Harmonics in electrical engineering

Harmonics are caused by non-linear consumers in the electrical network. These consumers do not consume electricity in proportion to the applied voltage, which leads to distortions in the current and voltage curves.

1. Nonlinear loads: Devices such as frequency converters, switching power supplies, LED drivers, or electric welding machines have nonlinear characteristics. They draw current in pulses or only during certain phases of the mains voltage.

2. Distortion currents: These nonlinear current draws cause distortions in the mains current. The resulting current waveform contains additional frequency components in addition to the fundamental frequency (50 Hz or 60 Hz).

3. Fourier analysis: From a mathematical point of view, every distorted current or voltage waveform can be represented as the sum of sinusoidal oscillations of different frequencies. These additional frequency components are the harmonics, whose frequencies are integer multiples of the fundamental frequency (e.g., for a fundamental frequency of 50 Hz: 150 Hz for the 3rd harmonic, 250 Hz for the 5th harmonic, etc.).

4. Reaction on the grid: The harmonics generated feed back into the supply grid and have a negative impact on other consumers or equipment.

Networks with a high proportion of power electronics are particularly affected, as modern electronic devices often do not consume sinusoidal currents. This increases the degree of distortion and can place an increasing strain on the network.

Harmonics cause a number of problems in electrical networks and equipment. The most important ones are:

 Increased heating reduces the service life of electrical appliances

 Overloading of the power grid and resonance effects

• Harmonics can resonate with the network impedance, leading to dangerous voltage distortions and overcurrents.
• This increases the risk of equipment damage or network instability.

 Malfunctioning of electronic devices

• Controls, protective relays, and sensitive measuring devices can be disrupted or triggered incorrectly by harmonics.
• Data loss or communication errors can occur in IT systems.

 Impairment of voltage quality

• Distortions in the grid voltage caused by harmonics can have a negative impact on other consumers in the grid.
• A high distortion content (THD – Total Harmonic Distortion) leads to poor grid quality.

 Reduced energy efficiency

• The additional reactive power and higher losses caused by harmonics lead to inefficient energy consumption (reduced power factor).
• In large systems, this can result in significant additional costs.

To avoid these problems, harmonic filters, active compensation systems, and optimized grid structures are necessary.

Harmonics cause a special form of reactive power known as distortion reactive power (Qd).

• In an ideal network with purely sinusoidal voltage and current, there is only displacement reactive power (Q1), which is caused by phase displacement between current and voltage.
• Harmonics generate additional distortion currents that do not contribute to active power but still load the grid.
• These distortion currents lead to losses due to eddy currents and remagnetization, which causes increased heating of transformers, lines, and motors.

Since conventional reactive power compensation systems (e.g., capacitor banks) are usually only designed for displacement reactive power, they cannot compensate for the distortion reactive power caused by harmonics. Instead, active filters or special chokes are required.

In general, harmonics can be reduced by various measures. Technical solutions are often used for this purpose.

Examples of measures to reduce harmonics:

• Selection of products with integrated solutions
  Active Power Factor Correction (aPFC): Particularly suitable for variable loads.
   
• External harmonic filters
  Active harmonic filters (AH filters) can detect harmonic currents and compensate for them in a targeted manner
  Passive filters: E.g., mains chokes or capacitors and inductors compensate for harmonic frequencies
   
• Use of more powerful transformers
  Transformers with the highest possible RSC value (short-circuit ratio)

Ideal for critical infrastructure such as hospitals, data centers, or industrial production facilities: Active harmonic filters from ZIEHL-ABEGG protect your application from power grid distortions and power losses!

Harmonics play a crucial role in ventilation technology, especially in ventilation systems used in buildings, industrial plants, and critical infrastructure. They affect not only the efficiency and longevity of the systems, but also the security of supply and operational safety.

Modern ventilation systems consist of speed-controlled drives, which are often operated with integrated control electronics (EC motors) or external frequency converters (AC motors). These converters are typical generators of harmonics, as they place a non-linear load on the mains power supply.

Stable ventilation systems are essential for operational safety and health protection, especially in critical infrastructure such as hospitals, data centers, airports, and clean rooms.

• Efficiency: Reduction of energy losses and unnecessarily high operating costs.
• Durability: Protection of motors, converters, and controls against overload.
• Reliability: Critical infrastructure must not be endangered by grid distortions.
• Sustainability: High grid quality is a prerequisite for energy-efficient buildings of the future.