The Rise of Harmonic Distortion in Modern Power Systems

Why Harmonic Studies Are Now Critical for Grid Stability, Compliance, and Asset Protection

Modern power systems are undergoing a profound transformation. Traditional grids once dominated by large synchronous generators and linear loads have evolved into complex, inverter-rich networks driven by:

• Renewable generation (solar, wind)
• Battery Energy Storage Systems (BESS)
• Electric vehicle charging infrastructure
• Variable Speed Drives (VSDs)
• HVDC systems
• Power-electronic-dominated industrial loads
• Cable-heavy distribution and transmission systems

While this transition has improved sustainability, flexibility, and efficiency, it has introduced a serious and growing technical challenge:

Harmonic distortion.

At Keentel Engineering, we provide advanced harmonic studies, resonance analysis, mitigation design, and full regulatory compliance support for HV, MV, and LV networks.

This article explains:

• What harmonics are
• Why harmonic distortion is increasing
• How harmonics affect equipment and protection systems
• UK harmonic compliance framework (ER G5/5 & IEC standards)
• The three-stage harmonic assessment process
• Why early harmonic analysis protects your investment
• How Keentel Engineering delivers turnkey harmonic compliance
  

1. The Ideal Power System: Pure Sinusoidal Operation

In an ideal electrical system, voltage and current waveforms are perfectly sinusoidal at a single fundamental frequency:

• 50 Hz in the UK and Europe
• 60 Hz in North America

A pure sinusoidal waveform:

• Contains only one frequency component
• Has zero distortion
• Is symmetrical
• Has no DC offset
• Completes one full cycle every 20 milliseconds (for 50 Hz systems)

Why does this matter?



Because distortion-free sinusoidal supply ensures:

• Minimal transformer heating
• Reduced copper and core losses
• Stable protection relay operation
• Lower electromagnetic interference
• Reliable inverter performance

However, modern grids are no longer purely sinusoidal.

2. What Are Harmonics?

Harmonics are frequency components that are integer multiples of the fundamental frequency.

In a 50 Hz system:

• 2nd harmonic = 100 Hz
• 3rd harmonic = 150 Hz
• 5th harmonic = 250 Hz
• 7th harmonic = 350 Hz

Mathematically, any distorted waveform can be represented as the sum of:

• The fundamental frequency
• Multiple harmonic frequency components



This concept is based on Fourier series decomposition.

In practice, distorted voltage and current waveforms are simply the combination of multiple sinusoidal signals at different frequencies.

3. Why Harmonic Distortion Is Increasing

The growth of harmonic distortion is directly linked to the widespread adoption of non-linear and inverter-based technologies.

Major Contributors:

1️⃣ Inverter-Based Renewable Generation

Solar PV, wind turbines, and BESS rely on power electronic conversion systems.

2️⃣ Variable Speed Drives (VSDs)

Widely used in industrial motor control.

3️⃣ EV Charging Infrastructure

Fast chargers inject high-frequency harmonic currents.

4️⃣ Cable-Dominated Networks

Underground cables increase system capacitance, raising resonance risk.

These systems naturally generate harmonic frequency components.

As grid strength decreases (low Short Circuit Ratio environments), harmonic interaction becomes more severe.

4. Technical Impacts of Harmonics

Harmonics are not merely waveform imperfections. They have measurable technical and financial consequences.

4.1 Equipment Overheating

Harmonic currents increase RMS current levels.

Because heating is proportional to I²R:

• Cables overheat
• Switchgear insulation degrades
• Motors experience torque ripple
• Transformers suffer additional eddy current losses

Even small harmonic content increases thermal stress significantly.

Keentel Engineering performs:

• Harmonic thermal impact studies
• Cable ampacity adjustment
• Transformer harmonic loading assessments
• Equipment derating calculations
  

4.2 Transformer Derating

Transformers are particularly sensitive to harmonics.



Harmonics cause:

• Increased eddy current losses
• Higher stray losses
• Neutral overheating from triplen harmonics (3rd, 9th, 15th)
• Delta winding circulating currents

Keentel provides:

• IEEE-based transformer harmonic loading analysis
• K-factor evaluation
• Derating recommendations
• Thermal modeling
  

4.3 Protection System Maloperation

Modern protection relays rely on clean waveforms for:

• Differential protection
• Overcurrent detection
• Frequency elements
• Earth fault detection
• Synchronism check logic

Excessive harmonics can cause:

• False tripping
• Protection blinding
• Incorrect inrush detection
• Delayed operation

Keentel performs:

• Protection-harmonic interaction analysis
• Relay stability verification
• EMT-based modeling
• Harmonic restraint validation
  

4.4 Voltage Distortion and THDv

• Senior engineer oversight
• Constructability validation
• Owner standard compliance
• Review milestone enforcement

Our QA/QC system ensures drawings are:

• Precise
• Consistent
• Complete
• Buildable



This dramatically reduces RFIs and field markups.

4.5 Resonance – A Major Grid Risk

Resonance occurs when harmonic frequency coincides with the natural frequency of the network.

Two types:



• Parallel resonance → voltage amplification
• Series resonance → current amplification

Resonance risk increases in:

• 33 kV / 66 kV / 132 kV cable networks
• Capacitor bank installations
• Weak grid interconnections
• BESS-dominated systems

Keentel Engineering performs:

• Frequency scan analysis
• Impedance vs frequency studies
• Harmonic stability assessments
• Grid-forming inverter interaction analysis
  

5. UK Harmonic Compliance Framework

The UK enforces strict harmonic limits through:

• ER G5/5
• IEC 61000-3-6
• Utility-specific requirements

All Distribution Network Operators require harmonic compliance for new connections.

G5/5 introduced:

• Updated planning limits
• Stage 1, 2, and 3 harmonic assessment methodology
• Headroom allocation principles
• Detailed modeling requirements for inverter-based systems

Keentel Engineering prepares complete G5/5 compliance submissions for:

• Renewable projects
• BESS installations
• Industrial facilities
• Data centers
• Transmission-level projects
  

6. The Three-Stage Harmonic Assessment Process

Stage 1 Initial Screening

Used for small LV or low-impact connections.



Includes:

• Preliminary emission estimates
• Headroom comparison
• Simplified compliance checks
  

Stage 2 Detailed Harmonic Assessment

Required for:

• 1–20 MW PV plants
• BESS projects
• Industrial sites with VSDs
• Weak grid connections

Includes:

• Harmonic current injection modeling
• Frequency-dependent network modeling
• Individual harmonic compliance checks
• THDv calculations
• IEC summation methodology

Keentel performs Stage 2 studies using advanced simulation platforms.

Stage 3 – Advanced Harmonic & Stability Study

Required for:

• 20 MW generation
• Weak grids (low SCR)
• Resonance-prone networks
• Projects with failed Stage 2 results

Includes:

• Frequency scan analysis
• Inverter impedance modeling
• Harmonic stability assessment
• Sub-synchronous resonance evaluation
• Filter design and tuning



This is where advanced engineering expertise becomes critical.

Keentel Engineering specializes in full Stage 3 harmonic stability studies.

7. Why Harmonic Studies Go Beyond Compliance

Harmonic analysis is not just about meeting regulatory limits.

It protects against:

• Multimillion-dollar retrofit filter installations
• Equipment damage
• Project delays
• Operational penalties
• Performance guarantee failures
• Asset lifespan reduction

Early-stage harmonic modeling reduces project risk significantly.

Keentel integrates harmonic studies during:



• Concept design
• Grid connection application
• EPC design phase
• Pre-commissioning validation
  

8. Keentel Engineering Harmonic Study Services

We provide:

✔ Stage 1–3 ER G5/5 Studies
✔ IEC 61000-3-6 Compliance
✔ Frequency Scan & Resonance Detection
✔ Harmonic Stability for Grid-Forming & Grid-Following Inverters
✔ Passive & Active Filter Design
✔ Transformer Derating Assessment
✔ Protection Interaction Studies
✔ Power Quality Measurement & Validation
✔ BESS Harmonic Compliance Modeling
✔ Utility Submission & Technical Reports

We support:

• Renewable developers
• BESS investors
• Utilities
• EPC contractors
• Industrial operators
• Data center developers
  

20 In-Depth Harmonic FAQs