On the official website of Atlant, it is possible to download the instruction manual for household refrigerators, where it is written that the supply voltage is 220-230 V( the last digit is in favor of European standards) when the nominal deviation is 10% each way. If the voltage drops below 200 V, it’s not a fact that the equipment will work. Protection against voltage surges is needed not solely for the reason indicated. Short-term overloads are more dangerous, unhindered by the frequency of passing the filter. When such a tsunami reaches the e-filling, everything becomes possible. Any microcircuit marked limits, above which the functioning leads to failure. Protection of technology becomes the main task when it comes to power surges.

## Why protect equipment from power surges

Let's try to find a protection device against power surges and study the instructions. I liked the information provided by the catalogs of the Spanish manufacturer RTR Energia. On the subject of a three-phase harmonic filter, it is written:

- Products are designed to filter harmonics with frequencies of 134 and 189 Hz.
- The transmission coefficient at the filtering frequencies is 14% and 7%, respectively.
- The purpose of the listed measures is explained. Due to these characteristics, it is possible to suppress the 5th harmonic( 5 x 50 = 250 Hz).As a result, there is no resonance between the inductive load impedance and the capacitor bank, which naturally protects the input circuits from overloads.

Let us clarify that reactive power in industrial networks is considered to be a parasitic effect, does not perform useful work, but requires a substation resource. As a result, the average man pays for the kWh active power, enterprises have to unfasten their jet power as well. This increases spending, and, we emphasize, does not benefit the consumer. To compensate for the reactive part of the load, large enterprises install blocks of capacitors at the input of consumers. Each is characterized by power in kVAR, capable of redemption.

As a result of such activities and there is a threat of overload. We struggle for reactive power compensation in order to reduce energy costs, and we obtain resonance at the above frequencies. As a result, the imaginary part of the resistance vanishes, and large energy runs here and there, which is emitted exclusively as heat in the active part of the load. This is again a loss. In addition, based on the manufacturer's data, it is possible that our saving capacitor blocks may already be out of order. To prevent additional blocks are put out of chokes( one per phase), omitting the limiting frequencies of transmission of the entire system.50 Hz of the useful voltage almost does not suffer.

## What are harmonics and wave analysis of industrial voltage

Let's understand what harmonics are, how network protection against power surges depends on them. It turns out that the forms of various vibrations are difficult to analyze. And this is required by all means in order to predict the result of the system, including the forecast of the operation of the surge protection unit. Requires knowledge of parameters.

Physicists and mathematicians thought and decided that any fluctuation in nature is decomposed into a spectrum. Performs direct and inverse transform using Fourier methods. This is a set of mathematical formulas implemented in practice at home. True, you have to use the discrete Fourier transform. It is optimized just for the application of numerical methods( programming).As a result, it turned out that:

- Any oscillation is represented as a set of sinusoidal signals. For example, for a pure sine wave consists of a single dash. On the frequency of the sinusoid. The mains voltage is ideally provided at 50 Hz. And the spectrum consists of a single harmonic.
- In practice, the waveform is different from sinusoidal. Additional complexity: the final spectrum is determined by the Fourier functions exclusively for an infinite signal. Our voltage shows the start( power on) and terminate( power off).A number of harmonics appear in the spectrum. These frequencies are proportional to the main 50 Hz. For example, 100, 150, 200, etc. Now readers understand that from the information of the manufacturer RTR it is not difficult to know the importance of filtering the fifth harmonic of 250 Hz. To accomplish the task suppress frequencies of 134 and 189 Hz. Why? Only scientists will answer this question. This is somehow connected with the peculiarities of the equipment and the transition processes in the network.
- If you look at GOST 13109, you will see some interesting comments and requirements for the industrial network. For example, short-term deviations of the nominal from the norm can not exceed 10%.It reminds those values for which the Atlant refrigerators were created. The fact simply says that the Belarusians adhered to the standards. Long-term withdrawal from the nominal cannot exceed 5%.The thresholds for each harmonic are determined. Are expressed by harmonic coefficients. This number is approximately equal to the ratio of the amplitude in the spectrum of the main signal of 50 Hz to the magnitude of the harmonic( frequency, 100, 150, 200, etc.).We see that the form of the voltage is clearly defined and it is written that the consumer has the right to demand the fulfillment of the specified parameters( try to sue the garage cooperative).
- Finally, for individual pulses, the signal spectrum goes to infinity and becomes continuous. In this regard, most of the input filters are based on a low-frequency circuit. As through the gate passes 50 Hz and additionally a small area, and all the above is cut off. The reason is that power surges cause changes in the spectrum that are detrimental to the equipment.