What causes harmonics in an alternator?

Causes of Harmonics in an Alternator

Harmonics in an alternator or a generator are higher frequency components superimposed on the fundamental (desired) sinusoidal waveform of the output voltage or current. These harmonics can significantly affect the performance, efficiency, and lifespan of electrical systems. Understanding the root causes of harmonics in an alternator is critical for both minimizing their presence and mitigating their effects.

Main Causes

  • Non-linear Loads: The most prominent cause of harmonics are non-linear loads, which draw current in abrupt pulses, rather than in a smooth sinusoidal manner. Examples include electronic devices, variable frequency drives, compact fluorescent lamps, and computers.
  • Slot Harmonics: Mechanical constructions in alternators, such as the slots used for winding the conductors, can create slot harmonics. The interaction between the rotor's magnetic fields and the stator slot causes fluctuations in the air gap flux density, generating harmonics.
  • Saturation of the Magnetic Core: When the magnetic core of the alternator operates near or in saturation, the relationship between the magnetic flux and the excitation current becomes non-linear, leading to the production of harmonics.
  • Parasitic Capacitance and Inductance: The inherent parasitic elements like capacitance and inductance within the alternator can resonate at certain frequencies, which amplifies harmonic content.

Effects of Harmonics

Harmonics can have several detrimental effects on the electrical system, including increased heating in equipment, reduced efficiency, possible overloading of cables and transformers, malfunctions in sensitive electronic equipment, and distorted voltage waveforms.

Mitigation Strategies

  • Proper Design and Selection: Opt for alternators designed to minimize harmonics through improved slot design, selection of materials, and appropriate sizing.
  • Use of Filters: Install harmonic filters to counteract the effects of harmonics and improve the power quality.
  • Regular Maintenance: Regular inspection and maintenance of electrical systems help in identifying and mitigating harmonic sources early.
  • Load Management: Effective management and distribution of non-linear loads across the electrical system can help in reducing the overall harmonic impact.


While it's challenging to eliminate harmonics entirely from an alternator, understanding their causes plays a crucial role in effective management and mitigation. Addressing the problem requires a comprehensive approach, combining proper alternator design, strategic load management, and the use of harmonic filtering technologies.

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