Short Answer:

Harmonics in power systems are distortions in voltage or current waveforms caused by non-linear loads like inverters, variable frequency drives, and electronic devices. These waveforms deviate from the ideal sinusoidal shape and contain multiple frequencies.

Harmonics negatively affect power systems by overheating transformers and motors, increasing losses, causing malfunction in protective devices, and damaging sensitive equipment. Managing harmonics is important to maintain power quality, efficiency, and safety in electrical networks, especially where modern electronic loads are widely used.

Detailed Explanation:

Harmonics and their effects on power systems

In an ideal AC power system, the voltage and current waveforms are perfect sinusoids at the fundamental frequency (50 Hz or 60 Hz). However, the widespread use of non-linear loads introduces additional frequency components into the system, called harmonics. These harmonics are integer multiples of the fundamental frequency (e.g., 150 Hz, 250 Hz), and they distort the original waveform.

The presence of these harmonics is a major power quality issue, especially in modern grids where computers, industrial drives, LEDs, UPS systems, and renewable energy sources are extensively used. These devices draw current in pulses rather than smoothly, injecting harmonics into the network.

Major Effects of Harmonics in Power Systems

1. Increased Heating in Equipment:
   • Harmonics cause additional current flow through devices like transformers, cables, and motors.
   • This results in extra I²R losses, leading to overheating, reduced efficiency, and shorter lifespan of equipment.
2. Transformer Derating:
   • Transformers exposed to high harmonic content must be derated (used below their full capacity) to avoid overheating.
   • Harmonics also increase eddy current and hysteresis losses in transformer cores.
3. Overloading of Neutral Conductors:
   • In three-phase systems, odd triplen harmonics (3rd, 9th, etc.) add up in the neutral wire.
   • This can lead to overheating of the neutral conductor, which may go unnoticed until failure occurs.
4. Malfunction of Protective Devices:
   • Relays, circuit breakers, and meters may operate incorrectly due to distorted current or voltage waveforms.
   • Harmonics interfere with the normal functioning of overcurrent and differential protection systems.
5. Voltage Distortion:
   • Harmonic currents flowing through the system impedance create voltage distortion.
   • This can affect connected loads, especially those sensitive to waveform shape like medical devices and communication systems.
6. False Tripping and Equipment Malfunction:
   • Harmonics can trigger false alarms or tripping in electronic control circuits, UPS systems, and programmable logic controllers (PLCs).
7. Reduced Power Factor:
   • Harmonic currents do not contribute to useful power, leading to a lower true power factor.
   • This results in higher apparent power (kVA), increasing utility charges and reducing system efficiency.
8. Interference with Communication Lines:
   • High-frequency harmonics can cause electromagnetic interference (EMI), affecting nearby control and data transmission systems.
9. Resonance Conditions:
   • Under certain conditions, harmonic frequencies can resonate with system inductance and capacitance, leading to very high voltages or currents that can damage equipment.

Sources of Harmonics

• Variable frequency drives (VFDs)
• Switched-mode power supplies (SMPS)
• Compact fluorescent and LED lights
• UPS systems and battery chargers
• Arc furnaces and welding equipment
• Inverters used in solar and wind energy systems

Harmonic Mitigation Techniques

1. Passive Filters:
   • Use of inductors and capacitors tuned to absorb specific harmonic frequencies.
2. Active Filters:
   • Power electronic devices that detect and cancel out harmonics dynamically.
3. Isolation Transformers:
   • Prevent the propagation of harmonics from one part of the system to another.
4. K-rated Transformers:
   • Special transformers designed to handle harmonic-rich environments.
5. Good System Design:
   • Minimizing non-linear loads on the same feeder, using shielded cables, and grounding properly.

Conclusion:

Harmonics significantly affect power systems by distorting waveforms, increasing heating, reducing efficiency, and causing malfunctions in equipment and protection systems. As modern power networks include more electronic and non-linear loads, managing harmonics becomes essential for ensuring reliable, safe, and efficient operation. Proper filtering, equipment selection, and monitoring are key strategies to reduce their harmful impact.