Where most harmonics are 2nd to 51st harmonics?

IN any system containing nonlinear loads that use phase-angle control or abrupt switching, particularly those that draw a non-sinusoidal current. The specific range of "2nd to 51st" is a classic signature of certain technologies.Here are the most common places where you would find such a wide harmonic spectrum:

1. The Classic Example: Thyristor-Controlled Reactor (TCR) in SVC Plants

This is the most direct answer to your question. As discussed, a Thyristor-Controlled Reactor (TCR) is the primary generator of a continuous spectrum from the 2nd to the 51st harmonic. If you were to measure the current waveform at the terminals of a TCR, its harmonic distortion would be characterized by this exact range.

2. Industrial Facilities with High-Power AC Voltage Controllers

Any industrial process that uses phase-angle control with thyristors (SCRs) or triacs to vary the power to a resistive or inductive load will generate this spectrum.

• Industrial Heating: Large electric arc furnaces, induction heating furnaces, and resistance welding equipment. The intense and rapidly changing current draw creates a massive amount of distortion.

• Large Lighting Dimmers: Very old or industrial-grade incandescent or transformer-based lighting systems using phase-angle dimmers.

• Soft Starters for AC Motors: While they are only active during startup, during that period they inject a similar harmonic spectrum into the supply network.

3. Magnetic Core Saturation (A special case for even-order harmonics)

The presence of 2nd, 4th, 6th... (even-order) harmonics is a specific red flag. They are less common in standard power electronic circuits and point to a particular phenomenon:

• Transformers and Reactors Operating in Saturation: When the magnetic core of a transformer or reactor is driven into saturation (e.g., due to overvoltage, geomagnetic storms, or incorrect design), the magnetizing current becomes asymmetrical and rich in even-order harmonics, particularly the 2nd. This is a classic scenario where you would see the 2nd harmonic prominently within that 2nd-51st range.

4. Arcing Loads

• Electric Arc Furnaces (EAFs): This is a major source. The electric arc itself is a highly nonlinear and chaotic load. Its voltage-current characteristic is erratic, generating a very broad and continuous spectrum of harmonics, including all orders from the 2nd up to very high frequencies. The random nature of the arc ensures a wide distribution.

5. Uncommon and Problematic Cases

• Half-Wave Rectifiers: A half-wave rectifier draws current only for one half of the cycle. This creates an asymmetrical (DC-offset) and highly distorted waveform that is rich in even-order harmonics (2nd, 4th, 6th...) as well as odd-order harmonics. While rare in professional design due to their negative impact, they can be found in very cheap or faulty consumer power supplies.

Why Don't We See This More Often with Modern Electronics?

Modern switch-mode power supplies (in computers, servers, LED drivers) and variable frequency drives (VFDs) use a different mechanism: diode/transistor bridge rectifiers by a DC capacitor.

• These draw current in short, sharp pulses at the peak of the voltage waveform.

• This type of nonlinearity primarily generates odd-order harmonics (3rd, 5th, 7th, 9th, 11th...).

• The 3rd harmonic and its multiples (triplens) are usually the highest magnitude.

Look for large, powerful industrial equipment that uses thyristors to "chop" the AC waveform (like TCRs) or involves unstable electric arcs (like Arc Furnaces).

The presence of a continuous, wide spectrum including prominent even-order harmonics (2nd, 4th) is a strong indicator of phase-angle control or core saturation, as opposed to the pulse-like current drawing of modern rectifiers, which primarily creates odd-order harmonics.