Harmonic Distortion and Generator Performance: Causes, Effects, and Solutions

Introduction

Many electrical systems are more than simple resistive load operators. There are many modern devices used, such as computers, UPS systems, variable frequency drives (VFDs), LED lighting, battery chargers, data centres, electric vehicle chargers, and numerous electronic devices. But these devices produce harmonic distortion and affect the generator performance.

Today we will dive into harmonic distortion, understand its process, and know how you can avoid it for better generator performance.

What is Harmonic Distortion?

Harmonic Distortion is a multiple of an integer of 50Hz or 60Hz frequency. It is often produced when the electrical current deviates from the normal pure sine wave waveforms and produces pulses instead of continuous current.

The ideal system has the following features.

• Voltage follows a smooth sine wave.
• Current follows the same sine wave.
• Frequency remains constant (50 Hz or 60 Hz).

Harmonic distortion occurs due to nonlinear equipment that draws current in pulses instead of continuous formats.

Examples

There are technically two examples. One is for the 50Hz current, and another is for the 60Hz current systems.

For 50Hz.

For 60Hz.

Why Harmonic Distortion is Increasing

If you are wondering why harmonic distortion is increasing, it is because of several equipment factors and many more problems discussed below.

Common Sources of Harmonics

Many facilities comprise far more electronic tools than traditional buildings. These electronic tools are often involved with harmonic production.

We have uncovered a few common sources of harmonics that don’t produce a consistent waveform.

• Variable Frequency Drives (VFDs)
• UPS systems
• Switched-mode power supplies
• LED lighting
• Battery charging systems
• Electric vehicle chargers
• Data centre equipment
• Solar power inverters
• Industrial rectifiers
• Medical imaging equipment
• CNC machines
• Telecommunications equipment

Typical Harmonic Producing Loads

The harmonic load production is typically different for each device. A few devices produce very low harmonics while others can create extensive pulses in the current.

Here is how each device and load produces the harmonic range.

Linear Loads vs Nonlinear Loads

There is a significant difference between linear and nonlinear loads. For example, a linear load follows the pure sine wave, while a nonlinear load doesn’t follow the pure sine wave form and produces harmonic distortion.

Examples of Linear Loads are as follows:

• Resistance heaters
• Incandescent lamps
• Traditional motors
• Electric ovens

Nowadays, the following nonlinear loads are pretty commonly used.

• Computers
• UPS systems
• VFDs
• LED lighting
• Battery chargers
• Inverters
• Medical equipment

The typical difference between the two quantities is listed below.

How Harmonics Affect Generator Performance

One of the key reasons to understand harmonics is to learn about their impact on generator performance. Compared to utility grid systems, generator systems have high internal impedance and voltage distortion.

Harmonic Distortion can develop several issues related to generator performance. We have uncovered a few issues as below.

Factor #1: Increased Generator Heating

One of the most significant issues with generator performance is the increased generator heating. Nonlinear loads create harmonic distortion and affect the following components of the generator.

• Generator windings
• Rotor
• Stator
• Core
• Exciter
• Bearings

Current losses in these components create additional heating and high temperature conditions. Therefore, generator performance reduces significantly when the temperature is pretty high.

Factor #2: Reduced Generator Efficiency

Generator efficiency is the performance of the Generators and reduced fuel consumption. High-performance generators produce more clean energy and reduce the environmental impacts.

However, harmonic distortion can also cause reduced generator efficiency due to the following effects.

• Copper losses increase.
• Iron losses increase.
• Eddy current losses increase.

Overall efficiency decreases due to the above losses and impacts the overall generator performance.

Example Efficiency Impact

Factor #3: Voltage Waveform Distortion

A sine wave offers cleaner current and smoother performance. When there is a distortion in the voltage, the performance goes down. Here are a few issues due to harmonic current flows.

• Voltage becomes distorted.
• Peak voltages become irregular.
• Sensitive electronics may malfunction.
• Protective devices may operate incorrectly.

Effect of Distorted Voltage

Do you know the real-time effects of voltage distortion? Here are a few discussed.

• Computer failures
• PLC communication errors
• UPS alarms
• Instrument inaccuracies
• Sensor malfunctions
• Motor vibration

Factor #4: Reduced Voltage Regulation

Many power systems have installed automatic voltage regulators. They maintain the voltage and produce the quality waveforms.

But when harmonic distortion occurs in the system, voltage regulation becomes a challenge. A few typical effects are:

• Voltage instability
• Slow AVR response
• Voltage oscillation
• Poor regulation under changing loads

Factor #5: Increased Copper Losses

Copper losses increase according to the current. Harmonics are involved with the elevated copper losses and increased heating of the system.

Harmonics increase the RMS current, causing effects such as:

• Windings carry more current.
• Resistance losses increase.
• Additional cooling becomes necessary.
• Insulation ages faster.

Factor #6: Increased Iron Losses

Iron Losses depend on the two key factors— Eddy current and hysteresis. Because of higher frequencies of harmonics, here is how the increased iron losses occur.

• Eddy currents increase rapidly.
• Core heating rises.
• Generator efficiency declines.
• Magnetic components experience additional stress.

Factor #7: Reduced Generator Capacity

One of the key issues due to harmonic distortion is the reduced generator capacity. Whenever harmonic distortion occurs, generators can’t perform up to their rated capacities.

Therefore, issues often occur, causing reduced capacity. For example, a generator has a capacity of 100kW. With nonlinear loads, it may perform up to 80 kW.

Here are a few more generator capacity issues listed below.

Examples

Effect of Harmonic On Generator Components

The maximum effet of harmonics is on the generator components. Here are a few components of generators with the harmonic effects on them.

Cooling System

One of the major effects of the harmonics is the overheating of the components due to copper, iron, and current losses. Your cooling system has to work harder to fight the excessive heating.

Therefore, here is the effect of the harmonics on the cooling systems.

• Higher cooling fan workload
• Increased radiator temperature
• Reduced cooling efficiency
• More frequent maintenance of cooling components

Automatic Voltage Regulator (AVR)

Automated voltage regulator corrects and regulates the voltage. Due to harmonics, it can experience several issues, such as:

• Voltage sensing becomes less accurate.
• Voltage regulation becomes unstable.
• Response time may increase.
• Voltage fluctuations become more frequent.

Bearings

There are a few types of the harmonics that cause the bearing issues. They cause impact the bearings in the following ways.

• Bearing pitting
• Electrical fluting
• Premature bearing wear
• Increased vibration
• Noise during operation

Rotor

Rotor experiences the induced current through the strator windings. Harmonics also impact the rotors as does the strator windings.

These current cause:

• Rotor heating
• Increased eddy current losses
• Magnetic imbalance
• Reduced operating efficiency

Overheating of the rotors can cause early deterioration and selective damage of the rotor components.

Stator Windings

Stator windings of generators are crucial components containing the output current. Since harmonics increase the RMS current flowing through the current windings causing higher PR copper losses.

Here are a few impacts of the harmonics on the strator windings.

• Increased winding temperature
• Faster insulation aging
• Reduced generator efficiency
• Higher risk of winding failure
• Increased maintenance requirements

Harmonic Mitigation Techniques

If you are ready to dive into harmonic mitigation, we have discussed a few techniques that can effectively reduce the harmonics.

Technique #1: Passive Harmonic Filters

Passive filters use inductors, capacitors, and resistors tuned to specific harmonic frequencies.

Advantages

Compared to other types, passive harmonic filters have a few benefits, such as:

• Cost-effective
• Simple installation
• Low maintenance
• Effective for common harmonics

Limitations

There are a few limitations as well. For example:

• Fixed performance
• May require tuning if loads change
• Potential resonance if improperly designed

Technique #2: Active Harmonic Filters

Unlike passive filters, active harmonic filters actively monitor the system in real-time and eliminate the harmonics by injection of the compensating currents.

There are a few benefits of active harmonic filters.

• Dynamic harmonic correction
• Handles varying loads
• Improves power quality
• Reduces voltage distortion
• Enhances generator performance

Technique #3: Line Reactors

Line reactors also have a significant impact and help create impedance between generator and nonlinear load systems. This impedance reduces the flow of harmonics.

The common applications and usage of the line reactors are:

• Variable Frequency Drives
• Industrial motor control
• Manufacturing facilities

Technique #4: Isolation Transformers

Isolation Transformers can be a good solution as they isolate the harmonics. Depending on the types and systems, isolation transformers reduce certain harmonic currents and offer the following benefits.

• Improved power quality
• Reduced electrical noise
• Better protection for sensitive equipment

Technique #5: Multi-pulse Rectifiers

Multi-pulse rectifiers have a proven record in the removal of the low-order harmonics. Instead of traditional 6-pulse rectifiers, modern facilities utilise and operate:

• 12-pulse rectifiers
• 18-pulse rectifiers
• 24-pulse rectifiers

These rectifiers help minimize the low-order harmonics and increase the generator reliability.

FAQs

• How can harmonic distortion be reduced?

To reduce harmonic distortion, we have several techniques and options, such as installing passive or active harmonic filters, using line reactors, selecting low-harmonic equipment, balancing loads, and properly sizing the generator.

• Can harmonics increase fuel consumption?

Yes. Harmonics cause increased fuel consumption due to decreased efficiency and reduced generator performance.

• What is a good Total Harmonic Distortion (THD) level?

For reliable operations and high performance, voltage THD below 5% is often considered the ideal or a good practice.

• Is harmonic distortion harmful to generators?

Yes. Excessive harmonics cause several issues, such as increased heating, reduced efficiency, distorted voltage, shortened insulation life, overloaded neutral conductors, and reduced overall generator reliability.

• What causes harmonic distortion in generators?

Nonlinear loads, when connected to generator systems, cause harmonic distortion. Common examples are UPS systems, VFDs, LED lighting, battery chargers, computers, and rectifiers.

• Why should harmonic distortion be monitored regularly?

Regular monitoring and maintenance avoid long-term issues. There will be no excessive heating, sudden downtime, or more issues with the system.

• Which harmonic orders are usually the most problematic?

3rd, 5th, and 7th harmonics are the most notorious and dangerous harmonic orders. They develop several issues, such as excessive heating or aggressive voltage distortion.

• Do all generators experience harmonic distortion?

Not necessarily. Generators with nonlinear loads experience harmonic distortion.

Conclusion

Harmonics can be dangerous for your generator systems. They affect the internal components, cause sudden failures, and increase generator downtime. Therefore, you should understand and choose those generators with linear loads and stable performance.

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