Impact of Harmonics on the Electrical Network Distribution

Abstract

Today, electronic devices are used in all areas of human activities. However, these equipments generate a signal distortion of the electrical parameters of the voltage source that supplies these non-linear loads. When the level of distortion reaches a certain threshold value, it causes a premature deterioration of the electrical loads and even of the power supply devices (transformers, circuit breakers, etc.). So, it is important to control this variation. This chapter develops techniques or scenarios to understand the source of harmonics following several scenarios by combining linear and non-linear loads. In addition, this chapter will discuss methods of measuring harmonics using electrical analyzers.

1. Introduction

Today, electrical energy has become the pedestal of socio-economic development in every country. However, the rate of electricity access in sub-Saharan Africa is low, at 50.6% in 2021 [1]. In the context of technological expansion, the impact of climate change and the energy transition, it is necessary to increase the coverage rate in the electricity field. This has allowed to technological evolution in the power system chain. In other words, the conventional power system, which consists of generating, transmitting and distributing has modernized (smart grid) [2]. The smart grid is a dynamic, stable, flexible, resilient and controllable system.

Mainly with the management function via programmable controllers, the hybrid systems have become the optimal solutions for meeting electrical energy demand efficiently [3]. So, the redeployment of renewable energies in electricity production ensures a smooth energy transition and reduces the rate of CO2 emissions [4].

In addition, the electronics integration into electrical systems and the developments of electrical technology and/or electronic devices have allowed the proliferation of non-linear loads consuming little electrical energy from the users of electrical energy. Electronic converters and non-linear loads generate disturbances in the network such as an increase in the rate of harmonics, current unbalance and consumption of reactive energy, etc. The use of electronic devices in an electrical installation impacts the quality of the electrical energy of the grid and the proper functioning of the devices [5]. The permanent presence of harmonics has harmful technical and economic consequences. It distorts the quality of the energy distributed and reduces the lifespan of the loads and the elements of the distribution grid, which allow the transmission of energy to the customers [6].

However, to ensure the quality of electrical energy in accordance with EN 50160 and IEEE 1159–2009 standards, passive and active techniques must be developed [7].

The first technique (passive) is detailed in this document. It consists of having historical electrical data from the electrical grid. This involves taking measurements with accurate electrical devices. Electrical analyzers are the most suitable for studying the quality of electrical energy. Indeed, they make it possible to record in real-time all the electrical quantities and the electrical disturbances of the electrical systems. In this chapter, it is also a question of approaching the analysis of the mitigation and the sources of electrical disturbances and their mode of propagation.

2. Definition of linear and non-linear loads

According to EN 50160, an electrical harmonic is a component of sinusoidal signal voltage or current and frequency multiple of the fundamental frequency (50 Hz).

2.1 Linear load

A linear load in electricity is any load that draws a current of the same shape as the voltage, in other words quasi-sinusoidal. For example, for a resistive load, we find the representation of the current and the tension which are all of identical form in Figure 1.

Figure 1.

Example of a waveform of the electrical signal of a linear load [8].

2.2 Nonlinear load

A nonlinear load is a load that draws a current that distorts the shape of the voltage. With a variable speed drive (as a load), we find the behavior or forms of the electrical magnitude as shown in Figure 2.

Figure 2.

Example of the waveform of the electrical signal of a nonlinear load [8].

3. Fundamental indicators of electrical harmonics

The study of harmonics is based on signal theory. However, mathematical tools are essential in signal processing. Harmonics are defined as sinusoidal signals of multiple frequencies at the considered fundamental frequency. Thus, Fourier’s theorem is one of the methods that allows development of any periodic signal of distorted waveform into sums of sinusoidal signals of different amplitudes.

In the field of physics, more particularly in industrial applications such as the distribution of electrical energy, measurement instruments have been designed to measure and analyze the level of harmonic disturbance [7, 9, 10].

In fact, several approaches have been developed that take into account the harmonic part. Among these, that of Baudeau takes into account the presence of harmonics [11].

The active and reactive powers are expressed respectively by the Eqs. (1) and (2):

$$P={\Sigma }_n{V}_n\ast I_n\ast \cos {\varphi }_n$$E1

$$Q={\Sigma }_n{V}_n\ast I_n\ast \sin {\varphi }_n$$E2

With n: whole number defining the harmonic order.

Thus, the design power or apparent power is expressed by the following formula:

$$S^2=P^2+Q^2+D^2$$E3

With, D: distorting power (VAD), P: active power and Q: reactive power.

3.1 Power factor

An electrical parameter defining the level of quality of the power consumed is the power factor. It is used by the equation:

$$FP=\frac{P}{\text{S}}$$E4

With, P: active power, S: total apparent power (fundamental + harmonic components).

3.2 Order of harmonics

The order of the harmonics is the ratio of the frequency of the harmonic (fn) to the frequency of the referential or fundamental sinusoidal function (f1). It is written as follows [7]:

$$N=\frac{f_n}{f_1}$$E5

3.3 Effective value of the harmonic quantity

For a deformed magnitude and, in a steady state, the energy dissipated by the Joule effect is the sum of the energies dissipated by each of the harmonic components [7], i.e.:

The effective value of the harmonic magnitude.

$$\text{Y}=\sqrt{\sum _{n=1}^{n=\infty }\left(Y_n{}^2\right)}$$E6

3.4 Total harmonic distortion (THD)

This quantity allows us to detect grids polluted with harmonics, it can be evaluated with the harmonic distortion rate, according to the definition given by the IEC dictionary: this parameter, is also called harmonic distortion or distortion factor. The harmonic content can be calculated either with [9, 10]:

The global harmonic rate of distortion. It represents the ratio of the effective value of the harmonics Yn to the effective value of the fundamental Y1 [12, 13].

$$THD\left(\%\right)=100\frac{\sqrt{{\sum }_{n=2}^{n=\infty }{Y}_n{}^2}}{Y_1}$$E7

Where, Yn: effective value of (n-1) harmonics and Y1: effective value of the fundamental.

It is possible to calculate the individual distortion rate by using the Eq. (8) [7]:

$$THI\left(\%\right)=100\frac{Y_n}{Y_1}$$E8

The Eq. (9) is used to evaluate the THD in electrical network distribution fixed by the IEEE 519 standard provides guidelines for harmonic current limits at the point of common coupling (PCC) [14, 15].

$$THD\left(\%\right)=100\frac{\sqrt{{\sum }_{n=2}^{n=\infty }{I}_n{}^2}}{I_L}$$E9

I_n: the maximum rms value delivered in the fundamental state.

I_L: Current loads connected to the PCC.

4. Behavior of harmonics

Several indicators define the presence of harmonics, they make it possible to evaluate the quality of the electrical energy and also specify the types of distortions present. The C.A 8220 measuring device is the power analyzer used to measure the harmonic disturbances likely to be injected into the electrical distribution networks via electrical loads.

To study the behavior of the harmonic rate in the presence of electrical charges, several scenarios have been developed (Table 1).

Name of Loads	Power of Loads
Laptop	65 W
Ultrasound-machine	400 W
Air Compressor	750 W
Air Conditioner	1980 W
Water-heater	2200 W
Printer	365 W
Photocopier	1850 W
Fridge	75 W
TV	55 W
Energy-saving light bulb	9 W
Fluorescent Bulb	85 W
Incandescent Bulb	60 W
Cellphone charger	10 W

Table 1.

Power of loads used.

The principle consists of connecting the analyzer to the load terminals (see Figure 3) to record the harmonic rate of the loads summarized in Table 2.

Figure 3.

CA8220 analyzer overview [16].

Table 2.

Some results obtained at the terminals of the targeted loads.

In single-phase mode, the analyzer is connected in this experiment as follows (Figure 4).

Figure 4.

Single-phase connection [16].

The results presented in this part, are to evaluate the harmonic rate of some devices and then to observe the behavior of the content of the harmonics according to the scenarios:

• The combination of moderately polluting loads (a compressor and an air conditioner);

• The combination of highly polluting loads (computers and ultrasound machines) and a pure load (water heater).

The figure below gives some illustrations of the measurement devices and the principle of data collection (Figure 5).

Figure 5.

Mesure des harmoniques électriques générés par les appareils monophasés.

5. Results obtained

Based on the measurement principle explained above, it appears that the level of distortion varies according to the technology of the electrical charges. The table below summarizes the level of harmonic distortion recorded at the terminals of the targeted electrical devices.

5.1 Combination: water heater, air conditioner, compressor, ultrasound machine and computer

However, by connecting the combination of these devices to a low-voltage power supply (220 V, 50 Hz). As shown in Figure 6 we observe a variation of the harmonic rate.

Figure 6.

Variation of the harmonic rate produced by the combination of linear and non-linear loads.

5.2 Summary of results

Tables 2 and 3 below summarize respectively the global harmonic rate of each device and the variation of the harmonic rate according to the combinations of these devices.

CODE	Loads	THDA
1	Computer	194.5
2	Computer + Ultrasound	64.9
3	Computer + Ultrasound + Heater	4.9
4	Computer + Ultrasound + Heater + Compressor	5.2
5	Computer + Ultrasound + Heater + Compressor + Air-conditioner	8.4
6	Heater + Compressor + Air condition	7.9
7	Compressor + Air condition	13.44
8	Computer + Heater	2.82

Table 3.

Variation of harmonic rate.

5.3 Analysis and interpretation of results

The first scenario begins with the powering up of a computer, we obviously see that the harmonic rate is high, estimated at 194.5%. This type of load can then be classified as a very polluting load. Once this computer and an ultrasound scanner are supplied at the same time, this combination leads to a drop in the Total Harmonic Distortion (THD) to 64.9%, thus the combination of two polluting loads of different contents leads to a significant drop in the THD. This time, in scenario 3, it is a case of supplying the devices of scenario 2 and a resistive load (the water heater) at the same time, the result obtained is very interesting because the harmonic rate is low with a THD of 4.9%. This explains the impact of resistive loads in the attenuation of harmonic pollution. As demonstrated in scenario 3, scenario 6 describes a consequent attenuation of the harmonic rate also due to the water heater in the presence of non-linear loads (the air conditioner and the compressor), both of which consume energy. However, when the water heater is removed from the system, a rise in the THD is observed.

6. Conclusion

The experimentation carried out in this chapter has made it possible to observe the variation in the harmonic rate resulting from the use of nonlinear and linear loads. Eight (8) combinations of loads called “Scenario” have been developed in order to clearly identify the propagation of electrical harmonics in an electrical network. The results obtained have shown that the presence of linear loads significantly attenuates harmonic disturbances although they are energy-intensive. For example, turning on a computer (nonlinear load) and a water heater (linear load) drew a very low harmonic current (2.8%) compared to the THD of the computer (197.9%). Thus, linear loads contribute to maintaining the quality of electrical energy, particularly the waveform of the electrical signal that must exist in the equipment of subscribers even if the new WAEMU(UEMOA) energy efficiency policy tends to be replaced.

In perspective, in order to improve the energy efficiency policy, would it be necessary to deepen this experimentation in a grid made up only of electronic devices with low electrical consumption?