Transmission Reliability Margin Research Articles

Multiobjective Salp Swarm Algorithm Approach for Transmission Congestion Management

In the newly emerged electric supply industry, the profit maximizing tendency of market participants has developed the problem of transmission congestion as the most crucial issue. This paper proposes a multiobjective salp swarm algorithm (MOSSA) approach for transmission congestion management (CM), implementing demand side management activities. For this, demand response (DR) and distributed generation (DG) have been employed. For willingly reducing the demand, demand response has been called by providing appropriate financial incentives that supports in releasing the congestion over critical lines. Distributed generation implementing wind plant as renewable independent power producer (RIPP) has also been included in order to reduce the load curtailment of responsive customers to manage transmission congestion. The proposed incentive-based demand response and distributed generation approach of CM, has been framed with various strategies employing different thermal limits over transmission lines and has resulted into significant reduction in congestion and in-turn improvement of transmission reliability margin. Diversity has been obtained in multiobjective optimization by taking two and three objective functions, respectively (minimization of overall operational cost, CO2 emission, and line loading). The by-products of the proposed algorithm for multiobjective optimization are minimized demand reduction, optimum size, and location of DG. To examine the proposed approach, it has been implemented on IEEE 30-bus system and a bigger power system IEEE 118-bus system; as well as the proposed technique of MOSSA has been compared and found better than reported methods and two other meta heuristic algorithms (multiobjective modified sperm swarm optimization and multiobjective adoptive rat swarm optimization).

Evaluation of Transmission Reliability Margin Taking into Account the Time-Varying Correlation Characteristics of Wind-Solar Output

Evaluation of Transmission Reliability Margin Taking into Account the Time-Varying Correlation Characteristics of Wind-Solar Output

Performance analysis of hybrid techniques for evaluation of power transmission cost and loss allocation based on transmission reliability margin

Performance analysis of hybrid techniques for evaluation of power transmission cost and loss allocation based on transmission reliability margin

Quantifying TRM by Modified DCQ Load Flow Method

In the integrated power system network uncertainty can occur at any time. The transmission reliability (TRM) margin is the amount of transmission capacity that guarantees that the transmission network is protected from instability in the operating state of the system. The calculation of the available transfer capacity (ATC) of the transmission reliability margin should be included in a deregulated power system to ensure that the transmission network is safe within a fair range of uncertainties that arise during the power transfer. However, the TRM is conserved as a reliability margin to reflect the unpredictability of the operation of the electric system. Besides, the system operator (SO) utilizes the TRM value during unreliability by adjusting the ATC value some amount up or down to account for errors in data and uncertainty in the model. This paper describes a technique for TRM estimation by modified DCQ load flow method considering VAR transfer distribution factor. The main focus of this study is to get a new approach to determine TRM by incorporating with ATCQ considered reactive power and sensitivity w.r.t ATC considered voltage magnitude. This technique is applied to the IEEE 6 bus system, and results are compared with previous results for validation. The technique leads to more exact and secure estimates of transmission reliability margin.

Determination of transmission reliability margin for brownout

<abstract> <p>Power shortage is a severe problem in developing countries that are rolling to blackout, but today smart grids have the scope to avoid entire blackouts by transforming them into brownouts. A brownout is an under-voltage condition where the AC supply drops below the nominal value (120 V or 220 V) by about 10%. In a power system network, power shortages or disturbances can occur at any time, and the reliability margin analysis is essential to maintain the stability of the system. Transmission reliability margin (TRM) is a margin that keeps the network secure during any occurrence of disturbance. This paper presents a new approach to compute TRM in the case of brownout. The detailed assessment of TRM largely depends on the estimation of the available transfer power (ATC). In this method, the ATC of the system is calculated considering the effect of alternating current (AC) and direct current (DC) reactive power (Q) flow (DCQF). The entire procedure is carried out for the multi-transaction IEEE-6 bus system, and the results are compared to the current efficiency justification method. Numerical results demonstrate that the proposed technique is an effective alternative for calculating the TRM and is valid compared to the existing technique.</p> </abstract>

Reliability assessment by sensitivity analysis due to electrical power sequential tripping for energy sustainability

A drastic change has occurred over the last few years in the electrical power business, where a significant worldwide revolution has taken place and changing the design of electrical powers. It has become imperative for the utility to handle the electrical power reliably as poor performance can lead to electrical power outages which will inevitably have an adverse impact on a nation’s economy and society. Hence, the power company should consider devising suitable pre-emptive measures to avoid the possibility of electricity supply disruptions. These disruptions may have a potentially catastrophic effect on the running of the system, which may even include consumers having to bear monetary costs. This research looks at the valuations of risk and reliability cost/worth-based customer interruption cost due to static system sequential tripping. The performance of the suggested techniques are evaluated through comparing risk-based valuations and reliability cost/worth valuations corresponding to the transfer capability results which are correlated to the static system sequential tripping. The results have demonstrated that the unpredictable sequential tripping must not be ignored from the transmission reliability margin determination. Hence, the proposed techniques are likely to play an important role for energy sustainability of the future.

Research on Testing of Optical Fiber Wavelength Division Multiplexing System

In order to meet the requirement of long-distance high-speed data bus for information transmission in vehicles, optical fiber wavelength division multiplexing (FWDM) technology is used to realize the transmission of multiple optical signals by connector. Although wavelength division multiplexing technology has been widely used in the field of communication, the adaptability of the real-time control system needs to be further studied. In this paper, a prototype of the optical fiber wavelength division multiplexing system is tested and the test results are preliminarily studied, which provides a basis for evaluating transmission reliability margin and analyzing system failure.

Determination of transmission reliability margin using AC load flow

In a power system, transmission reliability margin (TRM) is a key factor that determines the available transmission capability (ATC) ensuring the secure operation of the transmission network during the occurrence of uncertainties. Before transmitting available power through the network, it is necessary to know the secure margin. The secure margin determines whether it’s safe for transmission or not. The exact calculation of the transmission reliability margin is quite challenging due to the random disturbances in the transmission network. This paper introduces an effective technique for determining the TRM by AC load flow, considering the available transmission capability and sensitivity of three distinct system parameters such as load, transmission line impedance, and bus voltage magnitude. Numerical results demonstrate that the proposed technique is an attractive solution for calculating the ATC, sensitivity with respect to ATC, and TRM considering the effect of system parameters. The whole process is done for the standard IEEE-6 bus system considering multi-transactions. Finally, the calculated TRM values are compared with the existing techniques for justifying the effectiveness of the proposed technique.

An Improved Mixed AC/DC Power Flow Algorithm in Hybrid AC/DC Grids with MT-HVDC Systems

One of the major challenges on large-scale Multi-Terminal High Voltage Direct Current (MT-HVDC) systems is the steady-state interaction of the hybrid AC/DC grids to achieve an accurate Power Flow (PF) solution. In PF control of MT-HVDC systems, different operational constraints, such as the voltage range, voltage operating region, Total Transfer Capability (TTC), transmission reliability margin, converter station power rating, etc. should be considered. Moreover, due to the nonlinear behavior of MT-HVDC systems, any changes (contingencies and/or faults) in the operating conditions lead to a significant change in the stability margin of the entire or several areas of the hybrid AC/DC grids. As a result, the system should continue operating within the acceptable limits and deliver power to the non-faulted sections. In order to analyze the steady-state interaction of the large-scale MT-HVDC systems, an improved mixed AC/DC PF algorithm for hybrid AC/DC grids with MT-HVDC systems considering the operational constraints is developed in this paper. To demonstrate the performance of the mixed AC/DC PF algorithm, a five-bus AC grid with a three-bus MT-HVDC system and the modified IEEE 39-bus test system with two four-bus MT-HVDC systems (in two different areas) are simulated in MATLAB software and different cases are investigated. The obtained results show the accuracy, robustness, and effectiveness of the improved mixed AC/DC PF algorithm for operation and planning studies of the hybrid A/DC grids.

Credibility Theory-Based Available Transfer Capability Assessment

Since the development of large scale power grid interconnections and power markets, research on available transfer capability (ATC) has attracted great attention. The challenges for accurate assessment of ATC originate from the numerous uncertainties in electricity generation, transmission, distribution and utilization sectors. Power system uncertainties can be mainly described as two types: randomness and fuzziness. However, the traditional transmission reliability margin (TRM) approach only considers randomness. Based on credibility theory, this paper firstly built models of generators, transmission lines and loads according to their features of both randomness and fuzziness. Then a random fuzzy simulation is applied, along with a novel method proposed for ATC assessment, in which both randomness and fuzziness are considered. The bootstrap method and multi-core parallel computing technique are introduced to enhance the processing speed. By implementing simulation for the IEEE-30-bus system and a real-life system located in Northwest China, the viability of the models and the proposed method is verified.

A Cooperative Game Theory Approach for Usage and Reliability Margin Cost Allocation under Contingent Restructured Market

Restructuring of Electricity supply industry introduced many issues such as transmission pricing, usage, loss and reliability margin (TRM) allocation. Many methodologies have been proposed to address these issues. In this paper authors propose a graph theory based combined methodology which involves modified Kirchhoff matrix for transmission usage and reliability margin allocation. For optimal usage allocation at base case cooperative game theory is used. Further, novel reliability indices are developed for optimal transmission usage and cost allocation under N-1 contingency condition. Full and partial recovery models of transmission cost allocation are also developed. First, the transmission usages are allocated to users for base case power flow by modified Kirchhoff matrix. For allocating transmission usage cost under contingency, line outage impact factor (LOIF) and line outage distribution factor (LODF) are calculated. Further these factors are modified and calculated at maximum loading condition of line. Hence these reliability indices are called line outage impact factor at maximum flow (LOIFM) and line outage distribution factor at maximum flow (LODFM). With the help of these indices maximum transmission usage cost is recovered from the users. For usage cost allocation under contingency condition Modified MW-mile approach is used. Results are shown for the sample 6 bus system and IEEE 14 bus system.

A Power Flow Tracing based Method for Transmission Usage, Loss & Reliability Margin Allocation

Restructuring of Electricity supply industry introduced many issues such as transmission pricing, transmission loss allocation and congestion management. Many methodologies and algorithms were proposed for addressing these issues. In this paper a graph theory based method is proposed which involves Matrices methodology for the transmission usage, loss and transmission reliability margin (TRM) allocation for generators and demands. This method provides loss and TRM allocation in a direct way because all the computation is previously done for usage allocation. The proposed method is simple and easy to implement in a large power system. Further it is less computational because it requires matrix inversion only a single time. A comparison between proposed method and already exiting methods also presents. Results are shown for the sample 6 bus system and IEEE 14 bus system.

BC Hydro's Transmission Reliability Margin Assessment in Total Transfer Capability Calculations

NERC requires considering the uncertainties in assessing the total transmission capability (TTC) by calculating a term called transmission reliability margin (TRM). As part of a new BC Hydro TTC calculator, an improved 2m +1 point estimation based method (PEM) was developed to estimate the standard deviation of TTC due to the uncertainties of system parameters including forecasted system load, generation patterns, inter-tie schedules and change in projected load and dispatch conditions as a result of system stress. The standard deviation of TTC is used to determine TRM. The developed method has now been accepted as part of new BC Hydro's TTC calculator for determining TRM in real-time and pre-scheduling timeframes. Typical results on BC Hydro's large scale system, which were obtained using the developed TRM method, are presented in this paper. The presented TRM method has already been filed as an attachment to a BC Hydro's report to NERC for meeting the mandatory reliability compliance.

A Multipurpose Matrices Methodology for Transmission Usage, Loss and Reliability Margin Allocation in Restructured Environment

In the era of power system restructuring there is a need of simplified method which provides a complete allocation of usage, transmission losses and transmission reliability margin. In this paper, authors presents a combined multipurpose matrices methodology for Transmission usage, transmission loss and transmission reliability margin allocation. Proposed methodology is simple and easy to implement on large power system. A modified Kirchhoff matrix is used for allocation purpose. A sample 6 bus system is used to demonstrate the feasibility of proposed methodology.

Comprehensive Evaluation Research on Grid-Connected Wind Power Based on Fuzzy Interval Analytic Hierarchy Process

The characteristics of wind power such as wave properties, intermittence, seasonal nature, counter regulation and so on have negative effect on power grid; grid-connected wind power on a scale is limited. To aim at the problem that there lacks quantification evaluation method on grid-connected wind power, an comprehensive evaluation index system concerning safety, adequacy, power quality and economy on the power grid which wind power is accepted. By using current advanced fuzzy interval analytic hierarchy process (FIAHP) , analyzing index such as static stability reserve coefficient, peak margin and transmission reliability margin and so on, coming up with the potential risk, thus on the condition of system safety and steady operation, penetrating power can be maximization, utilization rate improved. At last, analysis of the example proves that the evaluation index system and evaluation method is scientific and feasible.

Power transmission cost allocation using power flow tracing and reliability benefit

Power transmission cost allocation methods have been varied depending on local context of electricity supply industry. There is a common principle that transmission line capacity should be properly allocated to accommodate actual power delivery with adequate reliability margin. This paper therefore, proposes a method that allocates transmission embedded cost to both generators and loads in an equitable manner, incorporating probability indices to allocate transmission reliability margin among users in both supply and demand sides. Probabilistic indices so called transmission internal reliability margin (TIRM) and transmission external reliability margin (TERM) decomposed from Transmission reliability margin (TRM) are introduced, making true cost of using overall transmission facilities. A numerical example on a simple six-bus system with multiple-circuit transmission lines which represent a characteristic of practical system is also presented to illustrate the application of the proposed method. Key words: Cost allocation, transmission pricing, reliability benefit, power flow tracing and reliability margin.

A novel approach to determine transmission reliability margin using parametric bootstrap technique

The determination of available transfer capability (ATC) must accommodate a reasonable range of transmission reliability margin (TRM) so that the transmission network is secure from uncertainty that may occur during a power transfer. This paper presents a computationally accurate method in determining the TRM with large amount of uncertainty using the parametric bootstrap technique. The parametric bootstrap technique is used to randomly generate a bootstrap sample of system operating condition with large uncertainty selected at a certain percentage of bootstrap confidence interval. The bootstrap sample is used in the determination of TRM at every time interval. Then, a new value of ATC at the current time interval is calculated by considering the TRM at the same time interval. The effectiveness of the proposed TRM method in providing new ATC value is validated on the Malaysian power system. The results have shown that the proposed method provides accurate estimation of TRM in which it is relatively similar to the TRM result obtained by the standard deviation of uncertainty which is incorporated in the Monte Carlo simulation technique. Further comparisons have been made in terms of accuracy and total time computation in order to verify the robustness of parametric bootstrap in determining the TRM as compared to the non-parametric bootstrap technique.

Chronological simulation for transmission reliability margin evaluation with time varying loads

This paper has as objective to assess the chronological variations in the Available Transfer Capability (ATC) caused by uncertainties associated with hourly load fluctuations and equipment availabilities. The system states resulting from these uncertainties are generated using the Monte Carlo Method with Sequential Simulation (MCMSS). The ATC for each generated state is evaluated through a linear optimal power flow based on the Interior-Point Method. These ATC values have been used to generate the probability distribution of the hourly ATC. This probability distribution enabled to estimate the Transmission Reliability Margin (TRM) for a specified risk level. The results, with a modified version of the IEEE Reliability test System, demonstrate that the time dependent uncertainties have a significant impact on the TRM.

Differential evolution based method for total transfer capability evaluation

The application of Differential Evolution (DE) to compute the Total Transfer Capability (TTC) in deregulated market is proposed in this paper. The objective is to maximize a specific point-to-point power transaction without violating system constraints using DE. This algorithm is based on full ac optimal power flow solution to account for the effects of active and reactive power flow, voltage limits, and line flow limits. The real power output of generators in source area and the real power of the loads in the sink area were adjusted to obtain the maximum transfer capability. In order to calculate TTC more accurately, Transmission Reliability Margin is incorporated in the calculation of TTC by considering single and multiline outages and also a three phase to ground fault near a bus and clearing it by isolating the faulty line after certain time interval. The performance of the proposed method is tested on the modified IEEE-30 bus system and results are compared with that of Particle Swarm Optimization method (PSO). Further, the results are compared with other published results using CPF and EP. It is found that DE provides more reliable results than other methods. Keywords: Total transfer capability, available transfer capability, transmission reliability margin, differential evolution, particle swarm optimization.

Determination of transmission reliability margin considering uncertainties of system operating condition and transmission line outage

The uncertainty of system operating conditions is a part of consequences which may cause to the volatility of a transmission system. This will hinder the performance of transmission system to effectively transfer the power between areas. Therefore, accurate estimation of transmission reliability margin (TRM) is required to ensure effective power transfer between areas during the occurrence of uncertainties. The power transfer is also called as the available transfer capability (ATC) in which it is the information required by the utilities and marketers to instigate selling and buying the electric energy. The TRM is estimated by taking into account the uncertainties of line outages and system parameters generated by the bootstrap technique. A case study of Malaysia Power System is used to verify the robustness of bootstrap technique in the TRM determination. The results show that the combined impact of several uncertainties which significantly affect the value of TRM. Copyright © 2010 John Wiley & Sons, Ltd.