EN 61558-2-17:1997

SLOVENSKI STANDARD
01-julij-1999
Safety of power transformers, power supply units and similar - Part 2-17:
Particular requirements for transformers for switch mode power supplies (IEC
61558-2-17:1997)
Safety of power transformers, power supply units and similar -- Part 2-17: Particular
requirements for transformers for switch mode power supplies
Sicherheit von Transformatoren, Netzgeräten und dergleichen -- Teil 2-17: Besondere
Anforderungen an Sicherheitstransformatoren für Schaltnetzteile
Sécurité des transformateurs, blocs d'alimentation et analogues -- Partie 2-17: Règles
particulières pour les transformateurs pour alimentation à découpage
Ta slovenski standard je istoveten z: EN 61558-2-17:1997
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME
CEI
INTERNATIONALE
IEC
61558-2-17
INTERNATIONAL
Première édition
STANDARD
First edition
1997-02
PUBLICATION GROUPÉE DE SÉCURITÉ
GROUP SAFETY PUBLICATION
Sécurité des transformateurs, blocs d'alimentation
et analogues –
Partie 2:
Règles particulières pour les transformateurs
pour alimentation à découpage
Safety of power transformers, power supply units
and similar –
Part 2:
Particular requirements for transformers
for switch mode power supplies
 IEC 1997 Droits de reproduction réservés  Copyright - all rights reserved
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61558-2-17 © IEC:1997 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_________
SAFETY OF POWER TRANSFORMERS, POWER SUPPLY UNITS
AND SIMILAR –
Part 2: Particular requirements for transformers
for switch mode power supplies
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61558-2-17 has been prepared by IEC technical committee 96:
Small power transformers, reactors and power supply units and special transformers,
reactors and power supply units: Safety requirements.
It has the status of a group safety publication in accordance with IEC Guide 104: Guide for the
drafting of safety standards, and the role of Committees with safety pilot functions and safety
group functions (1984).
The text of this standard is based on the following documents:
FDIS Report on voting
96/52/FDIS 96/75/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This part 2 is intended to be used in conjunction with IEC 61558-1. It was established on the
basis of the first edition (1997) of that standard.
This part 2 supplements or modifies the corresponding clauses in IEC 61558-1, so as to
convert that publication into the IEC standard: Particular requirements for transformers for
switch mode power supplies.
61558-2-17 © IEC:1997 – 5 –
When a particular subclause of part 1 is not mentioned in this part 2, that subclause applies as
far as is reasonable. Where this standard states "addition", "modification" or "replacement", the
relevant text of part 1 is to be adapted accordingly.
In this standard, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type.
In the text of the standard the words in bold are defined in clause 3.
Subclauses which are additional to those in part 1 are numbered starting from 101;
supplementary annexes are entitled AA, BB, etc.

61558-2-17 © IEC:1997 – 7 –
SAFETY OF POWER TRANSFORMERS, POWER SUPPLY UNITS
AND SIMILAR −
Part 2: Particular requirements for transformers
for switch mode power supplies
1 Scope
Replacement:
This part 2 of IEC 61558 applies to associated power transformers for switch mode power
supplies, single-phase or polyphase, air-cooled:
– separating transformers;
– isolating transformers;
– safety isolating transformers,
having a rated supply voltage not exceeding 1000 V a.c. and a rated frequency of 500 Hz
to 1 MHz, the rated output not exceeding:
– 10 kVA for single-phase transformers;
– 16 kVA for polyphase transformers.
NOTE 1 – For higher frequencies, this standard may be used as a guide.
The no-load output voltage or the rated output voltage do not exceed:
– 1000 V a.c. or 1 415 V ripple-free d.c for separating transformers;
– 500 V a.c. or 708 V ripple-free d.c for isolating transformers.
NOTE 2 – For isolating transformers, the rated output voltage may be up to 1000 V a.c. or 1415 V ripple-free
d.c. in accordance with the national wiring rules or designed for special purposes.
– 50 V a.c. r.m.s. and/or 120 V ripple-free d.c for safety isolating transformers.
This standard is applicable to dry type transformers. The windings may be encapsulated or
non-encapsulated.
NOTES
3 For transformers filled with liquid dielectric or pulverized material, such as sand, additional requirements are
under consideration.
4 In locations where special environmental conditions prevail, particular requirements may be necessary in
accordance with IEC 364-5-51.
5 For higher output no-load voltages, additional requirements are necessary but this section may be used as a
guide.
2 Normative references
This clause of part 1 is applicable.

61558-2-17 © IEC:1997 – 9 –
3 Definitions
This clause of part 1 is applicable except as follows:
Addition:
3.1.101 switch mode power supply: A power supply incorporating a transformer for which
the rated frequency is different from the frequency of the input circuit.
4 General requirements
This clause of part 1 is applicable.
5 General notes on tests
This clause of part 1 is applicable except as follows:
5.2 Addition:
If the tests of 14.101 and of clause 15 are made on a specially prepared specimen, one
additional specimen is needed.
5.12 Replacement:
The transformers for switch mode power supplies shall comply with the relevant section of
IEC 61558-2 and the conditions under which they are used in the appliance or equipment shall
be in accordance with their marking. However, if they are used in an appliance or equipment
for which a relevant appliance or equipment standard exists, they may be tested under the
conditions present in the appliance or equipment for which they are intended.
Consequently a transformer for switch mode power supply tested under conditions present in
the appliance or equipment for which it is intended has to comply with the following clauses,
subclauses or parts thereof, all other clauses, subclauses or parts thereof being considered to
be covered by the relevant product standard:
1 - 2 - 3 - 4 - 5.1 - 5.2 - 5.3 - 5.4 - 5.5 - 5.6 - 5.7 - 5.12 - 7.1 - 7.2 - 7.5 - 8.2 - 8.11 - 14.101 - 18.1 -
18.2 - 18.3 - 19.1 - 19.12 - 20.9 - 26.1 - 26.2 - 26.3 - 26.101 - 26.102 - 26.103 - Annexes A, C, D,
G, K, L, M, N, P.
NOTE – Attention is drawn to the fact that if the appliance or equipment standard does not include tests for
short-circuit or overload protection of the transformer, relevant tests of clause 15 may have to be made.
6 Ratings
This clause of part 1 is applicable except as follows:
Addition:
6.101 The no-load output voltage shall not exceed:
– 1000 V a.c. or 1415 V ripple-free d.c. for separating transformers, for a.c. the preferred
values for the rated output voltage being: 72 V, 120 V, 230 V, 400 V, 440 V and 660 V;

61558-2-17 © IEC:1997 – 11 –
– 500 V a.c. or 708 V ripple-free d.c. for isolating transformers, for a.c. the preferred
values for the rated output voltage being: 72 V, 120 V, 230 V, 400 V and 440 V;
– 50 V a.c. and/or 120 V ripple-free d.c. for safety isolating transformers, for a.c. the
preferred values for the rated output voltage being: 6 V, 12 V, 24 V, 42 V and 48 V.
6.102 The rated output shall not exceed 10 kVA for single-phase transformers and 16 kVA
for polyphase transformers.
Preferred values for the rated output are:
10 VA, 16 VA, 25 VA, 40 VA, 63 VA, 100 VA, 160 VA, 250 VA, 400 VA, 630 VA, 1000 VA,
1600 VA, 2500 VA, 4000 VA, 6300 VA and 10 000 VA for single-phase transformers;
100 VA, 160 VA, 250 VA, 400 VA, 630 VA, 1000 VA, 1600 VA, 2500 VA, 4000 VA, 6300 VA,
10000 VA and 16 000 VA for polyphase transformers.
6.103 Rated frequencies range from 500 Hz to 1 MHz
6.104 The rated supply voltage shall not exceed 1000 V a.c.
7 Classification
This clause of part 1 is applicable.
8 Marking and other information
This clause of part 1 is applicable except as follows:

61558-2-17 © IEC:1997 – 13 –
8.11 Addition:
or Fail-safe separating transformer
F
F
Non-short-circuit-proof separating transformer
or
Short-circuit-proof separating transformer
or
(inherently or non-inherently)
or Fail-safe isolating transformer
F
F
Non-short-circuit-proof isolating transformer
or
Short-circuit-proof isolating transformer
or
(inherently or non-inherently)
Fail-safe safety isolating transformer
F
Non-short-circuit-proof safety isolating transformer
Short-circuit-proof safety isolating transformer
(inherently or non-inherently)
9 Protection against accessibility to hazardous live parts
This clause of part 1 is applicable except as follows:
9.2 Addition before the first paragraph:
– For safety isolating transformers:
Live parts of the output circuit, at a no-load output voltage not exceeding 35 V peak a.c. or
60 V ripple-free d.c., may be accessible in all cases.
Addition of the following new text after the second dash:
–for isolating and safety isolating transformers:
• parts giving access to live parts which are normally connected to an output circuit,
which because of the nature of its use, is accessible, provided that, for no-load output
voltages exceeding 35 V peak a.c. or 60 V ripple-free d.c. only one pole becomes
accessible.
61558-2-17 © IEC:1997 – 15 –
10 Change of input voltage setting
This clause of part 1 is applicable.
11 Output voltage and output current under load
This clause of part 1 is applicable.
12 No-load output voltage
This clause of part 1 is applicable except as follows:
Addition:
12.101 The no-load output voltage shall not exceed:
– 1000 V a.c. or 1415 V ripple-free d.c. for separating transformers;
– 500 V a.c. or 708 V ripple-free d.c for isolating transformers;
– 50 V a.c. and/or 120 V ripple-free d.c. for safety isolating transformers,
under any circumstance even when independent output windings which are not intended to be
connected in series are connected in series.
13 Short-circuit voltage
This clause of part 1 is applicable.
14 Heating
This clause of part 1 does not apply except as follows:
14.101 For transformers where the switching frequencies are not higher than 40 kHz in
general the test methods and the values from table 1 can be used.
NOTE – For transformers in which frequencies are higher than 40 kHz, test methods and values are under
consideration.
For transformers where switching frequencies are not higher than 40 kHz an additional
thermocouple or equivalent temperature measurement method shall be used to determine the
temperature of the insulation material between the windings. In particular, the temperature of
the insulation material between input and output windings shall be measured to ensure that the
maximum temperature of the classified material is not exceeded by the additional losses
caused by high switching frequencies and the voltage wave shapes, which contain even higher
harmonics frequencies.
This can be achieved by preparing a special specimen with a thermocouple or equivalent
placed in the hottest area in agreement with the manufacturer so that the effect on the normal
functioning of the unit is minimized.
NOTE – Care has to be taken that the magnetic behaviour of the thermocouple has no effect on the reading of
the temperature.
Compliance is checked by calculation or measurements.
...