Oil-less DGA Sampling (Prospective Trial)
National Grid Electricity System Operator
National Grid TO Innovation Team
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Innovation Funding Incentive
Gas Distribution Networks
According to theory, with the oil being exposed to a very large surface area
membrane, the gas contained within the oil will transfer to the low concentration
gas space on the far side of the membrane to achieve equilibrium. This process
will be faster and more efficient with the greatest surface area profile. Ceramic
membranes offer this property. It is expected the membranes will be formed from
aluminium nitride and coated with a 5µm layer of various polymers. The choice
of polymer is a major goal of this trial.
The final field device will be a steel cylinder containing a series of very strong
aluminium nitride tubes which give a potential surface area for the oil to act on of
some 20m2 or above.
The device will be designed to gently circulate oil to and from the same sample
valve. The surrounding container (purged on delivery with argon) will begin to
assimilate diagnostic gases from the oil. Diagnostic gas will be removed from the sampling system by syringe and analysed by a laboratory.
This is a prospective trial to test the effectiveness of direct oil-gas separation
across high surface area ceramic membranes coated with hydrophilic
The aim is to prove the functionality of membrane extraction to be used on oil
filled transmission assets where the oil content is of very low volume and
successive sampling results in the requirement to top up.
The end of trial will deliver quantitative data concerning extraction efficiency and
most suitable membranes to use in the construction of a field worthy sampling
It is expected that the trial will deliver as far as a proposed technical drawing of
the field trial system, if not a working prototype to demonstrate the technology
The second part of this work is to look at key molecular species which can
identify winding faults, generated when copper in contact with oil pushes
upwards to temperatures of 600 DegC and above.
Identifying a key marker species may assist in distinguishing transformers
suffering from winding faults from those suffering from non-critical overheating
faults such as core-frame circulating currents.