Requirements for a welding transformer. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric welding. Requirements for a welding transformer. Encyclopedia of radio electronics and electrical engineering

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Unlike conventional transformers, a welding transformer (especially a household one) must have minimal dimensions and weight.

The specifics of the welding transformer lies in the fact that it is not loaded at all 100% of the time of its inclusion. The degree of loading is determined by the duration of the load:

where t_p - duration of the working cycle, t_ц - the total cycle time, consisting of a working cycle and a pause.

The cycle duration is taken equal to:

5 min for manual arc welding sources;
10 min for mechanized welding sources.

It is usually considered that the PV of a welding transformer does not exceed 60%. For a household welding transformer, an even lower value of PN = 20% is taken. This circumstance allows, by increasing the current density in the windings, to reduce the total cross section of the winding without a significant deterioration in its thermal regime.

To calculate current density for any value of PN, you can use the formula

where J_n - current density for an arbitrary value of PN, A/mm2; J - current density for long-term operation, A/mm2; PN - the required value of PN.

Let's calculate current density in copper windings welding transformer, designed for PV = 20%, if the current density J = 3,5 A/mm2 is allowed during long-term operation of the same transformer.

Since aluminum has a higher resistivity than copper, it is necessary to choose a current density 1,6 times less for it. That is, if a density of 8 A / mm2 is permissible for copper, then for aluminum it is 5 A / mm2.

Author: Koryakin-Chernyak S.L.

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