Breimer-Roth GmbH produces single-phase and three-phase transformers as Isolation Transformers (galvanic isolation) or as Autotransformers Made in Germany with a construction capacity of up to 1,000,000 VA. The voltage in the input and output can be from 1 V up to 1,000 volts (1 KV).
On customer request input voltage and output voltage with or without taps and additional separate windings as well as the construction power of the transformer are adapted, standard in the frequency 50/60 Hz, other frequency ranges are of course possible. Optionally we offer also the suitable housings in the protection class IP 23 – IP 65. In addition to DIN EN 61558 – previously DIN VDE 0570 – we also produce the transformers with UL/CSA approval.





Bau von Transformatoren - Breimer-Roth

Standards of transformers from Breimer Roth

Control Transformers EN 61558-2-2, Isolating Transformers EN 61558-2-4, Safety Transformers EN 61558-2-6, Autotransformers EN 61558-2-13 and in UL 5085 Low Voltage Transformers (XPTQ2) and UL 1446 Electrical Insulation System (OBJY2). DIN VDE 0570 has been replaced by DIN EN 61558.

Transformer protection classes

Our transformers are divided into three protection classes according to the constructive nature of their protection against dangerous body currents:

  • Protection class I (protection by protective conductor)
    • Device with protective conductor connection and basic insulation
  • Protection class II (protection by protective insulation)
    • Device without protective conductor connection with double or reinforced insulation
  • Protection class III (protection by protective extra-low voltage)
    • Device in which protection against electric shock is based on SELV supply and in which no voltages higher than SELV are generated.

SELV is a voltage that does not exceed < 50V AC or < 120V smoothed DC between conductors or between a conductor and ground.

Classification of transformers into non-short-circuit proof, conditionally short-circuit proof or short-circuit proof:

  • Non-short-circuit proof transformer: transformer without protection device against excessive temperature rise. The protection device must be implemented by the user.
  • Conditionally short-circuit proof transformer: transformer that contains a protective device such as a fuse, overcurrent trip, or temperature limiter that opens the primary or secondary circuit when the transformer is overloaded or short-circuited.
  • Short-circuit proof transformer: a transformer in which the temperature does not exceed specified limits when the transformer has been overloaded or short-circuited and after overload or short-circuit is removed, the transformer continues to operate.

Tolerances in line voltage and the associated variations in rated power have been taken into account in all our series in accordance with the relevant standards.

The core of the single-phase transformers up to a power of 3 kVA consists of a DIN-EI-laminations For higher powers, we use UI laminations with two coils, with the second coil connected in parallel or in series, and our grain-oriented strip-cuts for an optimized magnetic field. A special design is the toroidal transformer, which we produce up to 3 kVA and freely selectable voltage and current. In this case, the iron core can be adapted more flexibly according to the installation situation in terms of height and diameter.
In the case of three-phase transformers, we use 3UI core laminations with coil formers up to a power rating of 50 kVA. For larger transformers above 50 kVA, we use our individually optimized strip-cuts with threaded air core coils and built-in cooling channels.

Insulation classes:

Up to a power of 3500 VA the three-phase transformers are manufactured in insulation class B, from 4000 VA in insulation class F. In our series type BDH we offer insulation class H with reduced construction size.


The connection is made by terminals, from a current of more than 340 A on cable lugs or copper plates.

Direct current supply:

In addition to AC voltage and AC current, it is also possible to transform a DC voltage with defined voltage and current on the primary coil and/or secondary coil. In principle, the construction of these power supplies with a core and coil(s) is identical to the AC transformers with at least one primary winding and one secondary winding each, additionally rectifiers and heat sinks are installed. On request also available without capacitors and with a certain residual ripple.
By using different manufacturing techniques in our company we are able to optimize the magnetic flux in the iron core and thus significantly reduce the power losses in no-load operation as well as in continuous operation. An optimized magnetic field can only be achieved by using high quality electrical sheets and accurate manufacturing.

Structure and functionality of transformers

A transformer consists of a magnetic circuit, this is called the core, and has at least two windings with a fixed number of turns through which current flows. The windings facing the electrical voltage (line voltage) are called the primary side (primary coil), and the side with the load and electrical load is called the secondary side (secondary coil). By applying an AC voltage to the primary coil, an induced voltage is generated on the secondary coil due to the changing magnetic flux in the iron core. Here, the voltage from the input can be transformed into a higher or lower voltage at the output. The voltage and current at the output determine the power of the transformer. A transformer cannot change the frequency in this process. Manufacturing technology for the core and the quality of the transformer core used affects the magnetic circuit. The magnetic circuit (magnetic field) should ideally produce low eddy current losses and have low remagnetization losses (hysteresis losses).
Another aspect is the resistances in the winding. Only with layered and ordered windings on the primary coil and the secondary coil and the best winding metal can the winding losses be reduced. The voltage is controlled with the number of turns on the coil. The current determines the diameter of the winding metal. Generally, we always use copper for our windings.
Except for silver, copper has the best conductance with γ = 56. Aluminum, on the other hand, has only γ = 36. Aluminum thus follows with a gap of about 35 percent. Copper is thus the best metal and aluminum “only” the second best of the technically and economically usable conductor materials for electrical energy. All other metals cannot be considered as conductors of electricity, and alloys generally have considerably lower conductivity than pure metals. Silver or gold are ruled out altogether because of their high price.
With our products, the customer basically has the choice of using a cost-optimized variant with regard to purchasing or a loss-optimized variant when operating the transformer. For this purpose, we can provide decision-making aids for the selection of the right series on the basis of payback calculations and Co2 savings.