NewLifT will provide knowledge and improve the decision basis for transformer producers and users with regards to introducing new insulation liquids in transformers.
The transformer plays an essential role in transmission of electrical power. Traditionally, many transformers have been filled with mineral oil which poses some challenges related to its environmental footprint and fire hazard. Alternative liquids with partially favorable properties are available, but knowledge on their functional properties is lacking. The role of the insulating liquid is to act as a coolant and electrical insulation between the conductors, commonly referred to as windings, in the transformer. In addition to the liquid insulation, the transformer also contains solid insulation in the form of paper.
NewLifT will focus on thermal properties of new insulating liquids, using mineral oil as a baseline. The first step will be to make a dynamic model that can calculate the thermal distribution in a transformers that contains liquids with varying viscosity. In addition to this, other important aspects related to thermal properties will be investigated:
-Ageing models that take temperature and moisture dynamics into account will be developed and verified using an experimental rig.
-It will be investigated how, particularly at which temperature, bubbles are formed in various liquids. This will set an upper limit on the operating temperature of the transformer, seeing as bubbling will lead to catastrophic failure.
-A temperature-controlled rig will be built to investigate how temperature affects initiation of breakdown between two electrodes. Datasets that show how the electrical withstand ability depends on temperature will be measured for different liquids. For example, different liquids may have varying properties when it comes to crystalline precipitation, which may influence their electrical withstand capability, particularly at low temperatures.
Use of ecofiendly materials is a prerequisite for the green shift in electric power system. Knowledge of their functionality and properties is required for getting them accepted. Liquid-insulated power transformers are key components in power systems. Their insulation system is made of liquids and liquid impregnated cellulose. These materials play the crucial role of insulating high-voltage parts avoiding short circuit. Additionally the solids provide mechanical support, and the transformer insulating liquids (TIL) act as a coolant. Mineral oils (MO) have been the dominating TIL for more than a century. Current design and practices are based on MOs properties and functional behaviour. Now new TILs with environmental, HSE-related, and technical advantages have arrived on the market. The new TILs require improved modelling and adjusted transformer designs to cope with differences of the various liquids. In the future the transformers also have to handle more demanding dynamic thermal stresses from load variations from renewables and transport charging. There is now a lag between current requirements for transformers and available information on performance and standards of the non-mineral TILs, resulting in a barrier for industry to take the new materials into use. NewLifT will establish new knowledge on thermal behaviour of the TILs and the insulation systems.
-Based on experimental studies, fluid-dynamic thermal models of cooling of transformer windings under load transients at artic temperatures will be developed. The models will be validated for liquids with various thermodynamic properties.
-The of moisture dynamics between oil and cellulose will be studied and the impact of temperature and humidity variations on cellulose ageing models used to derive improved ageing models.
-Temperature limits for safe operation at high temperature (water vapour bubbling) and low temperatures (impact on liquids voltage withstand) will be derived based on experimental studies.