IEC TS 63346-2-3:2025
(Main)Low-voltage auxiliary power systems - Part 2-3: Design criteria - Low-voltage AC auxiliary power systems for substations
Low-voltage auxiliary power systems - Part 2-3: Design criteria - Low-voltage AC auxiliary power systems for substations
IEC TS 63346-2-3:2025 specifies common rules and requirements for the design of low voltage (LV) AC auxiliary power systems (APSs) intended to be installed in substations, mainly covering the configuration of AC power sources, system wiring, protection, electric equipment selection and physical layout.
For the purpose of interpreting this document, an AC APS in this document is considered as follows:
- with a nominal voltage up to and including 1 kV AC;
- providing LV AC power to substation AC loads.
Though it is discussed where necessary, AC loads as well as high voltage (HV) part is beyond the scope of this document.
Substations in this document refer to those which are part of an electrical system and contain equipment that either receives and distributes electrical energy or transforms voltages to the levels required by the loads they supply, or both.
General Information
Standards Content (Sample)
IEC TS 63346-2-3 ®
Edition 1.0 2025-11
TECHNICAL
SPECIFICATION
Low-voltage auxiliary power systems -
Part 2-3: Design criteria - Low-voltage AC auxiliary power systems for
substations
ICS 29.240 ISBN 978-2-8327-0800-2
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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 6
4 Abbreviated terms . 7
5 General requirements . 7
5.1 General . 7
5.1.1 System function . 7
5.1.2 Basic requirements . 8
5.2 Environmental conditions . 9
5.3 Electrical requirements . 9
5.3.1 Nominal voltage and nominal frequency . 9
5.3.2 Current rating . 10
5.3.3 System earthing . 10
5.3.4 Over-voltage protection and insulation coordination . 10
5.3.5 Harmonic distortion withstand capability . 11
6 Load . 11
6.1 General . 11
6.2 Load classification . 11
6.2.1 Classification by the degree of importance of the load . 11
6.2.2 Classification by load operation mode . 12
6.2.3 Classification by load operation duration . 13
6.3 Load calculation . 13
6.3.1 Station service transformer sizing . 13
6.3.2 Load calculated by parts . 14
7 System structure and wiring . 15
7.1 General . 15
7.2 Power supply of LV AC APS . 15
7.2.1 Power sources . 15
7.2.2 Selection of power sources . 16
7.3 Wiring of AC APS . 16
7.3.1 Configuration of power sources . 16
7.3.2 Wiring principles . 17
7.3.3 Typical wiring diagrams . 18
8 System protection and control . 21
8.1 Protection . 21
8.2 Control and signal . 21
8.3 Measurement and electric energy measuring . 22
9 Equipment selection . 22
9.1 General requirement . 22
9.2 Station service transformer . 22
9.2.1 General . 22
9.2.2 Electrical performance requirement . 23
9.2.3 Construction requirement . 23
9.3 AC distribution boards . 23
9.3.1 General . 23
9.3.2 Type selection . 24
9.4 Protective device . 24
9.4.1 General . 24
9.4.2 Electrical performance requirement . 24
9.4.3 Combination of protective devices . 24
9.5 Conductor . 25
9.5.1 General . 25
9.5.2 Conductor cross-section . 25
9.6 UPS . 25
9.7 Diesel generator . 26
9.7.1 General . 26
9.7.2 Electrical performance requirements . 26
10 Physical layout of APS . 26
10.1 General . 26
10.2 Station service transformer . 26
10.3 Diesel generator . 27
10.4 Power distribution room . 27
Annex A (informative) Typical AC loads in substations . 29
Annex B (informative) Applications of TN system in LV AC APS . 30
Bibliography . 31
Figure 1 – Diagram of basic single busbar arrangement . 18
Figure 2 – Diagram of sectionalized single busbar arrangement . 19
Figure 3 – Diagram of sectionalized single busbar with physical separation . 19
Figure 4 – Diagram of sectionalized single busbar with dedicated standby power
supply . 20
Figure 5 – Diagram of a typical wiring in France. 21
Table A.1 – Typical AC loads in substations . 29
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Low-voltage auxiliary power systems -
Part 2-3: Design criteria - Low-voltage AC auxiliary power systems for
substations
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