What are Harmonics? Harmonics can be best described as the shape or characteristics of a voltage or current waveform relative to its fundamental frequency. But what does that mean? Well, the ideal power source for all power systems are smooth sinusoidal waves. These perfect sine waves do not contain harmonics. When waveforms deviate from a sine wave shape they contain harmonics. These current harmonics distort the voltage waveform and create distortion in the power system which can cause many problems.
The Destructive Effects of Harmonic Distortion
A power system’s ability to perform at optimal levels is compromised when harmonic distortion enters the system. It creates inefficiencies in equipment operations due to the increased need for power consumption. The increase of overall current required creates higher installation and utility costs, heating, increased energy consumption and decreasing profitability.
Some of the effects the harmonic can cause, to the equipment, to the installation, or both, are:
Added efficiency losses to the system composed by electrical installation and equipment.
Disturbances in electronic equipments, causing “logical” faults in digital circuits.
Unwanted overload (or need to oversize) for transformers, wirings.
Malfunctions of motors and generators.
Unwanted Circuit Breakers tripping or Fuses blowing.
The harmonics mitigation/suppression can report quantifiable benefits for industry critical processes, IT systems, data centers, etc., in terms of overall installation cost, energy bill reduction, and protection against process interruptions and equipment faults.
How are they Generated?
The main cause of the harmonics generation are the “non-linear” loads. So, before talking about harmonics, we need to define what is a “linear” load and what a “non-linear” load.
Linear load It is a load that draws instantaneously proportional current to the applied voltage, i.e., its impedance is maintained constant along the whole alternating period. For public electricity supply of 50 or 60 Hz sinusoidal voltage, this will mean a pure sinusoidal current also. Linear loads can be classified as resistive (electrical heaters, incandescent light bulbs), capacitive (capacitors usually found as part of systems or equipments), inductive (transformers, motors), or combinations of some of them.
In opposition to linear-loads, a non-linear load changes its impedance with instantaneous applied voltage, that will lead to a non-sinusoidal current draw when the applied voltage it’s so. In other words, this kind of load does not have a constant relation current vs. voltage along the alternating period. The simplest circuit to represent a non-linear load is a diode-rectifier, with its multiple variants (full-wave diode rectifier, half-wave diode rectifier, single-phase or three-phase). Some examples of non-linear loads, capable of injecting harmonics into an electrical distribution, are: industrial equipments (welding, arc furnace), variable frequency drives (VFD), line-switched rectifiers, switch-mode power supplies, lighting ballasts … and also modern electronic equipments, at low load levels, even they could be designed to optimize efficiency around it’s rated working point. All these circuits can contain semiconductor power devices such as diodes, thyristors (SCR’s), transistors, and/or switching of loads or circuits.
Transformers: Transformers by themselves, or forming part of active front-ends, can have the ability to cancel certain load harmonics. In fact, what they do is to discriminate certain harmonics to circulate upstream in the installation, rather than eliminate them.
Passive harmonic filters consist usually of resonant filters composed of Inductors and Capacitors (and sometimes damping resistors) tuned to cancel or trap a certain harmonic frequency, usually of low order (5th, 7th, 11th,..), to minimize the current distortion at PCC. Such effect is obtained by tuning the resonance frequency of LS -CS at that 5th harmonic.
Active harmonic filters are power electronic equipments to cancel (or reduce) current harmonic pollution of an installation. The working principle consists in measuring the current harmonics of the load, and generate in real-time the same harmonics but in phase opposition, in such way that the addition of both currents seen from the electrical installation contains nearly no harmonics, but only the fundamental f1. This yields to THDi lowering, at levels typically below 5%. They also have the capability of reducing reactive power of the load, i.e., increasing power factor to nearly 1. Due to its design and working principle, the distortion minimization is achieved for all load leves (within active filter capacity), and they are not affected by resonances nor line impedances.
The Alphonso Centralized Smart Energy Savers are Special Auto Transformer Equipment with Active Filters, Voltage Optimizers, PF Correction and Smart Meter Systems. Helping users to mitigate Harmonics. But also, Improves Power Quality, Increase Load health, Reduces Energy Consumption and In Turn, Reduces Bills Significantly.
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