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How to Minimize harmonic Distortions | EC Guidelines for measurement & Control Harmonics Distortions



Introduction: Harmonics distortion


Harmonic distortion is the alteration of the voltage pattern of a sinusoidal wave due to non-linear loads like VFDs, fluorescent ballasts, computer power supplies, battery chargers, etc., which draw electricity differently than non-electronic equipment.


How to Minimize harmonic Distortions | Energy Conservation Guidelines for measurement & Control Harmonics Distortions

The non-linear loads lead to harmonics distortions in the overall electrical system. Limiting the harmonics is important to avoid harmonic injections to the grid and consequent voltage distortion at the grid level. This article provides guidelines to limit the harmonics.



1. Management and control for harmonics distortions


The industry shall undertake the following:


A. Determine the magnitude of harmonic distortion at points of common coupling (PCCs) in the electrical system.


B. Identify the sources of harmonics in the electrical distribution network for their operational status. The harmonics may be induced due to either partial malfunctioning or total failure of the equipment.

C. Use the following measures to minimize harmonic distortions:


  • Pulse width modulation (PWM) in AC drives.

  • Drive with effective choke filtering.

  • Tuned LC (inductive and capacitance) filters

  • Standard cabling and earthing practices.

  • Shunt filters or harmonic traps.

  • External active filters.


2. Measurement and recording for harmonics distortions


The industry shall measure and record the following:


A. Total voltage distortions and total current distortions at PCCs on monthly basis.


3. Maintenance and inspection for harmonics distortions


The industry shall undertake the following:

A. Inspect operational status of different harmonic filtration systems installed in electrical distribution network on monthly basis.

B. Carry out scheduled preventive maintenance of harmonics filters as per OEMs instructions.


4. Necessary measures when installing new facilities for harmonics distortions


The industry shall consider the following:


A. Select transformer with built-in passive harmonic filtration for low voltage distribution network.


B. Undertake the assessment of the non-linear devices and select a suitable size of filtration/tuned LC filters in the electrical distribution network.


Target components for harmonics distortions


The industry shall ensure the following:

A. Total harmonic voltage distortion in the range as specified in the below Table:

Total harmonic distortion (THD) is the ratio of the root mean square of the harmonic content, considering harmonic components up to the 50th order and specifically excluding inter harmonics, expressed as a percentage of the fundamental. Harmonic components of order greater than 50 may be included when necessary.

B. Total harmonic current distortion in the range as specified in the below Table:

Isc: Maximum short-circuit current at PCC

IL: Maximum demand load current (fundamental frequency component) at PCC

h: Integral multiples of fundamental frequency (f), for example, 3 ≤h< 11 means distorted frequency in the distribution network lies between 3f and 11f.

TDD: Total demand distortion, harmonic current distortion in % of maximum demand load current (15 or 30 minutes demand)

The industry shall monitor the following common monitorable parameters as shown in the below Table to assess the magnitude of harmonic distortion at PCCs.

Source: Energy Conservation Guidline for MSME Sector by BEE, MoP, GoI.

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