Power transmission

By Morné Bosch, general manager for sales and marketing, ArmCoil

In terms of a company’s bottom line, stoppage of this large piece of equipment, whose substitution is expensive and involves a lengthy process, is unacceptable. As such, emphasis is on reducing the costs associated with a transformer’s life cycle in efforts to guarantee its reliability and durability. It is therefore essential to monitor its operating conditions, its insulation system and the working conditions of its accessories and other components in efforts to extend the ‘life’ and reduce the costs of transformers. Research and development of new technologies and advanced predictive maintenance techniques has greatly contributed to reduce supply stoppages, thereby ensuring improved reliability of energy supply. Several studies undertaken highlight the importance of optimising maintenance processes and diagnoses of substation equipment such as transformers. These studies are from various universities and engineers in Brazil and India who struggle with similar situations to those faced in sub-Saharan African countries. The prevailing question in each case is “Do we replace now or do we maintain the unit until failure?”

Addressing the solution

Stoppages can be properly managed through planning ahead and based on informative decisions. The aim is to prevent unplanned stoppages thereby supplying electricity uninterrupted to emergency facilities such as hospitals, infrastructure such as railways, intensive power users such as mines and domestic users. The term ‘stoppage’ indicates that the service of a piece of equipment was interrupted, specifically meaning that it was removed from operation due to a defect or fault. The situation becomes even more troubling when it comes to power transformers. Taking into account the age of electrical grids across the world, there are many countries in which these transformers are approaching their ‘end of life’. This means that the transformers are urgently in need of being optimised through higher availability and reliability. However, due to ever increasing pressure to decrease costs, managers are continuously searching for alternatives to reduce the associated life cycle costs of installed assets and thereby improving the return on investment (ROI) of this equipment. This is normally achieved through the lowest possible cost and with a minimal environmental impact. With this in mind, ArmCoil developed the On Site Condition Analysis (OSCA) service to provide cost effective solutions for a complete range of solutions to meet the demand for optimising the performance of transformers through the asset’s prolonged life cycle. OSCA is supported by the company through many years of experience in the repair and manufacturing of transformers across South Africa and into Africa. This enables ArmCoil’s qualified employees to service transformers effectively and quickly on almost any installation.

Judge for yourself

Prolonging and optimising the extent of the transformer life cycle and performance through higher availability and reliability is achievable through the OSCA service as informed decisions produce the best results. This is why ArmCoil offers a cost-effective and unique solution for On Site Condition Analysis, which includes the following cases outlined below.

On Site Condition Analysis Phase 1

Using non-intrusive methods to conduct equipment assessment and registration, followed by a second process that involves visual inspections and oil sampling, with the aim of acquiring a general ‘health status’ of the asset/s. This also allows ArmCoil to map out all the locations for various substations and free standing transformers thereby ascertaining the priority status of each individual transformer. The analysis is carefully and thoroughly investigated based on the information retrieved from the assets. This places the client in an advantageous position in terms of being made aware of the risk of the immediate or imminent failure for critical assets in high and low populated locations. With this information, the client can make calculated and informed decisions based on factual evidence found and presented by the service provider. Once all the information is captured and compiled, a strategically prioritised schedule is presented for approval. Below is a basic summary of oil sampling types:

  • Dissolved gas analysis (DGA): This is the most sensitive and reliable technique used for evaluating the ‘health’ of the oil and indicates possible internal faults. The types of possible faults indicated are corona, arcing, sparking, overloading, overheating and possible paper breakdown.
  • Breakdown voltage test: This assesses the insulating properties of the oil – the lower the resulting breakdown voltage, the poorer the quality of the oil.
  • PCB (Polychlorinated Biphenyls) content: This is purely a health and environment issue, which has absolutely no impact on the asset’s performance. PCBs can be compared to organ failure. This is a very serious problem in South Africa and must be treated with respect and importance. The only viable solution is to replace the contaminated oil, as purification will not reduce the PCB content.
  • Acidity content test: The acid content increases over time in any oil cooled transformer due to the interaction between moisture, temperature and oxygen. This reaction turns into sludge, which settles in between the windings and other internal parts.
  • Moisture content test: Contamination occurs during interaction between the air and the transformer oil through the breather. It is advisable to check the silica gel and change out regularly.
  • Furanic testing: This test determines the paper deterioration in the transformer through direct measurement of its tensile strength/ degree of polymerisation (DP). These are used to evaluate the ‘end of life’ of the paper insulation.

On Site Condition Analysis Phase 2

After prioritising the critical and non-critical assets according to their individual determined health status from Phase 1, the On Site Condition Analysis service costs are further reduced due to restriction of components or the entire asset. As an example, after determining that an aged transformer is rapidly approaching a catastrophic failure when no ‘stoppage’ options are available, ArmCoil would supply or manufacture an exact ‘drop-in replacement’ unit for the next maintenance shutdown to assist with minimum stoppage. The aged, or potentially failed asset, would be removed and discarded safely without any impact on the environment and minimum loss of income to the owner of the transformer. The OSCA services from ArmCoil are carried out in conjunction with the owner’s specifications of the critical assets; and a variety of complete solutions will be implemented to extend the ‘life cycle’ of the identified aged transformers.

On Site Condition Analysis Phase 3

Upon reaching the Phase 3 level, the ‘life cycle’ of an aged transformer has been extended or improved, as shown through various reports obtained during the On Site Condition Analysis. This analysis is useful in that it may be used to reduced insurance premiums; and the reliability of the assets is also determined through the service events exclusive to ArmCoil’s OSCA service. Of strategic importance are the quarterly or annual recommendations that are proposed for monitoring purposes, oil sampling and asset replacement for this phase. Undertaking these phases results in reducing expenditure on routine inspections through ArmCoil’s mobile technicians.