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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. 

IEC61000

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 3
Odd harmonics
multiple of 3
Even harmonics
Harmonic
Order
h
Harmonic
Voltage
%
Harmonic
Order
h
Harmonic
Voltage
%
Harmonic
Order
h
Harmonic
Voltage
%
5 6 3 5 2 2
6 5 9 1.5 4 1
11 3.5 15 0.4 6 0.5
13 3 21 0.3 8 0.5
17 ≤ h ≤ 37 2.27 x (17/h) – 0.27  21 < h ≤ 39 0.2 10 ≤ h ≤ 40 0.25 x (10/h) + 0.25 

IEC 61000-2-4:2002

Harmonic Order
h
Class 1 
Harmonic Voltage 
%
Class 2 
Harmonic Voltage 
Class 3 
Harmonic Voltage 
5 3 6 8
7 3 5 7
11 3 3.5 5
13 3 3 4.5
17 2 2 4
17 < h ≤ 49 2.27 x (17/h) – 0.27 2.27 x (17/h) – 0.27 4.5 x (17/h) – 0.5 
Harmonic Order
h
Class 1 
Harmonic Voltage 
%
Class 2 
Harmonic Voltage 
Class 3 
Harmonic Voltage 
3 3 5 6
9 1.5 1.5 2.5
15 0.3 0.4 2
21 0.2 0.3 1.75 
21 < h ≤ 45  0.2 0.2 1
Harmonic Order
h
Class 1 
Harmonic Voltage 
%
Class 2 
Harmonic Voltage 
Class 3 
Harmonic Voltage 
2 2 2 3
4 1 1 1.5
6 0.5 0.5 1
8 0.5 0.5 1
10 0.5 0.5 1
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 Rsce Admissible individual harmonic current Ih/Iref a 
(%) 
Admissible harmonic parameters (%) 
I5 I7 I11 I13 THC/Iref PWHC/Iref
33 10.7 7.2  3.1 2 13 22
66 14 9 5 3 16 25
120 19 12 7 4 22 28
250 31 20 12 7 37 38
350  40 25 15 10 48 46
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.
a Iref = reference current; Ih = harmonic current component

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
Rsce
Admissible individual harmonic current Ih/Iref a 
(%) 
Admissible harmonic parameters (%)
I5 I7 I11 I13 I17 I19 I23 I25 I29 I31 I35 I37 THC / Iref  PWHC / Iref
33  10.7 7.2 3.1 2 2 1.5 1.5 1.5 1 1 1 1 13 22
≥250 25 17.3 12.1 10.7 8.4 7.8 6.8 6.5 5.4 5.2 4.9 4.7 35 70
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.
a Iref = reference current; Ih = harmonic current component

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.

Marine Standards

The marine standards set forth by the classification societies define acceptable distortion levels. Like the grid standards, these are not concerned with the harmonic current injection, but only with the resulting voltage distortion. This is logical on a marine vessel or offshore installation, the island configuration with generators. The table below details both total harmonic distortion limit and individual harmonic limit on the voltage for a number of major classification societies, namely DNV GL, ABS, RS and KR:

Classification SocietyTHDU limitIndividual harmonic limitReference
DNV GL
Det Norske Veritas /
Germanischer Lloyd
< 8 %  < 5 % Rules for classification: Ships (Oct. 2019)
Part 4, Chapter 8, Section 2, 1.2.7
ABS
American Bureau of Shipping
< 8 % < 5 % Rules for Building and Classing Steel Vessels (Jul. 2019)
Part 4, Chapter 8, Section 2, 7.21
BV
Bureau Veritas
< 8 % ≤ 15th: 5 %, then falling logarithmic to 1 % at 100th Rules for Classification of Steel Ships (Jan. 2020)
Part C, Chapter 2, Section 2, 2.4.2 
LR
Lloyd’s Register
< 8 % None of the harmonics above 25th shall exceed 1.5 %  Rules and Regulations for the Classification of Ships (July 2019)
Part 6, Chapter 2, Section 1, 1.8.3
RINA
Registro Italiano Navale
< 10 % ≤ 15th: 5 %, then falling logarithmic to 1 % at 100th  Rules for the Classification of Ships (Jan. 2020)
Part C, Chapter 2, Section 2, 2.2.2
CCS
China Classification Society
< 10 % ≤ 15th: 5 %, then falling linearly to 1 % at 100th Rules for Classification of Sea-Going Ships (Jul. 2018)
Part 8, Chapter 15.2.2.2
RS
Russian Maritime
Register of Shipping
< 10 % ≤ 15th: < 10 % 16th – 99th: falling logarithmic to 1 %
100th – 200th: < 1 %
Rules for the Classification and Construction of Sea-Going Ships (Jan. 2020)
Part XI, Section 2.2.1
KR
Korean Register
< 8 % < 3 % Rules for the Classification of Steel Ships (2019)
Part 6, Chapter 1, Section 8

Note that DNV GL, ABS and KR all have individual harmonic limit that is not dependent of harmonic order – which means that the maximum of 5 % of for example DNV GL applies equally at 5th harmonic as well as at 49th harmonic! Surely, 5 % is much more damaging at higher harmonic orders. CCS, BV, RINA and RS circumvents this by specifying a falling curve from 15th harmonic to 100th harmonic – linear curve for CCS and logarithmic for BV, RINA and RS. Also note that CCS specifies the curve until infinite harmonic order, which technically makes it impossible to determine compliance, as no instrument have infinite bandwidth!

IEEE 519-2014

A commonly used and very important standard is IEEE 519-1992, and more recently IEE 519-2014. The standard, among other things, puts two requirements on harmonics; and absolute maximum THDU level, and a variable maximum TDD level. All limits are applied to the Point of Common Coupling (PCC), which is the interface between utility (sometimes called operator) and consumer. The PCC can be located at any voltage level. In some cases, the PCC is considered to be an internal point in a system of particular interest; this is not in line with the original intention of the IEEE 519, which considered only the connection point between operator and user (consumer). These concepts are illustrated in the figure below:

IEEE519 standard

Below is Table 1, from IEEE 519 (2014), p6, “Voltage distortion limits”, as outlined below:

 

Table 1 (IEEE 519-2014, pg. 7) Voltage Distortion Limits

Bus voltage V at PCCIndividual harmonic (%)Total harmonic distortion THD (%)
 V ≤ 1.0 kV 5.0 8.0
 1 kV < V ≤ 69 kV 3.0 5.0
 69 kV < V ≤ 161 kV 1.5 2.5
 161 kV < V 1.0 1.5a

a High-voltage system are allowed up to 2.0% THD where the cause is an HVDC terminal whose effects will have been attenuated at points in the network where future users may be connected.

Note that these levels are absolute, and not depending on the size of the operator/utility or the consumer. Also note that the resulting distortion level is the result of the combination of the background distortion and the load distortion created by the consumer.

Following below is an excerpt from Table 2 (IEEE 519-2014, pg. 7, replacing table 10.3, p78, “Current Distortion Limits for General Distribution Systems” in IEEE 519-1992). This table is of importance as it defines target levels to be achieved depending on the short circuit ratio ISC/IL. ISC is the rated short circuit current at PCC, and IL is the maximum demand load current at PCC.

 

Table 2 (IEEE 519-2014, pg. 7)
Current distortion limits for systems rated 120 V through 69 kV

ISC/IL  Individual harmonic limits (Odd harmonics) a,b TDD Required
 3 ≤ h < 11  11 ≤ h < 17  17 ≤ h < 23  23 ≤ h < 35  35 ≤ h ≤ 50
<20c 4.0 2.0 1.5 0.6 0.3 5.0
20<50  7.0 3.5 2.5 1.0 0.5 8.0
50<100 10.0 4.5 4.0 1.5 0.7 12.0
100<1000 12.0 5.5 5.0 2.0 1.0 15.0
>1000 15.0 7.0 6.0 2.5 1.4 20.0

a Even harmonics are limited to 25% of the odd harmonic limits above
b Current distortions that result in a dc offset, e.g., half-wave converters, are not allowed
c All power generation equipment is limited to these vales of current distortion, regardless of actual Isc/IL.
ISC = maximum short circuit current at PCC
IL = maximum demand load current (fundamental frequency component) at PCC

Note the major difference in how harmonics are limited at the current and at the voltage. For voltage harmonics, all requirements are absolute. For current harmonics, the authors of IEEE 519 chose to limit the current harmonics depending on how strong the voltage source is. This is reasonable and understandable; a strong grid will be able to suppress current harmonics to a much larger degree without the voltage being influenced than a weak grid. In very weak grids, voltage distortion and current distortion may have similar values. Hence, it can be argued that current emission requirements must be stricter in weaker grids.

Total Demand Distortion 

Total Demand Distortion (TDD) is defined as the ratio of the root mean square of the harmonic content, considering harmonic components up to the 50th order and specifically excluding interharmonics, expressed as a percent of the maximum demand current. Harmonic components of order greater than 50 may be included when necessary.

THDI uses the instantaneous fundamental current as reference. TDD uses the maximum demand current (maximum current) as reference. This means, at 100% load THDI = TDD. The difference between THD and TDD can be quite dramatic, as illustrated below.

lEEE519

TDD, not THDI. Be sure to make it clear if the requirement from the customer is TDD or THDI before specifying your ADF size. Preferably only specify THDI at 100% load or use TDD instead!

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