Voltages, currents and frequencies


Minimum voltage
1 V, by parallel connection of more windings it is possible to reach even smaller voltages, for example for welding transformers


Maximum voltage
300 V per winding for toroidal transformers. By series connection of windings it is possible to reach even higher voltages, in total 5000 V with toroidal transformers. 15 000 V are possible with high voltage transformers built with bobbins and a special winding construction.


Minimum current
Imin is zero for transformers with static voltage.


Maximum current
Imax is 2000 A. Toroidal transformers reach a very high wire cross section due to a special winding construction. Cylinder windings are done with copper sheets. Like this we reach currents up to 10 000 A.


Default voltages primary
2 x 115 V or 230 V
The international, country specific mains voltages can be given on request. The brochure “Electric Current Abroad” of the U.S. Department of Commerce doesn’t only have voltages, but also common plug types listed. In Germany this brochure can be gotten from the ZVEI, Frankfurt.


Voltage tolerance primary
The voltage tolerance is considered conform to EN 61558 §15 with 0,94 times to 1,06 times of the value during the transformer design.


Default voltages secondary
2 x 6 V or 2 x 9 V or 2 x 12 V or 2 x 15 V or 2 x 18 V or 2 x 22 V or 2 x 24 V or 2 x 30 V or 2 x 38 V or 2 x 42 V or 2 x 55 V or 110 V. Of course other voltages are possible on request.


Voltage tolerance secondary
The secondary voltages are reached at the rated power. During no-load or partial load the voltages are higher. The voltage tolerance of the winding is determined conform to EN 61558, the norm 46435 and/or the internal house norm.


Frequencies
48 - 60 Hz sinusoidal for metal sheet transformers resp. line transformers with laminated core. Higher frequencies 60 Hz are possible with metal sheet transformers, e.g. for 400 Hz board nets of air planes or ships.


Non-sinusoidal voltages
Non-sinusoidal voltages have to considered during the design.  Ferrite transformers can manage frequencies up to the MHz range. Here we test voltages and inductance.


Duty cycle
Non-stop operation: Operation for an unlimited time
Short-time duty: Operation for a limited amount of time, whereas the start-up is from a cold condition an the pauses between the operation are enough, if the device can cool down to ambient temperature.
Periodic duty: Operation in a series of determined identical cycles. We can consider any periodic cyle during the calculation and simulation.


Safety voltages
ELV: Voltage, that doesn’t exceed the upper limit of voltage range 1 of IEC 60449
SELV: Voltage, that doesn’t exceed 50 V alternating current or 120 V smoothed direct current between the conductors or between a conductor and earth in a circuit which is separated from the supplying net with an isolating transformer.
SELV-circuit: ELV-circuit with safety isolation against other circuits and no grounding connectors or touchable conductive parts.
PELV-circuit: ELV-circuit with safety isolation against other circuits. Due to reasons of operation this circuit may be grounded and/or conductive parts that can be touched may be grounded as well.
FELV-circuit: ELV-circuit, which has the ELV-voltages for reasons of operation but doesn’t meet the requirements that are made to SELV and PELV.


Autotransformers
Autotransformers have a connected input and output winding. In other words there is only one winding with a tapping. A second winding is saved. The transferable power is higher at the same type size as a normal transformer.
Load factor: fb = 1 - Udown/Uup
Auto transformer output: Pauto = Poutput x fb

Example:
Input 115 V, Output 230 V, Output power 200 VA
Load factor: fb = 1 - 115 V / 230 V = 0,5
Auto transformer output: Pauto = 200 V x 0,5 = 100 VA

Consequently the autotransformer only needs half the type size of an isolating transformer.
Attention: The autotransformer has no galvanic separation between input and output. The dangerous ground potential is at the output.


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