Load Ratio Control Transformer Research Articles

Appropriate Volt–Var Curve Settings for PV Inverters Based on Distribution Network Characteristics Using Match Rate of Operating Point

This paper describes the process of setting up an appropriate volt–var curve for the reactive power control of a photovoltaic (PV) inverter interconnected to a distribution line that is voltage controlled by a load ratio control transformer (LRT). Computer simulations with 360 patterns of volt–var curves applied to five actual distribution line models are presented. The number of patterns was narrowed down to 23 by using voltage, distribution-line loss, number of LRT tap operations, and a new evaluation index, the match ratio. When a power-factor constraint is imposed on the PV inverter, it may not output the reactive power according to the volt–var curve depending on the active power output. The match rate is an index to show the percentage of the operating points of the PV inverter that conform with the volt–var curve. By evaluating the match rate, it can be demonstrated if the PV inverter efficiently contributes to the voltage control, which greatly contributes to narrowing of the volt–var curve. It is demonstrated that the volt–var curve obtained using the proposed method is superior in terms of voltage controllability, distribution line losses, and the number of LRT tap controls.

Unbalanced Voltage Compensation with Optimal Voltage Controlled Regulators and Load Ratio Control Transformer

Penetration of equipment such as photovoltaic power generations (PV), heat pump water heaters (HP), and electric vehicles (EV) introduces voltage unbalance issues in distribution systems. Controlling PV and energy storage system (ESS) outputs or coordinated EV charging are investigated for voltage unbalance compensation. However, some issues exist, such as dependency on installed capacity and fairness among consumers. Therefore, the ideal way to mitigate unbalanced voltages is to use grid-side equipment mainly. This paper proposes a voltage unbalance compensation based on optimal tap operation scheduling of three-phase individual controlled step voltage regulators (3ϕSVR) and load ratio control transformer (LRT). In the formulation of the optimization problem, multiple voltage unbalance metrics are comprehensively included. In addition, voltage deviations, network losses, and coordinated tap operations, which are typical issues in distribution systems, are considered. In order to investigate the mutual influence among voltage unbalance and other typical issues, various optimization problems are formulated, and then they are compared by numerical simulations. The results show that the proper operation of 3ϕSVRs and LRT effectively mitigates voltage unbalance. Furthermore, the results also show that voltage unbalances and other typical issues can be improved simultaneously with appropriate formulations.

Study on a Voltage Estimation of Tap‐Changing Transformer in Consideration of SVC Introduction

SUMMARYRecent years, installation of photovoltaic (PV) system is active by the environmental problem and feed in tariff system. Due to PV's output fluctuation, the static var compensator (SVC) made by power electronics technology is planning to install in distribution system. The SVC is expected for maintain the voltage. But SVC differs in a theory of operation of the existing voltage controller load ratio control transformer (LRT) and step voltage regulator (SVR). Because the SVC operation makes the system impedance changes, the existing voltage controller may not operate effectively. In this study, the intelligent‐control method which used the radial basis function (RBF) network is proposed. This method can reduce the effects of the SVC operation by including the performance characteristics of SVC in the conventional method. An advantage of unnecessary arrangement attention of the SVC setup node and easy cooperation with the existing equipment is obtained by applying this method.

The Development and Practical Application of Improved Voltage Management with Load Ratio Control Transformer

The Development and Practical Application of Improved Voltage Management with Load Ratio Control Transformer

Effectiveness of optimization updating the control parameters of advanced SVRs

This paper discusses the novel voltage control method in the distribution system using the electronic devices. In order to stabilize the power flow of the system, voltage in the system is traditionally controlled by devices such as load ratio control transformers (LRTs) installed in the distribution substation and step voltage regulators (SVRs) installed in the distribution line according to their fixed control parameters. In this paper, the authors verify the optimal interval of updating the control parameters of advanced SVRs using the determining method of control parameters.

無効電力制御器の導入を考慮したタップ切替変圧器の電圧推定に関する検討

Recent years, installation of PV system is active by the environmental problem and feed in tariff system. Due to PV's output fluctuation, the Static Var Compensator (SVC) made by power electronics technology is planning to install in distribution system. The SVC is expected for maintain the voltage. But SVC differs in a theory of operation of the existing voltage controller Load Ratio control Transformer (LRT) and Step Voltage Regulator (SVR). Because the SVC operation makes the system impedance changes, the existing voltage controller may not operate effectively. In this study, the intelligent-control method which used the RBF network is proposed. This method can reduce the effects of the SVC operation by including the performance characteristics of SVC in the conventional method. An advantage of unnecessary arrangement attention of the SVC setup node and easy cooperation with the existing equipment is obtained by applying this method.

Study on operation method and analysis in distribution system under large-scale introduction of photovoltaic and gas cogeneration systems

This study assumes a case installing photovoltaics (PV) and gas cogenerations (GC) with connections to distribution system in most of houses, which makes an issue of rising voltage. Generally, rising voltage is controlled by lowering the feeder voltage by Load Ratio control Transformer (LRT). However, it cannot sufficiently operate against too many PVs in the distribution lines. In this paper analysis of the voltage profiles in this difficult situation and basic examination of operation method to solve the problem are presented. First, the simulation model representing the distribution systems in detail is introduced. Proper tap position settings to consider the sudden changes of PV generation are considered to avoid the violation of voltage limit. In addition GC power generation which can operate to support the shortage of power supply is considered to achieve a stable power system operation without voltage violation. The results, voltage deviation has occurred in the introduction rete of 80%. However, the stoppage of the operation of GC at a terminal, voltage within the allowable limits is obtained.

Control of Multistage SVRs using Voltage Sensor in Distribution System with Large Amount of Photovoltaic Generations

In Japan, in order to reduce greenhouse gas emissions, Photovoltaic generation (PV) is being focused on recently. According to Japanese governmental policy, a large amount of PVs will be introduced into the distribution system in the near future. However, the output of PV depends on weather conditions and climate may change rapidly or randomly. As a result, voltage in distribution system with many PVs will fluctuate; nevertheless, distribution network operator must keep voltage in network within adequate range determined by law. By contrast, Step Voltage Regulator (SVR), which is located on distribution line to control voltage, has time delay to operate against voltage change. Hence, SVR could cause voltage deviation from adequate range when a large amount of PVs are connected to network. From this point of view, several novel equipment that control voltage flexibility such as Static Var compensator (SVC) and Battery are being noted lately. Although, this kind of device using power electronics technology is usually expensive, and huge cost is necessary to introduce these devices into many distribution systems in which there are lots of PVs. For this reason, it is necessary to control voltage with established device such as LRT (Load Ratio control Transformer) and SVR over the next 10 or 20 years, but these devices have several issues such as voltage deviation in case that there are a lot of PVs. The authors focused on SVR and analyzed the cause of voltage deviation by SVR. By analyzing several cases, the authors found the causes of voltage deviation and effective control method of SVR. In proposed method, it can realize to both reduce the cost and keep voltage within adequate range even if there are a lot of PVs in the distribution system.

Cooperative Voltage Control Method by Power Factor Control of PV Systems and LRT

Recently, the number of system interconnection of the renewable energy sources (RES) such as the photovoltaic generation (PV) and wind power generation is increasing drastically, and there is in danger of changing the voltages in a distribution system by the precipitous output variation of RESs. In this study, the authors propose one voltage control method of the distribution system by the power factor control of plural PV systems in consideration of cooperation with the load ratio control transformer (LRT) of laggard control response installed beforehand in the distribution system. In the proposed method, the slow voltage variation is controlled by LRT, and the steep voltage variation uncontrollable by LRT is controlled by plural PV systems, as a result, all the node voltages are controllable within the proper limits. In order to verify the validity of the proposed method, the numerical calculations are carried out by using an analytical model of distribution system which interconnected PV systems.

A Study on Estimation Method of Reactive Power Control of DGs in Distribution Systems with a large amount of PVs

Abstract To solve the energy and environmental issues, it is expected that a large amount of Distributed Generators (DGs) such as renewable energy are introduced to power systems. In distribution systems with many DGs, the voltage maintenance becomes an important issue due to the reverse power flow. Although reactive power control of DG is effective for the voltage maintenance, the increase of distribution power loss may be caused by such a reactive power control. Additionally, the decrease of active power output of DG may be also required for the reactive power control when its reserve capacity is not sufficient. Thus, it is desired to reduce the amount of reactive power controlled by DGs. On the other hand, in general, distribution systems consist of High Voltage Systems (HVSs) and Low Voltage Systems (LVSs). Most voltage control equipments such as Load Ratio control Transformer (LRT) and Step Voltage Regulator (SVR) are included in HVSs, and DGs are introduced mainly in LVSs. To reduce the reactive power of DGs, the utilization of equipments in HVS is important. However, it is required for system operators to estimate the occurrence of reactive power control of DGs properly. Hence, we developed a new state estimation method of DGs by using sensor information supposing that existing section switchgears will be replaced with new ones that can measure voltage and current using their attached sensors.

Voltage Control Method by SVC in Consideration of Cooperative Control with LRT and Determination Method for Rated Capacity and Control Parameters of SVC

In recent years, the number of connection of distributed generators (DGs) such as the photovoltaic generation (PV) and wind power generation is increasing, and there is in danger of changing the voltages in a distribution system by the precipitous output variation of DGs. In this study, the authors propose one voltage control method of a distribution system by the static var compensator (SVC) in consideration of cooperation with the load ratio control transformer (LRT) of laggard control response installed beforehand in the distribution system. The proposed method may be able to make the rated capacity of SVC small and may be able to reduce the aggravation of power factor of the distribution system, by setting up the dead band of voltage control appropriately. And the authors propose one determination method of the necessary minimum rated capacity and optimum control parameters of SVC in view of the cost of equipment and high-speed controllability. In order to verify the validity of the proposed method, the numerical calculations are carried out by using a distribution system model.

Determination of the optimal control parameters of voltage regulators installed in a radial distribution network

AbstractThis paper presents a new computation method to determine simultaneously the optimal parameters of several voltage regulators such as the load‐ratio control transformer (LRT) and step voltage regulator (SVR) installed in a radial distribution network. The proposed method determines a combination of their control parameters by minimizing the weighted sum of deviations of line voltage from the upper and lower voltage limits and the amounts of voltage violations by referring to the stored data measured by IT switches, which are sectionalizing switches with sensors installed in the distribution feeder. The optimization algorithm is based on particle swarm optimization (PSO), which is one of the nonlinear optimization methods, by using the concept of swarm intelligence. In order to confirm the validity of the proposed method, numerical simulations are carried out on a distribution network model. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Optimal Distribution Voltage Control and Coordination With Distributed Generation

In recent years, distributed generation, as clean natural energy generation and cogeneration system of high thermal efficiency, has increased due to the problems of global warming and exhaustion of fossil fuels. Many of the distributed generations are set up in the vicinity of the customer, with the advantage that this decreases transmission losses. However, output power generated from natural energy, such as wind power, photovoltaics, etc., which is distributed generation, is influenced by meteorological conditions. Therefore, when the distributed generation increases by conventional control techniques, it is expected that the voltage change of each node becomes a problem. Proposed in this paper is the optimal control of distribution voltage with coordination of distributed installations, such as the load ratio control transformer, step voltage regulator (SVR), shunt capacitor, shunt reactor, and static var compensator. In this research, SVR is assumed to be a model with tap changing where the signal is received from a central control unit. Moreover, the communication infrastructure in the supply of a distribution system is assumed to be widespread. The genetic algorithm is used to determine the operation of this control. In order to confirm the validity of the proposed method, simulations are carried out for a distribution network model with distributed generation (photovoltaic generation).

Methods of determining introduction limits of dispersed generation systems in a distribution system

Recently, there has been growing interest in utilizing DGS (dispersed generation systems) to integrate various generation resources and to meet changing electricity demand. In the long term, as much more introduction of both small- and large-capacity DGSs into the distribution system is expected, complete integration of this new technology into the utility system will bring about changes of design strategy and structural makeup of the system. Thus, a study is necessary to determine the introduction limit of DGS into the traditional distribution system without any facility change. In this paper, the authors propose methods of determining the introduction limits of DGS from the viewpoint of voltage regulation in distribution systems using LRT (load-ratio control transformer) and LDC (line drop compensator) as the control scheme. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 48–58, 1997

Parallel Operation of Load Ratio Control Transformers Using Reverse Reactance Compensation [includes discussion

When transformers with automatic load ratio control are operated in parallel, a miethod of preventing excessive circulating current is required. Some of the methods used are extremely complex, requiring additional equipment and control connections between units. The combination of resistance compensation to produce constant voltage at the load center as well as reverse reactance compensation to limit the circulating current between units is applicable to many circuits where more complicated means of parallel operation are now used. This system has the advantage of requiring no additional equipment and no control connections between units. The relations developed show that satisfactory performance in limiting circulating current between units and maintaining voltage can be secured in many cases. The best performance is obtained when the power factor of the circuit is high and substantially constant, and when the power factor of the circulating current is low. However, variations in load power at light loads have little effect on the performance. Equations for calculating the performance of this control on paralleled circuits are derived.

Operation of Load-Ratio Control Transformers Connected in Parallel and in Networks

SUBSTATIONS equipped with automatic load-ratio control equipment are frequently operated with their secondaries in parallel. The units may be physically together, the secondary tie being a bus; or they may be some distance apart connected together by a tie line or group of tie lines as in a primary network. At the present time large numbers of factory-built distribution substations are being sold, and well over half of them are equipped for some form of network operation. As with most voltage regulators, automatic load-ratio control equipment is usually controlled by means of a line-drop compensator and a contact-making voltmeter.∗ This automatic control equipment has two principal functions: 1. It serves to maintain some specified voltage regulation at some point on the distribution system. 2. It serves to maintain regulator stability and to keep circulating currents at a minimum.

Operation of load-ratio control transformers connected in parallel and in networks

Operation of load-ratio control transformers connected in parallel and in networks

Operation of load-ratio control transformers connected in parallel and in networks

Operation of load-ratio control transformers connected in parallel and in networks