Definitions of terms

Fuse protection
Design primary line protection (if necessary) to be slow – rule of thumb 1.5 … 2 x rated current, secondary always fuse to rated current (take into account starting current of loads e.g. motor)

Connections
0 – 50A to standard transformer terminals, 50 – 340A terminal blocks on head angle, a b 340A cable lugs or copper busbars. This can also be deviated from depending on the design.

Connected load
Always specified as apparent power in VA or kVA with cos ϕ =1, otherwise active power in W or kW plus cos ϕ of the connected machine, calculation 1ph transformer: P = U x I : cos ϕ , 3ph transformer P = U x I x √3 : cos ϕ

Tapping
Transformers can be designed with taps on both the input and output side. Taps on the input side are used, for example, to adapt and use the transformer at different mains voltages.

Conditionally short-circuit-proof transformer
This is a 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.

cos ϕ
Is determined by the load, e.g. motor, contactor. With cos ϕ = 0.5, the apparent power = 2 x active power), Pschein x cos ϕ = Pwirk

Inrush current
Describes the inrush current that occurs when switching on, depending on the phase. Transformers generally have an inrush current between 8 and 20 times the rated current. Toroidal cores, on the other hand, have up to 80 times the rated current. As a result, high back-up fuse values are required. Countermeasures can be: inrush current limiters, constructive measures in the transformer calculation.

Iron losses
Are remagnetization losses and also occur when the transformer is unloaded during operation. They depend on the induction, mains fluctuations (e.g. mains voltage +/-10%) and the frequency (e.g. 50Hz, 60Hz)

Fail-safe transformer
This is a transformer that fails permanently as a result of improper use, but does not pose any danger to the user or the environment.

Frequency
Determines the induction and iron losses, any 50Hz transformer can be operated at 60Hz. But not vice versa!

Separate winding
Transformers with separate windings have no conductive connection between individual windings and are galvanically isolated. The type power corresponds to the rated power.

High voltage
Voltages over 1000 volts

Extra-low voltage
Voltages below 50 volts

Copper weight
Can provide information about the winding losses and the associated efficiency for the same size.

Short-circuit proof transformer
This is a transformer in which the temperature does not exceed specified limit values if the transformer has been overloaded or short-circuited and is still operational after the overload or short-circuit has been removed.

Short-circuit voltage (uk)
This is the voltage that must be applied to the input winding so that the rated output current flows when the output winding is short-circuited. It is specified in % of the rated input voltage.

No-load output voltage (U0)
Is the voltage of an unloaded transformer at the rated input voltage and rated frequency.

No-load current (I0)
Is the current drawn by an unloaded transformer at the rated input voltage and rated frequency.

Non-short-circuit proof transformer
This is a transformer without protection against excessive temperature rise. The protective device must be implemented by the user.

Low voltage
Voltages from 51 to 1000 volts

Economy winding
In an economy winding, there is a conductive connection between the primary and secondary winding. In addition, there is a significant saving in material with economy windings.

Vacuum impregnation
Protection against moisture and aggressive atmospheres. Also bond the core plates to each other and the windings to each other and to their insulation. This achieves a high level of noise insulation and better thermal coupling of the winding.

Transformer power loss
The power loss of a transformer is made up of iron losses (caused by induction and mains frequency) and copper losses (caused by the current through the winding and its temperature). Iron losses are idle losses and are therefore always present. They can be optimized by the structure and type of core plates. Copper losses are load-dependent, they are always specified at rated load or rated current and can be influenced by the quality of the winding and the amount of copper weight.