What are the main sources and effects of harmonics in induction motor drives?

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Induction motor drives are widely used in industrial and domestic applications for their high efficiency, reliability, and low maintenance. However, they also generate and consume harmonics, which are voltage and current components with frequencies that are multiples of the fundamental frequency. Harmonics can cause various problems in the power system, such as power losses, overheating, interference, and distortion. In this article, you will learn about the main sources and effects of harmonics in induction motor drives, and some methods to reduce them.

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Dmytro Kniaziev

Top #1 LNG Electro Technical Expert. | PRO_LNG SETO | Interview Preparation | Personal Consulting, Trainings | ExProof…

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Halil Deveci

Electromagnetic Design Engineer
Amir Kermanizadeh

Ph.D. Research Scholar

1 Harmonic sources

The main sources of harmonics in induction motor drives are the power converters, such as rectifiers, inverters, and cycloconverters, that convert the alternating current (AC) from the grid to the direct current (DC) or variable frequency AC for the motor. These converters use switching devices, such as diodes, transistors, and thyristors, that chop the input voltage or current waveform into pulses, creating harmonics. The magnitude and frequency of the harmonics depend on the type, number, and configuration of the switching devices, as well as the load and the power factor of the motor.

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Amir Kermanizadeh

Ph.D. Research Scholar
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If the power source is intended to be devoid of any time harmonics, the emergence of space harmonics in induction motors may be attributed to several factors: 1. Non-sinusoidal distribution of windings due to the limited number of stator slots. Large slot openings within the motor construction. Inappropriate pairing of stator and rotor slot numbers. 2. Irregularities or variations in the air gap due to eccentricity and bearing faults. 3. Narrow air gap. 4. Saturation of the motor's magnetic core. 5. Occurrence of torque pulsations during motor operation. The presence of space harmonics subsequently leads to the generation of time harmonics that are injected back into the power source.

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2 Harmonic effects

The harmonics generated and consumed by the induction motor drives can have a detrimental effect on both the motor and the power system. For example, they can cause power losses in components such as transformers, cables, and capacitors, reducing efficiency and power quality. Furthermore, harmonics can lead to overheating in the motor windings, core, and bearings, as well as in the power system components, resulting in thermal stress, insulation degradation, and reduced lifespan. Additionally, they can interfere with communication and control signals in the power system, causing noise, errors, and malfunction of sensitive devices. Lastly, harmonics distort the voltage and current waveforms in the power system, leading to voltage fluctuations, flicker, and harmonic resonance.

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Amir Kermanizadeh

Ph.D. Research Scholar
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Harmonics create negative and positive sequences of rotating magnetic fields at different speeds, which interfere with the fundamental magnetic field. This interference leads to noise, vibrations, shaft voltage, and additional losses and heat generation in the machine.

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3 Harmonic reduction

To reduce the harmonics in induction motor drives, there are two main approaches: passive and active. Passive methods use passive components, such as filters, reactors, and chokes, that are connected in series or parallel with the power system or the motor to block or absorb the harmonics. Active methods use active components, such as converters, controllers, and compensators, that inject opposite harmonics or correct the power factor to cancel or mitigate the harmonics. The choice of the method depends on the harmonic level, the cost, the performance, and the compatibility of the solution.

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Dmytro Kniaziev

Top #1 LNG Electro Technical Expert. | PRO_LNG SETO | Interview Preparation | Personal Consulting, Trainings | ExProof | High Voltage | LPG | Electrical Propulsion
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1. Install passive or active harmonic filters to smooth out harmonic distortions. 2. Choose Pulse Width Modulation (PWM) inverters, which generate fewer harmonics. 3. Ensure cables and transformers are correctly sized to avoid harmonic amplification. 4. Use isolation transformers to block higher-order harmonics from spreading through the system. 5. Improve the power factor, reducing the impact of harmonics on the overall electrical system. 6. Check my page for more el.technical info on LNG fleet.

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Amir Kermanizadeh

Ph.D. Research Scholar
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Design and manufacturing Level: -Accurate machine design. -Accurate manufacturing. Consumption Level: -Employment of filters.

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4 Harmonic standards

In order to guarantee the proper operation and protection of the power system and the motor, certain standards and regulations are in place to identify acceptable limits and guidelines for harmonics in induction motor drives. The IEEE 519 standard is one of the most widely used and defines the harmonic limits for voltage and current distortion at the point of common coupling. The IEC 61000 standard covers the electromagnetic compatibility aspects related to harmonics, such as emission, immunity, and measurement. Additionally, EN 50160 is another standard that specifies the characteristics of voltage supplied by public distribution systems, including harmonic limits.

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5 Harmonic analysis

To measure and monitor the harmonics in induction motor drives, there are various tools and techniques that can be employed. Harmonic analyzers can measure and display the harmonic spectrum, the total harmonic distortion (THD), and other parameters of the voltage and current waveforms. Power quality meters measure and record the power quality parameters, such as voltage, current, power factor, frequency, and harmonics, over a period of time. Simulation software programs can model and simulate the behavior and performance of the power system and the motor under different harmonic conditions.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Halil Deveci

Electromagnetic Design Engineer
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Even if an induction machine is supplied with a purely sinusoidal wave, there will be space harmonics due to the slotted structure of the machine. Unlike time harmonics, space harmonics are independent of the source of the machine. Magnetomotive force (MMF) in the airgap, is produced by the winding and change in each slot axis. Each phase produces an alternating MMF stepped in nature. A multiple-stage traveling wave consists of the sum of these alternating waves. Space harmonics cause similar problems with time harmonics like the torque ripple, vibration, noise, increased losses, etc. The only way to suppress and manipulate these harmonics is by implementing structural changes to the core and the winding in the design phase of the machine.

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What are the main sources and effects of harmonics in induction motor drives?

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1 Harmonic sources

2 Harmonic effects

3 Harmonic reduction

4 Harmonic standards

5 Harmonic analysis

6 Here’s what else to consider

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