021-951-2316 info@powertx.co.za

Buying medium voltage equipment is expensive, with units costing up into the hundreds of thousands of rand’s.  Maintenance on your transformers, switchgear and miniature substations is essential, a lot like the servicing of your car.

A basic annual inspection and oil sampling will cost the customer (depending on the number of equipment items to be done) a few thousand rand at most, whereas a critical failure can cost hundreds of thousands of rand’s money-wise, but could lead to many more times that cost, in downtime, property damage and even, heaven forbid, injuries or loss of life.  As with life, failure to attend to the small problems leads to them becoming bigger, critical problems.

The initial assessment and inspection, done by our friendly, experienced and trained technical team, is much like an annual visit to your GP, except we come to your site.  The team will come through, do a visual inspection and take photographs of your equipment in order to note any faults, such as oil leaks, a low oil level, evidence of rusting and general condition and safety around your equipment.  After this, they will take a sample of the mineral insulating transformer oil, which will be sent to an independent, SABS, SANAS and ISO accredited laboratory for the necessary oil analysis tests.

A fire at a substation in Eikenhof on August 27, 2018 has led to a power outage in parts of Johannesburg.
Image: Twitter/@Rand_Water

These tests are the most fundamental part of the inspection, as their results will give a clear indication of the internal workings of the transformer and give an idea of any possible problems which may need resolving.  There are a plethora of tests which can be performed on the oil, however, we will only be concentrating on the essential ones.  One should bear in mind that while each test shows a specific result, the actual condition of your equipment is shown by taking all the individual results and using the information to come to a holistic view.

The tests are:

Moisture content:

Oil and water doesn’t work well and neither does water and electricity.  The three combined reduce the lifespan of your equipment and leads to a host of other problems. This test shows the amount of water (measured in parts per million, or ‘p.p.m’) in the oil.  If it’s above the prescribed minimum, oil filtration would be needed to remove it from the system.


Dielectric strength:

90% of transformers in the South African market use mineral insulating oil.  The purpose of the oil is to prevent arcing between the 3 phases of the core and windings of the transformer.  Without proper maintenance, the dielectric strength or the amount of volts the oil can withstand, steadily decreases. This test shows the kV (kilo volt) resistance strength of the oil in the equipment. If its’s too low, corrective action in the form of oil filtration would be needed.

Acidity content:

Nobody would want acid poured on their arm, right? As the oil in a transformer ages (and especially if routine maintenance is not done) it degrades.  This degradation, combined with the moisture in the oil and the deterioration of the cellulose insulating paper, creates a chemical reaction which leads to the formation of organic and inorganic acids.  Seeing as these acids would then start breaking down the copper, steel and cellulose paper of the internal workings of your transformer, this is obviously not a good thing. If the acid result is above the maximum recommended level, an oil change would be needed.


Dissolved gas analysis:

This is one of the most critical analysis tests available.  As transformers work, combustible gasses like hydrogen, acetylene, ethylene methane and ethane build up in the oil, the levels of which show if your transformer is having problems.  Problems like arcing, corona, overheating and overloading.  As with general analysis as mentioned earlier, the individual results are informative, but it’s the broad picture that really shows what’s going on.  Different combinations of gasses at different results will indicate different specific problems in the unit, which would mean the transformer would need to be opened up and inspected to find the root cause of the problem.

Furanic analysis:

A.K.A Nothing lasts forever. While transformers do have a long lifespan (we have come across units from the 1950’s that are still in working condition) all things come to an end. The paper used in the manufacturing process of the core and windings of transformers, known in the trade as Kraft paper, gradually degrades over time. The molecules of paper in the oil can be counted using specialised equipment, and the result indicates the expected remaining lifespan of the equipment, allowing the client to budget for a new unit and preventing unwanted downtime and costs.


At Power Transformers, customer service is our highest priority. We have a dedicated support and servicing team available. We offer full service contracts as well as fast ad-hoc response to any short term or emergency needs.

Please contact us regards your medium voltage maintenance needs.