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 Line Reactors


Line Reactors



ATL Transformers Line Reactors conform to EN 61558, EN 5008-1 and -2, EN 50082-1 and -2

Frequency range:
Test voltage:
Good EMC conditions
High thermal stability
Insulation class
Max. ambient temperature:
Fire class:
Prepared for protection index I
Safety class:
Voltage range:
Double dip varnish and bake

50 Hz – 1 kHz
Winding – core 2,5 kV

B or F

0 – 400 V, other values on request

The given energy is only a guideline value



can be chosen, the inductance is determined by type size and energy
can be chosen, the current is determined by type size and energy

Tolerance of energy +/- 20% Tolerances as low as +/- 2.5% achievable on request.
Terminals can be either shock proof block term;s conforming to VBG4 / terminal studs (brass nickel plated) lugs or flying leads


Uk – calculation of a choke’s voltage drop

The voltage drop of a smoothing coil and thus the voltage reduction of the connected load at the output can be determined as follows. The inductive or reactive reactance (XL) of the smoothing choke can be calculated with the inductance of the choke (L) and the mains frequency (fmains).

XL = ω . L = 2 π  fmains . L


The voltage drop (Uk) of the smoothing choke can be calculated with the rated current (IN) and the inductive reactance of the choke (XL):

for one-phase smoothing coils: Uk = IN . XL
for three-phase smoothing coils: Uk = IN . XL . √ 3



Calculation of the voltage drop (Uk) of an one-phase smoothing coil (Uk) with an inductance of
L = 0,3 mH, a current of I = 100 A and a rated voltage of 230 V at f = 50 Hz.

Reactance: XL = ω . L = 2 . 50Hz . 0,3mH = 0,094Ω
Voltage drop: Uk = IN . XL . = 100A . 0,094Ω  = 9,4V
Or given as percentage to mains voltage: UK% = Uk /  Umains  = 9,4/ 230 = 4%


At an american net with U = 110 V at f = 60 Hz, the choke acts as following:

Reactance: XL = ω . L = 2 . 60Hz . 0,3mH = 0,113Ω
Voltage drop: Uk = IN . XL . = 100A . 0,113Ω = 11,3V
Or given as percentage to mains voltage: UK% = Uk /  Umains = 11,3/ 110 = 10,2%


This means the same choke will have more than twice the Uk, if operated in an american net.


ATL chokes are calculated to have a small Uk%. Especially cut cores and cores made of amorphous and nanocrystalline materials have a small Uk% and thus low losses and a very good attenuation of harmonics.




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.

Read More About Transformer Standards

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.

Read More About Transformer Temperature & Insulation

Transformer Screening

Definitions of ATL screens

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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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..

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Transformer Frequency
Effect of 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.

Read More About Transformer Frequency


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