Electricity and Control March 2020

TRANSFORMERS, SUBSTATIONS + CABLES

Condition monitoring on transformers

Power transformers are expensive and critical equipment in power systems and play a significant role in the transmission and distribution of electricity. Electricity + Control put some questions to Gert Nel, Transformer Division Manager at condition monitoring specialistWearCheck, about the best measures to maintain transformers in good working order.This is his response.

A lthough transformers are generally reliable, failures do occur. There are many degradation mechanisms operating in the components and subsystems that will, over time, limit the equipment’s useful operating life. Transformer asset managers generally aim to achieve the required levels of safety and reliability from their fleet of transformers at minimum cost. Condition monitoring that provides the relevant checks and information is therefore essential to efficient decisions in respect of transformer asset management. Without this information only the most basic maintenance activities can be done – such as time-based maintenance, replacement before end of life, or repair after failure. Signs of trouble usually appear before electrical machinery or equipment fails. The condition of power generation, transmission or distribution system assets can be determined through regular analysis of the insulating liquid. Testing can detect developing problems in the apparatus, such as local overheating at a loose connection or electrical discharge between turns, so problems can be managed. Transformer fluids, or oils, degrade as a result of oxidation and operation. Degradation of the oil produces sludge and other by-products that can cause equipment to fail. Various other conditions can adversely affect the performance of the oil and the apparatus. Condensation, leaking gaskets, internal arcing, for example, can affect the dielectric properties of the liquid significantly as well as the physical condition of the insulation. With proper diagnostic testing, equipment failures can be avoided. WearCheck’s Transformer Division provides oil analysis services to any operation that generates power or uses electricity. Nel says, “For example, we monitor transformers operated by municipalities, solar farms, wind farms, shopping malls and casinos. We monitor very small transformers run by housing complexes – up to

At a glance ■ Condition monitoring that provides the relevant checks and information is essential to effective transformer asset management. ■  Signs of trouble usually appear before electrical machinery or equipment fails.The condition of power generation, transmission or distribution system assets, can be determined through regular analysis of the insulating liquid. ■  Regularly scheduled oil testing is a cost-effective and sound maintenance practice that serves to extend the life of transformers.

the massive transformers servicing cities and large industrial operations.” The data gathered is analysed by experts and recommendations are made on remedial actions where required. All the analyses and recommendations are based on relevant standards and the company’s long-established expert knowledge in this field. Nel says, “We can conduct once-off tests, although we always recommend regular condition monitoring as the best approach to preventive maintenance. It is preferable to establish wear

WearCheck senior transformer consultant Ian Gray (centre with black shirt) with the transformer testing team on site for a customer.

Electricity + Control

MARCH 2020

21