The Harmonics You See May Not Be Yours

Based on our experience in assisting customers with harmonic analysis across many facilities, both within industrial plants/Building and at the Point of Common Coupling (PCC),as well as through discussions with responsible personnel at various levels,we have found that:

If operators are able to correctly understand and interpret measurement results, this will lead to decisions that are aligned with the actual condition of the electrical system.

🎯 Objective of This Article

This article focuses on measurement results at the Point of Common Coupling (PCC)and is intentionally written as a guideline for stakeholders within industrial facilities, whose technical backgrounds may vary, ranging from:

• Personnel without direct electrical engineering knowledge

• To those involved in technical operations and management

Therefore, the content is presented in a way that is easy to understand, emphasizing overall concepts and perspectives rather than in-depth technical details.

🔍 Sources of Harmonics at the PCC

In general, harmonic levels measured at the PCC can be classified into three main sources:

1️⃣ Background Harmonics from the Power Grid

Some harmonics are not directly generated by loads within the plant ,but are instead transmitted from the power grid or from other users connected to the same network.

Common characteristics include:

• Harmonic voltage levels remaining high

• Even when the plant has few non-linear loads

• Or during periods when the plant is not in operation

These harmonics reflect the overall condition of the grid,rather than the electrical behavior of a single facility.

2️⃣ Loads Within the Plant

Non-linear loads such as VFDs, rectifiers, UPS systems, or invertersare direct sources of harmonics.

In this case:

• Measured harmonic levels typically vary with production conditions

• Making it relatively clear to correlate the issue with internal plant operations

3️⃣ Changes in the Power Supply Source

Changes in the power supply source, such as:

• Switching from the utility supply to a generator

• Or reconnecting to a different substation

can also affect harmonic levels,as the characteristics and strength of the electrical system change.

📊 What Do Harmonic Levels at the PCC Tell Us?

Harmonic measurements at the PCC provide valuable insights into multiple aspects of the electrical system.

✅ 1. Identifying the Source of the Problem

They help indicate whether harmonics are likely caused by:

• Internal plant loads

• Or background harmonics from the grid

This is a critical starting point before drawing conclusions.

✅ 2. Distinguishing Plant-Level vs. Grid-Level Issues

• If harmonic levels remain high even when the plant is not operating

  → The issue is likely grid-related

• If harmonic levels change with plant operation

  → The issue is typically related to the plant’s own system

✅ 3. Assessing Future Risk

Harmonic levels at the PCC help evaluate:

• How much margin remains in the electrical system

• And whether there is a risk when adding more non-linear loads in the future

✅ 4. Supporting Decisions on Where to Mitigate the Problem

Understanding harmonic levels at the PCC helps determine whether mitigation should be applied:

• At the load side

• At the system side

• Or, in some cases, whether immediate action is unnecessary and monitoring and planning are more appropriate

✅ 5. Serving as a Reference Point for Standards

Harmonic standards such as IEEE 519define the PCC as the primary reference point for evaluating impacts on the power system.

Therefore, measurements at this point are particularly meaningful.

⚠️ Examples of Poor Solution Design Due to Misunderstanding System Behavior

To illustrate this clearly, consider common real-world scenarios:

❌ Case 1: Grid-Originated Harmonics Mitigated at the Plant Load

If harmonics at the PCC originate from background grid harmonics,but mitigation equipment is installed only at the plant load side, the result is:

• No significant reduction in harmonic levels at the PCC

• Despite the investment made

This often leads to the misconception that “the installed equipment is not working,” when in fact the root cause was addressed incorrectly from the beginning.

❌ Case 2: Measurements Taken During Temporary Power Supply Operation

In some cases, measurements are taken while using:

• A temporary power supply

• Or a generator instead of the normal utility supply

This often results in:

• Higher-than-normal harmonic voltage levels

If mitigation solutions are designed based on this datawithout considering the supply context,once the system returns to normal operation,measured values may differ significantly,causing the proposed solution to fail to meet real operating conditions.

🧠 Conclusion

Starting with a correct understanding of the dataleads to targeted solutions,reduces risk, and avoids unnecessary investment.

Before asking,“What equipment should we install?”it may be more important to ask first:

“Do we truly understand the behavior of our electrical system?”