ATL Transformers Academy
ATL design and deploy leading magnetics to the rail network and its principle contractors. We offer the highest specifications on the market while maintaining competitive pricing against alternative legacy technology. Our magnetics are approved for use by Network rail, Crossrail, London underground and are widely used to support Designers, Route asset manager, maintainers & Installers. As the preffered solution in rail ATL’s New generation of magnetics, eco-rail® is raising the bar on quality and performance, delivering unprecedented levels of weight/size reduction, ergonomics, Carbon reduction and safety.
ATL Academy Transformer Screening
Transformer Screening
Definitions of ATL screens
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Safety isolating earth screen |
A metallic material (typically copper foil) between the primary and secondary windings offering isolation to ground between the two windings sometimes referred to as: Separation of dangerous active components by use of a conductive shield, which is located between the two parts and is connected to an external earth terminal.
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Static screen |
A static screen is used to attenuate line disturbances and voltage peaks in high frequency conditions (EMC-transformer). The static screen has a green/yellow terminal. To control operativeness, the screen can be equipped with a terminal at the beginning and a terminal at the end. One terminals is cut off after the test. A better attenuation can be achieved by installing two static screens. One screen is connected to the protection conductor and has a green/yellow terminal. The second screen has a secondary potential and a black connection.
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Magnetic screening |
The magnetic screen lowers the outer magnetic stray field of the transformer. The screening is implemented by an encasement with highly permeable material. The material, e.g. mu-metal, can be built as a housing around the transformer or installed as a metal sheet. Magnetic screening usually doesn’t have a terminal. Both ways of screening raise the dimensions of the transformer or lower the power at the same size.
Further terms to this topic: EMC-transformer, mu-metal, mu-metal pot, voltage disturbances, EMC-screen, special screen, capacitive screening, grid-to-plate capacity, permeability |
Transformer Safety Standards
Low voltage Low power Transformer Standards EN61558-1
The old VDE 0550 and VDE 0551 transformer standards do not exist anymore. The previous EN 60742 (VDE 0551) transformer standards is outdated now also.
The up-to-date standards for transformers are now BS EN 61558 IEC 60076 (VDE 0570). Part 1 of the standard explains general requirements and tests. Part 2 lists special transformer types like safety isolating transformers (part 2-6) or SMPS transformers (part2-17) a separate standard, which still has a connection to part 1, for general requirements.
For larger power and voltage ranges IEC 60076 is consulted. Consisting of many parts this standard covers an array of transformer products from Dry type, Oil filled & Cast resin transformers.
UL5085 is typically adopted for UL approved transformers.
Transformer Temperature & Insulation
ATL Transformer Design
Our transformers are designed in a way that does not allow impermissible temperatures. The insulating materials have at least class E conforming to IEC 85, mostly class F (155 deg C) & class H (180 deg C) and on request even higher temperature classes. For the technical calculation, the temperature is calculated at 1,06 times the primary voltage in rated operation and in short-circuit case.
Transformer Voltages
Low voltage
Low voltages are rated voltages that are not higher than 1000 V AC.
High voltage
High voltage is defined as a voltage, that is higher than a low voltage of 1000 V. The maximum we are able to produce at the moment is at 50 kV AC.
The AC high voltage output has the following special characteristics: One terminal is connected to earth (minus pole, green/yellow connector) and the other terminal is connected to the high voltage side (plus pole or “hot side”).
Current is calculated with the power I = P/U and is usually given in [mA].
The frequency is at 50 Hz sinusoidal. For special fields of application, frequencies can be higher. We already built transformers with 20 kV and 1000 Hz.
The insulation test primary – secondary is done with 120% of the high voltage value..
Line Reactors
TL Transformers Line Reactors conform to EN 61558, EN 5008-1 and -2, EN 50082-1 and -2
Transformer Frequency
Transformer universal EMF equation
If the flux in the core is purely sinusoidal, the relationship for either winding between its rmsvoltage Erms of the winding , and the supply frequency f, number of turns N, core cross-sectional area a and peak magnetic flux densityB is given by the universal EMF equation.
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