of house, reproduce and complete table 5 |
Number of lighting
points
Type of
control
^Number of
socket outlets
Special
circuit
Area
Palour
Security
Table 5
By using PROMOTELEC Label (norm) N < 5, give the number of sub–circuits for lighting, socket
outlets and specialized circuits.
| (4 marks) (6 marks) |
iii. | # Draw the partition diagram indicating the cross–sectional area of each conductor and the range of each fuse used to protect the sub–circuits. |
