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Investigating the problems which may arise during distribution network operation and design planning requires the deployment of significant and expedient approaches which in turn may help to tackle such problems. One beneficial approach to deal with those issues is through the application of the load flow analysis or the design and power flow analysis. The main focus of energy managers is how to optimally maximize the integration capacity of PV power flow since the integration of the solar photovoltaic (PV) system into existing electrical distribution networks will result in changes in various aspects including voltage value, power factor, power losses, reactive power distribution as well as the power flow of the distribution network.
Therefore, the purpose of this paper is to delve into the quality analysis of large scale, grid- connected solar PV system in the Palestinian distribution networks. In addition to the load flow analysis, the analysis conducted in the present paper comprises power factor, harmonic distortions, the status of protective devices and active power flow at different PV penetration levels.
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In fact, the power flow analysis of a distribution network containing solar PV system crucially underlies studying the steady-state features of integrating large-scale PV power grid into distribution networks. Thus, Electrical Transient Analyzer Program (henceforth ETAP) software is utilized in order to conduct the proposed system analysis.
With regard to the use of the solar electricity technology, namely solar PV power systems, Palestine proves to be one of the most promising countries. This is due to the fact that the major part of Palestine receives a high-intensity solar radiation as well as several peak sun hours.
This technology would be apt to provide a high performance ratio while improving reliability at a lower cost as it converts solar power to electrical energy [1, 2]. In recent years, PV power generation has proliferated in Palestine; moreover, the penetration rate of PV installed capacity in power grids has been increasing. An increase in the total capacity of PV power plants is estimated by the end of 2020; it is expected that it will reach 130 MV [2].
Added to this, the PV system in Palestine has become an alternative energy source for various industrial and commercial facilities. Nevertheless, one must keep in mind the fluctuations in the active power output of PV power supplies which lead to hugely affecting the power flow of distribution networks; consequently, voltage quality problems occur, such as voltage deviation and fluctuation [3, 4].
This paper focuses on analyzing the power flow of the grid-connected solar system in Tulkarm's distribution networks at various irradiance levels. This analysis also includes short circuit as well as solar farm's reactive power analyses. The unpredictable nature of the solar energy source has a great impact on the power system's operation and planning. Therefore, the existing condition will be analyzed, and the effect of the integration of solar power generators in the Palestinian distribution network is evaluated. As a case study, the researcher analyzes the solar PV system installed in the city of Tulkarm distribution station. The analysis of solar PV system was simulated in ETAP software so as to analyze the system operations before and after solar PV installation.
Power flow distribution, dynamic characteristics and power quality specifically undergo changes due to solar PV connection to the grid. In a study conducted by the authors of [5, 6], the deterministic load flow (DLF) was employed to examine problems related to grid-connected power flow. Although the study suggested distributed power access processing as a method to tackle grid-connected power problems, it was found that real-time intensity was the main factor in randomly determining the output of PV power generation. In other words, the deterministic power flow calculation method does not prove to be sufficient to manifest and evaluate the affecting factors and extents. Under-voltage is the main reason behind fault occurrence in distribution networks. That is to say that the reactive power cannot be transmitted over long distances in case of heavy loads, making it crucial for the reactive power to be generated close to the point of utilization.
For years, on the other hand, other studies on power systems have been undertaken by electrical engineers by employing distinctive programming tools [6]. Abnormal conditions may occur in the network, namely generating source or transmission line outages; under-frequency load shedding problems may arise as well. The initial transient behavior of the system in such cases is examined using load flow analysis.
The penetration factor rate of the distributed PV capacity suggests the PV power supply’s ultimate capacity to access the network under the restrictions imposed by the electrical network’s diverse parameters [8]. The authors of [9] put forward a penetration capacity calculation method based on the transient stability of the power system. They also investigated the effects of load level and distributed power grids’ location changes on the accessible capacity.
The authors of [10] suggested the distribution of power capacity based on an optimization model, which was solved by creating an artificial intelligent algorithm while keeping into consideration the existing network conditions. In the literature review of [11], a voltage control strategy was proposed based on the voltage-adjusted maximum admission capacity calculation method. The main reason behind this suggestion is to enhance the PV penetration rate as well as the operating state. The literature concluded that distribution network voltage fluctuations manifest as a consequence of PV power supply output changes.
The present paper focuses on the PV power generation system by constructing/using the steady-state analysis which examines the correspondence between different solar radiation levels and the solar PV power output in terms of the PV access capacity and PV access point. Additionally, this paper studies the impact of the large-scale centralized PV grid in case of connected PV system.
The network consists of a power grid that supplies 4 feeder lines through a 3 phase swing bus and a 150 mm2, .91 km long cable to connected to the following feeders (1): Nazlet Eissa is connected to a load of (0.611 MVA) through 630 KVA transformer. As for feeder (2), it is connected using a 150 mm2, 1.17 km long cable: Baqa Alsharqia which is connected to load of (2.078 MVA) through 2.5 MVA transformers. To connect feeder (3), however, a 150 mm2, 1.11 km long cable is used; Qaffin is connected to a load of (2.356 MVA) through 3 MVA transformers as well as an existing 80 KVAR LV capacitor bank. Following the three previously-mentioned feeders, feeder (4) is connected using a 150 mm2, 4.33 km long cable; Nazlat is linked with a load of (2.078 MVA) through 3.58 MVA transformers and an existing 680 KVAR LV capacitor bank, as illustrated in Figure 2 below. The PV system is connected directly to the distribution network.
The overview of PV system was simulated in ETAP as a single line diagram. The solar farm included 7600 solar panels joined 19*400 in series and parallel respectively, each of 340 Wp per panel. The overall capacity of the PV system was 2516 kW; the system was internally connected through cables. .
The system is analyzed by adopting a steady-state process using load flow analysis. Furthermore, harmonic analysis of current and voltage waveforms, when a sinusoidal voltage is applied to a non-linear load, is also made. Likewise, the short circuit analysis is carried out to get the full load short circuit current and to determine the protective devices ratings.
The PV system enhances the autonomy of the network and reduces the cost of electrical energy. Due to this fact, local energy providers deem the implementation of a huge photovoltaic system as one of the most challenging aspects concerning network stability and safety.
The expected annual energy output of PV system and total real energy consumption from electrical grid (IEC) per month:
According to the data above, the penetration rate of PV system will be around 10% of the total electrical grid load demand.
The purpose of power flow analysis is to determine the active and reactive power flows and to identify their currents and voltages. The power flow program uses interactive methods to solve nonlinear nodal equations. Different methods are used to solve these equations, such as Newton-Raphson, Fast-Decoupled, and Gauss-Seidel methods [13, 14].
Power flow analysis classifies the buses in a power system as follows:
The impedances of the loads and the generators are not included but are calculated using the system impedances [15, 16].
PV power generation system chiefly consists of inverters, control modules, PV cell arrays, along with other parts. When the trend impact analysis is conducted, the PV power generation unit’s modeling does not need to count the dynamic characteristics of the control system adjustment process; nevertheless, its first and foremost focus must be the result of its steady-state output.
On the one hand, the integrating PV systems with distribution networks could bring many benefits: energy losses and the decrease in the maximum demand charge, for instance. It could also improve the bus voltages of the network and reduce electrical losses. On the other hand, different technical issues may arise. It is possible that the interconnected photovoltaic power generation system may generate harmonics due to using AC/DC converters as well as isolation transformers. The single line diagram of the network with PV is shown in Figure 7.
The PV is connected to the network using a 3 phase 2 km long cable of area 240 mm2, to a point of common coupling using MCCB 2500A.
After using ETAP software to study the estimated impact of PV generator installation and interconnection with 22.15 kV grid network, the results can be presented in Figure 8. In addition to this, the power supply, power factor and losses before and after installing PV system.
A direct proportionality is apparent in the relationship between the solar module’s output and irradiance. To put it differently, the output of the solar module increases at the same rate as the incident irradiance is. The position of the sun and weather conditions throughout the day play a major role in determining irradiation levels. The power output varies at different irradiation levels in accordance with the sun's position in the sky.
The reactive power is essential to guarantee the efficiency of the grid-connected system. For instance, in order to avoid voltage-related problems, the reactive power must be balanced. The load flow analysis demonstrates the rate of absorption of both reactive and apparent powers from the grid before and after installing PV system, as shown in Figures 10&11.
The traditional distribution network is usually an open-loop operation where the single-supply radial structure network, as illustrated in Figure 8, could be put to use so as to keep the regular distribution operation in equilibrium. The previous results point out the accepted value; this implies that the integration of solar power into electrical grids will reduce the consumption from IEC and that the inverter must be set to a maximum power factor of 98%. The analysis results presented in Table 5 show that the voltage drop as well as electrical losses are reduced after PV installation. The dynamic changes of voltages before and after PV system.
In theory, voltage and current waveforms which lack even harmonics have one fundamental frequency, i.e., DC voltage and current frequency are at 0 Hz, and AC voltage and current frequency are at 50/60 Hz. The harmonic analysis module has many functions including simulating harmonic current and voltage sources, reducing interference, designing and testing filters, detecting harmonic-related problems as well as reporting harmonic voltages and violations of current distortion limits.
The results indicate that THD-U is below 5% and 8% for 22kV & 400 V, respectively, within the permissible limits of voltage real profile; that is, it does not exceed the limits set by the standard IEEE Standard 519-2014. It can be inferred that, with respect to voltage distortion, the effect of PV system operation is negligible.
The results show that the injection of solar power through solar inverters causes the injection of harmonic currents into the power system. However, the THD values after the use of PV plants are still less than 5 %, and they do not give rise to any problems according to different international standards such as International Electrotechnical Commission (IEC).
Most of PV systems are usually integrated in distribution networks which are part of the power system. In order to provide a high quality and uninterrupted energy supply from these PV systems, the selected sources and loads for the distribution networks should be taken into account, and power flow analysis should be performed. In this study, the power flow data of a designed distribution network were obtained by using ETAP software program.
The load flow analysis results indicate that the implementation of PV solar generation station in Tulkarm distribution network improved the voltage profile and increased the stability of the system. Distribution lines’ losses were found to decrease as a result of the implementation of the solar system. The applied analyses have shown that the distribution network of Tulkarm is in good status and its voltage profile is healthy both before and after the use of the PV generation system. The connection of the PV plant caused the injection of some voltage harmonics that started to spread over the network. However, the amount of generated harmonics was within the international limits stated by different standards.
Integrated Power Flow Analysis with Large-Scale. (2024, Feb 17). Retrieved from https://studymoose.com/document/integrated-power-flow-analysis-with-large-scale
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