Superconducting traction transformer

An ongoing project to develop HTS traction transformers for the Chinese Fuxing high-speed train is demonstrating that the high-power density can be reached using high-temperature superconductors (HTS). The findings are spectacular: the existing 6.5 MVA traction transformers can be replaced with drop-in superconducting transformers, achieving targets of less than 3 tons transformer system weight and 99.5 % efficiency compared to 6 tons and 95 % in the existing devices. The key to achieving these impressive figures is minimizing the AC loss of the HTS windings. New high-performance wire, high current HTS Roebel conductor, high aspect-ratio windings, and flux diverters placed at the winding ends all contribute to reducing the electrical loss to less than 2 kW

Superconducting transformers – Part II

Superconducting transformers using high current density High Temperature Superconductor (HTS) wire cooled with liquid nitrogen can be lighter and more efficient than conventional power transformers. This paper describes the 1 MVA 11/0.415 kV HTS transformer developed by a New Zealand - Australian team, featuring HTS Roebel cable in the 1.4 kA-rated low voltage winding. Comparison of HTS and conventional transformer designs at 40 MVA rating shows lower lifetime cost of losses makes HTS base-load transformers cost-competitive in higher energy cost markets. Power density - more MVA in a restricted footprint - could be a decisive advantage in mobile applications

Greener pastures 1 - The greener pasture project: managing nutrients in dairy pastures

As dairy farmers have strived to maintain profitability, many have farmed more intensively. More cows are milked and increasing inputs of fertiliser and purchased feed are used per hectare. However, these increased nutrient inputs have far exceeded the increase in nutrient output in milk production. The increasing nutrient surplus (inputs minus outputs) from intensification on dairy farms has met with increasing community concern about the environmental footprint of the dairy industry. In some other countries, dairy farmers who have intensified by increasing nitrogen inputs are now faced with legislation controlling the amount of fertiliser nitrogen that they can use. The Greener Pastures project was set up to assist the Australian dairy industry meet the two major challenges managing high performing pasture systems: maintaining profitability while meeting the expectations of a community that is increasingly sensitive to environmental issues.https://researchlibrary.agric.wa.gov.au/bulletins/1130/thumbnail.jp

Greener pastures 4 - Managing potassium in dairy pastures

We undertook three studies into the potassium requirements of high rainfall pastures: 1. Between 1999 and 2009, soil testing was conducted in 48 dairy paddocks at Vasse Research Centre (VRC) in the south-west of Western Australia (WA). This study will be referred to as the VRC soil test study. 2. Between 2002 and 2007, a potassium experiment was undertaken at Boyanup to improve our knowledge of potassium requirements of intensively grazed ryegrass pastures. This will be referred to as the Boyanup potassium experiment. 3. Between 2006 and 2010, potassium experiments were undertaken on two partner farms of the Greener Pastures project. These will be referred to as the partner farm potassium experiments.https://researchlibrary.agric.wa.gov.au/bulletins/1126/thumbnail.jp

Greener pastures 3 - Managing phosphorus in dairy pastures

Between 1999 and 2009, soil testing was conducted in 48 dairy paddocks at Vasse Research Centre (VRC) in the south-west of Western Australia (WA). This study will be referred to as the VRC soil test study. Phosphorus experiments were undertaken on partner farms of the Greener Pastures project to improve our knowledge of the phosphorus requirements of intensively grazed ryegrass pastures. These are the partner farm phosphorus experiments.https://researchlibrary.agric.wa.gov.au/bulletins/1125/thumbnail.jp

Greener pastures 5 - Managing sulphur in dairy pastures

During 1999-2009, soil testing for sulfur (S) was undertaken on 48 paddocks at the Vasse Research Centre (VRC) at Busselton, in the south-west of Western Australia (WA). Paddocks had been grazed intensively by dairy cows and their young stock over a period of 10 years, as part of the Vasse Milk Farmlets and Greener Pastures farming system projects. Pasture consisted of annual ryegrasses with some subterranean clover. Soils in the 48 paddocks were 1-2 m sand to sandy loam over massive clay, known locally as Abba sand. For many soils in the region, including Abba sands, the topography is flat and the soils are waterlogged from June to early September in the typical May to November growing season. Samples of the top 10 cm of soil were collected from each paddock in April 1999 and January- February 2000-2009, during the dry period before fertiliser was applied. These are the standard sampling depth and sampling time for soil sampling of dryland pastures in WA. Soil samples were collected while walking on the same diagonal path across each paddock each year between two permanent markers located on fences. Samples were collected using 2.5 cm diameter metal tubes (10 cm long; known locally as pogos) that were pushed into the soil by foot every 2-3 m, with 50-100 samples collected per paddock, depending on the size of the paddock.https://researchlibrary.agric.wa.gov.au/bulletins/1128/thumbnail.jp

Greener pastures 7 - A fresh look at nutrient losses from intensively managed pastures

Dairy farmers in Western Australia have a long history of being concerned for the environment in which they live and work, from early involvement with Landcare District Committees through to participating in the various programs run in DairyCatch. They have planted trees, organised soil testing programs, carried out salinity surveys and, more recently, have signed up for effluent, nutrient and irrigation water management programs. Many of these programs produce benefits both on and off the farm—they can improve the farm environment, increase farm productivity and reduce nutrient losses to surface and ground water. The wider community has supported farmers with funding from both State and National landcare programs.https://researchlibrary.agric.wa.gov.au/bulletins/1135/thumbnail.jp

AC Loss Calculation on a 6.5 MVA/25 kV HTS Traction Transformer with Hybrid Winding Structure

HTS wire cost is a critical factor for successful commercialization of HTS traction transformer technology. Wire cost might be minimized without significantly increasing AC loss by introducing a hybrid winding structure: the end-part of the windings is wound with high-cost high-I c wires; the central-part of the windings is wound with low-cost low-I c wires. We report AC loss simulation results on HTS windings with both HV and LV windings wound with REBCO wires. The 2D axisymmetric FEM simulation was carried out using H-formulation. The HV windings are wound with 4 mm-wide wires and LV windings are wound with 8/5 (eight 5 mm - wide strands) Roebel cables. Both HV and LV windings have a hybrid structure in order to reduce the wire cost. Flux diverters are placed at the end of the windings to reduce AC loss. Significant HTS wire cost reduction could be achieved without compromising AC loss by using hybrid windings. This may help commercialize HTS traction transformer technology

Cooling systems for HTS transformers : impact of cost, overload, and fault current performance expectations

In a future commercial marketplace HTS transformers will compete with oil-immersed copper transformers - highly developed, efficient and reliable. Although HTS can offer reduced weight, lower load losses, and perhaps current limiting capability, to have any chance of commercial competitiveness the total cost of ownership (TCO) taking into account purchase price, installation and lifetime operating costs, must be lower than the conventional alternative. In addition the HTS transformer in operation must meet regulatory and network operator expectations not easy to satisfy with high current density HTS wire and cryogenic operation. The cooling system for e.g. a 40 MVA 3-phase HTS transformer needs to provide for a total thermal load at 66 K of around 3 kW, dominated by current lead and AC loss. The TCO perspective shows that one of the commercially available cryocoolers options is clearly best for closed-circuit cooling systems in this application. A 3-phase vacuum-insulated glass-epoxy composite cryostat for an HTS transformer with warm iron core is perhaps the single most expensive component of the cryogenic system. A hybrid cryostat, with vacuum insulation around the cores and foam insulation around the transformer tank can provide adequate thermal performance at a fraction of the cost. Overload capability without loss of lifetime is often counted an advantage of HTS transformers. However AC loss increases non-linearly with current, typically increasing by a factor of 10 for a doubling of current. Providing this amount of reserve capacity in a cryocooler can be prohibitively expensive. This, and the need for back-up cooling capacity during cryocooler maintenance or malfunction, has important consequences for system design and cost. For most grid applications HTS transformers will need to match the fault current and recovery performance of conventional transformers: to withstand the fault current drawn by a zero impedance short for 2 seconds to allow time for the grid protection system to isolate the fault, and then to recover to normal operation while carrying rated current. For HTS transformer windings immersed in subcooled liquid nitrogen the withstand time will be largely determined by the mass of the conductor. Recovery after the fault will depend on the boiling heat transfer characteristics of the winding, which can be seen as an important facet of cryogenic system design for transformers. Solid conductor insulation, rather than paper wrap, and subcooled operation provide for maximal heat transfer during recovery

Greener pastures 6 - Managing soil acidity in dairy pastures

During 1999-2009, soil testing for pH (in CaCl2) was used to determine lime application for 48 paddocks at the Vasse Research Centre at Busselton, in the south-west of Western Australia (WA). Paddocks had been grazed intensively by dairy cows and their young stock over a period of 10 years, as part of the Vasse Milk Farmlets and Greener Pastures farming system projects. Pasture consisted of annual ryegrasses with some subterranean clover. Soils in the 48 paddocks were 1-2 m sand to sandy loam over massive clay, known locally as Abba sand. For many soils in the region, including Abba sands, the topography is flat and the soils are waterlogged from June to early September in the typical May to November growing season. No major liming program had been undertaken in the 48 paddocks before April 1999, and soil testing in 1999 indicated soil pH for the top 10 cm of soil was 4.0-5.0 in all paddocks. Soil acidification was therefore identified as a major problem, and a liming program was undertaken to rectify the problem, starting in 1999.https://researchlibrary.agric.wa.gov.au/bulletins/1127/thumbnail.jp