Technologies - Medium-frequency transformer

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Medium-frequency transformer

evaluated

The main transformer contributes considerably to losses in traction system (especially in 16,7 Hz systems). Modern power electronics allow for a more efficient and much lighter alternative: the medium frequency transformer operating at 400 - 800 Hz or comparable frequencies.

Technology field: Optimisation of traction technologies



General information

General criteria

	Status of development: test series
		German DB developed a prototype of medium frequency transformer with 1 MVA permanent power for 15 kV 16 2/3 Hz system. Transformers of this power class are used in EMUs on local lines. The prototype has undergone stationary testing, integration into a vehicle for driving tests is planned (as of 1999). Alstom is going to continue the development begun by DB. There is also medium frequency technology for auxiliary power converters. This technology is however not considered here.

	Time horizon for broad application: in > 10 years
		Manufacturers estimate 2-3 year development time after kick-off. The medium frequency transformer could be produced in series some time between 2005 and 2010. To become a standard in new stock it would then take approx. another decade.

	Expected technological development: highly dynamic
		Eddy currents limited the DB prototype to 96,2 % efficiency (without power electronics). Replacing aluminium by copper parts, the transformer itself (without power electronics) could reach 98,5 % efficiency according to DB experts. This would raise efficiency of the whole component (including the required power electronics) to 94 %. In long-term perspective power electronics might altogether replace the on-board transformer.

	Motivation:
		Weight and volume The under-floor space for integrating the main transformer into an EMU is very limited. Small and light transformer technlogy is therefore an important requirement for decentralized traction. Multi-system operability The medium frequency transformer is inherently multi-system operable. Energy efficiency is a positive side effect.

	Benefits (other than environmental): big
		Volume reduction The small dimensions of medium frequency transformers are ideally fitted for EMUs because of limited build-in space. Mass reduction The advantages of a reduced transformer mass are numerous and range from advantages for car-body construction (less shear stress require less car-body stabilisation measures) to reduced wear. Multi-system operability The medium frequency transformer is inherently multi-system operable.

	Barriers: medium
		Complexity High amount of power electronics. Very complex compared to conventional transformer. Main problem: Ensure operational reliability despite complexity. Can be solved by redundant construction: individual cascade modules may be switched off if broken down.

	Success factors:
		(no details available)

	Applicability for railway segments: high
	Type of traction: electric - AC
	Type of transportation: passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines, freight
		Main benefits in 16 2/3 Hz systems but conceivable for all electric vehicles. Ideal transformer solution for EMUs due to small dimensions.

	Grade of diffusion into railway markets:
	Diffusion into relevant segment of fleet: 0 %
	Share of newly purchased stock: 0 %
		(no details available)

	Market potential (railways): highly uncertain
		(no details available)

	Example:
		(no details available)

Environmental criteria

Economic criteria

Application outside railway sector (this technology is railway specific)

Overall rating