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Harmonic distortion: THD and TDD

Enter the harmonics you measured at the point of common coupling and get voltage THD or current TDD, checked against the IEEE 519-2022 limits for the voltage level and the Isc/IL ratio.

IEEE 519-2022table 1, voltage limitsIEEE 519-2022table 2, current limits from 120 V to 69 kV

Example cases

Harmonic distortion: THD and TDD

TDD

— %

Current THD

— %

Individual harmonics

—

Highest harmonic

—

I_sc/I_L ratio

—

TDD limit

— %

Harmonic spectrum

Measured harmonic
IEEE 519-2022 individual limit

Each bar is one harmonic. The yellow mark is its individual limit; red bars exceed it.

Harmonic by harmonic

Order	Value	Limit	Limit used

What it means at the PCC

Standards and references

IEEE 519-2022, table 1, voltage limits
IEEE 519-2022, table 2, current limits from 120 V to 69 kV

Scope

Engineering estimate with the assumptions stated on the page; it does not replace a study or the manufacturer's data. Tiza Group accepts no liability for decisions based only on this result.

Tiza Group S.A.S. · Bogotá, Colombia

tizagrp.com · [email protected] · Phone and WhatsApp +57 305 725 2061

Open this calculation with the same data: https://tizagrp.com/en/tools/harmonic-distortion-thd/

What it is for

For a quick check of a power quality measurement: whether the voltage distortion the plant receives, or the current distortion it injects into the grid, stays within the IEEE 519-2022 limits, which harmonic fails and by how much. It also compares the spectrum of a drive before and after a filter.

How it is calculated

IEEE 519-2022definitions, harmonics up to order 50

THD = √(Σ M_h², h = 2 a 50) / M₁ · 100TDD = √(Σ I_h², h = 2 a 50) / I_L · 100

M is the voltage or current of each order and I_L the maximum demand load current at the PCC (15 or 30 minute average). Individual current limits are given in % of I_L, and voltage limits in % of the fundamental.

Table 1, voltage limits at the PCC (unchanged from 2014):

Voltage at the PCC	Individual harmonic (%)	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	1.5 (2.0 if caused by an HVDC terminal)

Table 2, current limits for systems from 120 V to 69 kV, in % of I_L:

Isc/IL	2 ≤ h < 11	11 ≤ h < 17	17 ≤ h < 23	23 ≤ h < 35	35 ≤ h ≤ 50	TDD
< 20 (and all power generation)	4.0	2.0	1.5	0.6	0.3	5.0
20 to < 50	7.0	3.5	2.5	1.0	0.5	8.0
50 to < 100	10.0	4.5	4.0	1.5	0.7	12.0
100 to < 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

IEEE 519-2022even harmonics and generation

Even harmonics: in the 2022 edition, orders 2, 4 and 6 are limited to 50 % of the table value and even orders above 6 to 100 % (in 2014 all even harmonics were 25 %). Currents with a DC offset, such as those of half-wave converters, are not allowed. All power generation uses the Isc/IL < 20 row, whatever its actual ratio.

Isc/IL = 1000 exactly falls between the "100 to < 1000" and "> 1000" rows; the tool uses the first one, which is the stricter.

Values from IEEE Std 519-2022, tables 1 and 2, checked against their reproduction by manufacturers of power quality analyzers and harmonic filters. For a PCC above 69 kV (tables 3 and 4) we could not check the values against a primary source: the tool calculates TDD but does not compare it.

Limits of the calculation

IEEE 519 is assessed at the point of common coupling and statistically, with measurements over a week or more (percentiles of very short and short time values), not with a single reading; this tool compares one spectrum.
It does not assess interharmonics, resonances or the contribution of each load.
If inverter-based generation at the site is at least 10 % of the average annual demand, IEEE 519-2022 refers to IEEE 1547 or IEEE 2800 for the current limits.
IEEE 519 applies from 120 V; the utility may set other limits in its interconnection agreement.
A diagnosis and a solution need a harmonic study.

Frequently asked questions

How is voltage THD calculated?

It is the square root of the sum of the squares of the voltage harmonics from order 2 to 50, divided by the fundamental and multiplied by 100. For example, with 4 % fifth harmonic and 3 % seventh, THD is √(4² + 3²) = 5 %.

What is the difference between current THD and TDD?

THD divides the distortion by the fundamental current at that moment; TDD divides it by the maximum demand load current IL at the point of common coupling. At light load THD looks high even when the harmonic amperes are small, which is why IEEE 519 sets the current limits as TDD and as a percentage of IL.

What is the voltage THD limit in IEEE 519-2022?

At the point of common coupling: 8 % up to 1 kV, 5 % from 1 to 69 kV, 2.5 % from 69 to 161 kV and 1.5 % above 161 kV. Each individual harmonic has a lower limit: 5, 3, 1.5 and 1 % respectively.

We carry out your power quality study

We measure with class A analyzers (in Colombia, or elsewhere on request), model the network to find resonances, compare with IEEE 519 and size the solution: filters, reactors or configuration changes.

See the power quality study

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