Interview with Lester Geldenhuis, Chief Engineer at Eskom
With twenty years of experience in power transformers maintenance, operations and condition monitoring, I have spent a long time in the specification area and in the oil condition monitoring sector. For the last four years I have been serving as the chairman of the Eskom’s working group for operation and maintenance of transmission transformers.
This group focuses on the issues around transformers, tap-changers, bushings, and oil maintenance. We examine the oil condition and perform condition monitoring tests, based on which we look further at the performance of the asset and how to improve our maintenance to get extra out of transformers.
We perform condition monitoring in the transmission sector within Eskom on the equipment of 132 kV and above voltage levels. Eskom Transmission Group has about 570 transformers, between 5 MVA and 2000 MVA, installed in about 150 transformers. We had an older fleet, but applying our project replacement strategies, we managed to bring down the average age of our transformers from about 28-30 years to 26-27 years. When replacing older transformers, we look at parameters such as degree of polymerisation (DP), transformer performance, etc. The improved reliability on transformers came from a good condition-based maintenance program supported by an excellent transformer specification that was implemented in the early 2000.
Eskom’s transformer specification
In 2001-2002 we started a big drive to examine Eskom’s specification requirements for transformers and bring them up to better standards. A lot of issues were addressed during this process, and now that the company has introduced the new transformer specification we are seeing the benefits of that. We developed quality control as well as steps that we felt necessary, which include going to the manufacturer, doing the design reviews, and being involved in manufacturing.
Previously, we had a lot of issues with our transformers that followed from the shortcomings of the old specification, which didn’t include the ability of the design to take care of the faults we later found on our transformers. The failure rate for our transmission transformers used to be above 2 % but today we don’t see the failures that we saw in the past, which used to be related to the winding or the active parts. Today we see bushing failures and failures of old-type tap-changers, and this is what we are addressing through better maintenance.