Transformers

Transformers Protection classes

Our transformers are divided into three protection classes according to the design 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 through protective insulation)
  • Device without protective conductor connection with double or reinforced insulation
• Protection class III (protection by safety extra-low voltage)
  • Device in which the protection against electric shock is based on the supply with SELV and in which no voltages higher than the SELV are generated.

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

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

• Non-short-circuit proof transformer: Transformer without protection against excessive temperature rise. The protective device must be implemented by the user.
• Conditionally short-circuit-proof transformer: Transformer that contains a protective device such as a fuse, an overcurrent release or a temperature limiter that opens the primary or secondary circuit if the transformer is overloaded or short-circuited.
• Short-circuit-proof transformer: Transformer in which the temperature does not exceed specified limit values if the transformer is overloaded or short-circuited and remains operational after the overload or short-circuit has been removed.

The tolerances in the mains voltage and the associated fluctuations in the rated output have been taken into account in all our series in accordance with the relevant standard.

Up to an output of 3 kVA, the core of the single-phase transformers consists of a DIN EI section (used for smaller transformers), which is created from grain-oriented or non-grain-oriented transformer core laminations and a coil with at least one primary winding and one secondary winding, depending on the required power loss. For higher power ratings, we use UI laminations with two coils, whereby the second coil is connected in parallel or in series and our grain-oriented strip cuts are used for an optimized magnetic field. A special design is the toroidal transformer, which we produce for you up to a power rating of 3 kVA and freely selectable voltage and current. The height and diameter of the iron core can be adapted more flexibly to the installation situation.
For three-phase transformers up to an output of 50 kVA, we use 3UI core laminations with coil formers; for larger transformers over 50 kVA, we use our individually optimized strip sections with threaded air coils and integrated cooling channels.

Insulation material classes:

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

Connections:

The connection is made via terminals, from a current of over 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 a defined voltage and current on the primary coil and/or secondary coil. In principle, the design of these power supply units with a core and coil(s) is identical to the AC voltage transformers, each with at least one primary winding and one secondary winding, with the addition of a rectifier and heat sink. Also available without capacitors and with a certain residual ripple on request.
Thanks to 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 and continuous operation. An optimized magnetic field can only be achieved by using high-quality electrical sheets and careful manufacturing.

Structure and function of transformers

A transformer consists of a magnetic circuit, known as a core, and has at least two current-carrying windings with a fixed number of turns. The windings facing the electrical voltage (mains voltage) are referred to as the primary side (primary coil), the side with the load and the electrical load is referred to as the secondary side (secondary coil). When an AC voltage is applied to the primary coil, an induced voltage is generated on the secondary coil by the changing magnetic flux in the iron core. 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. The manufacturing technology for the core and the quality of the transformer core used have an effect on the magnetic circuit. Ideally, the magnetic circuit (magnetic field) should generate low eddy current losses and low remagnetization losses (hysteresis losses).
The resistances in the winding must also be taken into account. Winding losses can only be reduced with layered winding and ordered turns on the primary coil and the secondary coil and the best winding metal. The voltage is regulated by the number of turns on the coil. The current strength determines the diameter of the winding metal. We always use copper for our windings.
Copper has the best conductivity with γ = 56, except for silver. Aluminum, on the other hand, only has γ = 36. Aluminum follows with a gap of around 35 percent. Copper is therefore 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, and alloys generally have a considerably lower conductivity than pure metals. Silver or gold are ruled out completely due to their high price.
With our products, the customer can always choose whether to use a cost-optimized version in terms of purchasing or a loss-optimized version for operating the transformer. We can provide you with decision-making aids for choosing the right series based on amortization calculations and CO2 savings.