Distribution Network Power Supply Research Articles

Application of ETAPTM eTraXTM software package for digital simulation of distribution network that feeds an AC traction power supply system

Voltage unbalance in power systems feeding AC traction power systems is a worldwide known problem. One of the main aspects of this problem is the negative effect of voltage unbalance on motor loads causing operating problems and economic damage. It is necessary to perform unbalanced power flow studies and calculate voltage unbalance indexes to assess this negative effect of voltage unbalance and the develop of compensating measures during the design stage. Usually, calculations of the AC traction power supply system and the distribution network feeding it are carried out separately during the design of new lines of railways electrified by alternating current (AC) and reconstructing of existing ones. This approach is a source of deviations in the power flow studies because the lack of consideration of mutual influences between the traction power system and the distribution power system. In this paper, we compare a digital model in which the traction power supply system and the distribution network are modeled separately with a model that considers mutual influences between the traction and external power supply systems, including power flows through the traction network caused by the distribution network (transit currents). For digital modeling of these processes, authors used ETAPTM software with eTraXTM package. It allows to run unbalanced power flow studies when the generation and load are being changed over time, including train movement. During a separate simulation of the traction power system and distribution network, traction network was modelled using the equivalent sources connected to traction substation buses and the distribution network was modeled taking into account the fact that traction load was given from the simulation of the traction power system. The traction load was considered as lumped loads connected to the traction substation buses.At the same time, in both cases, the unbalanced power flow study was carried out by the phase domain method. Based on the results of two models comparison, it was concluded that the combined model containing a traction power supply system and distribution network, is more effective in terms of improving the accuracy of assessment voltage unbalance in accordance with current regulatory and technical documents on power quality.

Provision of high quality power supply in distribution networks with renewable energy sources

Features of practical application of the developed multifunctional tools which provide reliable power supply and standard voltage quality characteristics in electrical networks of small power systems (microgrid) are considered. It is noted that these distribution systems have a number of known advantages over traditional power supply systems. In particular such system typically includes several sources of distributed generation, distribution substations, power storages and energy converters, which allows such a “Microgrid Plus” system to function offline or synchronously with an external power system. In microgrid, high-quality electrical supply can be achieved by, for example, using unregulated and controlled filtering-balancing devices or hybrid filtercompensating converters as well as the use of renewable energy sources and power accumulation system. The main aspects of the practical implementation of the power unit of a multifunctional bi-directional electric power converter as a part of a unified 300 kW inverter module for use in modern multimodal energy storage systems of significant power with different types of energy sources are considered. It is shown, that use of bi-directional converters in the system of energy accumulation can provide the required level of power quality in «Microgrid Рlus» in normal operating modes, in particular, the values of the THD of the input and output currents of these converters are several percents. In addition, they may, if necessary, compensate reactive power in these microgrid. The practical application of mentioned systems contributes to the implementation of the general concept of Smart Grid & Energy Storage, which aims at expanding the capabilities of renewable energy and integrating into smart electrical networks.

Research on Single-Phase Grounding Fault Location Technology

In view of the complex structure, large scale and high failure rate of distribution network, as well as many branch lines, large transition resistance, difficult to detect fault signals and difficult to locate accurately., A single-phase grounding fault location method based on single-terminal measurement for distribution network with multi-dominant transmission lines is proposed. This method can solve the problem of reliable monitoring of small current grounding fault through data processing and analysis of measuring units installed at substation equipment and line end, find grounding fault line in time, find fault point, and adopt corresponding treatment measures to block the impact scope of user branch line accident, restore the power supply of non-fault line as soon as possible, and reduce the outage time. Providing further reliable power supply fundamentally solves the problems of reliability and safety of power supply in distribution network. This method only needs to synchronously measure the voltage and current at each end of the line when the parameters of the line are known. The method is simple and the measurement accuracy is high. By locating the single-phase-to-ground fault of multi-dominant power lines, the results show that the method is correct and accurate.

Optimization of Power Supply Capacity of Distribution Network Considering the Participation of Power Sales Companies in Spot Power Trading

As an important part of the electricity trading market, the power sales company is an important part of the electricity trading market. It can not only be used as the main body to buy electricity from the market transaction but also as the main body to transmit electricity to the market and users, which changes the power flow distribution of the distribution network and has a certain impact on the power supply capacity of the distribution network. Based on the dual roles of power sales companies, this paper, first, analyzes the interaction between market transactions and power supply capacity of distribution networks. Second, considering the internal controllable distributed generation and controllable load participating demand-side response, a double-layer model of distribution network power supply capacity considering the participation of power sales companies in spot trading is established. According to the characteristics of the model, this paper uses the improved repetitive power flow algorithm and the original dual interior point method to solve the model. Finally, the improved IEEE33 node is verified. The example shows that the power sales company participates in the power transaction by flexibly adjusting the power purchase and sale strategy, which not only ensures the profit but also improves the power supply capacity of the distribution network.

Research on Single-Phase to Ground Fault Simulation Base on a New Type Neutral Point Flexible Grounding Mode

There are some problems existing in the traditional grounding mode of the distribution network. To solve them, this paper proposes a flexible grounding method for neutral point. This paper analyzes the advantages and the disadvantages of single-phase ground faults occurring at different neutral grounding points and summarizes the characteristics of several existing grounding arc elimination technologies for distribution networks. Depending on the actual data of a 10-kV substation, the ATP-EMTP was used to build a 10-kV distribution network model, and an arc model based on arc length control was used for single-phase ground fault simulation. According to the simulation results, it was known that the overhead line network of arc suppression coils was compared. Permanent ground faults occur in pure cable networks which are grounded by small resistances. Flexible grounding systems have significant benefits in suppressing the inrush currents at fault points when an intermittent arc single-phase-to-ground fault occurs, the flexible grounding system causes intermittent arcing. The voltage is clearly inhibited. The flexible grounding method has certain reference value for improving the reliability of distribution network power supply and providing the safe operation of the system.

Research on Optimal Operation of AC/DC Active Distribution Network Based on SOP

The development of AC/DC active distribution network promotes the improvement of distribution network power supply mode. As a new-type power electronic device, Soft Open Point(SOP) has many benefits for the grid operation. In this paper, the AC/DC active distribution grid was constructed firstly and the control strategy of the back-to-back voltage source of SOP was analyzed in detail. Secondly, a mathematical model was established to reduce the system loss and to improve the node voltage over-limit condition. Considering these problems can be taken as multi-objective and nonlinear optimize problems, this paper put forward the improved genetic algorithm to solve it. Finally, the results of the simulation indicates the effectiveness of the proposed algorithm.

Research on New Scheme Based on Secondary Reclosing Distribution Network Protection

The research on the rapid secondary reclosing technology proposed by Shandong Electric Power Grid (short delay primary reclosing + long delay secondary reclosing) and boundary switch reclosing and fixed value matching system within the framework of the grid is introduced in this paper. The different distribution network structure identifies the selection of relevant matching principle and secondary reclosing scheme, which changes the current mode which puts emphasis on the safe operation of the system side. The secondary reclosing shortens the user power outage time, achieves the reliability of the user's power supply, improves the quality of power, and provides a high quality distribution network for the users. By continuously optimizing the reclosing strategy and the corresponding protection configuration setting principles, the system to respond to the actual user needs is fully coordinated to improve the reliability of power supply of distribution network.

Сравнительный анализ результатов экспериментального исследования несимметричных режимов работы трехфазного трансформатора и данных полнофазного моделирования

Achieving better energy efficiency and quality of electrical power supply in distribution networks is a multipronged problem, which should be solved with reference to unbiased criteria. Data obtained from load flow analysis of the network under study serve as the main criterion in estimating the efficiency of technical solutions and administrative measures aimed at decreasing technical and commercial losses and improving the key electric energy quality indicators. At the same time, achieving better accuracy of a numerical analysis of electrical networks with loads unevenly distributed among the phases, including, in particular, distribution networks, still remains a significant problem in the electric power industry. The single-line equivalent circuits, which are conventionally used in engineering applications, do not allow the steady-state operating conditions of a three-phase electric network containing multiple sources of imbalance to be analyzed with sufficient accuracy. Under such conditions, it is reasonable to make a shift for using a three-phase representation of the network under study. This approach involves the need to construct three-phase equivalent circuits of electrical equipment, determine their parameters and use them for analysis. The article describes a conceptual approach for constructing the three-phase model of a three-phase two-winding transformer with a wye - grounded wye winding connection circuit, which is widely used in distribution networks. The following experiments were carried out on the test bench: open-circuit test, short-circuit test, load operation tests, open-circuit test under zero sequence supply voltage, and open-circuit test and load operation tests with one phase disconnected. Part of the experimental data was used to calculate the parameters of the three-phase equivalent circuit and to model a three-phase transformer in the MATLAB environment based on the described method.A comparison between the simulated and the experimental data testifies that the performed simulation of various transformer operating conditions yields highly reliable and accurate results. In the balanced mode, the maximum and minimum errors of simulating the main parameters were found to be 4.78 and 2.13%, respectively. In the unbalanced mode, the maximum and minimum errors of simulating the main parameters were found to be 6.6 and 0.78%, respectively. The obtained results allow a conclusion to be drawn that the proposed model of a three-phase two-winding transformer with the wye - grounded wye winding connection circuit adequately reflects the properties of a real transformer. The proposed technique allows the key properties of a three-phase transformer to be revealed, namely, the redistribution of magnetic fluxes among the magnetic core legs and the presence of voltage across the secondary winding when one of the primary winding phases is open. It can also be inferred that a three-phase transformer has a balancing effect.

Simultaneous Switching Noise Enabler in High-Speed Biomedical Systems by Integrated Plane Coupling

The performance of high-speed biomedical systems is adversely affected by switching noise caused by inductance in the power supply distribution network. In a high-speed medical system, signals are switched at rates up to 5 Gbps and discrete capacitors are ineffective in reducing the noise at this rate. The noise may affect patient care. Integrated plane coupling effectively minimized simultaneous switching noise by creating high capacitance between the planes. Although the suppression of electromagnetic interference due to switching noise on the component and printed circuit board is difficult, the integrated plane coupling at the front-end of the design cycle was shown to eliminate noise. The effect of switching noise coupling was investigated and a solution is reported. A test board was analyzed and the results were compared with simulations. This approach was shown to be effective in minimizing switching noise in high-speed biomedical systems.

Research on the Voltage Influence of Active Distribution Network with Distributed Generation Access

Distributed generation (DG) has an important influence on the voltage of active distribution networks. A unidirectional power distribution network will be transformed into a bidirectional, multiple power supply distribution network after DGs access to the distribution network and the direction of power flow is also changed. Considering the traditional forward and backward substitution algorithm can only deal with the equilibrium node and PQ nodes, so the other types of DGs should be transformed into PQ nodes, then its impact on active distribution network can be analyzed via the forward and backward substitution algorithm. In this paper, the characteristics of active distribution networks are analyzed firstly and a novel approach is proposed to convert PI nodes into PQ nodes. Finally, a novel forward and backward substitution algorithm is adopted to calculate the power flow of the active distribution network with DGs. Extensive validation of IEEE 18 and 33 nodes distribution system indicates that this method is feasible. Numerical results show that when DG is accessed to the appropriate location with proper capacity, it has a significant capability to support the voltages level of distribution system.

Study and Application of Evaluation Hierarchy on Power Supply Capability of Distribution Network

Against the lack of quantitative assessment method on power supply of distribution evaluation hierarchy on power supply of distribution network is proposed. In addition to some common indices, the hierarchy includes some new indices such as load balancing degree of main transformers, substations and lines, coordination of power supply between high and medium voltage network, matching degree of power supply and transmission capability etc. Besides that, evaluation process is put forward. In accordance with urban and rural areas, the respective adaptive scoring standards and weight values are given. The power supply capabilities of distribution network of two districts in Chongqing, China are evaluated based on the hierarchy proposed in this paper. The example proves that the method and evaluation hierarchy can not only evaluate the power supply of distribution network scientifically, find the weak link, but also guide the planning and construction of network.

Power converters for future LHC experiments

The paper describes power switching converters suitable for possible power supply distribution networks for the upgraded detectors at the High Luminosity LHC collider. The proposed topologies have been selected by considering their tolerance to the highly hostile environment where the converters will operate as well as their limited electromagnetic noise emission. The analysis focuses on the description of the power supplies for noble liquid calorimeters, such as the Atlas LAr calorimeters, though several outcomes of this research can be applied to other detectors of the future LHC experiments. Experimental results carried on demonstrators are provided.

System Voltage Sag Performance Estimation

This paper describes an analytical method for evaluating the voltage sag performance of a power-supply distribution network. The severity of voltage sag, as a result of system fault, is quantified by its magnitude and duration, and illustrated using a voltage sag density table. Since different loads have a different tolerance level to voltage sags, different evaluation algorithms are proposed in this paper to account for each type of sensitivity. It is illustrated that once the failure rates of the power components making up a system are known, the number and severity of the ensuing voltage sag events can be readily estimated. These estimates would be useful for predicting potential impacts on the operation of sensitive loads and for planning mitigating solutions to improve or maintain the power quality of the supply system. The possibility of incorporating other influencing factors from the behavior of the load and the fault events is also discussed.

Scaling Analysis of On-Chip Power Grid Voltage Variations in Nanometer Scale ULSI

This paper presents a detailed scaling analysis of the power supply distribution network voltage drop in DSM technologies. The effects of chip temperature, electromigration and interconnect technology scaling (including resistivity increase of Cu interconnects due to electron surface scattering and finite barrier thickness) are taken into consideration during this analysis. It is shown that the voltage drop effect in the power/ground (P/G) distribution network increases rapidly with technology scaling, and that using well-known countermeasures such as wire-sizing and/or decoupling capacitor insertion which are typically used in the present design methodologies may be insufficient to limit the voltage fluctuations over the power grid for future technologies. It is also shown that such voltage drops on power supply lines of switching devices in a clock distribution network can introduce significant amount of skew which in turn degrades the signal integrity.

Measurements and analysis of PLL jitter caused by digital switching noise

When integrating analog and digital circuits onto a mixed-mode chip, power supply noise coupling is a major limitation on the performance of the analog circuitry. Several techniques exist for reducing the noise coupling, of which one of the cheapest is separating the power supply distribution networks for the analog and digital circuits. Noise coupling from a digital noise-generating circuit through the power supply/substrate into an analog phase-locked loop (PLL) is analyzed for three different power supply schemes. The main mechanisms for noise coupling are identified by comparing different PLLs and varying their bandwidths. It is found that the main cause of jitter strongly depends on the power supply configuration of the PLL. Measurements were done on mixed-mode designs in a standard 0.25-/spl mu/m digital CMOS process with a low-resistivity substrate. The same circuits were also implemented with triple-well processing for comparisons.

Delay insensitive RSFQ circuits with zero static power dissipation

Total power dissipation in RSFQ circuits consists of two parts, dynamic and static. Dynamic power is dissipated in Josephson junctions performing useful logical and data transmission operations. This dissipation is fundamental and proportional to the data rate (at 4 K, of the order of 10/sup -18/ Joule per bit). Static power is dissipated in resistors used by RSFQ circuits to distribute dc bias current between Josephson junctions. This part of dissipation is not intrinsic to RSFQ circuits and in principle can be eliminated. The goal of this work is to show that Delay Insensitive (DI) RSFQ primitives can be modified so that resistors are no longer required in the dc power supply distribution network, so that the on-chip static power dissipation is absent. In this report we present the schematics for such primitives, define the class of circuits that allow resistor-free current distribution network, and formulate the requirements to the design of this network.

Spatial characterization of process variations via MOS transistor time constants in VLSI and WSI

This paper is the first large-scale experimental characterization of spatial process variations for a parameter that is directly involved in timing issues: the MOS transistor time constant. This is achieved by measuring the oscillation period of highspeed (500 MHz) CMOS ring oscillators that are implemented at different locations on individual dies and over wafers. Novel phenomena are observed, improving our understanding of how process variations affect the performance of synchronous systems, particularly in clock distribution networks. We observed four components contributing to period variations: an environment-dependent component, a process-dependent component of lower spatial frequency, a random component analogous to white noise, and a component depending on the geometry of the power-supply distribution network.

Packaging impact on switching noise in high-speed digital systems

Owing to the ever-increasing clock frequency in digital circuits and systems, simultaneous switching noise (SSN), caused by fast rise/fall pulse edges in combination with parasitic inductance in the power supply distribution network, is becoming a severe problem in many high-speed digital system designs. It is quantitatively shown that the influence of SSN, which is negligible when the rise/fall time is long (> 5 ns), becomes a critical factor, limiting system performance in the sub-nanosecond rise time region. Based on theoretical analyses and computational simulations in respect to various packaging techniques, technical solutions and design guidelines for reducing SSN are summarised.