Key Takeaways
- Harmonics are components at multiples of the fundamental frequency that distort the sine wave.
- Non-linear loads (inverters, rectifiers) generate them; measured with THD.
- They cause overheating, false tripping and capacitor failure.
- A power-quality analyzer is essential for measurement.
- Filtering: detuned (passive) compensation or an active harmonic filter (AHF).
Harmonics are one of the most common problems degrading power quality in modern industrial facilities. As variable frequency drives, LED drivers and rectifier loads have become widespread, the harmonic problem has grown too. This article explains what a harmonic is, what problems it causes and how it is filtered.
What Is a Harmonic? Harmonics are distorting components — seen at exact multiples of the fundamental frequency (50 Hz), such as the 3rd, 5th and 7th harmonic — that cause grid voltage and current to deviate from the ideal sine wave. Non-linear loads (inverters, rectifiers, UPS) generate harmonics because they draw current in pulses. The distortion level is measured with THD (Total Harmonic Distortion).
What Problems Do Harmonics Cause? High harmonics cause overheating of transformers and cables, overloading of the neutral conductor, false tripping of protection devices, measurement errors and, most importantly, resonance that makes compensation capacitors fail. This is often the hidden answer to "why won't the reactive penalty go down."
How Are Harmonics Measured? To see the harmonic level, you need an energy analyzer capable of measuring power quality. The analyzer reports the amplitude of each harmonic component and the total THD value. A filter solution cannot be chosen without measurement.
How Are Harmonics Filtered? There are two main methods. **Passive filter (detuned compensation):** a shunt reactor in series with the capacitor moves the circuit away from a specific harmonic and protects the capacitor. Essential if THD is above 5%. **Active harmonic filter (AHF):** measures harmonic current in real time and injects an opposite-phase current to cancel harmonics; the most effective but most costly solution.
Harmonic Monitoring with SolarTools SolarTools continuously monitors the harmonic level and THD with power-quality-capable devices. This determines which filter solution is needed, shows whether the existing compensation is safe under harmonics, and reveals the hidden cause of the reactive penalty.
Frequently Asked Questions
What is a harmonic?
A distorting component at multiples of the fundamental frequency (50 Hz) that makes grid voltage and current deviate from the ideal sine. Non-linear loads like inverters, rectifiers and UPS generate them; the level is measured with THD.
How are harmonics filtered?
Two methods: a passive filter (a shunt reactor in series with the capacitor — essential above 5% THD) and an active harmonic filter (AHF — injects opposite-phase current to cancel harmonics, most effective but costly).
How do harmonics affect the reactive penalty?
In a high-harmonic environment, compensation capacitors resonate and get damaged, leaving compensation inadequate so the reactive penalty "won't go down." A solution cannot be found without measuring harmonics.
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