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Power quality – IEC 61000

In the IEC 61000-series block, there is a mix of standards with varying requirements. In Europe, the predominant standards are IEC 61000-2-2 which covers low frequency disturbances in public networks and IEC 61000-2-4 that covers low frequency disturbances in industrial and non-public networks. Note the term “low-frequency”; in this context, low frequency is up to 9 kHz, or the equivalent of the 180th harmonic in a 50 Hz grid.

IEC 61000-2-2 requires a maximum voltage distortion of 8 %, and IEC 61000-2-4 requires a maximum voltage distortion of 5 % (in class 1, protected supplies), 8 % (in class 2, industrial networks) and 10 % (in class 3, dedicated or heavy industry networks). The levels below are compatibility levels meaning that they cannot directly or easily be translated to acceptable emission levels. In other words, it is difficult to apply this standard to an installation or a piece of equipment in order to make sure if the machine or equipment will comply with regulation; rather, the limits will tell if an installation as a whole is compliant or not.

IEC 61000-2-2:2002

Odd harmonics non-multiple of 3Odd harmonics non-multiple of 3Odd harmonics multiple of 3Odd harmonics multiple of 3Even harmonicsEven harmonics
Harmonic Order hHarmonic Voltage %Harmonic Order hHarmonic Voltage %Harmonic Order hHarmonic Voltage %
563522
6591.541
113.5150.460.5
133210.380.5
17 ≤ h ≤ 37 2.27 x (17/h) – 0.2721 < h ≤ 390.210 ≤ h ≤ 400.25 x (10/h) + 0.25

IEC 61000-2-4:2002

Harmonic Order hClass 1 Harmonic Voltage %Class 2 Harmonic Voltage % Class 3 Harmonic Voltage %
5368
7357
1133.55
13334.5
17224
17 < h ≤ 492.27 x (17/h) – 0.272.27 x (17/h) – 0.274.5 x (17/h) – 0.5
4.5 x (17/h) – 0.5 Class 1 Harmonic Voltage %Class 2 Harmonic Voltage % Class 3 Harmonic Voltage %
3356
91.51.52.5
150.30.42
210.20.31.75
21 < h ≤ 45 0.20.21
Harmonic Order hClass 1 Harmonic Voltage %Class 2 Harmonic Voltage % Class 3 Harmonic Voltage %
2223
4111.5
60.50.51
80.50.51
100.50.51
10 < h ≤ 50 0.25 x (10/h) – 0.25 0.25 x (10/h) – 0.25 1

Additional standards cover regulation of individual pieces of equipment, such as IEC 61000-3-2 or IEC 61000-3-12. The latter cover limit for harmonic currents produced by equipment connected to public low voltage systems with more than 16 A but less or equal than 75 A per phase.

Table 3 – current emission limits for balanced three-phase equipment (IEC 61000-3-12 (2011), PG. 15)

Minimum RsceI5*I7* I11*I13*THC/Iref**PWHC/Iref**
3310.77.23.121322
66149531625
1201912742228
25031201273738
350402515104846

*Admissible individual harmonic current Ih/Iref (%), Iref = reference current; Ih = harmonic current component
**Admisable harmonic parameters (%)

The relative values of even harmonics up to order 12 shall not exceed 16/h %. Even harmonics above order 12 are taken into account into THC and PWHC in the same way as odd order harmonics. Linear interpolation between successive Rsce values is permitted.

As can be seen, like in IEEE 519, an increased Rsce (which is equivalent to Isc/IL) allows for higher current harmonics. (As a reminder, for a discussion on how current harmonics are converted into voltage harmonics, see Appendix C.) Again, this is reasonable and understandable in a system standard, however very confusing in a product standard. For a user of the product, it might be impossible to know the relevant limits – since interpolation is allowed, the exact limits must be calculated! From a testing standpoint, the requirements on the same product will vary wildly depending on where it is installed. To complicate things further, there are several tables outlining the harmonic requirements, and there is even a flowchart to determine which table to use. Below is table 5 from IEC 61000-3-12: 

Table 5 – current emission limits for balanced three-phase equipment under specified conditions (D, E, F) (IEC 61000-3-12 (2011) PG. 16)

Minimum RsceI5I7 I11I13I17I19I23I25I29I31I35I37THC / Iref**PWHC / Iref**
3310.77.23.1221.51.51.511111322
≥250 2517.312.110.78.47.86.86.55.45.24.94.73570

*Admissible individual harmonic current Ih/Iref (%), Iref = reference current; Ih = harmonic current component
**Admissible harmonic parameters (%)   

For Rsce equal to 33, the relative values of even harmonics up to order 12 shall not exceed 16/h %. The relative values of all harmonics from I14 to I40 not listed above shall not exceed 1% of Iref.

For Rsce ≥250, the relative values of even harmonics up to order 12 shall not exceed 16/h %. The relative values of all harmonics from I14 to I40 not listed above shall not exceed 3% of Iref.

Linear interpolation between successive Rsce values is permitted.

As can be seen, the table only specifies minimum and maximum levels, and the reader must interpolate to find the relevant level. In defense of the standard, it is stated that the Rsce = 33 level must be selected for full product compliance. However, since voltage limits are not defined in the same standard, there is no guarantee that the emission levels are compatible with the required harmonic distortion levels in other IEC 61000 standards!

It can be discussed whether the various IEC standards always fill the gap between compatibility levels and emission levels; this is beyond the scope of this text.