Drop of knowledge #15

Ecol lab – what happened in March?

1. 1. Assessment of the degradation and oxidation of electrical insulating oils →
2. 2. Upcoming conferences we are attending: →
3. 3. Element of the month →

1. Assessment of the degradation and oxidation of electrical insulating oils

The main tasks of electrical insulating oils are:

• Dielectric insulation
• Heat dissipation – cooling of the active part of the transformer
• Protection of solid insulation (cellulose) against atmospheric influences

In order for oil to fulfil its purpose and not adversely affect the components of an electrical machine such as a transformer, for example, it should meet a number of requirements.

Detailed information on the handling of mineral insulating oils can be found in the current standard EN 60422:2013-10 ‘Mineral insulating oils in electrical equipment. Recommendations for monitoring and maintenance’.

In addition to obvious parameters such as dielectric properties, i.e. breakdown voltage, resistivity and dielectric loss, and water content, oil degradation and oxidation should also be monitored.

Mineral oil undergoes thermal degradation and oxidation over time. This process is more rapid the greater the thermal load on the oil and the access of atmospheric oxygen.

As a result of ageing and catalytic processes, non-polar oil molecules undergo oxidation reactions to form polar products, including organic acids.

An increase in their content can lead to the formation of sludge and deposits which, when deposited on the active part and radiators, impair the heat transfer capacity of the unit.

Acidic oxidation products, by catalysing the hydrolysis of cellulose, affect the accelerated degradation of paper insulation. We assess the degree of ageing of electrical insulating oil by examining:

• interfacial tension, i.e. the stress at the oil-water interface,
• acid number,
• resistivity and dielectric loss factor.

Less frequently used, but carrying a large amount of information, is infrared spectroscopy.

4. Element of the month

Nickel (Ni, łac. niccolum) – is a silvery-white element belonging to the group of transition metals. This element in lubricating oil is responsible for the wear of lubricated machine components, but it is quite rarely found.

→ Nickel is an additive in stainless steel alloys, e.g. it occurs as an element of rolling bearings and gears (along with iron). It is commonly used in the metallurgy of valves, valve guides and some turbines.

→ Some assembly pastes contain nickel, which, when it gets into the oil, causes its purity to deteriorate.

→ Nickel-copper alloys are widely used in the marine industry as components of engine elements, especially heat exchangers. They are characterized primarily by high corrosion resistance in salt water conditions.