What is Harmonics in Power System

A phenomenon, the effect of which is far-reaching in power system, resulting in less efficiency, longevity and power quality-is the “Harmonics”. Imagine turning on a factory machine, connecting in your computer, or powering up a whole data center only to find out later that the energy isn't as "clean" as it appears to be. Harmonics are an unseen foe that lurks behind a sinusoidal wave's gentle curve. In today’s world, when practically every item relies on electronics, harmonics have become one of the largest hidden challenges in power systems

Table of Contents

• What is Harmonics in Power System?
• Power Harmonics Types
• How Harmonics are Produced in Power Systems?
• Effects of Harmonics in Power Systems
• Measuring Harmonics
• Mitigation of Harmonics
• Conclusion

What is Harmonics in Power System?

Current and voltage in electrical circuits are warped and depart from sinusoidal waveforms when harmonics are present. Non-linear loads attached to the distribution system are the source of harmonic currents. When the waveform of the current a load draws differs from that of the supply voltage, the load is considered non-linear. The supply voltage is distorted as a result of voltage harmonics produced by the flow of harmonic currents across system impedances.

Power Harmonics Types

Fundamental Harmonic or First Harmonic: The generator, whose frequency is known as the fundamental frequency, is the usual source of power. Either 50 Hz or 60 Hz will be the basic frequency. Every electrical and electronic device is made to run on this frequency.

Second Power Harmonic: The second harmonic is the waveform that has a frequency of 100 Hz (2 * 50 Hz). Consequently, the frequency of the second harmonic wave is double that of the fundamental harmonic. The secondary harmonic rises to a high value when the fundamental harmonic falls to zero, and vice versa. Negative sequence current flows in the electrical circuit as a result of the second harmonic's reversal direction. An alternative name for it is a negative sequence harmonic.

Third Power Harmonic: The frequency of the third harmonic is three times that of the fundamental harmonic. This harmonic is extremely harmful. The third harmonic current likewise drops to zero when the fundamental harmonic current does. Consequently, it causes the power system to produce zero sequence current. Another name for it is the "triplen" harmonic.

Fourth Power Harmonic: Four times the fundamental frequency would be the fourth harmonic frequency. The harmonic current also reaches a high value when the fundamental harmonic does, and vice versa for the negative side. Another name for it is a positive harmonic. In contrast to positive (4th, 7th, 10th) and negative sequence harmonics (2nd, 5th, 8th) currents, we can conclude that third order or triplen harmonics (3rd, 6th, 9th…) do not cancel out. High inductive reactors are commonly used in power systems to prevent third harmonic currents. However, system efficiency is impacted when unwanted harmonic current flows through the power system.

How Harmonics are Produced in Power Systems?

Nonlinear loads that transform AC line voltage to DC produce harmonics. Variable frequency drives (VFDs), computer power supplies, and energy-efficient lighting are examples of nonlinear electronic switching devices that produce harmonics to enter the electrical system.

The following are the general types of harmonic-producing loads, often known as nonlinear loads:

• Electricity for electrical devices VFDs, rectifiers, computers, LED lights, EV chargers, electronically commutated (EC) motors, etc.)
• Arcing equipment, such as fluorescent lights, arc furnaces, and welders
• Transformers, or iron-saturating devices

The most common and expanding harmonic sources available today are:

• EV chargers, battery chargers, EC motors, and VFDs
• Power supplies for computers and other devices
• Fluorescent and LED lighting

Effects of Harmonics in Power Systems

There are several detrimental effects that can result from the presence of harmonics:

1. Equipment Overheating

Increased RMS current brought on by harmonics can cause transformers, cables, and motors to overheat. Insulation failure and a shorter lifespan result from this.

2. Decreased Productivity

Harmonic currents represent wasted energy and reduce system efficiency because they don't contribute to productive labor.

3. Circuit breakers that trip for no reason

Power continuity may be disrupted by protection devices operating needlessly due to harmonic distortion.

4. Problems with Resonance

Dangerous overvoltages or overcurrents may result from system capacitance and inductance resonating at a harmonic frequency.

5. Neutral Conductor Overload

In three-phase systems, triplen harmonics, such as the third harmonic, accumulate in the neutral and have the potential to overheat it.

6. Communication Line Interference

High-frequency harmonic currents have the potential to disrupt sensitive equipment and neighboring communication systems.

7. Low Power Ratio

Harmonics raise the demand for reactive power and lower the real power factor, which raises electricity costs. In electrical systems, harmonic currents also raise the r.m.s. current and degrade the quality of the supply voltage. They put strain on the electrical system and may cause equipment damage. They might interfere with devices' regular operation and raise operating expenses. Transformer, motor, and cable overheating, protective device thermal tripping, and digital device logic errors are all signs of troublesome harmonic levels. Furthermore, high operating temperatures shorten the lifespan of many electronics. Because capacitive reactance diminishes with increasing frequency, capacitors are particularly sensitive to harmonic components of the supply voltage. In actuality, this implies that a sizable current can flow in the capacitor circuit from a comparatively tiny fraction of harmonic voltage.

Measuring Harmonics

Power quality analyzers or digital meters that are capable of harmonic analysis, are used to measure it.

The most common metric is Total Harmonic Distortion (THD):

Here, V_n is the RMS value of the nth harmonic voltage, and V₁ is the RMS value of the fundamental component.

Mitigation of Harmonics

Although harmonics cannot be totally removed, they can be reduced using the right methods:

1. Filters that are passive

• constructed with resistors, capacitors, and inductors.
• adjusted to take up particular harmonic frequencies.
• frequently used in medium- and low-voltage applications.

2. APFs, or active power filters

• Inject equal but opposing harmonic currents using power electronics.
• more expensive but more efficient than passive filters.

3. Filters that are hybrid

• a blend of active and passive filters.
• Make sure that performance and cost are balanced.

4. Phase-Shifting Transformer Utilization

• adds phase displacement to cancel some harmonics.
• Large industrial systems frequently employ it.

5. Better Design of Equipment

• Harmonics are greatly reduced when 12-pulse or 18-pulse rectifiers are used in place of 6-pulse rectifiers.
• superior VFDs and UPSs with integrated harmonic reduction.

6. Transformers with a K rating

Specifically made to resist harmonic currents without becoming too hot.

7. Management of Loads

Harmonic concentration is decreased by distributing nonlinear stresses among phases.

Conclusion

Despite being invisible to the human eye, harmonics have significant and expensive consequences on power systems. If ignored, they subtly undermine dependability by causing equipment to overheat, decreasing efficiency, and interfering with operations. The good news? Harmonics can be managed before they cause harm with the correct instruments, such as filters, more intelligent load management, and improved system design. Understanding harmonics is essential to providing clean, effective, and dependable power in the future in a society with delicate electronics and a never-ending need for energy.