PARAMETERS THAT AFFECT THE DEGRADATION OF TRANSFORMER OIL
BASIC INFORMATION
What Are The Parameters That Affect The Transformer Oil?
Heat
Just as temperature influences the rate of degradation of
the solid insulation, so does it affect the rate of oil degradation. Although the rates of both processes are different, both are
influenced by temperature in the same way. As the temperature rises, the rates of degradation reactions
increase. For every 10° (Celsius) rise in temperature, reaction rates double!
Oxygen
Hydrocarbon-based insulating oil, like all products of
nature, is subject to the ongoing, relentless process of oxidation. Oxidation
is often referred to as aging.
The abundance of oxygen in the atmosphere provides the
reactant for this most common degradation reaction. The ultimate products of
oxidation of hydrocarbon materials are carbon dioxide and water.
However, the process of oxidation can involve the production
of other compounds that are formed by intermediate reactions, such as alcohols,
aldehydes, ketones, peroxides, and acids.
Partial Discharge and Thermal Faulting
Of all the oil degradation processes, hydrogen gas requires
the lowest amount of energy to be produced. Hydrogen gas results from the
breaking of carbon–hydrogen bonds in the oil molecules.
All of the three fault processes (partial discharge, thermal
faulting, and arcing) will produce hydrogen, but it is only with partial
discharge or corona that hydrogen will be the only gas produced in significant
quantity.
In the presence of thermal faults, along with hydrogen will
be the production of methane together with ethane and ethylene. The ratio of
ethylene to ethane increases as the temperature of the fault increases.
Arcing
With arcing, acetylene is produced along with the other
fault gases. Acetylene is characteristic of arcing.
Because arcing can generally lead to failure over a much
shorter time interval than faults of other types, even trace levels of
acetylene (a few parts per million) must be taken seriously as a cause for
concern.
Acid
High levels of acid (generally acid levels greater than 0.6
mg KOH/g of oil) cause sludge formation in the oil. Sludge is a solid product
of complex chemical composition that can deposit throughout the transformer.
The deposition of sludge can seriously and adversely affect heat dissipation
and ultimately
result in equipment failure.
