The document discusses neutral sizing for electrical systems considering harmonic currents. It covers technical standard prescriptions from IEC 60364-5-52 allowing for smaller neutral conductor sizing if maximum harmonic neutral current is not greater than the reduced cross section. An example calculation is shown applying the criteria to different load scenarios. Typical harmonic contents are listed for sources like electronic loads, fluorescent lamps, and arc furnaces.

1. Angelo Baggini, angelo.baggini@unibg.it, Bergamo University - Engineering Department
Via Marconi 5, 24044 Dalmine (BG) – Italy
Leonardo Energy Academy
Neutral sizing

2. 1.Technical standard prescriptions
2.Theoretical background
• Harmonics
• Neutral current
3.Sizing criteria
4.Example
5.Typical hamonic contents

3. Technical standard
prescriptions

4. IEC 60364-5-52 Art. 524.3
For polyphase circuits where each phase conductor has a cross-
sectional area greater than 16 mm2 in copper or 25 mm2 in aluminium,
the neutral conductor may have a smaller cross-sectional area than that
of the line conductors if the following conditions are simultaneously
fulfilled:
• the expected maximum current including harmonics, if any, in the
neutral conductor during normal service is not greater than the
current-carrying capacity of the reduced cross sectional area of the
neutral conductor;
• the neutral conductor is protected against overcurrents according
to the rules of 431.2 of IEC 60364-4-43;
• the size of the neutral conductor is at least equal to 16 mm2 in
copper or 25 mm2 in aluminium.

5. Theoretical background

6. Theorethical background

7. Theorethical background

8. Theorethical background

9. Theorethical background

10. Theorethical background

11. Parameters
Harmonic Components
Individual Harmonic Distortion
Total Harmonic Distortion (THD)
(%)
a
100D
1
n
n
a
=
(%))(
2
2
12
2
∑∑
∞
=
∞
=
==
n
n
n
nt
a
a
DD

12. Balanced linear load
Harmonic distortion – Neutral current (1)
Theorethical background

13. Unbalanced linear
load
Harmonic distortion – Neutral current (2)
Theorethical background

14. Non linear load
Harmonic distortion – Neutral current (3)
Theorethical background

15. Zero sequence harmonics
Harmonic distortion – Neutral current (4)
Theorethical background

16. Zero sequence harmonics
Harmonic distortion – Neutral current (4)
Theorethical background

17. Zero sequence harmonics
Harmonic distortion – Neutral current (4)
Theorethical background

18. Zero sequence harmonics
Harmonic distortion – Neutral current (4)
Theorethical background

19. Sizing criteria

20. Sizing criteria
IEC 60364-5-52 Annex D
Reduction factors for harmonic currents
in four-core and five-core cables
Third harmonic
content of phase
current
(%)
Size selection is
based on phase
current
Size selection is
based on neutral
current
0-15 1,00 -
15-33 0,86 -
33-45 - 0,86
45 - 1,00

21. Example

22. INSTALLATION METHOD C
Example
Phases 3
Design load 37,5 A
Number of cores 4
Insulation EPR
Installation method Clipped to a wall

23. Example
• Cable size related to phase currents
⇒ 4 mm2
IEC60364-5-52

24. Office # 1
3 h = 22%
• IN = 37,5 · 0,22 · 3 = 24,7 A
• IF = 37,5 A
• IN < IF size related to phase current
Equivalent phase current:
⇒ 6 mm2
(IEC 60364-5-52 tab. A.52-5 )
6,43
86,0
5,37
=
Example

25. Sizing criteria
IEC 60364-5-52 Annex D
Reduction factors for harmonic currents
in four-core and five-core cables
Third harmonic
content of phase
current
(%)
Size selection is
based on phase
current
Size selection is
based on neutral
current
0-15 1,00 -
15-33 0,86 -
33-45 - 0,86
45 - 1,00

26. Office # 2
3 h = 40%
• IN = 37,5 · 0,4 · 3 = 45 A
• IF = 37,5 A
• IN < IF size related to neutral current
Equivalent neutral current:
⇒ 10 mm2
(IEC 60364-5-52 tab. A.52-5 )
3,52
86,0
45
=
Example

27. Sizing criteria
IEC 60364-5-52 Annex D
Reduction factors for harmonic currents
in four-core and five-core cables
Third harmonic
content of phase
current
(%)
Size selection is
based on phase
current
Size selection is
based on neutral
current
0-15 1,00 -
15-33 0,86 -
33-45 - 0,86
45 - 1,00

28. Lighting equipment (FLC)
3 h = 72% + 9 h = 33,9% + …
• IN = 37,5 · 1,30 · 3 = 146,2 A
• IF = 37,5 A
• IN > IF size related to neutral current
Equivalent neutral current:
− 35 mm2
(IEC 60364-5-52 tab. A.52-5 )
2,146
1
2,146
=
Example

29. Typical harmonic contents

30. Sources of harmonics
• Electronic loads
• Fluorescent lamps
• Arc furnaces
• Power transformers

31. Typical harmonic content

32. Typical harmonic content
CFLs
• Dispersion + Attenuation
THD approx 130%

33. Typical harmonic content
Electromagnetic ballasts
THD approx 20%

34. Typical harmonic content
Arc furnaces
Melting Refining

35. Typical harmonic content
Arc furnaces

36. Typical harmonic content
Power transformers

37. 1.Technical standard prescriptions
2.Theoretical background
• Harmonics
• Neutral current
3.Sizing criteria
4.Example
5.Typical hamonic contents

38. Thank you
| Presentation title and date
For more information please contact
Angelo Baggini
Università di Bergamo
Dipartimento di Ingegneria
Viale Marconi 5,
24044 Dalmine (BG) Italy
email: angelo.baggini@unibg.it
ECD Engineering Consulting and Design
Via Maffi 21 27100 PAVIA Italy