Definitions of transformers

ELTRA transformers

Control transformers

Isolating transformer

DIN VDE 0570 | DIN EN 60742 | DIN EN 61558

The control transformer is a separated transformer and intended for supplying auxiliary power circuits DIN VDE 0570 part 2-2. The input winding is separated from the output winding by at least basic insulation. Control transformers have a small voltage drop with an inductive load. In accordance with DIN VDE 0113 part 1, a control transformer must be provided for electrical systems if the installations or system have more than 5 electromagnetic actuation coils, relays or sim. or control and signal devices are fitted outside the control cabinets and machines and when electronic control or signal circuits are to be supplied.

Scope: rated supply voltage  1000 V | rated frequency < 500 Hz

DIN VDE 0570 | DIN EN 60742 | DIN EN 61558

The isolating transformer is a transformer with protective sep aration between the input and output windings. Isolating transformers are used for electrical separation of power circuits, in order to limit dangers, which can result from unintentional simultaneous contact of the earth and parts under voltage or metal parts, which could be under voltage, when there is a fault in the insulation system.
The protective measure “protective insulation” can be fulfilled by isolating transformers. VDE 0570 part 2-4 all apply for isolating transformers.

Scope: rated supply voltage 1000 V | rated output voltage 1000 V (load and no load) | rated frequency 500 Hz | rated output for single phase 25 KVA | rated output for three phase 40 KVA

Isolating transformer for the supply of medical rooms

Safety isolating transformer

DIN VDE 0570 / 0107 | DIN EN 60742 | DIN EN 61558

An isolating transformer for the supply of medical rooms with double or reinforced insulation between each part of the transformer except between the core and the body and screening between two windings. Single phase transformers have a midpoint for monitoring equipment of the secondary winding. The lead out of the midpoint shall be connected to a separate terminal. The transformers are used in electrical installations in hospitals and locations for medical use outside hospitals in IT systems. The provisions of DIN VDE 0107 11.89 apply.

Short circuit voltage max. 3% of the rated input voltage No-load input current max. 3% of the rated input current The inrush-current max. 12 times of the rated input current The rated output shall be between 3 KVA and 10 KVA The rated output voltage max 230 V a.c., single or three phase. Shutdown due to overloading is not permissible with these transformers. A monitoring device should be provided for checking the load (temperature or current) with an optical and acoustic signal.

DIN VDE 0570 | DIN EN 61558

A safety isolating transformer is an isolating transformer for supplying SELV- or PELV- circuits. Safety transformers are designed to supply a device or distributor power circuit in order to prevent impermissibly high or possibly dangerous contact voltage.
The protective measure “low safety voltage” can be fulfilled by safety isolating transformers.
DIN VDE 570 part 2-6 all apply for safety transformers.

Scope:  rated supply voltage 1000 V | rated frequency 500 Hz | rated output voltage 50 V a.c. or 120 V ripple free d.c. | rated output for single phase 10 KVA | rated output for three phase 16 KVA

Step transformer

Toroidal variable transformer

DIN VDE 0570 | DIN EN 61558 Step transformer

A step transformer is an auto transformer with tappings. This transformer is suitable as in-line transformer for electrical consumers. For example: speed control of motors for ventilators.

DIN VDE 0552 / 0570

toroidal variable transformers are used, if the fine adjustement of alternating voltage from zero up to the maximum value is required.

Auto transformer

Magnetic voltage regulators

DIN VDE 0570 | DIN EN 61558

An auto transformer is a transformer in which input and output windings have common parts. There is no galvanical separation. A distinction is made between core power and rated power. The core power can be calculated from the transformation ratio and the rated power with the aid of the table (auto transformer rating and examples).
A significant saving of materials is achieved with one-coil winding because the core power is smaller than the rated power.

It is calculated from the following formula: Pb = Pd x (1-(Uu/Uo))
Pb = Core power
Pd = rated power
Uu = Undervoltage
Uo = High voltage

DIN VDE 0550

Magnetic voltage regulators are used in powering sinks heavily dependent upon constant and uniform voltage. Even if the input voltage is heavily disorted and for loads continously fluctuating between  0 and 100 % it is possible to maintain virtually constant secondary voltages.

Power supply units

Stabilized power supply units

DIN VDE 0570 | DIN EN 61558   DIN EN 61131-2

The power supply units for supplying electronic circuits are single phase or three phase with silicon bridge rectifier, decoupling capacitor, smoothing capacitor, and varistor. The direct voltage is unregulated and residual ripple < 5%. For devices with  24 V d.c.  output voltage and a  ripple factor of  5% the following values are laid down:
Upper limit 28,8 V | Lower limit 20,4 V

These values are adhered to, independently of mains supply fluctuation (-10%   +6%).

DIN VDE 0570 | DIN EN 61558

Stabilized power supply units  are used,  if a constant output voltage with anespecially low ripple factor is required.

Rectifier devices

DIN VDE 0570 | DIN EN 61558

Rectifier devices are used, if no special requirements have been set for ripple voltage by the d.c. consumer. Isolating transformers and rectifier circuits of most basic design are employed here.


Starting transformers / reactors

DIN VDE 0532 / 0570 | DIN EN 60289 | DIN EN 61558

Reactors are resistances with a high inductive and low ohmic fraction. They find following applications:

  • Line reactors for limiting the short-circuit current to a predefined value
  • Smoothing reactors for reducing the ripple factor with pulse-form direct voltages.
  • Commutation reactors in system with controlled semi-conductors for limiting the commutation current.
  • Filter circuit reactors in compensation systems for protecting the capacitors from impermissible harmonic waves.

DIN VDE 0532 | DIN EN 60591   IEC 76 / 14

Starting  transformers  and  reactors  are  used  for  reducing  the starting  current  of  three  squirrel  cage  motors.

Following  dates  must  be  known:
rated voltage,  starting current,  run-up-time,  stars per hour and  the motor rated dates.