/pdf/mapping-of-grid-faults-and-grid-codes-1mbp0sk428.pdf

Mapping of grid faults and grid codes

Voltage and frequency fluctuation associated with renewable integration have been well identified by power system operators and planners. At the microgrid level, a novel device for the implementation of dynamic load response, which is known as the electric springs (ES), has been developed for mitigating both active and reactive power imbalances. In this paper, a comprehensive control strategy is proposed for ES to participate in both voltage and frequency response control. It adopts the phase angle and amplitude control which respectively adjust the active power and the reactive power of the system. The proposed control strategy is validated using a model established with power system computer aided design/electro-magnetic transient in dc system. Results from the case studies show that with appropriate setting and operating strategy, ES can mitigate the voltage and frequency fluctuation caused by wind speed fluctuation, load fluctuation, and generator tripping wherever it is installed in the microgrid.

Mitigating Voltage and Frequency Fluctuation in Microgrids Using Electric Springs

Optimum distributed generation placement with voltage sag effect minimization

The second part of this paper presents a practical implementation and application of the methodology for the stochastic assessment of the annual financial losses due to interruptions and voltage sags discussed in the first part of this paper. The costs of interruptions and voltage sags are determined separately and then combined in order to estimate the total financial losses in the network. The methodology is illustrated on a generic realistic distribution network with all relevant network components modeled appropriately. Finally, different network topologies are compared taking into account total financial losses in the network. It is shown that the inclusion of the financial losses due to voltage sags that may account for up to about 20% of the interruption costs may alter the network topology ranking.

Probabilistic assessment of financial losses due to interruptions and voltage sags - part II: practical implementation

This paper presents a method for stochastic prediction of voltage sags caused by faults in a power system. The area of vulnerability must be determined to estimate the expected sag frequency (ESF) at a sensitive load site. However, the area of vulnerability is not easy to identify in a large meshed network. In the paper, the residual phase voltage equations for balanced and unbalanced faults are presented, and an efficient method to determine the area of vulnerability in a large meshed network is described. An ESF estimation method based on information technology industry council (ITIC) curve is also described. The developed method was applied to the IEEE 30-bus test system.

Stochastic Estimation of Voltage Sags in a Large Meshed Network

This paper presents the influence of different types of transformer winding connections on the propagation of voltage sags caused by symmetrical and asymmetrical faults in the power system. Single and multiple transformers are considered. A particular propagation of voltage sags from customer buses to industry facilities through the transformers employed at the entrance of the facilities is highlighted in the study. Different winding connections, dominantly used in the U.K. distribution networks, were modeled at the service transformers. The study was performed on a generic distribution network, and a bus from the 11-kV distribution network was randomly selected. It was found that the performance of voltage sags inside the industry facility is a function of transformer connections used at the service transformer.

The influence of transformer winding connections on the propagation of voltage sags

This paper analyzes the influence of modeling of fault distribution along transmission line on the assessment of number and characteristics of voltage sags. The generic distribution network was used in all simulations. Different types of transformer winding connections were modeled and different (symmetrical and asymmetrical) types of faults were simulated. A line was selected from the previously identified area of vulnerability for a given bus and different faults having different distributions along the line were simulated. It was shown that depending on the fault distribution (uniform, normal, exponential) along the line, different numbers and characteristics of voltage sags could be expected at the selected bus.

The influence of fault distribution on stochastic prediction of voltage sags

This paper analyzes the influence of modeling of fault distribution along the boundary crossing lines of the area of vulnerability on the stochastic prediction of voltage sags and their characteristics. The study was performed on a generic distribution network, and all types of faults were simulated throughout the network. Two buses from the 11-kV distribution system were randomly selected and the areas of vulnerability due to each type of fault for specific sensitive equipment at the selected buses were determined. These areas were determined by assessing voltage sag performance at each phase separately. Finally, the influence of different fault distributions along the vulnerability area boundary crossing lines was considered. It was shown that the fault distribution along those lines influences strongly the number and characteristics of voltage sags at the customer connection point.

Propagation of asymmetrical sags and the influence of boundary crossing lines on voltage sag prediction

This paper presents a comprehensive method for stochastic prediction of the number and characteristics of voltage sags in large distribution networks. The novelty of the proposed approach is in probabilistic modeling of the failure of the protection system. The probability of the failure of the protection system is determined using a straightforward, decision tree based method. The paper highlights the effects of the protection system failure on the number and characteristics of voltage sags. The method proposed and its capabilities are demonstrated on the realistic size generic distribution system. The results presented in the paper show that the proposed method is superior to the traditional techniques used for the assessment of voltage sags as it results in higher accuracy of the prediction of the number and characteristics of voltage sags.

Stochastic prediction of voltage sags by considering the probability of the failure of the protection system

The envisaged increased penetration of distributed generation (DG) in electrical power networks poses challenging technical and contractual issues to both utilities and industry. Technical issues related to power quality, in particular to voltage-sag propagation and characteristics in networks with a large penetration of fixed speed wind DG are addressed. A comprehensive analysis of voltage-sag propagation in a realistic distribution network is performed. The influence of network topology, location and percentage of connected wind generation, network loading and load composition is investigated in detail. It is shown that the influence of DG on voltage-sag characteristics and propagation is strongly dependent on its location and on load composition.

M. T. Aung

Papers

The influence of transformer winding connections on the propagation of voltage sags

The influence of fault distribution on stochastic prediction of voltage sags

Propagation of asymmetrical sags and the influence of boundary crossing lines on voltage sag prediction

Stochastic prediction of voltage sags by considering the probability of the failure of the protection system

Influence of distributed wind generation and load composition on voltage sags