Harmonics in Electrical Systems: Effects & Solutions

Posted on Feb 28, 2025 in Electricity and Electronics

1. Difference Between Technical and Economic Costs

Technical costs are those that cause a loss of performance in an electrical installation. Economic costs are those that can be economically quantified, although in some cases, this may be difficult. Economic costs can be further divided into hidden costs and visible costs.

2. Technical Costs of Harmonics

Technical costs are those that cause a loss of performance in our installation, such as:

  • Loss of capacity on the energy distribution line
  • Transformer overload
  • Conductor overload
  • Voltage drop
  • Derating of transformers
  • Losses on lines and machines due to the Joule effect
  • Magnetic losses on electrical machines

3. Meaning of “Derating of Transformers”

This means that a transformer rated for 1000 kVA, due to harmonics, may only be able to supply 800 kVA. The presence of harmonics reduces the transformer’s effective capacity.

4. Difference Between Visible and Hidden Costs

Visible Costs:

  • Increased electricity consumption
  • Increased electricity peaks
  • Surcharges for reactive energy

Hidden Costs:

  • Energy losses and distribution power losses (due to the Joule effect and magnetic losses)
  • Enlargement of installations
  • Stoppage of the productive process

5. (Question 5 was missing in the original text)

6. Explanation of Pictures (Phase Shifts)

The pictures illustrate the phase relationships in a three-phase system. Ideally, the three phases (L1, L2, L3) are 120 degrees apart. The first picture shows the normal sequence: L1, then L2, and finally L3. The second picture shows a reversed phase sequence: L3, then L2, and finally L1. The final picture indicates that the three phases are in phase (homopolar), meaning they peak at the same time, which is characteristic of certain types of harmonics, particularly the third harmonic.

7. Loads That Generate Harmonics

Many types of loads can generate harmonics, including:

  • Frequency/variable speed drives
  • Discharge lamps
  • Rectifiers
  • AC/DC converters
  • Arc welding equipment
  • Induction ovens
  • Computers and laptops

8. Effects of Harmonics on Electrical Components

Conductors:

  • Heat in cables
  • Tripping of protection devices

Neutral Conductor:

  • Overcurrent flowing
  • Heat in cable
  • Premature degradation
  • Earth voltage
  • Tripping of protection devices

Transformers:

  • Overheating in the windings
  • Thermal insulation loss due to heating
  • Copper and metal loss (hysteresis)
  • Reduction in performance
  • Transformer saturation (creates distortion)

Motors:

  • Same effects as transformers
  • Vibrations in the axis
  • Mechanical wear on bearings and eccentric bearings
  • Torque reduction

9. Difference and Objective of Electronic Devices (ARSL vs. QNA-P)

The objective of both devices is to analyze harmonics. However, they differ in their method and precision:

  • ARSL: Measures the grid at certain intervals and provides average values. It essentially takes “snapshots” of the power quality.
  • QNA-P: Measures the grid instantly and continuously. It provides a “video” of the power quality, offering a more detailed and real-time analysis.

10. Types of Anomalies with Harmonics and Their Effects

Neutral Overload (Lighting and Computers):

  • Caused by the flow of the third harmonic.
  • Solution: Block or compensate for the third harmonic.

Tripping of Circuit Breakers:

  • Caused by high-frequency current leakage, often originating from EMI filters.
  • Solution: Filtering and the use of appropriate residual current circuit breakers.

Power Quality and the EN-61000-4-30 Standard

Ideally, the electric company provides a perfect sinusoidal wave. However, in reality, perturbations often exist. These perturbations can manifest as:

  1. Variations in Frequency: Caused by the incorrect operation of generating groups.
  2. Variations in Amplitude: Classified according to their duration (more or less than one cycle).
  3. Variations in Symmetry: In a three-phase system, each phase should peak at a different time. Harmonics, especially homopolar harmonics, can cause the phases to peak simultaneously.
  4. Induced High-Frequency Signals:

Electricity is a product and must adhere to quality standards. In the European Union, the standard that regulates electric supply quality is EN-61000-4-30.