I remember reading a long article in the journal for the SAIMechE - the South African Institute of Mechanical Engineers - some time ago, probably in the 90s. There were trials to see how long a train could be on the Sishen line.
I forget how long the trains were - perhaps 3 miles long and the tests routinely resulted in broken couplings. I am not sure but I don't think they had distributed power (as in 27vet's video).
I often wished I kept that article. I did find this related to train lengths on the Richards Bay to Ermelo line :
http://www.railcorpstrat.com/Downloa...20SAIMECHE.pdf