WESTERN CAPE BRANCH ENGINEERING BULLETIN - 1999 EDITIONS

April 99

1. Survey and Evaluation of Harmonic current sources in terms of IEC 1000-3-2 (1995) - B Fourie & G Atkinson-Hope
2. OHSA - GSR's 6 - 9.
3. Flashover incident 66KV
4. Danger aloft - injury to workers hanging street banner
5. Examnation model answers: November 1992 Question 7(a)
   The illumination of a passage is provided by ceiling luminaires, 4 m above the floor, each with a uniform lighting intensity of 800cd, with a distance of 6m between units. The candidate is permitted to discount the light provided by any unit more than 6m from a point considered and is required to determine the lighting intensity at floor level,
   (i) immediately below any unit and
   (ii) halfway between any two units.
   

June 99

1. Examination modelanswers: Legal knowledge Nov 1995
   (a) At what intervals is a boiler required to be inspected and tested?
   (b) Define a ‘portable gas container’.
   (c) What particulars are required to be marked in the machine room or machine compartment of every lift, escalator and passenger conveyor?
   (d) Minimum effective open-floor area per employee in indoor workplace?
   (e) Maximum equivalent noise level?
   (f) Define ‘hearing protectors’.
   (g) What is the minimum permitted interval between impulses of a fence energiser?
2. Examination model answers: Plant Engineering Nov 1992
   A load of 50kN is raised vertically by means of a simple, single plain frame indicated in the figure. When raising the 50kN load vertically the tie bar of the frame has a factor of safety of 5. While raising a 50kN load the load is displaced laterally so that the hoisting rope is at an angle of 45° to the vertical. The candidate is to calculate the factor of safety of the tie bar of the frame while the 50kN load is laterally displaced, with the hoisting rope 45° to the vertical.
3. Fatal accident - harbour quay wall extension ....The driver expected the assistant to cross the rear of the truck........
   

August 99 

1. Examination model answers: Legal Knowledge - Nov 1997
   (a) Define ‘portable electric tool’.
   (b) The use of a portable electric tool of which the operating volts exceeds 50, shall not be permitted unless it is protected by one of four means. State the FOUR means mentioned in the regulations.
2. Examination answers: Plant engineering - June 1999.
   A 5km, three-phase transmission line delivers 5 MW at 11kV at a power factor of 0.85 lagging.
   Each conductor has a resistance of 0.6 ohm and a reactance of 0.4 ohm per km.
   Calculate:
   a) The voltage of the sending end
   b) The efficiency of the transmission line
   c) The percentage regulalation of the trans-mission line
3. Boiler failure: single corrugated flue tube had collapsed .....on shutdown...
4. Electrical cable protection: thermal stress a cable can withstand .............
   

October 99 

1. Awkward pressure vessels - testing....access not provided for.........
2. Worm screw conveyor accident.....climbed over and fell into the screw receiving fatal injuries..........
3. Examination model answers. Legal Knowledge - June 1995
   (a) Where an employer requires any person to enter any place from or into which solid or particulate material is being discharged and where a danger exists of a person being engulfed by such solid or particulate material , certain precautionary measures have to be taken. Name ALL these measures.
   (b) With regard to a structure being demolished, every employer who performs building work shall, with respect to such demolition, ensure that certain steps are taken. Name these steps.
   (c) A person working in an elevated position, may only do so from certain positions. Name these positions.
4. Examination answers. Plant Engineering - Nov 1997. Question 7 (c)
   A 100 kVA transformer supplied with 2.2 kV has a turns ratio of 400:80. Primary and secondary resistances are 0.3 ohm and 0.01 ohm respectively, and the corresponding leakage reactances are 1.1 ohm and 0.035 ohm respectively.
   Determine:
   The equivalent impedance referred to the primary circuit
   The voltage regulation and the secondary terminal voltage for full load having a power factor of 0.8 lagging and 0.8 leading.
5. Examination model answers. Plant Engineering - Nov 1996
   A torque of 10840 Nm is applied to the ends of a 4.3m long cylindrical shaft with an OD 127mm and ID 76.2mm. The modulus of rigidity of the shaft is 4.1x 104 Mpa. Determine the maximum shearing stress and the angle of twist of the shaft.
   

December 99