Clause 5.6 of IEEE 519-2022 allows the individual harmonic current limits to be raised with a multiplier of 1.4 to 2.2 when the user reduces to 25 % of the limit the low orders that a six-pulse rectifier dominates. The method does not matter: more pulses, filters, phase-shifting transformers or active rectifiers.
Short answer
The individual harmonic current limits of IEEE 519-2022 can be multiplied by a factor of 1.4 to 2.2 if the user reduces the low harmonic orders to 25 % or less of the table limit. Table 5 (clause 5.6) says which orders have to be reduced for each factor. It does not matter how this is achieved: increasing the converter pulse number, a filter, a phase-shifting transformer or an active-front-end rectifier all work.
Table 5
Clause 5.6 allows the individual limits of Tables 2, 3 and 4 (those in Harmonic Current Limits and TDD by Isc/IL) to be raised when the user takes measures to reduce the lower-order harmonics. The multipliers are:
| Orders limited to 25 % of the value in Tables 2, 3 and 4 | Multiplier |
|---|---|
| 5 and 7 | 1.4 |
| 5, 7, 11 and 13 | 1.7 |
| 5, 7, 11, 13, 17 and 19 | 2.0 |
| 5, 7, 11, 13, 17, 19, 23 and 25 | 2.2 |
The reading is cumulative: for the factor 1.7 the four orders (5, 7, 11 and 13) have to be reduced, and for 2.2, all eight. Each multiplier requires that all the orders in its row stay at 25 % or less of the limit that applies to the installation.
An example with table numbers: an installation at 13.2 kV with an Isc/IL ratio of 30 has, for the range 2 to less than 11, an individual limit of 7.0 %. If it reduces the 5th and 7th harmonics to 1.75 % or less (25 % of 7.0 %), it can apply the multiplier of 1.4 and its limit for that range becomes 9.8 %. This is an operation on the tables, not a measurement result.
Where the orders in the table come from
A three-phase rectifier with p pulses mainly produces harmonics of order (p·n) ± 1, with n = 1, 2, 3, … Clause 5.6 gives the possible values of p: 6, 12, 18, 24, etc. At the other orders, the current is considerably lower.
| Converter | Characteristic harmonics (p·n ± 1) |
|---|---|
| 6 pulses | 5, 7, 11, 13, 17, 19, 23, 25 … |
| 12 pulses | 11, 13, 23, 25 … |
| 18 pulses | 17, 19, 35, 37 … |
The orders in Table 5 are precisely those first harmonics of a six-pulse converter. A converter with more pulses eliminates them as characteristic harmonics: the 12-pulse one no longer has the 5th or 7th, and the 18-pulse one has neither the 11th nor the 13th. That is why Table 5 rewards the reduction of those orders with a higher limit.
The definition of pulse number in clause 3.1 is the total number of successive non-simultaneous commutations that occur within the converter circuit during each cycle, without phase control. It is also the order of the main harmonic in the DC voltage.
Clause 5.6 includes an equation relating the multiplier to the pulse number. For this guide only the Table 5 values are used, which are the ones the standard presents as recommended.
Any method works, with one condition
The note to clause 5.6 clarifies the intent: the multipliers apply regardless of the method used to reduce the orders in the first column, as long as those orders are kept below 25 % of the limit in the corresponding table.
The methods the standard mentions:
- Harmonic filters.
- Phase-shifting transformers.
- Active-front-end rectifiers.
- Other reduction methods, which do not necessarily have an associated pulse number.
What it means for a drive project
Loads with six-pulse drives, with a diode rectifier, usually have the 5th and 7th as dominant harmonics. When the installation is close to its current limit, Table 5 offers an alternative to reducing all of the distortion: reduce only the dominant orders and receive in return more margin on the others.
The design questions are these:
- Which row of Tables 2, 3 or 4 applies to the installation, according to its Isc/IL ratio?
- Which orders are closest to their limit?
- Which solution reduces those orders to 25 % or less, and at what cost?
- Which multiplier is available, and is it enough to meet the other orders?
Answering them requires the network and load model, which is what a harmonic study does. The effect of each measure is described in Variable Frequency Drive Harmonics and in Active vs Passive Harmonic Filters. Before installing a filter, check resonance with the network, as explained in Capacitor Bank Resonance.
What Table 5 does not do
- It does not change voltage. The Table 1 voltage limits have no multipliers.
- It does not mention TDD. The clause speaks of the individual limits of Tables 2, 3 and 4.
- It does not eliminate the high orders. The multiplier raises the limit of each order, but the installation must meet all of them.
- It is a recommendation. The title of the table is “recommended multipliers”.
The six-pulse drive has another effect on voltage that this table does not touch: commutation notches, covered in Commutation Notches: IEEE 519 Annex C Limits. The limits apply at the point of common coupling (see PCC in IEEE 519: Where Harmonic Limits Apply).
We help you take advantage of the multipliers
At Tiza Group we carry out power quality studies, in Colombia, or elsewhere on request: we calculate the harmonics of your drives at the PCC, verify whether you comply and, if needed, define which orders to reduce and with what solution to qualify for the corresponding multiplier.
Related guides
- Harmonic Current Limits and TDD by Isc/IL
- Commutation Notches: IEEE 519 Annex C Limits
- Variable Frequency Drive Harmonics
- Active vs Passive Harmonic Filters
- Harmonic Filters IEEE 1531
References
- IEEE Std 519-2022, IEEE Standard for Harmonic Control in Electric Power Systems: clause 5.6 and Table 5 (recommended multipliers), with its note 8 (methods other than increasing pulses); clause 3.1 (pulse number); clauses 5.3 to 5.5 and Tables 2, 3 and 4 (base limits).
Frequently asked questions
If I install a 12-pulse drive, can I apply the Table 5 multiplier automatically?
Not automatically. The standard requires the orders in the first column to be at 25 % or less of the limit in the corresponding table. A 12-pulse converter does not have the 5th or 7th among its characteristic harmonics, but you must check that in the installation they stay below that 25 %.
Does the multiplier also raise the TDD limit?
Clause 5.6 speaks of raising the individual limits of Tables 2, 3 and 4. It does not mention TDD, so the Table 5 multiplier applies to the limits per harmonic order.
Do only converters with more pulses count, or also a filter?
Any method counts. The note to clause 5.6 includes filters, phase-shifting transformers and active-front-end rectifiers, as long as the orders in the first column of Table 5 stay below 25 % of the limit.