for INMR WEEKLY TECHNICAL REVIEW
(MEASURING ESDD AT REPRESENTATIVE SITES ALONG THE NETWORK)
Pollution flashovers, such as the massive ones that blacked out much of the Western Cape in 2000, have been recurring problems for South African power utility Eskom. Their strategy has therefore been to anticipate such events by constantly monitoring ESDD levels that affect insulators. This is done using a far-flung network of substations and other sites where directional dust deposit gauges (DDDG) as well as strings of reference glass insulators are installed. Apart from data collected using DDDGs at these locations, the second aspect of assessing ESDD involves taking readings of accumulated pollution on the surfaces of reference insulator strings composed of 7 standard glass shells. Each disc in the string is analyzed at different time intervals with the top and bottom units always functioning only as ‘dummies’.
A typical measurement begins with the metal cap of the disc wrapped with tape to prevent its deposited contamination from impacting the reading on the actual insulation surface. The glass is then washed thoroughly in a tub of de-mineralized water of constant one-liter volume before a meter reads conductivity of the resulting solution. Temperature of the water is also recorded to correct conductance values to a standard 20°C. Knowing the area of the glass disc (in this case 583.9 cm2
at the top and 704 cm2
at the bottom), associated ESDD values can be calculated for each. Readings are then averaged out and charted over time for every disc sampled from the string, along with information on precipitation collected from rainfall gauges, to allow a complete picture of the real pollution scenario.
ESDD readings for each disc typically vary by location in the string, with discs in certain positions more likely to accumulate pollution due to aerodynamic effects. All the data is then sent to Eskom’s planning department and to the individuals responsible for each substation as well as their supervisors, who can then take whatever remedial action may be required before
the onset of any problems.