2. Adverse effects of wind energy conversion units on distribution networks

The electrical power obtained from wind farm system adversely affects the voltage stability in the grid. To improve and maintain the voltage stability, prior understanding of the influences of such sources in terms of power quality and harmonics is significant for better operation and control of the grid.

## 2.1. Protection problems

coastline, which has given it enormous potential to generate electricity from wind and solar energies. Most of Libya's population lives on the coastline. The total population is approximately 6,273,000 [1]. Despite the potential to generate electric energy from wind and solar as a result of the excellent location, Libya's contribution to alternative energy remains negligible. The production of electricity in Libya depends mainly on fossil fuel sources. After the devastation in Libya since 2011, oil production in Libya has fallen, which has led to a sharp drop in state exports and a frequent shortage of electricity production [2, 3]. As a result of the economic development and reconstruction, the demand for energy will substantially increase in the near future. Therefore, the generation of energy from sustainable energy sources in the country must be taken into account, since it mainly depends on fossil fuels. To avoid the negative results in the near future such as the shortage of oil and gas supplies, and the reduction of emissions from conventional generation sources, the establishment of an urgent plan needs to be considered. However, renewable energy sources have been utilized in Libya since the 1970s, but in small-scale applications. In 1976, solar energy has been applied in the electricity cathodic protection stations for gas pipelines protection. Also, in 1979, four pilot stations in the field of communications were installed. In 1983, the installation of solar energy systems began to pump water for irrigation in El-Agailat city. In 2010, a 60 MW project was launched in Derna due to the high potential for wind power generation with wind speed of between 6 and

According to [5], 10% of the world's energy will be available through wind power in the next decade. Also, as a result of planning to make electric power from wind energy sources, one of the main sources of electricity in Libya, investigating and verifying the consequence of penetrating wind energy sources on the electrical grid is one of the most critical studies to provide optimum stability when integrating wind farms to the grid. The dynamic response of squirrel cage induction generator (SCIG) with direct grid connection is carried out. In [6, 7], a study proposed a 36 MW fix speed wind farm connected to the grid. It is found that the study was done through

calculating its power curve and investigating the effects of wind speed at the beginning.

Libya has enormous potential for solar and wind power generation. Figure 1 shows wind speed in several cities and regions in Libya. It shows the potential for high wind power production, as in Benina, Sirte, and Derna. From the research side, the possibility of [8].

7.5 ms<sup>1</sup> at a height of 40 m [1, 4].

40 Stability Control and Reliable Performance of Wind Turbines

Figure 1. Average wind speed for different cities in Libya.

The main function of protection system is to ensure the speed of operation and reliability to clear and isolate faulty equipment in case of a fault. The role of protection schemes is to minimize disturbing effects of fault currents and reduce the number of feeder outage. The penetration level of distributed generation (DG) influences the performance of protective relays and deteriorates the distribution network reliability.

The philosophy of protection systems in conventional distribution networks relies on the single direction of power flow from power plants toward the distribution network. The presence of DG turns out the distribution system operation comparable to the transmission system operation [9]. The arrangement of protection schemes becomes more difficult when further DG units connected to the distribution network since DG integration shifts the flow of the power and raises the short-circuit level. Therefore, the protective relays may not carry on its functions accurately, since the operation of the protective relays in the distribution level based upon the short-circuit sensitivity [10]. Introducing DGs to the distribution network associate further protection issues such as blinding of protective devices, false tripping, and reclosure-fuse miscoordination [11, 12]. Moreover, DG units can contribute a large current enough to trip the protective device on the feeder connecting the DG before the protective device on the faulted line, especially in synchronous machines based [13].

### 2.2. Power quality problems

Voltage regulation may become a challenge in the presence of DGs. Additionally, some DG technologies lack the ability to produce reactive power and compensate for voltage reduction on loaded busbars. The interruption of large DG units in case of faults could influence the reliability of the entire network. The disconnection of synchronous generators with huge capacities and the intermittent nature of DG based on renewable sources may cause voltage fluctuation, especially near these DGs [14, 15]. Some DG technology connected to the grid through power electronic converters such as wind turbine operates with doubly fed induction machine and photovoltaic may become a source of power quality problems too. Capacitors used for induction generators are also a source of harmonics in case of resonances in the network. The growth in integrating single-phase DGs in distribution network could influence the voltage profile and create an eminent unbalancing issue. When wind energy is penetrated into the grid, the power quality of the grid will be affected among other characteristics [16, 17]. The power quality of the grid containing wind systems must comply with the limits and requirements of the facilities. Therefore, the characteristics of the grid must be evaluated properly after the wind energy systems are connected to the grid. Prior knowledge of wind system characteristics must be adequately defined to avoid the drawbacks of connecting such sources. The electrical characteristics of wind turbines are usually specified by the manufacturer, not by specific site location. For this reason, when the electrical characteristics of a particular wind turbine are known, their impact on the power quality when connected to a particular location in the network can be predicted and calculated as a set of units. The necessity for quality requirements, detailed and applicable documentation on the power quality of wind sources is required. The International Electrotechnical Commission (IEC) started work to facilitate this in 1996. As a result, IEC 61400-21 was developed and, today, most large wind turbine manufacturers provide power quality characteristic data accordingly [18, 19].

The power extracting from wind depends on the covered area A of the rotor and the wind velocity Vw and the air density p. The generated mechanical power Pmech is generally computed

Power Quality and System Stability Impact of Large-Scale Distributed Generation on the Distribution Network:…

CPð Þ <sup>λ</sup>; <sup>θ</sup> <sup>A</sup>rV<sup>3</sup>

<sup>w</sup> (1)

http://dx.doi.org/10.5772/intechopen.74796

43

(2)

form wind energy using the coefficient of power Cp as follows [4]:

Vw, the rotational speed of the shaft wr and the rotor radius Rr.

shown in Figure 3.

be defined as:

3.2. Modeling of drive train

Figure 3. Power coefficient Cp (λ, θ) curves.

Pmech <sup>¼</sup> <sup>1</sup>

2

The performance coefficient Cp is a function of the A and θ that depends on the wind velocity

<sup>λ</sup> <sup>¼</sup> <sup>ω</sup>rRr V<sup>ω</sup>

(r.p.m) tends for speed of the rotor, Rr stands for e rotor (m) and Vw stands for velocity of wind (m/s). The power of the wind turbine versus wind speed and aerodynamic coefficients are

The behavior of the drive train dynamics is considered by taking three different model approaches such as single mass, double mass, and three mass model design in order to know which of the methods are more noticeable in detaining the performance of the network [17]. The study of drive train models depends upon the complexity of the network. If a study takes interest about the torsion fatigue, it just has to consider the dynamics of all parts of the networks [20, 21]. For these aim, double lumped mass or more accurate models are required. For that, when application targets on the interaction between wind farms and connected loads, the considered drive train model considered being a single mass model for the sake of simplicity. Due to the direct connection of generator shafts of the turbine, the model of drive train can
