HomeRegional NewsAfricaTips on best practices: oil-cooled transformer maintenance

Tips on best practices: oil-cooled transformer maintenance

Don’t be fooled into complacency by reported lifespan expectancies of over 30 decades for your transformer assets – to reach this impressive age, a maintenance regime supported by best practices being upheld is instrumental for transformer asset management and cannot be considered as an optional extra.

Switchgear protection panels in process of on-site evaluation.

In the current dynamic power market, where advances in technology are disrupting how energy is supplied and consumed, oil-cooled transformers remain a steadfast, critical and expensive asset. Based on this standpoint it is important to increase the operational lifespan of these assets.

This article first appeared in ESI Africa Edition 3, 2018. You can read the full digital magazine online or subscribe to receive a print copy.

Considering that transformer assets convert incoming power to suit your plant’s power consumption ratings it is sensible to maintain these assets to ensure that production is kept in a safe and continuously operational condition.

Operational oil-cooled transformers in all types of applications the world over are in various stages of their lifespan, which may range from 1 to 30 years and older.

However, where oil-cooled transformers have not exceeded, or come near to, the 30-year mark the following reasons have been found to stunt operational performance and lifespan:

  1. Budget constraints on maintenance and spare part spend;
  2. Conducting reactive and unplanned maintenance on assets (this can result in occurrences such as the breakdown of rewinding due to not having critical spares on site);
  3. Failure to implement preventative and planned maintenance programmes, which is far from ideal; and
  4. Purchase of refurbished transformers, which have been recycled a few times at escalated prices due to high demand from power consumers. This compounds the negative results of a reactive and unplanned maintenance situation – a very bad situation to be in.

These circumstances often result in the interruption of power to your plantor equipment, which means loss of production and, in turn, equates to loss of revenue and a serious knock to the return on investment of your assets!

Transforming your return on investment

The first call to action is for oil-cooled transformer owners and end-users to initiate and implement regular and cost-effective preventative failure and planned maintenance systems.

The importance of implementing a maintenance strategy cannot be over emphasised; anything else is simply not acceptable in today’s fast-paced and competitive environment.

Considerable information on suppliers, systems, procedures and more for transformer maintenance exists in various forms; however, having expert guidance is the most beneficial.

Based on ArmCoil’s years of hands-on experience in the industry and knowledge of available technology – including the market segment that the company successfully operates in – the simplest, most proven method of maintaining transformers will be briefly summarised in this editorial.

The ideal starting point for the maintenance of oil-cooled transformers – or any piece of equipment – is to have a recorded history, or baseline in the absence of historical information, of the asset to work from. Armed with this information, the asset’s condition can be accurately measured on a regular or yearly basis.

Another factor to consider (where possible) is to not switch from one supplier to another when budget constraints occur or procurement policies are amended.

Rather negotiate fixed rates with your supplier for a three-year maintenance contract thereby ensuring regular and continuous quality and consistency of the maintenance regime that is in line with your unique requirements.

To provide a high level of service, it is advisable to procure from ISO accredited companies that are familiar with the importance of quality, traceability and related high standard of working methods.

Alluding to the ideal starting point, best practice calls for the ‘as is’ condition of assets to be determined. This is achieved for operational oil-cooled transformers by conducting on-site oil sampling, thermal imagery, testing and visual inspections.

These samples, imagery, testing and visual inspections should be sent to you in a report format detailing all tests conducted along with the results. The report should also advise on any discrepancies identified and put forward suggestions to remedy the faults found.

There are eight specific areas, which are outlined here, to achieve the best onsite transformer evaluation. However, be aware that there is a specified method for taking oil samples and the containers used – contact either Eskom or the SABS to obtain the specification reference and ask your contractor for their procedure so that you may have confidence that oil samples are taken in the correct manner and weather conditions.

  1. DGA testing (dissolved gas analysis)

In the event of very light arcing/ flashing between connections gases are emitted, which accumulate within the transformer tank.

  1. Moisture content

This test measures the moisture content of the transformer.

  1. Furanic testing (winding insulation test)

This test measures the insulation around the electric conductors, mainly for the active coils/windings.

  1. Corrosive sulphur tests

In this test, the corroding of material inside the transformer due to corrosive reactions from ambient or high operating temperatures is measured. The test analyses the corrosive deterioration on all copper, steel, insulation and other materials.

  1. PCB test

It is important to trace the presence of any polychlorinated biphenyls (PCB), which are prohibited from use due to environmental and human safety issues.

  1. Thermal imagery

Used to identify hot and cold spots around the transformer, this test is also useful for checking that the cooling radiators are not blocked due to sludge build up. Note that a variety of equipment is available to conduct thermal imagery.

  1. Auxiliary equipment testing

This is to test the functionality of all the auxiliary parts including Buccholz relay, winding temperature indicators, pressure relieve valves, on- and offload tap changers, all types of breakers and the transformer’s parts’ list.

  1. Visual inspection

This is used as an opportunity to take photographs of the unit being evaluated and to note visual faults identified such as rust, leaks, loose cables, condition of paint, leaking valves, plinth condition, and the presence of pests. It is important to keep this visual representation for historical purposes.

Word of advice

These eight tests for on-site inspection are only a guideline of what can take place to maintain your transformers. The evaluations change from 11kV, 22kV, 33kV, 66kV, 88kV, 132kV and upwards as they naturally vary depending on the size of the transformer involved.

Therefore, it is important for the owner or end-user to detail what is required before the evaluation is conducted. Reputable contractors such as ArmCoil are willing to assist in creating specifications for client approval prior to any on-site inspection. ESI

This article first appeared in ESI Africa Edition 3, 2018. You can read the full digital magazine online or subscribe to receive a print copy.

About the author and company

Morné Bosch is the general manager for sales and marketing at ArmCoil (Pty) Ltd, a privately owned South African leading supplier and repairer of transformers and electric motors. ArmCoil’s mission is to enter into partnerships where it can add value to the supply, local manufacture, management, maintenance and repair of electric rotating machines and transformers.



Babalwa Bungane
Babalwa Bungane is the content producer for ESI Africa - Clarion Events Africa. Babalwa has been writing for the publication for over five years. She also contributes to sister publications; Smart Energy International and Power Engineering International. Babalwa is a social media enthusiast.