A. What is HVF?
The Harmonic Voltage Factor (HVF) is a measure of the distortion in a voltage waveform caused by harmonic components. It quantifies the impact of harmonics on the overall voltage quality in a power system.
Mathematically from IEC 60034-1, HVF can be expressed as:
Where:
un is the ratio of the harmonic voltage Un to the rated voltage UN
n is the order of harmonic (not divisible by three in the case of three-phase a.c. motors
k=13
B. Acceptable Limits of HVF
Different standards define acceptable limits for harmonic voltages. Some widely referenced standards include:
- IEEE 519:
- Total harmonic distortion for voltage (THD-V) should be ≤ 5% in industrial and commercial power systems.
- Individual voltage harmonics should be ≤ 3% of the nominal voltage.
- IEC 61000-3-2 / IEC 61000-3-4:
- Defines harmonic emission limits for electrical equipment.
- For power systems, individual voltage harmonics should be limited to ≤ 5% for each harmonic.
- EN 50160 (European Standard):
- Voltage THD should not exceed 8% for low-voltage networks.
- Individual harmonics have varying limits, e.g., 4% for the 5th harmonic.
- National Grid Codes:
- Many countries set their own harmonic voltage limits based on local conditions.
C. Effects of High HVF (Harmonic Voltage Distortion)
High harmonic voltage factor can cause several power quality issues:
- Overheating of Equipment. Transformers, motors, and generators experience increased losses, reducing efficiency and lifespan.
- Voltage Distortion & Malfunction. Sensitive electronic devices and control systems may fail or malfunction due to distorted waveforms.
- Increased Losses in Power System. Harmonics cause extra losses in transmission lines, cables, and transformers.
- Resonance Issues. Certain harmonics can interact with system reactance, leading to voltage amplification and equipment failure.
- Incorrect Meter Readings. Power meters may give inaccurate readings, leading to billing errors.
- Interference with Communication Systems. High voltage harmonics can cause electromagnetic interference (EMI), affecting communication networks.
D. Control & Mitigation of HVF
To reduce the Harmonic Voltage Factor, various methods are used:
- Use of Harmonic Filters:
- Passive Filters (LC filters): Absorb specific harmonic frequencies.
- Active Harmonic Filters (AHF): Inject opposite-phase harmonics to cancel distortions.
- Use of Line Reactors & Isolation Transformers:
- Reduce the impact of harmonics on sensitive equipment.
- Application of PWM-based Power Electronics:
- Modern variable frequency drives (VFDs) and UPS systems use Pulse Width Modulation (PWM) to reduce harmonics.
- Phase Balancing & Load Management:
- Ensuring balanced loads across three-phase systems reduces voltage distortion.
- Use of Low Harmonic Drives (LHDs):
- Specially designed drives that minimize harmonic generation.
- Grid Code Compliance & Monitoring:
- Regular monitoring and compliance with IEEE, IEC, and EN standards ensure system reliability.
E. Standards Governing HVF
The following standards define limits and control strategies for harmonics in power systems:
| Standard | Description |
|---|---|
| IEEE 519 | Limits harmonic voltage and current in power systems |
| IEC 61000-3-2 / 3-4 | Limits harmonic emissions for electrical equipment |
| EN 50160 | Defines power quality in European networks |
| IEC 61000-2-2 / 2-4 | Compatibility levels for voltage harmonics |
| National Grid Codes | Country-specific harmonic voltage regulations |
F. Conclusion
Harmonic Voltage Factor (HVF) is an important metric for assessing power quality. Maintaining HVF within standard limits ensures reliable system operation, reduces equipment damage, and minimizes power losses. Regular monitoring, use of filters, and compliance with international standards help in effective harmonic control.