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ENERGIX-Stort program energi

Dynamic loading of transformer insulation

Alternative title: Dynamisk belastning av transformatorisolasjon

Awarded: NOK 14.0 mill.

Power transformers are key components in the electric energy system. Transformer failures may result in significant collateral damage and power outages. One cause of failures are large electromagnetic forces during short circuit events that can deform parts of the transformer, or possibly destroy it. To reduce this risk, the transformer insulation materials ? cellulose based materials that controls the internal temperature and keeps the electric current flowing where it should ? are clamped tightly together to counteract these forces. This is called clamping pressure. The electric energy system of today is continually exposed to more dynamical loading due to: 1) increased use of electric vehicles and ships using high-powered charging, 2) intermittent energy supply from wind power, and 3) an energy market that demands more frequent starts and stops in hydro power production. The dynamical loading causes large and rapid temperature fluctuations inside the transformer. This results in high pressures acting on the insulation because the different materials expand differently with increasing temperature. Gradually, this will cause an irreversible shrinking of the insulation. Over time, this will also reduce the clamping pressure and thus reduce the transformer's ability to withstand short circuit forces which increases the risk of failure. DynaLoad will study the long-term effect of rapid dynamic loading on the mechanical properties of the transformer insulation materials by: 1) Laboratory measurements on different insulation materials, 2) Numerical modelling, and 3) Continuous online measurements of the clamping pressure in a transformer in service. This transformer has an optical pressure sensor installed specifically for this project, and it is the world's first of its kind.

Power transformers are key components in the electric energy system. For power utilities, transformer failures are costly incidents that require expensive replacement work and may result in fires, explosions and significant collateral damage. Such failures are also costly for society causing potentially harmful outages and reduced security of energy supply. Mechanical deformation of transformer windings due to large electromagnetic forces during short circuit events is already a major cause for destructive transformer failures. This trend is likely to become more severe in upcoming years due to increased intermittent supply from renewable energy sources and heavy load cycling from e.g. high-powered charging facilities, which inevitably lead to new transformer operation schedules characterized by more frequent starts and stops, rapid power ramping, and an increased number of short-time overload periods. In DynaLoad, we address three specific challenges to combat this development: 1) Fundamental material research on improved mechanical endurance of winding insulation, 2) Modelling of the thermo-mechanical impact of rapid dynamic loading on transformer windings, and 3) Sensor-based condition monitoring of transformers in service. DynaLoad will through experiments and modelling contribute essential knowledge regarding the performance of transformer winding insulation materials and the design of transformers operating under new dynamic load patterns in the future flexible power grid. Combined with real-life sensor data, these results will pave the way for increased sensor-based condition monitoring of transformers, to prevent costly failures and allow more precise estimates of transformer life expectancy for cost-efficient reinvestment plans in the existing transformer fleet.

Funding scheme:

ENERGIX-Stort program energi