scope:

This part of IEC 61558 deals with safety aspects of control transformers and power supplies incorporating control transformers such as electrical, thermal and mechanical safety.

This Part 2-2 is applicable to control transformers and power supplies incorporating both control transformers and electronic circuits. This Part 2-2 is not applicable to external circuits and their components intended to be connected to the input terminals, output terminals or socket-outlets of the transformer and power supplies.

This Part 2-2 does not apply to transformers covered by IEC 60076-11.

This Part 2-2 applies to stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), independent or associated control transformers and power supplies incorporating a control transformer, having a rated supply voltage not exceeding 1 000 V a.c. and rated supply and internal operating frequency not exceeding 500 Hz.

The rated thermal output does not exceed:

- 25 kVA for single-phase control transformers and power supplies incorporating control transformers;

- 40 kVA for poly-phase control transformers and power supplies incorporating control transformers.

This Part 2-2 is applicable to control transformers and power supplies incorporating control transformers without limitation of the rated output subject to an agreement between the purchaser and the manufacturer.

This Part 2-2 is applicable to dry-type transformers. The windings may be encapsulated or non-encapsulated.

The no-load output voltage or the rated output voltage does not exceed 1 000 V a.c. or 1 415 V ripple-free d.c.

For independent control transformers and independent power supplies incorporating control transformers, the no-load output voltage and / or the rated output voltage is not less than 50 V a.c., or 120 V ripple free d.c.

Control transformers covered by this Part 2-2 are used only in applications where double or reinforced insulation between circuits is not required by the installation rules or by the end product standard.

NOTE 1 Normally, the control transformers and power supplies incorporating control transformers are intended to be used with equipment to provide voltages different from the supply voltage for the functional requirements of the equipment. The protection against electric shock may be provided (or completed) by other features of the equipment, such as the body. Parts of output circuits may be connected to the input circuits or to protective earth.

This Part 2-2 is applicable to control transformers and power supplies incorporating control transformers associated with specific equipment, to the extent decided upon by the relevant IEC technical committees.

NOTE 2 Attention is drawn to the following:

- for control transformers and power supplies incorporating control transformers intended to be used in vehicles, on board ships and on board aircraft, additional requirements (from other applicable standards, national rules, etc.) may be necessary;

- measures to protect the enclosure and the components inside the enclosure against external influences such as fungus, vermin, termites, solar-radiation, and icing should also be considered ;

- the different conditions for transportation, storage, and operation of the control transformers and power supplies incorporating control transformers should also be considered;

- additional requirements in accordance with other appropriate standards and national rules may be applicable to control transformers and power supplies incorporating control transformers intended for use in special environments, such as tropical environments.

NOTE 3 Future technological development of control transformers and power supplies incorporating control transformers may necessitate a need to increase the upper limit of the frequencies, until then this Part 2-2 may be used as a guidance document.