A smart load management system based on the grasshopper optimization algorithm using the under-frequency load shedding approach

Power system blackouts have become a serious problem for electric utilities especially in recent years. Different forms of system instability have emerged in recent blackouts, such as voltage instability and frequency instability. To counteract each form of system instability, special algorithms have been designed in the protection system, e.g. Under Frequency Load Shedding (UFLS) and Under Voltage Load Shedding (UVLS) schemes. One of the major weaknesses of these algorithms is that combination of different forms of instability is not considered in their design, while any one form of instability may not occur in its pure form. This is particularly true in highly stressed systems and for cascading events. This paper presents an adaptive algorithm to combine UVLS and UFLS schemes. The purpose of this method is to enhance the flexibility of under frequency relays and increase the security of power system during large disturbances by improving system voltage stability margins. In the proposed algorithm, loads with greater voltage decay are shed sooner. In this way, locations of load shedding become dependent to the location of disturbance and voltage stability margins of the system are enhanced. Indeed, load shedding is performed faster for severe events accompanying large voltage or frequency declines. Using this load shedding method, faster reactions could be obtained for major system failures. This way, system blackouts could be better controlled. Performance of the proposed method is compared with the conventional UFLS method. In this paper, dynamic model of the Khorasan HV network of Iran national grid is used for simulation. This network includes 75 high voltage 400 kV and 132 kV buses with about 2700 MW of generation. Performance of the schemes has been evaluated using dynamic simulations as well as the P-V curves, and reactive power margins for a number of events. Simulation results show that conventional UFLS algorithm will not necessarily result in acceptable voltage stability margins for the system following a disturbance. Meanwhile, the proposed algorithm improves voltage stability margins. The proposed algorithm is suitable for saving system stability after occurrence of major system disturbances.

In recent years several catastrophic power systems blackouts have occurred worldwide. Various reasons have been declared for these failures. Economical limitations due to power system restructuring restrictions, inadvertent operation of protective relays and inefficient design of conventional load shedding schemes are of the most important reasons causing these blackouts. In fact, due to both economical and technological restrictions, it is not possible to completely prevent these blackouts. However, with the aid of some protection and control strategies, frequency and intensity of these blackouts may be reduced. One of the important protection strategies used for this purpose is a class of protection schemes known as ‘System Protection Schemes’ or ‘Wide Area Protection Schemes’. One of the most commonly used types of system protection schemes, generally accepted after the north-eastern blackout of 1965, is Under Frequency Load Shedding (UFLS) scheme. Conventional under frequency load shedding scheme is designed to retrieve the balance of generation and consumption following a disturbance. In the conventional load shedding method frequency settings, time delay settings and the amount of load to be shed in each step are constant values. The loads to be shed by this scheme are also constant load feeders and are not selected adaptively. Using this constant non-adaptive load shedding algorithm is not the most efficient scheme for all power system disturbances. In some combinational disturbances, events causing frequency to drop are followed by other events causing voltage drop. In these cases, since loads are voltage dependent, total system load is reduced and system frequency might not decrease so much to activate UFLS relays. However, the system could eventually collapse due to voltage instability. In many such cases the system would survive if the load shedding relays operate adaptively and appropriately. For example if for large disturbances, higher frequency settings and lower time delays are used adaptively, a faster load shedding response is obtained and as a result system collapses may be prevented. In this paper a new UFLS algorithm is proposed. The purpose of this algorithm is to adaptively adjust speed of load shedding based on the magnitude of disturbance. In this method rate of frequency decline is used as a criterion to determine intensity of disturbance. Thereby, for large disturbances higher frequency settings and lower time delays are used. Application of the proposed algorithm to the simulated model of Khorasan network in Iran confirms its satisfactory performance. As the results of simulations show, several voltage collapse instabilities may be prevented by using the proposed adaptive UFLS method.

This paper demonstrates the design and implementation of smart on-line fast load shedding to maintain system stability and operation when a major generating unit is suddenly tripped. The design stage included load flow and transient stability study cases to determine system stability limits, transient frequency variation curves and transient voltage profiles. Numerous outage scenarios that cover all possible operating conditions are simulated and key system stability parameters are identified. A fast load shedding priority list has been provided by system operations and has been included as needed into transient stability simulation cases to maintain system stability and generation/load balance. Fast load shedding logic diagrams are developed with triggering parameters including generating unit breaker status and on-line frequency measurements. On-line measurements of system generation, tie line flow and loads are continuously monitored and fed into a PLC system that processes information and issues load shedding trip signals to maintain balanced generation/load and stability. This fast load shedding scheme has been tested in real time outages several times, and proved to be accurate and in agreement with transient stability simulation results. Since its implementation, this load shedding scheme has successfully saved the oil field power system from total shutdown and maintained system operation after sudden tripping of major generating units

A new comprehensive framework for cascading outage simulation in power systems

This paper describes a smart load shedding scheme that monitors plant loads, plant generation and generation/utility supply reserve to select the minimum number and lowest priority loads for shedding. The paper first gives an overview of industrial power system dynamics undergoing loss of supply contingencies and existing load shed practices, such as undervoltage, underfrequency, frequency rate of change or contingency based load shedding. It will examine the impact of speed of load shedding on stability. The paper goes on to describe a load shed system that continuously calculates the generation reserve available and shed-able load available in real time by acquiring analog power measurements from generators and utility supplies through IEC61850 GOOSE (Generic Object Oriented Substation Event) messaging. This fast load shed scheme uses the reliability and redundancy of modern Ethernet networks and has simplicity compared to traditional systems. Application solutions are presented and analyzed that handle the required data acquisition using communications and protection devices typically present at an industrial facility, along with means to disseminate load shedding commands with sub-cycle speed to thousands of shed-able loads. Actual performance results from such a load shed system are presented.

This paper describes a smart load shedding scheme that monitors plant loads, plant generation and generation/utility supply reserve to select the minimum number and lowest priority loads for shedding. The paper first gives an overview of industrial power system dynamics undergoing loss of supply contingencies and existing load shed practices, such as undervoltage, underfrequency, frequency rate of change or contingency based load shedding. It will examine the impact of speed of load shedding on stability. The paper goes on to describe a load shed system that continuously calculates the generation reserve available and shed-able load available in real time by acquiring analog power measurements from generators and utility supplies through IEC61850 GOOSE (Generic Object Oriented Substation Event) messaging. This fast load shed scheme uses the reliability and redundancy of modern Ethernet networks and has simplicity compared to traditional systems. Application solutions are presented and analyzed that handle the required data acquisition using communications and protection devices typically present at an industrial facility, along with means to disseminate load shedding commands with sub-cycle speed to thousands of shed-able loads. Actual performance results from such a load shed system are presented.

Under-frequency load shedding (UFLS) schemes are the latest safety measures applied for safeguarding the integrity of the grid against abrupt frequency imbalances. The overall inertia of electrical power systems is expected to decrease with an increased penetration of renewable energy as well as elements connected through power electronic interfaces. However, voltage source converter-based high voltage direct current (VSC-HVDC) links can provide virtual inertia through a control loop that allows for a reaction to occur at certain frequency fluctuations. This paper evaluates a UFLS scheme that considers the injection of virtual inertia through a VSC-HVDC link. A genetic algorithm (GA) is used to determine the location of the UFLS relays, the activation threshold of each stage, the delay time and the percentage of load shedding at each stage. It was found that the virtual inertia causes the nadir to delay and sometimes reach a greater depth. Furthermore, the implemented GA approximates the frequency response to the limits set with the constraints, reducing the load shedding but achieving a steeper nadir and a lower steady-state frequency level than traditional UFLS. The simulations were performed using the IEEE 39-bus test system.

The traditional load shedding schemes––––under frequency load shedding (UFLS) and under voltage load shedding (UVLS), are designed independently and they constitute the last line of defense against frequency and voltage instability. However, the traditional load shedding schemes are not capable of dealing with combined instabilities. Moreover, a new Adaptive load shedding under load shedding method was proposed based on wide area measurement information just because the traditional load shedding schemes was not optimization algorithm. The main purpose of the method goal is to set up an emergency load shedding strategy, considering the recovery system of frequency stability at the same time, improved the voltage stability. This process has two steps, first of all, when considering the system disturbance amplitude and classifying the degree of interference according to system disturbance, Furthermore, the voltage sensitivity analysis was considered to determine the shedding location and corresponding shedding value. Finally, this algorithm was applied in IEEE 10-generator 39-bus test system. The implementation emergency of traditional and new shedding load two methods Under the system by different levels of power disturbances, comparing and analysand the feasibility and effectiveness of the new project. The results showed that the new method avoiding shedding over, more shedding part of the reactive power load, and then improving the system voltage, also avoiding damage to the voltage stability in the process of the system restore.

The aim of this research work is to develop a load shedding methodology to improve the frequency response of low inertia grids by attaining satisfactory voltage stability. In recent times, wind energy integration has considerably increased in many power grids. Consequently, conventional synchronous machines are being replaced from dispatch. Unlike traditional synchronous machines, variable speed wind turbine generators usually do not take part in frequency regulation without supplementary control mechanism. During substantial wind penetration, a power system may have a small number of online synchronous machines. As a result, synchronous inertia and governor responsive reserve significantly reduce. Under such situation, a system has to rely on load shedding as a last line of defense to rescue the system frequency following a large contingency. However, the conventional Under-Frequency Load Shedding (UFLS) strategy may lead to larger frequency deviation and higher amount of load cut in certain cases. A new load shedding methodology is presented in this paper to overcome this challenge. Unlike conventional UFLS technique, higher proportion of load shedding is applied to relatively weaker buses in terms of voltage stability in the proposed mechanism. Based on reactive power margin, which is an index to specify voltage stability, a general expression to quantify load shedding is derived. Also, the adaptability of the proposed strategy to various load levels is ensured. Later on, performances of the developed strategy are explored in a low inertia wind dominated test network. Simulations are executed considering various penetration levels of wind power and for two severe contingencies - loss of 550 MW interconnection and loss of 650 MW interconnection. Investigations reveal that the proposed load shedding methodology ensures satisfactory frequency response in all simulation cases. Also, the developed technique yields less frequency deviation and load cut compared to the conventional UFLS mechanism. Therefore, the reported load shedding scheme is found to be more competent to concurrently maintain frequency and voltage stabilities in renewable dominated power systems.

Against the backdrop of continuously increasing renewable energy penetration, the large-scale integration of wind power has significantly altered the output characteristics of generation units. The growing volatility of wind power output exacerbates the complexity of frequency regulation, potentially rendering traditional under frequency load shedding (UFLS) strategies inadequate. Investigating methods that leverage the frequency regulation capabilities of doubly-fed induction generators (DFIGs) and coordinated demand-side load clusters to participate in UFLS holds significant research value for enhancing power system frequency stability, reducing load curtailment, and improving power supply reliability. Therefore, this paper proposes an optimized UFLS strategy considering large-scale wind power integration. The frequency response models of wind turbines and thermostatically controlled loads (TCLs) in grid frequency regulation are analyzed, and the configuration principles for implementing UFLS in power systems are elaborated. A simulation model incorporating both wind turbines and TCLs in frequency regulation is developed, and UFLS simulations are conducted based on the operational conditions of a regional power grid. The results demonstrate that the participation of wind power and TCLs in frequency regulation not only ensures grid security but also significantly reduces load curtailment.

Preventive and corrective control applications in power systems via Big Bang–Big Crunch optimization

In this paper, we have proposed some under-frequency load shedding (UFLS) schemes for implementation in the Khorasan Network. In this regard, we have suggested a new relation to determine the number of substations required for load shedding at each frequency step, using which, the guideline of IGMC is well observed for the UFLS schemes. In the analysis of the proposed schemes, after reviewing the required constraints, their features have been analyzed in terms of three basic aspects: 1.The amount of load shedding at each frequency step; 2.The frequency response and its stability after disturbance (generator or tie-line outage or sudden load increase); 3.The geographical distribution of substations in each scheme; The Khorasan grid was modeled in the DigSilent Power Factory software with all the actual information of loads and power plants as well as the required dynamic parameters to analyze the frequency of the system in the contingency. The results of this study will be highly effective and useful in the quantitative evaluation of UFLS and selecting the optimal schemes.

This article introduces a relatively current method named grasshopper optimization algorithm (GOA) for explaining power system based dynamic economic load dispatch (DELD) problem. However, like other optimization approaches, GOA suffers from premature convergence and a slow convergence rate. Thus, to boost the convergence mobility of GOA, oppositional based learning (OBL) is merged with the GOA approach. Moreover, another improvization, namely, chaotic concept, is also integrated with the GOA to improve its solution quality. The suggested oppositional based chaotic grasshopper optimization algorithm (OCGOA) method is applied to handle the DELD problem in the most efficient manner. Among the renewable energies, intermittent wind energy (WE) is the most sustainable one and remains technically and economically advantageous for electrical energy generation. The thermal and wind based power systems are hybridized, so that power generation is distributed among the operating units in an equivalent manner such that overall cost and loss part are optimized until all practical constraints are fulfilled. The production cost of the unpredictable wind generation power is further incorporated in the operational cost by employing a probability density function (PDF) formula. The precision and performance of the suggested GOA and OCGOA approaches are validated on 6-unit and 10-unit DELD systems for conventional and wind based energy systems. The efficacy and performance of the suggested OCGOA is judged by comparing it with conventional GOA and other presently developed meta-heuristic optimization techniques found in the literature.

Under-Frequency Load Shedding (UFLS) can increase power system reliability by preventing total system collapse during emergency operating situations when load exceeds generation. UFLS is required by The North American Electric Reliability Council (NERC) for large consumers and has been implemented by utilities across the country. When the frequency drops to some predefined set points, feeder breakers are opened to shed loads in favor of maintaining generation/load balance. With increasing pressure to improve system reliability through more sophisticated controls and SCADA (Supervisory Control And Data Acquisition) equipments, electric utilities are encouraged to apply more localized frequency sensing and load shedding schemes on the distribution system. This research work aims at studying the effects of voluntary load shedding for different load shedding scenarios using the simulation package PSS/E. In addition, a consumer- based load shedding controller is proposed, designed and developed.

With high penetration of non-synchronous wind generations replacing conventional generators, the inertia of power system will reduce. A large disturbance in such a power system can cause faster frequency change in this power system and might invoke emergency defence strategies like underfrequency load shedding. The impact of low inertia caused due to displacement of conventional generators by wind penetration on the power system frequency is investigated in this paper. The possibilities of improving frequency with increase in primary reserve supplied from conventional generators are analyzed. This paper further explores the capabilities of wind turbines to provide support during underfrequency to prevent load shedding. Maximum wind penetration possible without causing load shedding following a large disturbance is also investigated.