Harmonics: Causes, Consequences And Solutions
Nowadays the world is inconceivable without power electronics. Power supplies, Uninterruptible Power Supplies (UPS), motor speed variators, fluorescent lighting start-up ballasts, power converters ..., walk at ease through our homes and businesses. Its usefulness and the comfort that we have assumed are undeniable. However, they have caused us a serious problem for the distribution and consumption of electricity: the harmonics of electric current .
We can approximate the concept of harmonic distortion to a "malformation" of the electric current that reaches our homes and businesses. This "malformation" is caused by electronic equipment that consumes electrical energy in a "non-linear" way, that is, in a non-continuous way over time. This way of consuming electricity causes the sine wave form of the electric current to be distorted. This distortion can be broken down into different components, known as harmonics. The greater or lesser presence of harmonics is measured with a quantity known as the Harmonic Distortion Rate (THD).
The presence of harmonics in an installation, or electrical distribution network, can cause innumerable problems, such as:
Overheating in the conductors, especially in the neutral of the installations, due to the film effect.
Unusual Shooting of Automatic and Differential Switches.
Decrease in the power factor of an installation and aging and even destruction of the capacitor banks used for correction due to resonance and amplification phenomena.
Vibrations in electrical panels and couplings in telephony and data networks.
Deterioration of the voltage waveform, and consequent malfunction of electrical devices.
Heating, degradation of insulation, packing and braking in asynchronous motors.
Degradation of transformer insulation, loss of power supply capacity in transformers.
All these effects lead to significant economic losses due to:
Need for over sizing of the conductors and the powers contracted in a facility.
Need to replace more frequently the devices and machines damaged by the harmonics.
Production stops due to untimely firing of the protection and control elements.
Now, how can we detect the presence of harmonics in our installation? In addition to the observation of the effects caused and the experience of the maintenance technicians, we can resort to instruments such as oscilloscopes, multi meters and clamps of true effective value (TMRS), harmonic measuring multimeters and electrical network analyzers, in addition to the existence of specialists and professionals that can make us a diagnosis of the harmonic problems of our installation.
Knowing what they are, the effects they produce and how they can be detected, let's now look at some of the multiple solutions that exist:
Over dimension of conductors and plates. Use of a neutral for each phase.
Use of star-delta isolation transformers, with secondary in zig-zag or with secondary secondary.
Passive filters such as the antiarmonic impedances or the so-called "resonant shunt", formed by passive elements such as inductances and capacitors. Active filters and "clean" converters.
Use of "superimmunized" differentials calibrated to withstand high THD rates.
Separation of the non-linear elements of "clean loads" in an electrical installation.
Smoothing impedance, connected to non-linear loads. Filters in loaders and feeders.
Alerted of the presence of the harmonics and informed of their characteristics, strengths and weaknesses, we can arm ourselves and defend ourselves against them. For those who wish to deepen the subject, there are numerous treaties, publications and technical notebooks available. Here I have tried an approach to the problem they represent for consumers, in a simple, concise and easily understandable.
