scope:

This part of IEC 61558 deals with safety aspects of transformers, reactors, power supply units and combinations thereof such as electrical, thermal and mechanical safety.

This document covers the following independent or associated stationary or portable types of dry-type transformers, power supply units, including switch mode power supply units, reactors and combinations thereof in the field of safety. The windings can be encapsulated or non-encapsulated. They are not forming a part of the distribution network.

NOTE 1 The distinction between transformers, power supply units and switch mode power supply units is as follows:

- for transformers, there is no change in frequency. However, transformers (e.g. constant voltage transformers) can have an internal resonance frequency not exceeding 30 kHz;

- for power supply units, the internal operational frequency and waveform are different from the supply frequency and waveform, and the internal operational frequency does not exceed 500 Hz (see definition 3.1.19);

- for switch mode power supply units, the internal operational frequency and waveform are different from the supply frequency and waveform and the internal operational frequency exceeds 500 Hz and does not exceed 100 MHz.

The relevant parts of IEC 61558-2 can be found in the introduction of this document.

a) Stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), isolating and safety isolating transformers, independent or associated with the following characteristics:

- rated supply voltage not exceeding 1 000 V AC;

- rated supply frequency not exceeding 500 Hz;

and complying with the following values, unless otherwise specified in the relevant part of IEC 61558-2:

• for isolating transformers:

- rated output for single phase transformers, not exceeding 25 kVA, and for polyphase transformers not exceeding 40 kVA;

- no-load output voltage and the rated output voltage exceeding 50 V AC, and not exceeding 500 V a.c, or 1 000 V AC to be in accordance with the national wiring rules or for a special application.

• for safety isolating transformers:

- rated output for single phase transformers not exceeding 10 kVA, and for polyphase transformers not exceeding 16 kVA;

- no-load output voltage and the rated output voltage not exceeding 50 V AC between conductors, or between any conductor and protective earthing.

NOTE 2 Isolating and safety isolating transformers are used where double or reinforced insulation between circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).

b) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced) separating transformers, auto-transformers, variable transformers and small reactors, independent or associated with the following characteristics:

- rated supply voltage not exceeding 1 000 V AC;

- rated supply frequency not exceeding 500 Hz;

and complying with the following values, unless otherwise specified in the relevant part of IEC 61558-2:

- no-load output voltage or a rated output voltage for both independent and associated transformers not exceeding 15 kV AC, and for independent transformers, a rated output voltage not less than 50 V AC;

- rated output not exceeding the following values:

• 1 kVA for single-phase transformers;

• 2 kVAR for single-phase reactors;

• 5 kVA for polyphase transformers;

• 10 kVAR for polyphase reactors.

NOTE 3 Separating transformers are used where double or reinforced insulation between circuits is not required by the installation rules or by the appliance specification.

NOTE 4 Normally, the transformers of type b) are intended to be associated with the equipment to provide voltages different from the supply voltage for the functional requirements of the equipment. The protection against electric shock can be provided or completed by other features of the equipment, such as the body. Parts of output circuits can be connected to the input circuit or to the protective earthing.

c) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced), independent or associated power supply units and switch mode power supply units incorporating one or more transformer(s) of type a) or b) with the following characteristics:

- rated supply voltage not exceeding 1 000 V AC;

- rated supply frequency not exceeding 500 Hz;

- internal operational frequency for power supply units not exceeding 500 Hz and for switch mode power supply units not exceeding 100 MHz;

and with the following values, unless otherwise specified in the relevant part of IEC 61558-2:

• for power supply units and switch mode power supply units incorporating isolating transformers:

- rated output for single- phase or polyphase power supply units or switch mode power supply units not exceeding 1 kVA;

- no-load output voltage and the rated output voltage exceeding 50 V AC or 120 V ripple-free DC, and not exceeding 500 V AC or 708 V ripple-free DC, or 1 000 V AC or 1 415 V ripple- free DC to be in accordance with national wiring rules or for a special application;

• for power supply units and switch mode power supply units incorporating safety isolating transformers:

- rated output for single- phase or polyphase power supply units and switch mode power supply units not exceeding 1 kVA;

- no-load output voltage and rated output voltage not exceeding 50 V AC or 120 V ripple-free DC between conductors, or between any conductor and protective earthing.

NOTE 5 Power supply units and switch mode power supply units incorporating isolating and safety isolating transformers are used where double or reinforced insulation between circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).

• for power supply units and switch mode power supply units incorporating separating transformers, auto-transformers , and variable transformers:

- rated output for single-phase or polyphase power supply units and switch mode power supply units not exceeding 1 kVA;

- no-load output voltage and rated output voltage for both, independent and associated transformers not exceeding 15 kV AC, and for independent transformers, a rated output voltage not less than 50 V AC.

NOTE 6 Power supply units and switch mode power supply units incorporating separating transformers are used where double or reinforced insulation between circuits is not required by the installation rules or by the appliance specification.

This document also applies to transformers, power supply units, switch mode power supply units and reactors incorporating electronic circuits.

This document is applicable to transformers without limitation of the rated output subject to an agreement between the purchaser and the manufacturer.

This document does not apply to external circuits and their components intended to be connected to the input or output terminals or socket-outlets of the transformers, power supply units and switch mode power supply units, and reactors.

Attention is drawn to the following:

- for transformers intended to be used in vehicles, on board ships, and 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 like fungus, vermin, termites, solar-radiation, and icing are considered;

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

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

Future technological development of transformers can necessitate a need to increase the upper limit of the frequencies; until then this document can be used as a guidance document.