IEEE 519 standard limits
The IEEE 519 standard, titled Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, establishes the acceptable harmonic distortion limits for both voltage and current at the point of common coupling (PCC). Originally published in 1981 and periodically updated, it defines criteria to prevent power quality problems generated by non-linear loads.
Definition of IEEE 519 Standard
Section titled “Definition of IEEE 519 Standard”IEEE 519 imposes a total voltage harmonic distortion limit of 8% for systems with nominal voltage equal to or less than 1 kV at the point of common coupling. It is a recommended practice that assigns responsibilities to both the utility and the end user, delimiting the maximum voltage harmonic levels that the system can withstand and the maximum current harmonics that a load can inject.
Voltage Distortion Limits
Section titled “Voltage Distortion Limits”The voltage harmonic distortion limits specified in IEEE 519‑2014 are 8% for total THD in low voltage and depend on the nominal voltage level at the point of common coupling.
| Nominal voltage at PCC (kV) | Maximum individual harmonic (%) | Maximum THDv (%) |
|---|---|---|
| V ≤ 1 kV / V ≤ 1 kV | 5.0 | 8.0 |
| 1 kV < V ≤ 69 kV / 1 kV < V ≤ 69 kV | 3.0 | 5.0 |
| 69 kV < V ≤ 161 kV / 69 kV < V ≤ 161 kV | 1.5 | 2.5 |
| V > 161 kV / V > 161 kV | 1.0 | 1.5 |
Current Distortion Limits
Section titled “Current Distortion Limits”Current distortion limits are determined by the ratio of the available short-circuit current at the PCC (Isc) to the maximum demand load current (IL). An Isc/IL ratio less than 20 requires a TDD limit of 5.0% for harmonics of order less than 11.
| Isc/IL | h < 11 (%) | 11 ≤ h < 17 (%) | 17 ≤ h < 23 (%) | 23 ≤ h < 35 (%) | 35 ≤ h (%) | TDD (%) |
|---|---|---|---|---|---|---|
| < 20** | 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 |
* Even harmonics are limited to 25% of the values indicated.
THD Calculation
Section titled “THD Calculation”Total harmonic distortion (THD) of voltage is calculated as the square root of the sum of the squares of the harmonic components relative to the fundamental component.
THDv = (√(V₂² + V₃² + … + Vₙ²) / V₁) × 100 %
where V₁ is the RMS magnitude of the fundamental component and V₂, V₃ … Vₙ are the RMS magnitudes of the harmonics of order 2, 3 … n.
Point of Common Coupling (PCC)
Section titled “Point of Common Coupling (PCC)”The point of common coupling, defined by IEEE 519 as the interface between the utility system and the user system, is the location where distortion limits must be met. In typical industrial installations, this point is located on the low-voltage side of the service transformer, where the Isc/IL ratio is usually greater than 20 and the TDD must not exceed 8.0%.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between THDv and TDD?
Section titled “What is the difference between THDv and TDD?”THDv measures total voltage harmonic distortion referenced to the fundamental component, while TDD (total demand distortion) of current is referenced to the user’s maximum demand current, not the instantaneous fundamental.
Why is the 8% limit set for voltage THD at low voltage?
Section titled “Why is the 8% limit set for voltage THD at low voltage?”The 8% was established as a compromise between safe equipment operation and the economic feasibility of mitigation, avoiding excessive heating, additional losses, and malfunction of sensitive electronic devices.
How is the Isc/IL ratio obtained in an existing installation?
Section titled “How is the Isc/IL ratio obtained in an existing installation?”Isc can be calculated from the service transformer impedance and IL as the maximum demand current measured at the PCC during a representative period; both values must be coordinated with the utility company.
Do IEEE 519 limits apply on the high-voltage or low-voltage side?
Section titled “Do IEEE 519 limits apply on the high-voltage or low-voltage side?”It depends on the supply contract; they are normally applied at the PCC, which for industrial users is usually the medium or low-voltage connection point, where distortions affect other users.
What happens if current distortion limits are exceeded?
Section titled “What happens if current distortion limits are exceeded?”Exceeding limits can cause conductor heating, nuisance tripping of protections, electromagnetic interference, and contractual penalties, in addition to degrading supply quality for neighboring users.
Does IEEE 519 require measurement up to the 50th harmonic?
Section titled “Does IEEE 519 require measurement up to the 50th harmonic?”Yes, the standard recommends evaluating harmonics up to order 50, although in practice significant harmonics are usually concentrated below order 25 in most industrial installations.