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Industrial Harmonic Mitigation Solutions

Measure, reduce and verify harmonic distortion with an engineered active harmonic filter solution.

Harmonic Assessment AHF Capacity Selection Verified Results
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01. Decision Path

From Harmonic Symptoms to Verified Results

Harmonic mitigation equipment should primarily be selected based on on-site measurement data. For projects where measurements are not yet available, harmonic current may be estimated from transformer capacity, load factor, the proportion of nonlinear loads and load type for preliminary configuration. The final solution should be verified against on-site data.

  1. 01 RecognizeIdentify heat, trips and interference View Details
  2. 02 UnderstandLearn how harmonic distortion develops View Details
  3. 03 MeasureRecord THDi, THDv and spectrum View Details
  4. 04 LocateIdentify sources and measuring points View Details
  5. 05 MitigateSelect topology and AHF capacity View Details
  6. 06 VerifyCompare measured before/after results View Details

02. What Are Harmonics?

What Are Harmonics?

Harmonics are not a standalone fault; they are distorted currents generated by nonlinear loads. When large numbers of variable frequency drives, UPS systems, rectifiers, welding machines and similar equipment operate simultaneously, they draw non-sinusoidal current from the grid. As these harmonic currents flow through system impedance, they may cause voltage distortion and affect the operation of the wider distribution system.

Where Do Harmonics Come From?

Common harmonic sources in industrial facilities include:

VFDs
UPS Systems
Rectifiers
Welding
Induction Heating
Battery Chargers
Data Centers
Other Nonlinear Loads
Nonlinear loads draw non-sinusoidal current, creating harmonic components at multiples of the fundamental frequency.

Why Can THDi Reach 28% While THDv Is Only 3%?

This does not indicate a measurement error; it is a common condition in industrial power systems.

When selecting an AHF, we evaluate the complete power distribution system rather than relying on a single THDi or THDv value.

Typical factors include:

  • Transformer rating and impedance
  • Actual load current and operating level
  • System short-circuit capacity (grid stiffness)
  • Cable length and distribution-system impedance
  • Nonlinear load types and operating cycles

For example, depending on the measuring point and system conditions, THDi may reach 25% to 35% while THDv remains around 2% to 4%.

This does not mean the system is free of harmonics; it indicates that lower system impedance limits the resulting voltage distortion.

Harmonic Waveform Composition

Clean fundamental waveform (50 Hz) Clean 50 hertz fundamental current waveform A normalized sinusoidal current waveform plotted against time for two cycles. TimeCurrent
5th harmonic (250 Hz in this 50 Hz example) Fifth harmonic waveform in a 50 hertz example A normalized fifth-order sinusoidal component with five oscillations per fundamental cycle. TimeCurrent
7th harmonic (350 Hz in this 50 Hz example) Seventh harmonic waveform in a 50 hertz example A normalized seventh-order sinusoidal component with seven oscillations per fundamental cycle. TimeCurrent
Fundamental + 5th + 7th = distorted current Illustrative distorted current waveform A normalized fundamental current combined with smaller fifth and seventh harmonic components. TimeCurrent
Example based on a 50 Hz system. These are normalized illustrative waveforms, not field measurements. In a 60 Hz system, the 5th and 7th components would be 300 Hz and 420 Hz respectively. The actual waveform shape depends on the magnitude and phase angle of each harmonic component.

How Nonlinear Loads Generate Harmonics

The nonlinear load creates harmonic current. As that current flows through transformer, cable and source impedance, it may contribute to voltage distortion.
Important distinction

Voltage sags, outages and long-duration undervoltage require different analysis and are not corrected by an active harmonic filter.

03. Sources and Orders

Common Harmonic Sources and Typical Orders

The actual harmonic spectrum depends on equipment topology, control method, system impedance and operating condition. The values below are typical indicators for assessment, not a substitute for measurement.

Variable frequency drive, a common nonlinear industrial load

VFDs and Rectifiers

Six-pulse front ends commonly prompt checks of the 5th, 7th, 11th and 13th orders.

Industrial UPS system with nonlinear input current

UPS and IT Loads

Switch-mode power supplies and UPS rectifiers can create load-dependent current distortion.

Automated optoelectronics production equipment

Automated Production

CNC, semiconductor and automated lines combine many switching and rectifier loads.

Rack-mounted active harmonic filter for local or centralized compensation

Measured Mitigation

The source mix and operating cycle must be measured before the required AHF current rating is selected.

Source Typical harmonic indication Assessment notes
6-pulse VFD / rectifier h = 6k +/- 1; commonly 5th, 7th, 11th, 13th Motor drives, rectifiers and DC bus equipment.
UPS and switch-mode power supplies Low-order and high-frequency components Common in IT rooms, control rooms and backup systems.
Welding equipment Broad and varying spectrum Current changes with process stage and duty cycle.
Arc furnaces 3rd, 5th, 7th, 11th, 13th may be prominent Random fluctuation and flicker can appear with harmonics.
LED drivers Depends on driver topology Large groups can affect building power quality.
Data centers and IT loads 3rd and 5th are common concerns Neutral conductor loading should be checked in four-wire systems.
Battery chargers Rectifier-related characteristic harmonics Charging stage and control method affect spectrum.
CNC and automated production equipment Drive and rectifier related harmonics Servo drives, VFDs and power supplies may operate together.
For 6-pulse rectifiers, characteristic harmonics are often described as h = 6k ± 1, with the 5th, 7th, 11th and 13th treated as typical values rather than absolute results. Typical harmonic orders are indicative rather than guaranteed. Actual spectra depend on converter topology, pulse number, control method, system impedance, loading and existing reactors or filters.

04. Warning Signs and Business Impact

Warning Signs of Harmonic Problems

Harmonic problems often appear as heat, nuisance trips, interference and premature equipment failure, but measurement is required before confirming the cause.

Transformer & Cable Overheating

Possible signUnexpected temperature rise under normal loading.

VerifyMeasure RMS current, harmonic spectrum and temperature under the same operating condition.

Neutral Conductor Overheating

Possible signNeutral current remains high despite reasonably balanced phase loads.

VerifyMeasure neutral RMS current and triplen harmonic components in the three-phase four-wire system.

Capacitor Bank Problems

Possible signRepeated fuse operation, overheating, bulging or abnormal capacitor current.

VerifyCheck the harmonic spectrum, capacitor current and possible resonance conditions.

Nuisance Tripping

Possible signProtection devices operate without an obvious sustained overload.

VerifyReview event records and measure RMS current, peak current and waveform distortion.

PLC & Sensor Interference

Possible signIntermittent resets, communication errors or unstable measurement signals.

VerifyCorrelate fault timestamps with load switching and power-quality records.

Motor Noise, Vibration & Heating

Possible signAdditional noise, temperature rise or vibration without a clear mechanical cause.

VerifyCheck voltage distortion, current spectrum, load condition and mechanical factors.

If confirmed and left untreated:
Unplanned downtimePremature equipment agingHigher maintenance costReduced process reliability
These symptoms are not unique to harmonics. Overload, loose or incorrect wiring, undervoltage, transients and equipment faults can produce similar effects. Confirm the cause through measurement before selecting an AHF solution.

05. Measurement and Assessment

Measure Harmonics Before Selecting the AHF

AHF selection should begin with measurements taken at the correct locations and under representative load conditions. A single instantaneous THD value is not enough for reliable engineering.

Collect System Information

Review the single-line diagram, transformer data, load list and capacitor-bank information before deciding where to measure.

Select Measurement Points

Measure at relevant points such as the PCC, main bus, feeder and critical nonlinear load. Results from different points answer different questions.

Record Operating Conditions

Capture light load, normal production, peak load, startup and process cycles together with the measurement time.

Measure Key Values

Record RMS voltage and current, THDi, THDv, power factor and individual harmonic orders, not only one total THD number.

Analyze Harmonic Sources

Compare upstream and downstream measurements to identify dominant loads and distinguish background voltage distortion from load-generated harmonic current.

Define the Mitigation Target

Define equipment protection, internal power-quality needs, project requirements and any applicable limit at the PCC.

THDi indicates current waveform distortion; THDv indicates voltage waveform distortion. A PCC assessment is not interchangeable with a measurement at equipment terminals. AHF capacity must be based on the harmonic current to be compensated, load variation and the target, not only transformer kVA or one instantaneous THD percentage.
Current harmonic spectrum before AHF compensation during electric arc furnace operation
Harmonic Spectrum Before AHF CompensationMeasured spectrum from the published electric arc furnace application case. View Full Case Results.
Current harmonic spectrum after AHF compensation during electric arc furnace operation
Harmonic Spectrum After AHF CompensationMeasured spectrum from the published electric arc furnace application case. View Full Case Results.
These spectra are drawn from the published electric arc furnace application case. No additional measurement values are attributed to the images.

06. Where Should Harmonics Be Mitigated?

Choose Local or Centralized Compensation Based on the Source

The best location depends on whether harmonic current is concentrated at one large source or distributed across several panels and production lines.

A. Load-side / Local Compensation

Often suitable when one large nonlinear load dominates the harmonic profile.

  • Single large nonlinear load
  • Large VFD or rectifier
  • Single production line
  • Mitigation close to the harmonic source
  • Reduces harmonic current in that feeder and its upstream path

B. Grid-side / Centralized Compensation

Often suitable when several nonlinear loads contribute to bus or PCC distortion.

  • Multiple nonlinear loads
  • Main distribution cabinet or common bus
  • Distributed loads
  • Central improvement of bus or PCC power quality
  • Capacity selection considers load simultaneity and the harmonic current to be compensated

Local vs Centralized Compensation: System-level Single-line Diagrams

Local and centralized active harmonic filter compensation diagrams Two single-line diagrams show an AHF connected in parallel. The first uses a load-side CT near one nonlinear load; the second uses a grid-side CT to measure a main bus supplying multiple nonlinear loads. A. Load-side / Local Compensation Utility /Transformer PCC Main BusFeeder CT NonlinearLoad AHF (parallel) harmonic current toward upstream compensation current B. Grid-side / Centralized Compensation Utility /Transformer PCC Grid-side CT Main BusFeeders AHF (parallel) Load 1 Load 2 combined harmonic current
Red dashed arrows show harmonic current flowing toward the upstream system; green arrows show compensation current injected at the bus. In both arrangements, the AHF is connected in parallel with the electrical system, not in series with the main power circuit. Final CT direction and phase assignment must follow the approved project drawing.
Some facilities require a hybrid design with both local and centralized compensation. The correct arrangement depends on source distribution, cable loading, transformer loading and the target measuring point.

07. Connection and Control Methods

CT Position and Control Mode Affect Compensation Performance

Winzele AHF systems support grid-side or load-side CT installation, open-loop or closed-loop control, three-phase three-wire and three-phase four-wire systems, and parallel module configurations.

CT Position and Control Mode Comparison

Load-side and grid-side CT arrangements with single and parallel AHF modules Four system-level panels compare load-side CT open-loop measurement, grid-side CT closed-loop measurement, one AHF module and multiple parallel AHF modules. The detected current range is highlighted without showing terminal-level wiring. Load-side CT / Open-loop Grid CTLoad AHF CT detects load current Feed-forward control based on the measured load current; CT polarity,phase assignment and installation position must follow the approved design. Grid-side CT / Closed-loop Grid CTLoads AHF CT measures the upstream current after AHF compensation. Feedback measurement; CT polarity and phase sequence are critical. Single AHF Main BusLoads AHF 1 One AHF module selected according to the harmonic current to be compensated,load profile and mitigation target. Parallel AHF Modules Main BusLoads AHF 1 AHF 2 ... Modules share the bus in parallel. Parallel module configuration, CT arrangement andcontrol coordination must follow the approved product manual and project design.
System-level illustration only. It deliberately omits terminal numbers, conductor sizes and protection details because those must come from the approved AHF manual and project drawing. The highlighted ranges show what each CT arrangement observes.

08. Winzele Harmonic Mitigation Process

Assessment, Engineering, Equipment and Verification

Winzele harmonic mitigation work should move from measurement to engineering selection and commissioning support, then verify the actual result at the agreed measuring point.

01Site Data Collection
02Power Quality Measurement
03Harmonic Source Analysis
04Solution Design & AHF Capacity Selection
05Installation & Commissioning
06Performance Verification
Assessment → Engineering → Equipment → Commissioning Support → Result Verification.

10. AHF Capacity Selection Checklist

Information Needed for Correct AHF Capacity Selection

AHF capacity is selected primarily by the harmonic current to be compensated—not only by transformer kVA or total load current. Reliable selection also considers the measured spectrum, load variation, mitigation target and engineering margin.

Electrical System

  • System Voltage
  • System Frequency
  • Wire System
  • Transformer Rating
  • Transformer Impedance
  • Existing Capacitor Bank

Load Information

  • Total Load Current
  • Nonlinear Load Type
  • Nonlinear Load Rating
  • VFD / UPS / Rectifier Quantity and Rating
  • Power Factor
  • Load Variation and Operating Cycle

Harmonic Measurement

  • Measurement Point
  • Measured THDi
  • Measured THDv
  • Measured Harmonic Current (A)
  • Dominant Harmonic Orders
  • Target Mitigation Level
  • Proposed CT Installation Position

Installation Requirements

  • Indoor / Outdoor
  • Ambient Temperature
  • Altitude
  • Installation Preference
  • Communication Requirements
No Measurement Data Yet?

If measurement data is not available, send a single-line diagram, load list, equipment nameplates and operating information so our engineers can define the next assessment step.

11. Results and Project References

Measured Results Must Be Interpreted at the Measurement Point

The examples below reference published Winzele application articles. Actual results depend on system conditions, load profile, measurement point and solution configuration.

AHF current spectrum before compensation

Electric arc furnace: before compensation

Quantity: Current harmonic spectrum

Measurement point: Not identified in the published source

Load condition: Electric arc furnace operating

Reported condition: THDi fluctuating between 15% and 35%

Source: A Brief Introduction to the Applications of AHF

Project example: before AHF compensation
AHF current spectrum after compensation

Electric arc furnace: after compensation

Quantity: Current harmonic spectrum

Measurement point: Not identified in the published source

Load condition: Electric arc furnace operating with AHF dynamic compensation

Reported result: THDi controlled within 8%

Source: A Brief Introduction to the Applications of AHF

Project example: after AHF compensation

Additional published project references

The published AHF Active Harmonic Filter Application Case Compilation reports individual examples including THDi changing from 28% to below 5%, and another example with THDv changing from 8.5% to below 2% while THDi changed from 35% to below 5%. These are case-specific results, not general performance guarantees.

Oscilloscope view before AHF compensation
Before compensation: waveform viewQuantity: Current waveform. Measurement point: Not identified in the available source. Load condition: Not identified in the available source. THDi/THDv: Not provided with this image. Source: Winzele AHF application media.
Oscilloscope view after AHF compensation
After compensation: waveform viewQuantity: Current waveform. Measurement point: Not identified in the available source. Load condition: Not identified in the available source. THDi/THDv: Not provided with this image. Source: Winzele AHF application media.
Actual results depend on system conditions, load profile, measurement point and solution configuration.

FAQ

Harmonic Mitigation FAQs

Concise engineering guidance on measurement, CT location, AHF capacity selection and compliance expectations before a project is quoted.

What causes harmonics in an industrial power system?

Harmonic current is usually generated by nonlinear loads such as VFDs, rectifiers, UPS systems, welding machines, arc furnaces and switching power supplies. These loads draw current in a non-sinusoidal way.

What is the difference between THDi and THDv?

THDi describes current distortion, while THDv describes voltage distortion. Harmonic current flowing through system impedance can create voltage distortion, so both values and the measuring point matter.

How do I know whether my factory has a harmonic problem?

Warning signs include transformer or cable overheating, capacitor bank failure, nuisance tripping, control interference, motor overheating and unexplained losses. Measurement is still required before selecting equipment.

Where should harmonic measurements be taken?

Measurements are commonly taken at the PCC, main bus and critical nonlinear loads. The correct point depends on whether the target is utility compliance, bus power quality or local load mitigation.

How does an active harmonic filter work?

A CT measures current in real time, the controller extracts harmonic components, and the IGBT converter injects compensating current with opposite phase through a parallel connection.

Is an AHF connected in series or parallel?

An AHF is normally connected in parallel with the bus or distribution panel. It is not installed in series with the main power circuit.

Should the CT be installed on the grid side or load side?

Grid-side CTs are often used for centralized compensation, while load-side CTs can be used for local source compensation. Direction, phase sequence and wiring must match the control method.

How is AHF capacity calculated?

The required AHF current rating should be based primarily on the harmonic current to be compensated, load profile, dominant harmonic orders, mitigation target and an appropriate engineering margin. Transformer kVA alone is not enough.

Can multiple AHF modules operate in parallel?

Yes. Winzele AHF specifications list parallel capability up to 20 machines, with one control panel able to control up to 8 units. Parallel design should consider CT wiring and control coordination.

Can an AHF compensate reactive power and load imbalance?

Winzele AHF specifications include harmonic compensation, reactive compensation and three-phase load unbalance compensation. The enabled mode should be selected according to site priorities and device capacity.

Can AHF guarantee IEEE 519 compliance?

No unconditional guarantee should be made before assessment. IEEE 519 evaluation is related to the PCC, system conditions, load profile, background distortion and the final solution configuration.

What information is required for an AHF quotation?

Useful information includes single-line diagram, load list, transformer capacity and impedance, system voltage, wire system, THDi, THDv, harmonic spectrum, CT position and installation environment.

Requirements Form

Harmonic Measurement & AHF Capacity Selection Form

Provide the available electrical data. If you do not have measurement data, send your single-line diagram, load list, equipment nameplates and operating information.

Harmonic Mitigation Requirements

Complete the essential project information first. Measurement fields are optional and can be left blank when data is not yet available.

Required project information

Name, email and project message are collected by the existing inquiry form below.

Measurement data, if available

Optional: enter measured values only when they are available.

The existing form does not support file uploads. Send the single-line diagram and measurement report by email after submitting the inquiry.

Need a Measured Harmonic Mitigation Plan?

Share your system data and available measurement results with Winzele engineers. We will help define the assessment point, required AHF capacity, CT position and commissioning verification plan.

Request a Harmonic Assessment