How Harmonics Are Generated in Electrical Equipment (Part 1: Power Electronics & IT Loads)

Understanding Harmonic Generation in Electrical Equipment

In the previous blogs, we understood what harmonics are and their types. Now, the key question is:

👉 Where do harmonics actually come from?

Harmonics are primarily generated by non-linear loads, especially modern electrical and electronic equipment. These devices do not draw current in a smooth sinusoidal manner, leading to waveform distortion.

1. Linear vs Non-Linear Loads

Linear Loads

• Draw current proportional to voltage

• Maintain sinusoidal waveform

• Examples:

  • Heaters

  • Incandescent lamps

Non-Linear Loads

• Draw current in pulses

• Distort the waveform

• Main source of harmonics

Examples:

• SMPS

• Laptop chargers

• UPS systems

• LED drivers

• Variable Frequency Drives (VFDs)

  

  When a non-linear device operates:

  1. It draws current in short pulses instead of smooth waves

  2. These pulses distort the current waveform

  3. The distorted waveform contains multiple harmonic frequencies

     
     

  3. Harmonics in SMPS (Laptop Chargers, PCs)

  How It Works

  • AC is converted to DC using a rectifier

  • Capacitors draw current in short bursts

  Harmonic Effect

  • High 3rd and 5th harmonics

  • Poor power factor

  Where Seen

  • Offices

  • IT parks

  • Residential electronics

  4. Harmonics in UPS Systems

  Cause

  • Rectifier and inverter stages

  • Continuous switching operation

  Impact

  • Generates low-order harmonics

  • Affects upstream transformers

  5. Harmonics in LED Drivers

  Why It Happens

  • LED drivers use electronic circuits (SMPS type)

  Impact

  • Large number of LEDs = cumulative harmonics

  • Common in:

    • Commercial buildings

    • Street lighting

  6. Harmonics in Variable Frequency Drives (VFDs)

  Working

  • Converts AC → DC → Variable frequency AC

  Harmonic Source

  • Rectifier section draws non-linear current

  Impact

  • Dominant 5th and 7th harmonics

  • Major concern in industries

7. Combined Effect in Real Systems

In real installations:

• Multiple devices operate simultaneously

• Harmonics accumulate

• Leads to:

  • Transformer overheating

  • Neutral overloading

  • Voltage distortion

8. Key Takeaway

👉 Modern electrical systems = High harmonic environment

The more electronic devices you use, the higher the harmonic distortion in your system.

Wrapping Up

Harmonics are mainly generated by power electronic devices like SMPS, UPS, LED drivers, and VFDs. These devices draw current in pulses, creating waveform distortion.

Understanding these sources is critical for diagnosing power quality issues.

In the next blog, we will explore harmonic generation in transformers, motors, and other electrical equipment.

Do you find this blog helpful?

• Yes- Better understood
• Yes- Now I got
• No- I didnt get the concept