My THD-V reading is below 5%. Does that mean my system is safe?

According to IEEE 519-2022 and IEC 61000, a THD-V below 5% is within the acceptable limit for general distribution systems; however, this alone is not a sufficient criterion. Individual harmonics (especially the 5th and 7th) must also remain within their respective limits, current THD must be under control, and there should be no excessive accumulation in the neutral conductor. Argus EMS monitors all of these parameters simultaneously to provide a comprehensive power quality assessment.

What does it mean if the 3rd harmonic is dominant in the harmonic spectrum?

The 3rd harmonic (150 Hz) typically originates from single-phase nonlinear loads such as computers, LED drivers, and office equipment. In three-phase systems, the 3rd harmonic and its multiples (3rd, 9th, 15th, 21st) are zero-sequence harmonics that accumulate in the neutral conductor, leading to excessive neutral overheating and a potential fire risk. The harmonic spectrum analysis module in Argus EMS monitors this component on a dedicated channel and automatically generates an alarm when the threshold is exceeded.

In what formats can Argus EMS report THD data?

Argus EMS can report THD and broader power quality data in PDF, Excel (XLSX), and CSV formats. Reports are fully customizable by time range, measurement point, and parameter. In addition, the platform automatically performs IEEE 519 and ISO 50001 compliance checks and includes pass/fail status for each relevant clause directly within the report. Thanks to API support, reports can also be exported to third-party ERP or SCADA systems.

How to Interpret THD Measurement Results

What Is THD and Why Does It Matter?

Total Harmonic Distortion (THD) is a power quality indicator that expresses the ratio of all harmonic components present in an electrical system to the fundamental frequency component, stated as a percentage. In industrial facilities, variable frequency drives, UPS systems, electric arc furnaces, and LED lighting are among the primary sources of harmonic distortion. Elevated THD levels can cause transformer overheating, nuisance relay tripping, capacitor bank degradation, and increased energy losses. Periodic monitoring and accurate interpretation of THD measurements are therefore critical for both equipment longevity and energy cost management. Argus EMS, the energy management platform developed by Neva Otomasyon, allows you to monitor real-time THD data from a centralized dashboard.

THD Threshold Values and Standards

Interpreting THD measurements requires reference to internationally recognized standards, most notably IEEE 519-2022 and IEC 61000-3-2. The table below summarizes the generally accepted threshold values for both voltage THD (THD-V) and current THD (THD-I):

THD Type	Good (< %)	Acceptable (%)	Critical (> %)	Relevant Standard
Voltage THD (THD-V)	< 3	3 – 5	> 5	IEEE 519 / IEC 61000
Current THD (THD-I) – Low power	< 15	15 – 20	> 20	IEEE 519-2022
Current THD (THD-I) – High power	< 8	8 – 12	> 12	IEEE 519-2022
Neutral Conductor THD	< 10	10 – 30	> 30	IEC 61000-2-4

The Argus EMS dashboard visualizes these thresholds in real time using color-coded indicators (green / yellow / red), allowing operators to instantly identify which measurement point has entered the critical zone.

Step-by-Step THD Interpretation Process

When an engineer receives a measurement report, a systematic approach should include the following steps:

Step 1 – Classify the Data: Determine whether the measurement represents THD-V or THD-I. These two quantities point to different types of problems; voltage distortion affects the supply side, while current distortion affects the load side.
Step 2 – Examine the Harmonic Spectrum: Looking only at the total THD value is not sufficient. Examine the individual magnitudes of the 3rd, 5th, 7th, and 11th harmonics. Triplen harmonics (3rd, 9th, 15th) accumulate in the neutral conductor and can create a fire hazard.
Step 3 – Evaluate Trends Over Time: Even if an instantaneous value appears low, a rising trend on the trend chart is a warning sign. The trend analysis module in Argus EMS lets you compare historical data on a daily, weekly, or monthly basis.
Step 4 – Correlate with the Load Profile: Compare the hours during which THD spikes occur against production shift schedules. If distortion increases each time a specific piece of equipment starts, source identification becomes straightforward.
Step 5 – Plan Corrective Action: Based on measurement results, decide whether to implement a passive filter, an active power filter, or phase balancing. The cost-benefit analysis available within Argus shows which solution delivers the fastest return on investment.

THD Monitoring and Reporting with Argus EMS

The Argus EMS platform, developed by Neva Otomasyon, fully digitizes the power quality monitoring process end to end. The platform collects data from measurement points within seconds and automatically generates harmonic analysis charts. Customizable alarm rules ensure that the relevant personnel receive instant email or SMS notifications when a THD value exceeds a defined threshold. The reporting module exports IEEE 519 and ISO 50001 compliance reports in PDF or Excel format with a single click.

Argus's multi-point measurement architecture enables simultaneous monitoring of dozens of panels and transformer substations in large industrial facilities. This makes it possible to perform comparative analyses across different production lines and quickly identify the source responsible for the highest level of distortion. Energy managers can customize their Argus EMS dashboards to focus exclusively on the critical parameters most relevant to their operations.

Common THD Interpretation Mistakes

The most frequently encountered mistakes during THD analysis include:

Focusing only on the instantaneous value: A single low reading at one point in time can be misleading; statistical averages and worst-case values must be evaluated together.
Confusing THD-V with THD-I: These two measurements convey different information and cannot be used interchangeably.
Ignoring the neutral conductor: In three-phase four-wire systems, third-harmonic components accumulate in the neutral. If left unmeasured, this creates a serious risk of overheating and fire.
Treating standard limits as absolute targets: IEEE 519 limits represent maximum tolerances; targeting the lowest achievable values extends equipment life and reduces energy losses.