ANALYSIS OF ELECTRICAL DISTURBANCES ON THE OPERATION OF THE 7 MW PHOTOVOLTAIC SOLAR POWER PLANT CONNECTED TO THE MALBAZA ELECTRICITY GRID (NIGER)

1. Physics Department, University Abdou Moumouni (Niamey). 2. Electricity Department, School of Mines, of Industry and Geology (Niamey). ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 05 July 2020 Final Accepted: 10 August 2020 Published: September 2020

To increase the country's energy production, the State of Niger has built a 7MW photovoltaic solar power plant connected to the grid of the Nigerien electricity company in the department of Malbaza, Tahoua region (13 0 58'3.54 "North and 5 0 31'11.95 " East). In order to optimize the energy production of this plant, a study of electrical disturbances on the operation of the photovoltaic system has been conducted in this article. This was based on data on energy production as a function of irradiation and temperature, and electrical disturbances that caused a malfunction of the plant from January 1, 2019 to December 31, 2019. This analysis showed that, for an expected annual operating time of 4300.47hours, the solar plant operated normally at 95.37%. The remaining 4.43% comes from a disturbed regime linked to the grid (3.93%) and the solar power plant (0.7%). It has also been shown that the grid disturbances that caused the malfunction of the solar power plant are outages (83.02%), voltage fluctuations (8.03%), voltage dips (7.9%) and overvoltages (1.05%). At the solar power plant, two types of disturbances were recorded, including power failures (99.49%) and earth faults following current leaks (0.51%). Thus, the average annual availability of the grid is 95.58% and that of the power plant is 99.26%. The various results finally showed that apart from irradiation and temperature, grid availability is also a very important parameter to take into account in the energy production of a grid-connected photovoltaic system.
Of all the renewable energies, solar photovoltaic (PV) is of particular interest to Africa, since it has a significant solar source ⦍1]. Nowadays, solar photovoltaic plants are developing at a rapid pace and have reached a technical maturity that allows them to become an important segment of industry and energy.

ISSN: 2320-5407
Int. J. Adv. Res. 8(09), 169-180 170 Niger, a vast landlocked country in the Sahel, has an important solar resource. Sunshine is indeed characterized by an average duration of 8.5 hours per day and an average estimated level in the range 5 -7 kW / m 2 / day. Thus, to improve the country's energy production, the Nigerien authorities have thought about developing photovoltaic solar power plants. It is in this context that comes the construction project of a 7MW photovoltaic solar power plant connected to the electricity grid in Malbaza, which was commissioned in November 2018.
On the one hand, the connection of PV systems to the public electricity grid can have some impacts on: the change in power flows (bidirectional), the voltage plan, the protection plan, the quality of the energy, the planning of the network… And on the other hand, the characteristics, operation and disturbances on the utility grid can influence the operation of PV systems ⦍2].
This article aims to analyze the phenomena that disrupt the operation of this solar power plant. To do this, we will first review the literature on the electrical disturbances of a PV system connected to the grid and secondly present the materials and the method used to assess these disturbances on the 7MWp solar power plant of Malbazal; and finally present the results and discuss them.

Background :
Disruptions to the operation of grid-connected solar photovoltaic plants originate on the one hand from the electricity grid and on the other hand from the PV plants themselves.
Influence of the grid on PV plants: Disturbances on the grid strongly influence the operation of solar photovoltaic power plants. The phenomena at the origin of these disturbances are numerous and multifaceted. They generally come either from the intrinsic characteristics of distribution networks, or from the quality of the voltage degraded by other network users (consumers or producers), or from a combination of these two causes. These effects generally lead to unjustified decoupling of the inverters ⦍3]. The most common disturbances are: 1. Voltage variations and slow voltage fluctuations: Voltage variations are variations in the peak value of amplitude less than 10% of the nominal voltage and voltage fluctuations are a series of voltage variations or cyclical or random variations of the envelope voltage whose characteristics are the frequency of the variation and the amplitude. The voltage is amplitude modulated by an envelope whose frequency is between 0.5 and 25 Hz⦍4] ⦍5].Slow voltage variations are caused by the slow variation of the loads connected to the grid. Voltage fluctuations are mainly due to rapidly varying industrial loads such as welding machines, arc furnaces,… ⦍4] ⦍5].Their influences on the operation of the PV plant depend on the initial level of grid voltage, the operation of the inverter and the type of decoupling protection; 2. Voltage dips and blackouts: A voltage dip is a sudden drop in voltage at a point in an electrical power network, to a value between 10% and 90% followed by a recovery of the voltage after a short period of time ranging from 10 ms within seconds. The blackouts represent a particular case of voltage dips greater than 90% of the nominal voltage or total disappearance for a period generally between 10 ms and one minute for short cuts and greater than one minute for long blackouts. Voltage dips are associated with faults occurring on the grid, such as lightning strike of a grid structure or the contact of a tree with the line. However, they can be caused by sudden variations in the loads connected to the network as well as by inrush currents when transformers are energized and when motors are started [4] [7] [8]. A brief blackouts can usually be caused by a short circuit occurring in the network. This type of anomaly is characterized by its duration, which depends on the operating time of the protection devices. Interruptions are sometimes preceded by a voltage dip in the event of a fault occurring on the power source [4] [7] [8].Voltage dips are considered the most serious disturbances to quality of service due to their effects on sensitive processes. Their depth and duration vary depending on the characteristics of the network and the production groups connected to it [3]. In the event of a single-phase short-circuit in such a system, the two phases not affected by the fault can take a value up to 1.73 pu, ie the line voltage. In the event of a two-phase short-circuit, the phase not affected by the fault is characterized by an overvoltage that can go up to 1.5 pu [56] [75].The consequences of overvoltages are very diverse depending on the application time, the repetitiveness of the amplitude, the mode (common or differential), the stiffness of the rising edge and the frequency [56] [138]. They most often lead to a decoupling of the inverters from the network. 4. Influence of photovoltaic systems on the distribution network: In the past, distribution networks behaved like passive elements in which the power flows flow unidirectionally from the source substation to the end consumers. Due to the inclusion of decentralized production, power flows and voltages are impacted not only by loads but also by sources. In view of these technical specificities of photovoltaic installations, the connection of PV systems to the grid can have significant impacts on its operation [3] [4] [11]. The most significant influences of PV systems on the distribution grid are: 5. Influence on the voltage plane: The presence of PV generators has an influence on the voltage plan and on the grid control devices. The voltage generally varies according to the injections of active and reactive power on the network [3] [4] [11] [12]. In particular during a period of strong sunshine and low consumption, the voltage of certain nodes of the network may exceed the admissible threshold [3] [4].In addition, varying solar irradiance causes fluctuation of PV power, thus implying fluctuation of local voltage [13].A study conducted by the Tokyo University of Agriculture and Technology on some 550 PV installations in the locality of Ota City, showed that the injection of energy into the grid increases the voltage to a threshold causing the decoupling of certain systems; especially at the end of the week when consumption is low [3] [12]; 6. Influence on the protection plan: The contribution of PV systems to the fault current in the distribution network has low consequences on the protection level. However, the selectivity and the sensitivity of the network protections can be affected and cause unwanted tripping of the healthy feeder or blindness of the faulty feeder protection.Withtransformerless type inverters connected to the grid in neutral mode, a leakage current can be created and flow between the capacitance (of the PV panel and filter) and the earth. If the value of this leakage current reaches the differential protection threshold, a PV cut could occur [13] [14].Also, in the event of a shortcircuit on the network, the current from the latter supplied by the PV system can interfere with the detection of the fault by the protection devices provided on the network. Therefore, it is necessary to propose coordination strategies for the different protections -network, PV and consumption to ensure the correct operation of the short-circuit protections [13]; 7. Influence on the quality of Energy: Grid-connected PV systems can cause harmonic current injection, direct current injection into the grid, or phase imbalance. The presence of an electronic power interface can inject chopping harmonics into the network if the inverters are not equipped with effective filters. The consequences of these harmonics can be instantaneous on certain electronic devices: functional disturbances (synchronization, switching), untimely tripping, measurement errors on energy meters [3] [4]. A study carried out in Spain shows that current inverters (with high frequency transformer and with or without low frequency transformer) on the European market inject a DC component into the network [3] [15]. The presence of DC currents in distribution networks can affect the correct operation of differential switching devices, create errors on energy meters, affect the service life of network components, in particular through an increase in their corrosion and finally, contribute to the saturation of transformers [3]. The insertion of PV systems can also cause phase imbalance when using single phase inverters. If the power produced is not properly distributed between the 3 phases of the same three-phase PV system, then this system will contribute to unbalance the LV network. This phenomenon has been demonstrated in several studies [3] [16] [17].   These measuring and control devices allow all parameters of the solar power plant to be monitored from the control room. All of these parameters (electrical and metrological) are recorded by SCADA (Supervisory Control and Data Acquisition) and are accessible from the control room server. The method used to analyze the electrical disturbances on the power plant consists first of all in recording, through the SCADA, the various disturbances that have caused the disconnection of the inverters from the grid or the shutdown of the system, as well as their durations from January 1, 2019 to December 31, 2019. These disturbances will then be classified according to their origin whether they come from the grid or from the solar power plant itself. Finally, we calculate the technical availability of the plant and the network. Technical Availability is the parameter that represents the time during which the plant operates out of the total possible time during which it is able to operate, without taking into account the exclusion factors. The total possible time is considered to be the moment when the plant is exposed to irradiation levels above   The calculations of the monthly availability of the network and the solar power plant for the year 2019 as well as the energy production according to the irradiation and the temperature are summarized in Table 2 below: 1. analysis of the operation of the solar power plant: The analysis of the power plant's electrical disturbances for the year 2019 made it possible to draw the functional graph of the plant shown in Figure 5 below:   We note that for a total downtime of 168h53mn, the network presents four types of disturbances that caused the plant to malfunction. Among these disturbances, outages represent the largest proportion with 83.02% of the total downtime, followed by fluctuations with 8.03%, voltage dips with 7.9%, and finally overvoltages with 1.05 % ; 1. Analysis of disturbances from the solar power plant: The disturbances coming from the power plant itself are represented in the following figure 7:  Note that for a downtime of 30h13n41s, the power plant exhibits 99.49% of disturbances resulting from electrical failures and 0.51% of current leaks that have caused earth faults; 1. Analysis of the energy production of the solar power plant: Figure 8 below shows the variations in energy production as a function of temperature and site irradiation: The monthly temperature of the modules varies from 37.57 ° C (minimum value) in January to 37.79 ° C in December. The maximum monthly temperature is recorded in April with a value of 49.34 ° C.

Results and Interpretations:-
The monthly energy production varies from 1.118 GWh (maximum value) in January to 0. 9992 GWh in December. The minimum production is 0.904MWh obtained in May. The total annual energy is 12.19 GWh. The evolution of energy production occurs in the same direction as that of irradiation, but the increase in temperature has a negative effect on energy production. The same conclusions were demonstrated by SebbaghToufik et al in their article entitled "the study of the impact of climatic factors (temperature, sunshine) on the power of photovoltaic cells" ⦍19].
The analysis of Figure 8 also shows that the monthly irradiation values at the beginning of the year (January) and the end of the year (December) are respectively 196.29KWh / m 2 and 195.52Kwh / m 2 . Those of the temperature are respectively 26.93 ° C and 37.87 ° C; This shows that the different irradiation and temperature values at the start and end of the year corresponding to the start and end of the annual cycle, respectively, coincide with a few differences ready. The same conclusions were proved by Michael S. Okundamiya et al in their article entit led "Evaluation of varions global solar radiation models for Nigeria" ⦍20]. However, we note that the values of the monthly energy productions of January 2019 (1101.7MWh) and December 2019 (989 MWh) are clearly different with a productivity gap of 112.7MWh. This leads to the conclusion that there are other parameters which have an influence on the overall energy production of the plant apart from irradiation and temperature. 1. Analysis of the technical availability of the electricity network and the solar power plant: The variations in energy production as a function of the monthly technical availability of the network and the power station are shown in Figure 9 below.  The monthly technical availability of the network varies between 85.85% and 98.71% with an annual technical availability of 95.58%. The most disturbed months are: March, April, May with monthly technical availability of 85.85% respectively; 92.89% and 87.91%.
The higher the technical availability of the network and the power station, the higher the energy production and vice versa. When one of the technical availability (of the network or the power plant) is low, energy production always