Medium Voltage Distribution System Research Articles

Analysis and control strategy for a current-source based D-STATCOM towards minimum losses

This work deals with a Distribution Static Synchronous Compensator (D-STATCOM) based on a current-source converter for low and medium voltage distribution systems, specifically small and medium manufactures industries which are fined if the displacement power factor is below given limits. The D-STATCOM is analyzed using its mathematical model, showing the strong relation of the D-STATCOM power losses and its DC current level. Using the operating region of the D-STATCOM, an operating sub-region is defined such that the minimum DC current is used for a required reactive compensation, which leads to reducing the operating losses in the D-STATCOM. Also, Selective Elimination Harmonic is used to modulate the equipment to reduce the switching frequency while ensuring a desired current quality in the D-STATCOM input. As a result, a simple control strategy is proposed that uses a fixed modulation index while a phase control regulates the DC current to the lowest value required for reactive power compensation. Mathematical analysis jointly with simulated and experimental results corroborates the proposal, showing that it is possible to achieve a suitable compensation capability for improving the efficacy of the STATCOM.

ANALISA KEGAGALAN LIGHTNING ARRESTER PADA PENYULANG SULAHAN BANGLI

In the process of electrical power distribution, various types of interference can occur so that a protection system is needed to maintain the continuity and stability of electrical power distribution. Arrester is one of the main protection systems used to protect electrical equipment against overvoltages caused by lightning strikes. Penyulang Sulahan is a 20kV medium voltage distribution system that gets power supplies from Gianyar Substation 1/60 MVA and is located on a plateau that is prone to natural phenomena such as lightning. During 2016 there were three times the failure of conventional arresters. Based on these data, it is necessary to analyze the failure of arresters at Penyulang Sulahan so that the continuity of electricity can be better. The method used in this study is to collect data in the form of single line diagrams, disturbance data, and large grounding resistance on Sulahan Feeders. Next, compare Metal Oxide Arrester with Multi Chamber Arrester. The results obtained were grounding in the Feeder over 5 ohms which caused conventional arrester to not work properly. Multi Chamber Arrester is an arrester that has no effect on the value of grounding resistance. After installing the Multi Chamber Arrester, failure of arresters has decreased to one failure during 2017

Solar irradiance estimations for modeling the variability of photovoltaic generation and assessing violations of grid constraints: A comparison between satellite and pyranometers measurements with load flow simulations

Global horizontal irradiance (GHI) is typically used to model the power output of distributed photovoltaic (PV) generation. On the one hand, satellite estimations are nonpervasive and already available from commercial providers, but they have a limited spatiotemporal resolution. On the other hand, local estimations, e.g., from pyranometers, sky-cameras, and monitored PV plants, capture local irradiance patterns and dynamics, but they require in situ monitoring infrastructure and upgrading the asset of electrical operators. Considering that in most power systems, PV generation is typically the aggregated contribution of many distributed plants, are local GHI estimations necessary to characterize the variability of the power flow at the grid connection point (GCP) and detect violations of the limits of voltages and line currents accurately? To reply, we consider GHI measurements from a dense network of pyranometers (used to model the ground truth GHI potential), satellite estimations for the same area, and information about a medium and low voltage distribution system. We perform load flows at different levels of installed PV capacity and compare the nodal voltages, line currents, and the power at the GCP when the irradiance is from pyranometers and when from satellite estimations, deriving conclusions on the necessity, or not, of highly spatiotemporally resolved irradiance estimations.

Innovative Volt/VAr Control Philosophy for Future Distribution Systems Embedded With Voltage-Regulating Devices and Distributed Renewable Energy Resources

Conventional voltage-regulating devices such as load tap changers, voltage regulators, and local capacitor banks are commonly used for voltage-regulation purposes in medium-voltage distribution systems. Although such devices exhibit excellent capability for Volt/VAr control (VVC) support, fine-tuning of their controller parameters and enactment of Volt/VAr support by renewable distributed generation (DG) units is essential for effective and efficient operation of future distribution systems embedded with wind and solar-Photo-voltaic (PV) units. In this paper, an innovative algorithm is conceptualized for control set-point re-adjustment of different VVC devices for coordinated voltage control in distribution systems. The intended VVC strategy is able to minimize the voltage variations including voltage drop and rise cases mainly caused by power output of renewable DG units that cannot be solved by voltage regulating devices due to their time-delayed operation. Moreover, the control algorithm is proposed to be implemented online using advanced distribution management system for effective voltage control. The simulation studies are carried out using the test distribution system derived from an electricity network in New South Wales, Australia. The simulation results show that voltage regulation can effectively be achieved in renewable rich future distribution systems by applying the proposed tuning algorithm, which has been designed based on a new VVC philosophy.

High Impedance Arc Fault Detection Based on the Harmonic Randomness and Waveform Distortion in the Distribution System

High impedance arc faults (HIAFs) happening in the medium-voltage distribution system may result in damages to devices and human security. However, great difficulties exist in identifying these faults due to the much weaker features and the varieties when grounded with different surfaces. This paper presents an integrated algorithm to detect the HIAFs with high-resolution waveform data provided by distribution-level PMUs deployed in the system. An improved arc model is proposed, which can continuously imitate the randomness and intermittence during the “unstable arcing period” of arc faults. The integrated algorithm consists of two branches. First, the variations of HIAFs during unstable arcing period are identified with the unified harmonic energy and global randomness index, which can unify the scales of harmonic content in different fault situations and enlarge the disparities from non-fault conditions. Then, the waveform distortions of HIAFs during the stable arcing period are identified with discrete wavelet transform to extract the detailed distribution characteristics. The reliability and security of the proposed algorithm are verified with numerical simulations and field tests in a 10-kV distribution system.

Flexible AC Power Flow Control in Distribution Systems by Coordinated Control of Distributed Solar-PV and Battery Energy Storage Units

The flexible AC transmission systems (FACTS) have been used for controlling power flows in the transmission corridors to improve both the steady and dynamic states of operation. This paper proposes to extend the FACTS concept to power distribution systems, where the focus is in controlling renewable energy resources (RERs) and battery energy storage systems (BESSs) to provide a flexible AC power flow control in the distribution corridors of a medium voltage (MV) distribution system. The outputs of the proposed flexible AC power flow control system (FACPFCS) can be used to help the distribution network operator (DNO) to optimize the use of RERs and BESSs in the existing distribution grid to obtain the following benefits: congestion relief, sag reduction in long lines, mitigation of reverse power flow in the grid, deferral of distribution upgrade, Volt/VAr support, peak shaving, and a controllable storage bus that can act as a generator or load. To validate the proposed FACPFCS, simulation studies have been carried out using a practical radial distribution system topology derived from the electricity networks of New South Wales, Australia. The simulation results demonstrate that FACPFCS can provide an effective coordinated control of BESS and solar-PV units in the distribution systems to provide the mentioned benefits by controlling the power flows in the distribution lines.

Voltage fluctuation mitigation: fast allocation and daily local control of DSTATCOMs to increase solar energy harvest

This study presents a methodology for reactive power compensation provided by distribution static synchronous compensators (DSTATCOMs) to mitigate the voltage fluctuation and increase the solar energy harvest via photovoltaic (PV) inverters accordingly in medium-voltage distribution systems. An approximate method that uses one power flow run with the base-case system is analytically developed to offer a fast estimation of the location and size of DSTATCOMs to enhance the local voltage controllability over sunshine hours. This study then presents daily local reactive power control, where the control signals are calculated based on instantaneous measurements of the voltage at each bus without requiring any communications. The control method involves estimating the amount of reactive power support by the installed DSTATCOMs to reduce the voltage fluctuation during daytime while PV inverters are fully used to harvest the solar energy. At night-time, the DSTATCOMs operate as a master in voltage-controlled mode with other PV inverters in load mode if required to minimise the energy loss while improving the voltage profile. The proposed method has been tested on a 69-bus distribution system with 1 min load and 1 s solar power profiles and validated using a repeated power flow-based exact solution.

Robust voltage control algorithm incorporating model uncertainty impacts

This study addresses the voltage control problem of the medium-voltage distribution systems under uncertainty of the network model. A robust voltage control algorithm (RVCA) is developed in order to manage the voltage constraints considering uncertainties associated with the parameters of load, line, and transformer models. The RVCA determines a corrective solution that remains immunised against any realisation of uncertainty associated with the parameters of the network model. To this end, prior to formulating the voltage control problem, Monte Carlo (MC) simulations are used to characterise uncertain parameters of the network component models and load flow (LF) calculations are carried out to evaluate their impacts. The voltage constraints management under the uncertain environment is then formulated as a robust optimisation (RO) problem. The latter is constructed based on the results obtained through the MC simulations and LF calculations. Once the RO is solved, in order to check the robustness of the solution, system voltages are evaluated using the LF calculations considering the new set-points of control variables and uncertainty of network parameters. The simulation results reveal that neglecting model uncertainty in the voltage control problem can lead to infeasible solutions while the proposed RVCA, at an extra cost, determines a corrective solution which remains protected against the studied uncertainties.

Generalized distance-based protection design for DG integrated MV radial distribution networks — Part I: Guidelines

The critical advantages of distance protection render this protection principle a promising option for distribution systems, especially in light of integrating distributed generation. The first part of this two-paper series proposes complete guidelines for designing directly applicable and economically feasible distance protection schemes for medium-voltage radial distribution systems with distributed generation. These guidelines intend to take account of distributed generation, since they are designed to deal with its effect in terms of both directionality (bi-directional flow of short-circuit current) and protection dependability (intermediate infeed effect). Moreover, they are designed to address the concurrent effect of any other critical factor related to distance relay operation (e.g. fault resistance and zero-sequence compensation), as well as the coordination of distance relays with lateral protection means. The procedure is systematic and independent of specific distributed generation conditions, while, it has to be performed only once for a particular distribution system. Economic feasibility of the designed protection scheme is preserved, as it is intended to install the minimum number of distance relays, without using communication means. Furthermore, simplicity and direct applicability is ensured, as the proposed guidelines are implementable using existing distance relay technology.

Generalized distance-based protection design for DG integrated MV radial distribution networks — Part II: Application to an actual distribution line

The first part of this two-paper series proposes generalized guidelines for the design of distance protection in medium-voltage radial distribution systems with distributed generation. In this second part, these guidelines are applied to a real medium-voltage radial overhead distribution line of the area of Xanthi, Greece. A considerable penetration level of distributed generation is also assumed for this application. Based on the proposed guidelines, the designed protection scheme addresses all the factors affecting distance relay operation in distribution system applications, also dealing with any particularities of the specific distribution system examined. The installed distance relays prove to operate dependably and selectively against various faults, considering different fault types, fault positions, fault resistance and penetration level of distributed generation. In fact, selectivity is preserved between the distance relays and the remaining protection means (fuses) in the line, as well as between successive distance relays. Economic feasibility of the designed distance protection scheme is evidently taken into account, as the minimum number of distance relays is ultimately installed.

A 3P4SW Based UPQC to Improve Power Quality in Medium Voltage Distribution System

The adverse effect of power quality issues on power distribution system due to power electronics based controllers has tremendously increased in the modern power system; therfore, it is highly desired to design a novel power quality conditioner with a minimum number of switches to compensate voltage and current distortions. This proposed configuration reduces switching losses and also effectively alleviates the performance of the power quality conditioner. This paper introduces a configuration of 3P4SW (Three Phase Four Switch) UPQC (Unified Power Quality Conditioner) for both shunt and series APF (Active Power Filter) which can be implemented in medium voltage power grid. The major challenge of phase balance with only four switches in UPQC is accomplished by adaptive Self-tuning PID using neuro-fuzzy logic control and adaptive reference current generation scheme. This controller improves sag and swells compensation with better angle control via shunt and series converter performance and passive components design. The efficacy of proposed topology is tested on MATLAB/Simulink software and results are compared with the existing three phase six switch configuration (3P6SW).

State Estimation of Three-Phase Four-Conductor Distribution Systems With Real-Time Data From Selective Smart Meters

Distribution system state estimation (DSSE) has recently been tested and experimentally deployed in some practical distribution networks. Distinct features of distribution systems, such as diverse and unsymmetrical configurations as well as limited real-time measurements, prohibit the direct application of mature state estimation methods for transmission systems. Targeting at three-phase four-conductor configured unsymmetrical medium-voltage distribution systems (MDS) with neutral conductors and ground resistances, this paper proposes a weighted least square-based DSSE approach, in which voltages are chosen as state variables and load pseudo measurements of low-voltage distribution systems (LDS) are considered to compensate insufficient real-time measurements in MDS. Both rectangular and polar coordinates are studied, and voltage variables of neutrals and zero-injection phases are eliminated to reduce the scale of the DSSE problem. Moreover, in order to enhance the load pseudo measurement accuracy of LDSs, a clustering and partial least square regression-based load estimation model is proposed to leverage the real-time communication ability of smart meters. Case studies on a modified IEEE 123-bus distribution system with actual smart meter data illustrate the effectiveness of the proposed approaches.

Reducing voltage fluctuations using DSTATCOMs and reactive power of PV inverters in a medium voltage distribution system

This paper proposes local reactive power control to mitigate the voltage fluctuation in medium-voltage systems using DSTATCOMs and photovoltaic (PV) inverters. New expressions are developed to estimate voltage fluctuations and reactive power compensations by transforming line segment power-flow variables into nodal power injections. Using local measurements of voltages and solar powers, the method can provide a fast estimation of reactive power compensations to maintain the voltage at every bus. DSTATCOMs are also properly allocated to enhance the voltage controllability. Coordinated control of multiple reactive power resources is investigated as well. One-second solar irradiance along with one-minute home loads is used to demonstrate the effectiveness of the proposed method.

Protection Method for Radial Distribution Systems With DG Using Local Voltage Measurements

This paper presents a voltage-based protection method for distribution systems with distributed generation (DG). Considering the fact that any system fault is associated with a voltage dip at the faulted line ends, a novel protection relay characteristic is formulated from an extensive analysis of voltage behavior during fault conditions. The proposed method is independent of type, size, and location of DG units, as well as grid-connected or islanded (stand-alone) mode of operation of the distribution system. Moreover, the method is communication-less and uses only the local voltage magnitude to determine the relay operating time, hence, a low-cost protection method is provided. A threshold voltage level is defined outside the nominal voltage range. However, if under a fault condition the voltage dip is still within the nominal range, a current starter is used to trigger the relay. The effectiveness of the proposed method is verified by several simulation tests carried out on low voltage (LV) and medium voltage (MV) distribution systems under different fault condition and DG size and location for grid-connected and islanded modes of operation. The simulation results show the protection method is selective with appropriate speed, and the protection settings are independent of the distribution system modes of operation.

Mitigation of DER-Caused Over-Voltage in MV Distribution Systems Using Voltage Regulators

This paper presents an investigation on the performance of voltage regulators (VRs) in mitigating overvoltage problems caused by distributed energy resources (DERs) in medium-voltage (MV) distribution systems. The control method of VRs is found to be a crucial factor. Studies reveal that even advanced control modes of commercial VRs cannot be relied upon as effective solutions to manage every scenario. The main problems associated with local control methods are identified. A supplementary voltage control scheme is proposed to enhance the capability of VRs as a solution option. The proposed scheme addresses the problems due to local control methods with a minimal investment. The studies are accompanied by several simulations on IEEE 123 nodes system as well as an actual feeder facing such overvoltage problems. Merits of the proposed supplementary control scheme are also demonstrated through simulation results.

Wavelet-Based Time-Domain Solutions for Common-Mode Currents on Open-Form Conductors Modeled With Band-Limited Scattering Parameters

One of the technical challenges of future naval surface combatants in utilizing medium-voltage dc distribution systems is common-mode coupling and galvanic isolation for managing faults and personal safety. The behavioral modeling reported in this paper is computationally efficient to be used in modeling distributed common-mode currents and potentials throughout the open-form conductor, which in this case is the ship structure. Physics-based modeling is used to form a multiport S-parameter behavioral model of the ship structure that complements the S-parameter models of parasitic paths to grounded equipment enclosures and cables sheaths. A time-domain common-mode conduction example is presented to illustrate the workflow that converts physics-based models of elementary hull elements into a complete S-parameter behavioral model of an arbitrary hull structure with power cables running along it. Because of the measurement and the simulation bandwidth limitation, the frequency domain model based on S-Parameters is band-limited. A novel approach for reconstructing the system impulse response in the time domain from its band-limited S-parameter model is introduced using continuous wavelet transform utilizing fast Fourier transform.

A New Approach to Load Flow Analysis for Radial Distribution System - Application for Medium Voltage Distribution System in Morocco

This paper presents a load flow algorithm based on the backward/forward sweep principle, flexible for radial distribution system reconfiguration, with an improvement in ensuring a minimum number of searching for connections between nodes in the calculation sequence in the forward and the backward sweep, by organizing the radial distribution system information into a Main-Line and its derivations. The proposed load flow analysis is easy to implement and does not requires the use of any complex renumbering of branches and nodes, or any matrix calculation, with the only use of linear equations based in the Kirchhoff’s formulation.

Analytical Study Based Optimal Placement of Energy Storage Devices in Power Systems to Support Voltage and Angle Stability

Larger penetration of Distributed Generations ( DG ) in the power system brings new flexibility and opportunity as well as new challenges due to the generally intermittent nature of DG . When these DG are installed in the medium voltage distribution systems as components of the smart grid, further support is required to ensure a smooth and controllable operation. To complement the uncontrollable output power of these resources, energy storage devices need to be incorporated to absorb excessive power and provide power shortage in time of need. They also can provide reactive power to dynamically help the voltage profile. Energy Storage Systems ( ESS ) can be expensive and limited number of them can practically be installed in distribution systems. In addition to frequency regulation and energy time shifting, ESS can support voltage and angle stability in the power network. This paper applies a Jacobian matrix-based sensitivity analysis to determine the most appropriate node in a grid to collectively improve the voltage magnitude and angle of all the nodes by active/reactive power injection. IEEE 14, 24, and 123-bus distribution system are selected to demonstrate the performance of the proposed method. As opposed to most previous studies, this method does not require an iteration loop with a convergence problem nor a network-related complicated objective function.

Ensuring System Reliability: Distributed Energy Resources and Bulk Power System Considerations

Rooftop solar energy, storage batteries, and electric vehicles are changing the way people use and produce electricity. These are among the growing set of technologies called distributed energy resources (DERs) because they are typically connected to the utility at the medium-voltage distribution system. In general, the utility distribution system connects substations to homes and businesses. The effect of DE Rs on operating the power grid has been dramatic and exciting, and they provide both challenges and benefits to the entire grid: spanning utilization, distribution, and transmission voltage ranges. The zero-carbon resources among the broader family of DE Rs are critical in complying with state and federal energy policies. This, in turn, has required grid operators, utilities, regulators, consumer advocates, and lawmakers to reach out across traditional domains to engage in the robust dialog and coordination needed to integrate distribution-level resources to the larger high-voltage grid and the networked bulk power systems (BPSs).

A decomposition approach for integrated planning of primary and secondary distribution networks considering distributed generation

This paper presents a new model for optimal integrated planning of medium and low voltage distribution systems with penetration of distributed generation (DG) in the low voltage network. The proposed bilevel model takes into account in the upper and the lower levels, the medium and low voltage network planning respectively. This approach considers as conflict between these two agents (upper and lower levels), the size and location of the distribution transformers (DT), i.e. the incidence in both networks of the power flow circulating from the primary to the secondary system. The main objective of this approach is to find a joint global solution that establishes a balance to benefit the planning of both networks, by decomposing the problem in two subproblems (or levels). The upper and lower levels involve the costs of installing and upgrading the new and existing elements (branches, DT, substations and DG) and the cost of the energy technical losses. This problem is formulated as a mixed integer non-linear model, and is solved using a tabu search algorithm (TSA). To verify the efficiency of the proposed methodology, three cases of study are compared: (i) traditional integrated planning, (ii) bilevel integrated planning and (iii) bilevel integrated planning with DG in the LV network. The obtained results show the importance of considering both networks in a simultaneous way in the electric distribution system planning, which allows finding answers of lower global costs.