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General information
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Description
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Principle The main transformer accounts for a substantial share of traction losses. This is especially true in 16,7 Hz systems. An innovative transformer concept using ceramic high-temperature superconductors instead of copper as winding material could reduce the transformer losses almost to zero. HTSC Superconduction (the loss-free electric conduction properties of some materials at very low temperatures) was discovered in 1911. The superconductors known then were metallic and required cooling down to –269° C which was achieved only by expensive liquid helium. In 1986, ceramic materials were discovered having superconductive properties at much higher temperatures of about -196 °C. This temperature can be achieved by liquid nitrogen cooling allowing for a considerable reduction of costs and complexity of superconductor cooling. Possible applications of HTSC aim at - Optimisation of conventional equipment: motor, transformer, cable etc.
- Development of innovative equipment: magnetic energy storage, current limiter etc.
The transformer prototype made by Siemens Siemens AG has developed two prototypes of HTSC transformers (a 100 kVA model and a 1 MVA demonstrator) in order to show principal feasibility for railway-relevant power classes. The coils are made from Bi-2223 (Bi2Sr2Ca2Cu3O10) conductor tapes of 3 mm width and 0,3 mm thickness. These filaments of ceramic superconductors are embedded into a pure Ag or AgMg matrix and a jacket acting as an insulator in normal operation and providing a defined circuit in case of quenching (i.e. breakdown of superconduction). The coils are located around an iron core. The operating temperature of the transformer is 67 K (-206 °C). This temperature is produced by a surrounding cryostat based on liquid nitrogen (LN2) cooling. Figure XXX shows the layout of the 1 MVA demonstrator. Einscannen aus Weigel 2000! | General | | Nominal output | 1000 kVA | | Frequency | 50 Hz | | Voltage | 25 kV / 2 x 1.4 kV | | Current | 40 A / 2 x 360 A | | Core | | Height / width | 1080 / 622 mm | | Cross-section | 329.8 cm2 | | Induction | 1.7 T | | Cryostat | | Length (inside) | 1140 mm | | Width / height (inside) | 832 / 420 mm | | Winding (Bi-2223) | | Diameter (HV/LV) | 304 / 228, 382 mm | | Height | 5000 mm |
Source: Henning et al. 2000 Operational characteristics Due to the time-consuming cool down process and the low permissible temperature gradient to ensure minimum material stresses, the HTSC transformer has to be kept at operating temperature even during standstill periods. For standstill of up to seven hours the thermal time constant is sufficient to maintain HTSC material at operating temperature. Beyond that the cooling system must be supplied either from catenary or from external supply. Manufacturer Siemens AG (in co-operation with DB AG) and others |
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General criteria
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Status of development: prototype |
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R&D activities in various manufacturing companies. Siemens AG has built a 100 kVA model and a 1 MVA demonstration transformer. An on-board protoype is planned. |
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Time horizon for broad application: in > 10 years |
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If successfully tested, market introduction will be between 2005 und 2010 (according to Siemens AG). |
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Expected technological development: highly dynamic |
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(no details available) |
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Motivation:
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- Energy saving
- Mass and volume reduction
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Benefits (other than environmental): big |
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Mass and volume reduction
Siemens AG gives the following reductions in mass and volume:
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Mass incl. cooling
system |
Volume of core-and-coil
assembly |
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Conventional
transformer |
HTSC design |
Conventional
transformer |
HTSC
design |
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Regional
rail |
4800 kg |
2200 kg |
0,69 m3 |
0.36 m3 |
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Locomotive |
14500 kg |
8700 kg |
2.65 m3 |
2.33 m3 |
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High-speed |
9300 kg |
5400 kg |
1.6 m3 |
1.3
m3 |
Source: Weigel 2000. |
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Barriers: high |
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Technological
HTSC transformers are not a mature technology yet. Technological
uncertainties are medium.
Complexity
Especially the liquid nitrogen cooling system adds to the overall complexity
of the transformer system and is a technology railways have no experience
with.
Costs
Investment is high and maintenance costs are uncertain (as for all complex
innovative technologies) |
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Success factors:
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(no details available) |
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Applicability for railway segments: high |
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Type of traction: electric - AC
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Type of transportation: passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines, freight
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„Sufficiently reliable designs“ (Siemens) are currently possible and planned for locomotives, high speed trains and regional MU trains. Application in freight trains is also discussed. |
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Grade of diffusion into railway markets:
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Diffusion into relevant segment of fleet: 0 % |
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Share of newly purchased stock: 0 % |
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(no details available) |
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Market potential (railways): highly uncertain |
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If HTSC transformers become an accepted technology in railways, the corresponding market potential would be large. However, at present uncertainties are very high. |
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Example:
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Prototypes developed at Siemens AG. |
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Environmental criteria
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Impacts on energy efficiency:
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Energy efficiency potential for single vehicle: 5 - 10% |
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Energy efficiency potential throughout fleet: 2 - 5% |
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Siemens AG predicts the following efficiency improvements:
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Efficiency at rated
power |
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Conventional
transformer |
HTSC
design |
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Regional
rail |
92 % |
99,3 % |
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Locomotive |
93 % |
99,6 % |
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High-speed |
92 % |
99,7
% |
Source: Weigel 2000
Although these values refer to rated load, it is assumed that the relative
improvements are approximately true for all loads.
This yields the following elasticity table:
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Traction |
Brake energy
recovery |
Effect on efficiency of power
train |
Elasticity with regard to efficiency of power
train |
Effect on
total energy consumption for
traction |
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High speed
train |
electric |
No |
8 |
1,00 |
8 % |
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Yes |
8 |
1,11 |
9 % |
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Intercity
train |
electric |
No |
8 |
1,00 |
8 % |
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Yes |
8 |
1,12 |
9 % |
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Regional
train |
electric |
No |
8 |
1,00 |
8 % |
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Yes |
8 |
1,33 |
11 % |
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Suburban
train |
electric |
No |
8 |
1,00 |
8 % |
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Yes |
8 |
1,42 |
11 % |
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Freight |
electric |
No |
7 |
1,00 |
7 % |
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Range: |
7 – 11
% |
Source: IZT
These values refer to 16,7 Hz systems. For 50 Hz systems transformer losses
are generally smaller and the effect of HTSC transformers on total energy
consumption will be lower by 1 – 2 points giving a range of roughly 6 – 9
%.
Mass effects
The following gives an estimate of the order of magnitude of the secondary
effects due to the reduced mass of the HTSC transformer:
- High-speed train: The typical mass of a high-speed train is some 400 tons
(ICE 2). According to Siemens the mass of a HTSC transformer of the high-speed
power class is about 4 tons lower than for conventional transformer (cf.
Benefits). This corresponds to 1 % mass reduction which translates into an
almost negligible effect on total energy consumption of ~ 0,2 %.
- Regional train: The typical mass of a regional train will be approx.
100-200 tons. The mass reduction due to the HTSC transformer will be ~ 2,6
tons (cf. Benefits) corresponding to ~ 1-3 % which corresponds to a reduction
of total energy consumption of 1-2 %.
Total effect
Taking into account both mass and efficiency effects, one gets the following
energy efficiency potential:
- Main line and high-speed trains: 8 - 10 %
- Suburban and regional trains: 9 - 13 %
- Freight trains: 7 %
Standstill consumption
During standstill the power required for maintaining the system at operating
temperature is in the order of 1,2 kW for a 1 MVA transformer. It is about three
times higher if the main transformer is also used for auxiliaries during
standstill. According to Siemens, energy costs for standstill will still be
lower than for conventional transformers (cf. Infrastructure – running
costs). |
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Other environmental impacts: positive |
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Cooling agent
Liquid nitrogen is a cooling agent with less environmental impact than the
oil used for cooling conventional transformers. |
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Economic criteria
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Vehicle - fix costs: high |
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Siemens estimates initial investment costs to be double as high as for conventional 16,7 Hz train transformer. HTSC winding material is more expensive than conventional copper windings. Liquid nitrogen cooling systems are not yet in mass production. |
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Vehicle - running costs: significant reduction |
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For an annual operation of 125.000 km, Siemens has calculated the following
running costs for a regional train (German BR 424/425) with conventional and
HTSC transformer (assuming an energy price of 0,06 Euro/kWh):
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Maintenance
costs |
Energy
costs |
Total costs |
Advantage of
HTSC: |
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Euro/a |
Euro/km |
For
operation Euro/a |
For standstill
Euro/a |
Euro/a |
Euro/a |
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Conventional |
2675 |
0,46 |
57050 |
4994 |
64719 |
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HTSC |
4225 |
0,36 |
45625 |
3587 |
53437 |
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11282 |
Source: DB AG & Siemens AG (no year) |
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Infrastructure - fix costs: low |
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Maintenance requires infrastructure for supplying liquid nitrogen. |
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Infrastructure - running costs: reduced |
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Cooling system needs power supply even during stand-still periods. According to Siemens AG stand-still costs will amount to 3587 Euro/year (compared to 4994 Euro/year for conventional transformers) on regional line stock BR 424/425 and for 125000 km/year. |
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Scale effects: high |
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Being an innovative technology in the R&D stage, there will be large scale effects in case of market success. This refers to the HTSC transformer itself as well as to the cooling system. |
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Amortisation: 2 - 5 years |
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< 5 years according to Siemens AG. |
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Application outside railway sector
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Status of development outside railway sector: test series |
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ABB has successfully tested a 630 kW-3phase HTSC transformer at a Swiss electric utility for one year under regular operational conditions. |
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Time horizon for broad application outside railway sector: in > 10 years |
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(no details available) |
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Expected technological development outside railway sector: highly dynamic |
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(no details available) |
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Market potential outside railway sector: medium |
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According to the International Superconductivity Industrial Summit, the worldwide market for superconductor-based products and systems will rise to 122 billion US Dollars by 2020. Market estimates for HTSC transformers only are not available. |
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Overall rating
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Overall potential: very promising |
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Time horizon: long-term |
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HTSC transformer is a highly promising long-term innovation for the electric traction system. Present R&D and prototypes promise high (50 Hz systems) to very high (16,7 Hz systems) energy efficiency effects. Remaining technological uncertainties are medium. According to manufacturers profitability is high enough to ensure reasonably fast payback of high initial costs. Maintenance and downtime costs are difficult to predict. Despite these uncertainties, HTSC transformers appear as a long-term option deserving intensive R&D efforts and further co-operation between railways and manufacturers. |
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date created: 2002-10-09
