Keeping ester fluid transformers operating reliably - See more at: http://www.insulect.com/news/entr
Transformer Management, Environmental Influencers, Ester Fluid,
Environmental influencers, analysis of oil testing results and practical considerations for maintenance techniques were studied by a research team led by Dr Dan Martin from The University of Queensland. Their paper “State of the Art Review on Managing Vegetable Oil Filled Transformers” addresses considerations a condition monitoring engineer needs to know in order to keep vegetable oil filled transformers operating reliably.
THEIR GOAL WAS TO HELP UTILITIES UNDERSTAND WHAT IS NORMAL FOR VEGETABLE FILLED TRANSFORMERS AND WHAT SHOULD BE MONITORED.
The long term study included a number of transformers under varying conditions of which three were selected for further investigation:
An extensively monitored 50 MVA transformer located underground in Sydney city
A 10-16 MVA transformer in a snow prone cold climate Thredbo location
Twin 90 MVA transformers installed next to each other under identical operating conditions, where one contains vegetable oil and the other mineral oil
Oil Ageing & Quality - Accelerated ageing test results and transformer operating data were compared to provide as much insight as possible regarding the effects of ageing on vegetable oil quality.
Dielectric Dissipation Factor (DDF) - The differences in DDF and subsequent polarity of the two types of fluid were examined; in particular what DDF indicates in mineral oil versus vegetable oil. The recommendation being to focus on the rate of change in DDF rather than an absolute value as part of a maintenance program for vegetable oil filled transformers.
Dissolved Gas Analysis (DGA) – Though DGA is commonly used as a technique for fault indication, the researchers found certain gasses such as ethane can be an indicator of oxygen exposure during installation of transformers that are assembled on site. The advantage of such an indicator is that it can be an early warning prior to oil quality degradation.
Water Content – The team also studied varying parameters for analysis of water content in vegetable oil due to its unique properties in comparison to mineral oil.
Due to the inherent properties of mineral and vegetable oil, factors such as modified analysis parameters need to be taken into consideration when analysing data. As an example the team applied Duval’s triangle for non-mineral oil insulation to their analysis to ensure accuracy of results.
PRACTICAL TRANSFORMER MANAGEMENT
The research looked at polymerisation and the reality of its formation in sealed and free breathing transformers. The likelihood of impact on performance was also reviewed.
The effect of air exposure and oil circulation over time was examined and a real world view of operational transformers was taken into account when the resulting data was analysed. The tendency for gelling and increased viscosity in operational transformers was deemed quite unlikely to form due to the length of time a transformer would remain open during maintenance.
To help engineers and maintenance crews with quick identification, providing a distinction between transformers with vegetable or mineral oil is recommended. This can be achieved through the use of colour coding and/or labels supplied by vegetable oil manufactures.
To take full advantage of the benefits that vegetable oil provides such as reduced fire risk, life extension, cost benefits and environmental sustainability, the differing properties of vegetable oil should be taken into account when analysing results and implementing maintenance programs.
, Ester Fluid
, Oil Ageing
, Transformer Management