What Is Harmonic Analysis? How Is It Performed?

Harmonic analysis is an engineering study that determines the extent to which voltage and current waveforms in the electrical grid deviate from the ideal 50 Hz sine wave, identifies the frequencies causing this deviation, and assesses how it affects the power quality of the facility. In short, it is the process of measuring the high-frequency components injected into the grid by nonlinear loads—such as motor drives, UPSs, LED drivers, and welding machines—and comparing them to international standards such as IEEE 519 or IEC 61000. In this article, we discuss what harmonic analysis is, how it is performed step by step, which parameters (THD, TDD, individual harmonic ratios) are measured, the legal limits, and the risks that arise when analysis is not performed, with a focus on industrial applications.

If circuit breakers frequently trip, compensation capacitors swell, transformers overheat unexpectedly, or electronic circuit boards experience unexplained failures at your facility, it is highly likely that a harmonic analysis report is needed to identify the underlying cause.

What Are Harmonics? How Do They Form in the Power Grid?

In an ideal electrical system, voltage and current are pure sine waves at the fundamental frequency (50 Hz in Turkey). However, in today’s industry, a large portion of the load is now nonlinear in nature: variable frequency drives (VFDs), servo drives, rectifiers, uninterruptible power supplies (UPS), arc furnaces, welding machines, electronic ballasts, and switched-mode power supplies draw non-sinusoidal currents from the grid. These currents generate additional components in the form of exact multiples of the fundamental frequency (100 Hz, 150 Hz, 250 Hz, 350 Hz…). These components are called harmonics.

Mathematically, harmonics are decomposed into their components using the Fourier series. This allows us to see, on a case-by-case basis, the proportion of the 5th harmonic (250 Hz), the 7th harmonic (350 Hz), or the 11th harmonic present in the grid. The analysis process is, in fact, based on this decomposition.

The Nature of Harmonic Distortion: Current Harmonics and Voltage Harmonics

The topic of harmonics must be evaluated from two different perspectives:

Current harmonics (THDi): These represent the distortion injected into the grid by nonlinear loads within a facility. In other words, “the pollution the facility introduces into the grid.”
Voltage harmonics (THDv): This is the voltage deviation caused by these currents across the line impedance. In other words, “the distortion experienced by other equipment.”

Even if current harmonics are very high in a facility, voltage harmonics may still be low if the transformer’s short-circuit capacity is high. Therefore, looking only at THDv leads to an incomplete assessment; both parameters must be considered together.

Why Is Harmonic Analysis Performed? The Visible Effects of an Invisible Problem

The most challenging aspect of harmonic distortion is that it is not directly visible unless measured. Facility managers often encounter the consequences—such as blown fuses, overheating, and equipment failures—but may not realize the common cause of these issues until years later. The most common reasons for performing harmonic analysis in industry can be summarized under the following headings:

Frequent failure or swelling of compensation capacitors: Capacitors, whose impedance decreases at high frequencies, act as a magnet for harmonic currents and can be damaged by overloading.
Overheating of transformers and cables: Since harmonics increase the RMS current value, copper losses (I²R) rise; in transformers, iron losses also increase. This leads to a reduction in capacity (derating) and a shortened thermal life.
High current on the neutral conductor: In particular, the 3rd and 9th harmonics (the “triplet” harmonics, which are multiples of three) accumulate on the neutral in three-phase systems. If a neutral current higher than the phase currents is measured, the presence of harmonics is highly likely.
Unexplained tripping of relays and circuit breakers: False tripping becomes more frequent if electronic protection devices measure peak values rather than RMS values.
Shorter equipment lifespan: Excessive heating in motor windings, vibration in bearings, and localized failures in PLCs and driver cards are more common in facilities with high harmonic content.
Regulatory compliance: The facility must remain within certain limits in accordance with EPDK service quality regulations and the grid operator’s requirements. Exceeding these limits may result in penalties or denial of connection.

If one or more of these indicators are present at your facility, harmonic analysis is not merely a matter of good engineering practice; it is a direct issue of production continuity and equipment protection.

Basic Parameters Used in Harmonic Analysis

To understand a harmonic measurement report, several basic concepts must be clear.

THD – Total Harmonic Distortion

THD (Total Harmonic Distortion) is the ratio of the square root of the sum of all harmonic components other than the fundamental component to the fundamental component, expressed as a percentage. It is denoted as THDv for voltage and THDi for current. As a general rule:

THDv of 5% or less is considered an acceptable range in most power grids.
THDi, however, depends on the nature of the load and the size of the facility relative to the grid; it is compared to standards rather than a single “good” value.

TDD – Total Demand Distortion

A common mistake in industry is interpreting THDi in isolation. However, since THDi is calculated based on instantaneous current, it can appear artificially high when the facility is operating at low load. TDD (Total Demand Distortion), on the other hand, expresses harmonic current as a ratio of the facility’s maximum demand current (I_L). IEEE 519 primarily evaluates performance based on TDD. Therefore, it is important for the analysis report to include both THDi and TDD.

Individual Harmonic Ratios

In addition to the total distortion, it is also significant which harmonic is dominant. For example:

High 5th and 7th harmonic levels typically indicate 6-pulse rectifiers (conventional VFDs).
High 11th and 13th harmonics may indicate 12-pulse systems or large DC drives.
The 3rd, 9th, and 15th (triple) harmonics are prominent in buildings with a high concentration of switched-mode power supplies, LED lighting, and single-phase electronic loads.

Knowing the dominant harmonic is critical in determining which solution (passive filter, active filter, 12-pulse drive, K-factor transformer) is appropriate.

K-Factor, Crest Factor, and Other Metrics

In addition, parameters such as the K-factor (the suitability of transformers for harmonic loads), crest factor (peak-to-RMS ratio), flicker (Pst/Plt), and voltage imbalance are integral parts of a comprehensive power quality report.

How to Perform Harmonic Analysis: A Step-by-Step Measurement Process

Harmonic measurement is not simply a matter of “plugging in the device and looking at the screen.” A methodological approach is required to obtain accurate results.

Step 1 – Preliminary Facility Assessment and Review of the Single-Line Diagram

Before beginning the measurement, the transformer capacity, main panel, subpanels, compensation system, drive groups, and large motors are mapped out using the single-line diagram. This step is critical for selecting the correct measurement points. At the same time, information is gathered regarding the facility’s production cycle (shift hours, peak load hours).

Step 2 – Determining Measurement Points

Harmonic analysis should not be performed at a single point but at least at the following three levels:

PCC (Point of Common Coupling) / Grid connection point: This is where regulatory compliance is tested.
Main distribution panel: The facility’s overall harmonic profile is observed here.
Suspect subpanels or loads likely to generate harmonics: Points such as VFD panels, UPS outputs, and rectifier rooms are measured separately. This identifies the source of the harmonics.

Step 3 – Selection of the Appropriate Analyzer

A Class A-compliant (IEC 61000-4-30) power quality analyzer must be used for measurements. Class A devices guarantee the accuracy and measurement methodology required for the results to be accepted as a legal and technical reference. The device’s harmonic measurement depth (at least up to the 50th harmonic, preferably higher), sampling rate, data storage capacity, and time synchronization (particularly GPS support for multi-point measurements) are key technical criteria.

At this point, the AHA Analyzer (AH2222 portable model) developed by Aha Teknoloji, offers IEC 61000-4-30 Class A compliance, analysis capability up to the 100th harmonic, a sampling rate of 200 kS/s, and GPS time synchronization, making it a suitable solution for both inspection engineers and in-plant continuous monitoring applications. The device’s high sampling rate helps ensure that transient events and short-term harmonic spikes are captured without being missed.

Step 4 – Measurement Duration and Recording Interval

It is recommended that a standard harmonic analysis be conducted continuously for at least one week (7 days). This is because the load profile exhibited by the facility varies across different shifts, as well as during weekday and weekend conditions. Under IEC 61000-4-30, 10-minute and 3-second aggregations are used as the basis. A single day of measurement often does not represent the actual situation.

Step 5 – Points to Consider During Data Collection

Note whether the compensation system is active during the measurement; if possible, record two different scenarios (compensation on/off).
Current clamps are selected within a range appropriate for the measured current magnitude; otherwise, incorrect ratios will be obtained.
Correct phase sequencing is important to ensure that power direction indicators are not read in reverse.
Grounding and safety precautions for the device are taken in accordance with standards for live panel work.

Step 6 – Data Analysis and Reporting

After the recording is complete, using the analysis software:

THDv, THDi, and TDD time series are examined,
Individual harmonic ratios (H2–H50 or higher) are calculated,
Voltage and current waveform samples are reported,
Additional parameters such as phase imbalance, power factor, and flicker are included,
The results are compared against the limits specified in IEEE 519, EN 50160, and IEC 61000, and a compliance table is prepared.

A well-prepared report concludes by answering the questions: “Is there a problem? If so, where is it, and what is the appropriate solution approach?”

Legal Standards and Limit Values

There are three fundamental standards most commonly used in industry:

IEEE 519-2014

Regulates the amount of harmonic current (TDD) that industrial facilities may feed into the grid and the acceptable voltage harmonics on the grid. Key points:

The THDv limit for systems below 1 kV is generally 8%,
The THDv limit for systems between 1 kV and 69 kV is 5%,
Current harmonic limits are defined on a graduated scale based on the ratio of the facility’s short-circuit current (Isc) to the load current (I_L). The larger the facility is relative to the grid, the lower the permitted THDv becomes.

EN 50160

Defines the voltage characteristics provided to end users in public power grids; it sets limits for voltage harmonics, short- and long-term interruptions, flicker, and voltage unbalance. This is the standard that distribution companies are expected to comply with.

IEC 61000 Serisi

IEC 61000-4-7: Measurement methods for harmonics and interharmonics.
IEC 61000-4-30: Class and accuracy requirements for power quality measurement instruments (Class A, S).
IEC 61000-3-2 / 3-12: Harmonic current limits at the equipment level.

In Turkey, the EPDK’s Regulations on Service Quality for Electricity Distribution and Retail Sales define limits and measurement requirements in accordance with these international standards.

In Which Industries Is Harmonic Analysis a Priority?

In theory, every facility has some level of harmonic load. However, in certain industries, analysis is not merely “nice to have” but “absolutely essential”:

Textiles: Extensive use of VFDs, variable load characteristics.
Iron and steel, rolling mills, foundries: Arc furnaces and induction furnaces are significant sources of harmonics.
Automotive production lines: Welding robots, servo drives.
Petrochemicals, chemicals, pharmaceuticals: Environments where sensitive equipment and large motors coexist.
Cement and mining: Mills, conveyors, medium-voltage drives.
Data centers: UPS systems, server power supplies.
Hospitals: Imaging devices (MRI, CT), uninterruptible power supplies.
Shopping malls and large commercial buildings: The high density of LED lighting and electronic loads brings triplen harmonics to the forefront.
Renewable energy (solar/wind): Inverter-generated harmonics become critical under grid connection conditions.

What Happens If Harmonic Analysis Isn’t Performed? Risks and Hidden Costs

Failure to perform harmonic analysis often results not in an immediate failure, but in cumulative wear and tear. The most common scenarios are:

Compensation capacitors and reactors failing much earlier than expected,
Capacity loss and premature insulation aging in transformers,
Unexplained isolated failures in electronic circuit boards,
Reactive power penalties or high demand losses on utility bills,
Random shutdowns on the production line and resulting production losses,
Incorrect sizing of new equipment due to a lack of knowledge about the facility’s actual electrical profile prior to investment.

What these scenarios have in common is that the root cause is invisible. It cannot be analyzed unless it is measured; and it cannot be properly resolved unless it is analyzed.

What to Do After Measurement? Solution Approaches

The analysis report is a diagnosis; treatment is a separate phase. Different solution approaches are evaluated based on the dominant harmonic profile and load characteristics:

Passive harmonic filters: Target a specific harmonic; relatively economical; suitable for steady-state loads.
Active harmonic filters (AHF): Contribute to the attenuation of a broad spectrum (typically the 2nd–51st harmonics) through real-time harmonic injection in variable loads.
Hybrid solutions: Configurations that combine passive and active filters, providing an economic balance for high-power facilities.
12/18/24-pulse rectifiers: Designed to reduce harmonic generation at the source.
K-factor or winding-configured special transformers: Proper sizing for harmonic loads in new installations.
SVG / STATCOM systems: Help manage reactive power and components caused by imbalances.

At this point, Aha Teknoloji offers a product family covering every stage of the process from measurement to solution: The facility’s power quality is mapped using the AHA Analyzer; depending on the need, the improvement phase proceeds with Active Harmonic Filters (AHF), Varmatik SVG, and STATCOM solutions. This integrated approach helps ensure that measurement and solution are discussed within the same engineering framework, thereby helping to reduce time loss and integration risks in field applications.

Common Mistakes in Harmonic Analysis

· Conducting measurements for only one day or a few hours; overlooking weekday/weekend variations.

· Focusing solely on THDi and skipping the TDD calculation.

· Taking measurements with devices that do not comply with Class A standards and attempting to use the report as a legal reference.

· Selecting a filter without analyzing the dominant harmonic (if a passive filter is set to the wrong frequency, the risk of resonance increases).

· Leaving the compensation system unmonitored; yet, capacitors can create resonance points in the presence of harmonics.

Conclusion: You Can’t Manage What You Can’t Measure

Harmonic analysis is an invisible yet critical health check for modern industry. As the proportion of nonlinear loads increases each year, harmonic distortion is no longer an “optional topic”; it is an engineering discipline that must be directly addressed for energy efficiency, equipment lifespan, regulatory compliance, and production continuity. A measurement conducted with a Class A-compliant analyzer, over sufficient time and at the correct points, not only reveals the source of existing problems but also provides a solid data foundation for investment decisions (filters, SVGs, transformers, compensation).

If you are observing signs of power quality issues at your facility or wish to clearly understand the characteristics of your existing grid before making a new investment, a comprehensive harmonic analysis is the first step. Aha Teknoloji’s power quality analyzers and harmonic management solutions help you address this step and the subsequent improvement process all under one roof.