Grid-connected Solar Photovoltaic Research Articles

Improve The Conversion Efficiency and Electrical Output of The Solar PV System by Developing and Implementing a Cooling System

The performance of the grid-connected solar photovoltaic (PV) system in the present study is improved using cooling technology. This technology reduces the temperature of solar PV modules and thus increases their efficiency and lifespan. The current solar PV system has been installed in northern Baghdad in the city of Taji. This study included improving electrical power, conversion efficiency, and performance ratio. All of these improvements are achieved by cooling using water. The performance ratio (PR) and efficiency maximum values of the reference (unimproved) and improved solar PV modules are at 10:10 am at 88.30% & 96.30% and 13.4% & 14.6%, respectively. Improved and reference PV modules maximum solar radiation values occur at 12:00 pm at 1.91 W and 1.566 W, respectively. The maximum solar radiation values of the reference and improved PV modules are at 12:00 pm at 922.9 W/m2 and 1012.22 W/m2, respectively. The maximum daily gain of the power and solar irradiance are 22% and 10%, respectively. The significant innovation in the study is the successful performance optimization of the grid-connected solar PV system. Using different equations to study performance by following different behaviors. Along with improving and studying CIGS PV module performance.

A Comparative Analysis of Various Simulation Software for grid-connected Residential Building: A Case Study at Jeddah, Saudi Arabia

Saudi Arabia receives significant energy daily from solar radiation, making it one of the best places to use solar energy to meet its energy needs. Grid connected Photovoltaic (PV) systems provide the electrical energy available from the solar radiation into the grid. Different simulation tools are currently available used to assess the performance of solar PV systems. The present study was conducted to design and evaluate the performance of 15 kW grid-connected solar PV system under climatic conditions of in Jeddah, Saudi Arabia. Two simulation models, Helioscope and PVsyst were used in the analysis and the results were then compared. The annual energy production, specific production, energy injected into grid, and annual performance ratio (PR) are evaluated by the software’s around a whole year at the same climatic conditions. Results showed that the maximum annual solar irradiation in May was 2212 kWh/m2. The PR based on PVsyst simulation (78.04 %) was higher than that of the Helioscope simulation (74.8%) by about 4.15%. The maximum energy production in May was about 6.1 kWh. The energy production from the PVsyst and Helioscope is 28.98 and 25.9 MWh/year with 289.8 and 259.13 MWh/year energy injected into the grid, respectively.

A novel dynamic/adaptive K-nearest neighbor model for the prediction of solar photovoltaic systems’ performance

The inherent variability in solar Photovoltaic (PV) systems motivates developing dynamic and adaptive data-driven models capable of accurately predicting the systems’ performance. A dynamic/adaptive K-Nearest Neighbor (K-NN) model to estimate the conversion efficiency of a solar PV system is proposed in this work. The proposed model estimates the conversion efficiency of a test pattern based on three steps: (i) identifying the similar historical operational conditions experienced by the system, (ii) assigning a weight to each condition based on its similarity to the test pattern at hand, and (iii) computing the weighted average conversion efficiency of the test pattern. Thus, the proposed model is adaptive and dynamic as the nearest neighbors and the associated weights vary from one test pattern to another. The proposed model is applied to a 7.98 kWp rooftop grid-connected solar PV system at the Hashemite University in Jordan. Its effectiveness is evaluated by resorting to the Mean Square Error (MSE), Accuracy, Coefficient of Determination (R2), and Adjusted R2 (R2adjusted), and comparing the results with the traditional K-NN and other techniques adequately developed in the same context, such as Artificial Neural Network (ANN), Extreme Learning Machine (ELM), and Multiple Linear Regression (MLR). Results show that the proposed model exhibited superior performance across all metrics, with a performance gain reaching up to 45.2 % and 6.8 % for the MSE and R2adjusted, respectively, compared to the base MLR. Further, the simplicity and computational efficiency of the proposed model validate its practical deployment in predicting PV system performance.

Smart Grid Resilience for Grid-Connected PV and Protection Systems under Cyber Threats

In recent years, the integration of Distributed Energy Resources (DERs) and communication networks has presented significant challenges to power system control and protection, primarily as a result of the emergence of smart grids and cyber threats. As the use of grid-connected solar Photovoltaic (PV) systems continues to increase with the use of intelligent PV inverters, the susceptibility of these systems to cyber attacks and their potential impact on grid stability emerges as a critical concern based on the inverter control models. This study explores the cyber-threat consequences of selectively targeting the components of PV systems, with a special focus on the inverter and Overcurrent Protection Relay (OCR). This research also evaluates the interconnectedness between these two components under different cyber-attack scenarios. A three-phase radial Electromagnetic Transients Program (EMTP) is employed for grid modeling and transient analysis under different cyber attacks. The findings of our analysis highlight the complex relationship between vulnerabilities in inverters and relays, emphasizing the consequential consequences of affecting one of the components on the other. In addition, this work aims to evaluate the impact of cyber attacks on the overall performance and stability of grid-connected PV systems. For example, in the attack on the PV inverters, the OCR failed to identify and eliminate the fault during a pulse signal attack with a short duration of 0.1 s. This resulted in considerable harmonic distortion and substantial power losses as a result of the protection system’s failure to recognize and respond to the irregular attack signal. Our study provides significant contributions to the understanding of cybersecurity in grid-connected solar PV systems. It highlights the importance of implementing improved protective measures and resilience techniques in response to the changing energy environment towards smart grids.

Performance evaluation of three grid-connected monocrystalline silicon solar photovoltaic systems in Nepal

This study evaluates three grid-connected solar photovoltaic (PV) systems using four criteria: final yield, performance ratio, capacity utilization factor, and system efficiency. The PV systems were installed on the rooftop of the Nepal Telecom office at Sundhara, Pokhara, and Biratnagar. The generation data was collected through the web interface of the data logger installed at the sites. Long-term comparison (four years) of the plant at Sundhara and the same system comparison of plants at Pokhara and Biratnagar were performed. Long-term analysis of the plant at Sundhara found that the final yield decreased from 2.91 kWh/kWp in 2019 to 2.21 kWh/kWp in 2022. Similarly, the performance ratio decreased from 91.0% in 2019 to 67.3% in 2022, capacity utilization factor decreased from 12.1% in 2019 to 9.2% in 2022, and system efficiency decreased from 16.8% in 2019 to 12.5% in 2022. The same system installed at Pokhara and Biratnagar had slightly varied performance owing to the variation in meteorological parameters. The average air temperature at Biratnagar (26.7°C) was higher than at Pokhara (13.1°C) while the amount of solar radiation at Biratnagar was just higher by 4%. This led to the reduction of final yield by 9% at Biratnagar than at Pokhara as higher temperatures at Biratnagar caused more reduction in the power output from the solar panels. Finally, this study provides insights to researchers, PV installers, and panel manufacturers on the actual performance of grid-connected solar PV in Nepal.

Techno-Economic Feasibility Study of a 1.5 MW Grid-Connected Solar Power Plant in Bangladesh

This study addresses the pressing energy constraints in nations like Bangladesh by proposing the implementation of photovoltaic (PV) microgrids. Given concerns about environmental degradation, limited fossil fuel reserves, and volatile product costs, renewable energy sources are gaining momentum globally. Our research focuses on a grid-connected solar PV system model at Char Jazira, Lalpur, Natore, Rajshahi, Bangladesh. Through PVsyst 7.1 simulation software, we assess the performance ratio (PR) and system losses, revealing an annual solar energy potential of 3375 MWh at standard test condition (STC) efficiency. After considering losses, the system generates 2815.2 MWh annually, with 2774 MWh exported to the grid. We analyze an average PR of 78.63% and calculate a levelized cost of energy (LCOE) of 2.82 BDT/kWh [1 USD = 110 BDT]. The financial assessment indicates a cost-effective LCOE for the grid-connected PV system, with an annual gross income of 27,744 kBDT from selling energy to the grid and operating costs of 64,060.60 BDT/year. Remarkably, this initiative can prevent 37,647.82 tCO2 emissions over the project’s 25-year lifespan.

Photovoltaic capacity dynamic tracking model predictive control strategy of air-conditioning systems with consideration of flexible loads

Building photovoltaic (PV) power generation is intermittent, volatile, random, and uncontrollable; thus, the use of solar grid-connected power generation can lead to a series of problems, such as grid voltage fluctuations and power imbalance. As a typical flexible load, the scheduling and regulation of the heating, ventilation, and air conditioning (HVAC) system load can help a grid-connected solar grid achieve balanced and flexible operation. This study proposes a PV capacity dynamic tracking model predictive control strategy for air-conditioning systems with flexible loads. This strategy aims to effectively address the issue of unstable grid-connected output of solar PV systems. In particular, a solar radiation prediction model based on a long short-term memory neural network optimized by the grey wolf optimization algorithm was established, which effectively improved the model prediction accuracy. The cost function of HVAC flexible load control considers the law of solar PV output and the human thermal comfort model. A genetic algorithm (GA) is used to obtain the optimal control parameters for dynamic regulation. The GA was employed to efficiently and effectively optimize the control of flexible HVAC loads, considering the variability of the solar PV output and ensuring human thermal comfort. A dynamic regulation model was developed for a typical office building with a grid-connected solar PV power generation system. TRNSYS was utilized for verification based on the actual measured data and relevant meteorological parameters of the case building. A new evaluation metric, volatility, was proposed to evaluate net load fluctuation. The simulation platform based on the physical building yield results indicated a strong resemblance between the energy consumption curve under the predicted control conditions using the flexible model and the PV generation curve. Additionally, the net load volatility was measured to be 2.63. Compared with the predicted control condition without the flexible model, the net load volatility of the grid was reduced by 47.08%, and the energy-saving rate reached 10.89% in the summer.

Solar insolation and PV module temperature impact on the actual grid connected solar photovoltaic system in German Malaysian Institute

German Malaysian Institute (GMi) has a great potential for utilising solar photovoltaic (PV) electricity. In this study, the performance of a 3kW grid-connected solar PV (GCSPV) system is monitored using Sunny Portal web in conjunction with Sunny SensorBox. The daily solar energy that strikes a PV array cannot be totally transformed into grid-compatible electricity. As a result of power losses, the production of solar PV systems falls short of expectations. The primary objective of this study is to examine the influence of solar insolation and PV module temperature on the actual output of the GCSPV system compared to the predicted output system by considering elements that affect the conversion of solar power to electrical power in GCSPV systems. The study prediction method based on calculations was carried out. Prediction of output system considered all losses, including efficiency of PV module, solar insolation, temperature of PV module, dirt, manufacturer’s tolerance and module mismatch, the voltage drop in DC cables to inverter, and inverter efficiency. The data indicate that the average power generation is 7.26% lower than predicted by the system. The GCSPV system’s performance efficiency is diminished by the temperature increase and somewhat enhanced by an increase in solar insolation. Temperature has a crucial impact in the energy conversion process of PV module. The effectiveness of the PV module in generating energy and power is dependent on its operating temperature.

Performance Assessment of Four Grid-Connected Solar Photovoltaic Technologies under Similar Environmental Conditions in Nigeria

This research presents the performance of four grid-connected solar photovoltaic (PV) systems installed at the Adamawa State College of Health Technology, Mubi, Adamawa, Nigeria. The system consists of 3.5 kWp each of four different PV technologies. The mis and psi cells manufactured by China Sunergy and Conergy comprised 14 modules with a power capacity of 250 watts. The asi produced by Moser Baer consists of 10 modules, each having 350 watts, and the CIS manufactured by Solar Frontier has 20 modules, each having 175 watts. The PV was observed and recorded data from January 2022 to December 2022. The system performance was analyzed using eleven evaluation criteria. Based on the technical assessment of the systems for this location, the asi solar PV has the best annual performance. It demonstrated the most favorable performance ratio (PR) and capacity factor (CF) of 90.7% and 27.6%, respectively, when considering energy output, system yields, performance ratio, and capacity ratio. On the other hand, the msi system, manufactured by China Sunergy, exhibited significant efficiencies at both the panel and system levels, with values of 14.3% and 13.7%, respectively. This system stood out for its minimal overall losses, recorded at 7.78 hours, demonstrating superior efficiency and lower overall losses than the other systems under study. This study is critical because the result will provide valuable information to researchers in identifying the appropriate PV systems suitable for Nigeria. In addition, it will assist PV installers and manufacturers with updated information on the PV system with the best performance.

Investigating energy policies to boost grid-connected rooftop solar PV in Sudan

Abstract Grid-connected rooftop solar photovoltaic (PV) systems can reduce the energy demand from the grid and significantly increase the power available to it. However, rooftop solar PV has not yet been widely adopted in many sub-Saharan African countries, such as Sudan, although they are endowed with high solar radiation and in dire need of additional power. This paper investigates risks and policies to increase grid-connected rooftop solar PV adoption in Sudan. A simplified United Nations Development Program Derisking Renewable Energy Investment framework is adopted to investigate this over three stages. For Stage 1, a list of risks and barriers was produced based on a literature review of solar PV studies in Sudan and interviews with nine stakeholders. Affordability was the risk most often mentioned (eight times from nine interviewees), followed by concerns about poor utility grid infrastructure. For Stage 2, policy de-risking instruments and financial de-risking instruments were listed to overcome the barriers. These include the introduction of net metering, the use of a third-party organization to monitor policy implementation, upgrade of the grid infrastructure, public awareness campaigns and energy-saving schemes. For Stage 3, the levelized cost of electricity was estimated for a typical 2-kW rooftop PV system without policies (0.11 $/kWh) and with a net-metering policy (0.07 $/kWh).

Mitigation of the impacts of electric vehicle charging on energy-star ratings for residential buildings in India

Abstract The star-labelling programme for residential buildings was introduced by India in 2020 and applies to all residential buildings with no lower limit on the built-up area or electrical demand. The energy-star label for a residential building is awarded against the notified standard by the regulatory body and electric vehicles (EVs) have not been accommodated as a load for residential buildings. The energy consumption of an existing residential building is taken from a study already carried out and compared with the requirement of the Indian residential star-labelling programme with an EV as a plugged-in load. An annual energy gap of 6060 kWh for the existing residential buildings considered in this study for five-star building energy labels increases to 7784 kWh if the EV load is added to the building load. The residential building will lose two energy stars if it caters to the EV load and, to bridge this energy gap, the replacement of existing electrical appliances with five-star-rated energy appliances, employing grid-connected rooftop solar photovoltaics (PV) and retrofit of the building envelope are considered. The techno-economic potential of rooftop solar PV and building envelope retrofitting for existing residential buildings is explored using RETScreen® and eQUEST software, respectively. The study establishes that the installation of rooftop solar PV can accommodate the additional load of EVs and can bridge half and three-quarters of the energy gap to achieve five energy stars for an existing building with and without EVs, respectively. It is the most economical option among the options explored in this study. The target Energy Performance Index is achievable by high-end energy consumers (12 000 kWh/year) by additional measures, the replacement of inefficient electrical appliances and building envelope retrofitting in addition to the installation of rooftop solar PV.

Investigation of Transient Stability in Power System with Improved FRT Capable Solar PV Inverters

Most regions of the world have seen tremendous growth in distributed energy resources, especially photovoltaic (PV) generation. The penetration of PV generation into the power grid is high and hence it has a major impact in power system. The integration of solar PV plant into the power system has both negative as well as positive impacts on transient stability of the power system during faults. In this work, the proposed current amplitude limiting based Fault Ride Through (FRT) control algorithm is implemented in large scale power systems and enhancement of transient stability is also studied in terms of synchronous machine side and grid side parameters namely rotor speed deviation, load angle, relative rotor angle, active and reactive power. The transient stability of large-scale Grid Connected solar PV (GCPV) system is discussed in this article, when the system is incorporated with the proposed FRT control strategy. The large scale GCPV system is said to be stable, if the angular displacement between the machines in the system stays within predetermined limits. The parameters considered for transient analysis on the synchronous machine side are the rotor angle, rotor speed, and Critical Clearing Time. The proposed model is simulated in MATLAB Simulink and validated in 1 kW hardware setup of grid connected PV system which performs satisfactorily in terms of system parameters and transient stability improvement.

PI Controlled Bridged Grid-Connected Solar PV Network for Electric Vehicle Battery Charging

The Z-source inverter (ZSI) topology replaces multiple stages into a single stage in power conversion so it is going to be an appropriate topology for 1-phase grid-connected PV system. In this paper, the various z-source topologies are discussed as available in different literature. This paper has proposed a proportional and integral (PI) Controlled bridged grid-connected solar photovoltaic (PV) network for electrical vehicle charging. The different modulation techniques applied in these topologies have been described. The bridged grid-connected network equipped with solar modules can prove effective in developing charging infrastructures for electric vehicles (EVs) at residential or commercial complexes. The different parameters of this suggested topology may vary during different time instants of a whole day at different modes of procedure i.e solar PV generation to the grid, EV to grid, and both PV and EV to grid. The simulation work has been done with the PWM technique to obtain battery voltage and grid voltage, Fast Fourier Transform, and total harmonic distortion.

Effects of wind speed and temperature on economics and environmental impact assessment of different solar PV systems in Malaysia

This study aims to analyse the effect of temperature and wind speed on the performance of different types of photovoltaic (PV) systems at a different state in Malaysia and how it affects the economics and environmental impact assessment in the present year of 2018 as well as future years in 2030 and 2040. Three types of grid-connected solar PV modules namely Mono-Crystalline, Poly-crystalline, and Thin Film were selected to be implemented in different cities of Shah Alam, Chuping, Alor Setar, Ipoh and Kota Kinabalu. A mathematical model was adopted to estimate the performance characteristics of the solar PV modules. Based on the data in the present year, the highest power output produced by the Mc-Si module for Alor Setar city is given by 33.40 MWh/year while the lowest amount of power output provided by this PV panel is about 28.18 MWh/year in Shah Alam. Furthermore, an area of 144 m2 for the Mono-Crystalline PV module can satisfy the total energy requirement by the resident as it was the most profitable to be implemented compared to Poly-crystalline and Thin Film. The findings of this study can serve as important information on the economic viability of installing PV systems in the selected cities in Malaysia.

Fault Ride Through approach for Grid-Connected Photovoltaic System

This paper presents a fault ride-through approach for grid-connected photovoltaic (PV) systems, aimed at improving the system's response during voltage sags and limiting the maximum inverter current during symmetrical faults. A constant active current reactive power injection approach was developed for low-voltage ride-through (LVRT) operation of grid-connected solar PV inverters in low voltage grids. The method manages the active and reactive power references and satisfies grid code requirements while also addressing tripping problems caused by overcurrent. The approach improves the speed response of the power converters during voltage sags, resulting in better dynamic grid support. The authors evaluated the approach using a 2-kW single-phase grid-connected PV system and demonstrated its ability to inject the required reactive power during a fault to improve the voltage profile and achieve dynamic grid support requirements. The accuracy of the proposed methodology is identified to be 98.3%, and the detection time is reduced by a reasonable margin in accordance with the grid standards. Overall, the fault ride-through approach can enhance the performance and reliability of grid-connected PV systems, particularly in low voltage grids.

Large, grid-connected solar photovoltaic power plants renewable energy

As an essential part of renewable energy, the solar photovoltaic technic grows rapidly with two main types: off-grid and grid-connected systems. This paper focuses on grid-connected solar photovoltaic power plants and introduces the main physical principles of solar photovoltaics. Typical components of solar photovoltaic power plants are also presented, along with their functions. The extraordinary environmental impact and the relatively low and decreasing cost of grid-connected solar photovoltaics reflect its excellent development potential. Compared with other energy, grid-connected solar photovoltaics provides an alternative to conventional fossil fuel generation. With the improvement of silicon purification technology and the working efficiency of solar batteries, the scale of grid-connected solar photovoltaics power plants will be further expanded.

Power Quality Improvement in Fifteen Level PUC Converter for Solar PV Grid-Tied Applications

A fifteen-level packed U cell (FLPUC) converter with eight active switch counts for the grid-connected solar photovoltaic (GCSPV) application is introduced in this work. This converter has eight active switches with a PV source and two floating capacitors. This topology takes an edge over conventional configurations in terms of components required to achieve fifteen levels in converter output voltage. The mode of operation and switching states of the fifteen-level PUC converter are presented in detail. The active and reactive powers (PQ) control is incorporated for a grid-connected PV configuration, which in turn helps in an independent control over power injection into the grid. The maximum power operation is achieved for the first source connected to the PV array with the perturb and observe (P&O) MPPT technique and unity power factor is attained at the AC side. The voltages of floating capacitors are balanced at reference values using proportional-integral (PI) controllers to attain proper achievement of desired output voltage levels. Performance of the FLPUC based single-phase grid-tied system is analyzed under a constant and variable solar environment. This topology is modeled in MATLAB/Simulink, and test results are validated using real-time emulator to meet the IEEE-519 standard for power quality improvement.

Modeling and Performance Analysis of a Grid-Connected Photovoltaic System with Advanced Controller considering Varying Environmental Conditions

This paper presents a mathematical model of 255 kW grid-connected solar photovoltaic (SPV) system. To study the performance characteristics of the grid-connected SPV system, a new hybrid adaptive grasshopper optimization algorithm with the recurrent neural network (AGO-RNN) control technique was implemented. Furthermore, the power quality at the point of common coupling (PCC) has been studied using the conventional (PSO) and proposed AGO-RNN controllers. The characteristics of the PV system were analyzed under varying environmental (variable irradiance and temperature) conditions considering 3 different cases such as (i) standard test conditions (STC), (ii) variable radiation with constant temperature, and (iii) variable radiation with variable temperature. For each case, the total harmonic distortion (THD) has been calculated using the proposed AGO-RNN control technique, and the results were compared with particle swarm optimization (PSO) technique. The 255 kW PV model is initially developed and connected to a three-level NPC inverter, an MPPT-based perturbation and observation algorithm. Later, the PV model is controlled by an AGO-RNN pulse width modulation (PWM) controller and is then integrated to the main grid at PCC. The main advantage of this technique is exploiting the separate DC-DC converter between the SPV module and the inverter. Finally, the proposed grid-connected SPV system was simulated on MATLAB for analyzing the performance of the system based on its I-V and P-V characteristics, inverter voltage, grid power, gird voltage, grid current, power factor, and THD under different environmental conditions. The simulation results demonstrate that the current magnitude and THD of the SPVGC system are improved with the cutting-edge AGO-RNN controller compared to PSO in all three different scenarios, and this value is less than 1.6%, which is within the permitted limits of IEC 61727 standards.

A comprehensive review of grid-connected solar photovoltaic system: Architecture, control, and ancillary services

The installed capacity of solar photovoltaic (PV) based generating power plants has increased significantly in the last couple of decades compared to the various renewable energy sources (VRES). As a result, the increased penetration of solar PV-based generating units leads to several issues related to power quality, system stability, and reliability. In view of these concerns, various international standards and grid codes have been amended to address such critical issues. Therefore, most solar PV-based generating units have undergone several changes in operational and control structure. Subsequently, varieties of solar PV configurations and control structures have been proposed by several researchers to augment the desired operational features. This paper presents a comprehensive review of various solar PV configurations, control strategies, and ancillary services with multifunctional features within this context. The utilization and benefits of various configurations and their practical aspects have been discussed thoroughly for all the configurations and architectures. Apart from this, the control aspects of grid-connected solar PV systems are categorized into two important segments, namely, a) DC-side control and b) AC-side control. This article covers the important features, utilization, and significant challenges of this controller and summarizes the advanced control techniques available in the literature. Further, the various control techniques have been compared concerning different operational parameters, such as controller gains, duties, and selector quantities in tabular form with ready references. Furthermore, the concerns related to power quality, stability, and reliability of various techniques have been included for understanding the applicability of grid-connected PV systems. In the end, a detailed comparison of some available industrial inverters concerning their power ratings, voltage ratings, configurations, and advanced functions incorporated are also presented, which will help the researchers, academicians, and practicing engineers.

LVRT and Reactive Power/Voltage Support of Utility-Scale PV Power Plants during Disturbance Conditions

This paper proposes a control technique for a large-scale grid-connected photovoltaic (PV) plant that maintains the connection of an inverter to the grid voltage under different types of faults, while injecting a reactive power to accommodate the required grid connection. This control strategy is suggested to improve the low-voltage ride-through (LVRT) capability of grid-connected PV power generation plants. A 20 MW solar PV power plant is modeled and simulated using Matlab/Simulink. The power plant is composed of 10 parallel groups of arrays with a power rating of 2 MWp. The solar PV arrays are connected to a medium-voltage side-rated 22 KV to the utility grid. A dynamic analysis of the grid-connected large-scale solar PV power plant is introduced. This analysis is accomplished in order to determine the impact of three-phase short-circuits at the point of common-coupling (PCC), where the solar PV power station is connected to ensure a practical voltage level by injecting active and reactive power. The reactive power support allows for faster restoration of voltage values at the PCC. When subjected to transient disturbances, the stability of the studied system relies on both the type of the disturbance and the initial operating situation. The disturbance may be either small, resulting from electrical load changes, or large, such as from a transmission line short-circuit (fault) and significant generator loss.