Line Drop Compensation Research Articles

Combined Effect of CVR and DG Penetration in the Voltage Profile of Low-Voltage Secondary Distribution Networks

In this paper, the voltage profile of secondary networks under conservation voltage reduction and distributed-generation (DG) penetration is studied for the first time. Three networks in New York City, modeled in detail, are used as study cases. Interconnection of DG is proposed to eliminate localized low-voltage violations due to a voltage reduction of 4%, 6%, and 8% from the normal schedule. The selection of the type of DG is based on the requirements imposed by the various interconnection standards, most notably IEEE 1547, public service commission, and local utility regulations. It is found that a small percentage of DG penetration would alleviate voltage violations. The study shows that DGs installed in distributed networks improve voltage regulation, allowing utilities to use deeper voltage reductions during critical conditions. It is also shown that the network power factor is reduced when penetration of DG is high and, thus, the line drop compensation needs to be adjusted for the characteristics of the new power demand.

Multi-Phase State Estimation Featuring Industrial-Grade Distribution Network Models

This paper proposes a novel implementation of a multiphase distribution network state estimator which employs industrial-grade modeling of power components and measurements. Unlike the classical voltage-based and current-based state estimators, this paper presents the implementation details of a constrained weighted least squares state calculation method that includes standard three-phase state estimation capabilities in addition to practical modeling requirements from the industry; these requirements comprise multiphase line configurations, unsymmetrical and incomplete transformer connections, power measurements on ${ \triangle }$ -connected loads, cumulative-type power measurements, line-to-line voltage magnitude measurements, and reversible line drop compensators. The enhanced modeling equips the estimator with capabilities that make it superior to a recently presented state-of-the-art distribution network load estimator that is currently used in real-life distribution management systems; comparative performance results demonstrate the advantage of the proposed estimator under practical measurement schemes.

Evaluation of coordinated energy management system for grid and home in distribution system with PVs

AbstractThis paper presents a coordinated energy management system (EMS) based on time-of-use pricing. The proposed EMS consists of prediction, operational planning, and control stages. To minimize amounts of curtailed PV output, operational costs, and voltage violations, line-drop compensation parameters are determined based on an input-output relationship database in the grid EMS. In the home EMS, an energy equipment operational plan is developed with a stochastic optimization problem (SP) to accommodate unavoidable uncertainties. Numerical simulations based on an actual distribution system model are performed, confirming the improved performance of the proposed method compared with the conventional method.

Method for Determining Line Drop Compensator Control Parameters of Low-Voltage Regulator Using Random Forest

Compensation of a voltage within the appropriate range becomes difficult when a large number of photovoltaic (PV) systems are installed. As a solution to this problem, the installation of a low-voltage regulator (LVR) has been studied. In this paper, we propose a method for instantly and accurately determining the line drop compensator (LDC) method parameters as a part of a voltage management scheme, which consists of prediction, operation, and control. In the proposed method, the solution candidates of the proper LDC parameters are narrowed by using a random forest that learns the relationship between the power-series data and the properness of the LDC parameters, thereby reducing the computational cost. We performed numerical simulations to verify the validity of the proposed method. From the results, the LDC parameters can be rapidly and accurately determined. Additionally, the desirable voltage control performance is verified.

A Coordinated Voltage Control Approach for Coordination of OLTC, Voltage Regulator, and DG to Regulate Voltage in a Distribution Feeder

Integration of small-scale electricity generators, known as distributed generation (DG), into the distribution networks has become increasingly popular at the present. This tendency together with the falling price of the synchronous-type generator has potential to give DG a better chance at participating in the voltage regulation process together with other devices already available in the system. The voltage control issue turns out to be a very challenging problem for the distribution engineers since existing control coordination schemes would need to be reconsidered to take into account the DG operation. In this paper, we propose a control coordination technique, which is able to utilize the ability of DG as a voltage regulator and, at the same time, minimize interaction with other active devices, such as an on-load tap changing transformer and a voltage regulator. The technique has been developed based on the concept of control zone, line drop compensation, dead band, as well as the choice of controllers' parameters. Simulations carried out on an Australian system show that the technique is suitable and flexible for any system with multiple regulating devices including DG.

PSCAD/EMTDC를 이용한 배전계통의 선로전압조정장치와 전지전력저장장치의 모델링에 관한 연구

태양광전원이 연계된 배전계통에서 발생되는 과전압문제를 해소하기 위하여, 계통에서 발생하는 전압변동에 대응하여 전압을 일정하게 유지시킬 수 있는 선로 전압 조정장치(Step Voltage Regulator)의 도입이 제안되고 있다. 일반적으로 SVR은 전압조정 방법에 의하여 Tap위치를 결정한 후, 일정시간이 지나면 Tap이 동작하도록 운용된다. 하지만 지연시간(30sec) 이후에 Tap을 동작시키는 SVR의 특성에 의하여, 이 시간동안 수용가전압은 규정치를 벗어날 가능성을 가지고 있다. 따라서 본 논문에서는 배전계통의 상용소프트웨어인 PSCAD/EMTDC를 이용하여 LDC방법에 의한 SVR의 전압조정 모델링과, 양방향으로 유무효전력을 제어할 수 있는 전지전력저장장치(Battery Energy Storage System)의 모델링을 제안하였다. 또한 SVR의 문제점을 보완하기 위하여, BESS와의 협조방안에 대한 모델링을 제시하였다. 상기에서 제안한 모델링을 바탕으로 수용가의 전압특성을 분석한 결과, SVR과 BESS에 의하여 안정적으로 전압이 유지됨을 확인하여, 본 연구에서 제시한 모델링의 유효성을 입증하였다. 【In order to maintain customer voltage within allowable limit( $220{\pm}13V$ ), tap operation of SVR(step voltage regulator) installed in primary feeder could be carried out according to the scheduled delay time(30 sec) of SVR. However, the compensation of BESS(battery energy storage system) is being required because the customer voltages during the delay time of SVR have a difficultly to maintain within allowable limit when PV system is interconnected with primary feeder. Therefore, this paper presents modeling of SVR to regulate voltage with the LDC(line drop compensation) method and modeling of BESS to control active and reactive power bi-directionally. And also, this paper proposes the coordination control modeling between BESS and SVR in order to overcome voltage problems in distribution system. From the simulation results based on the modeling with the PSCAD/EMTDC, it is confirmed that proposed modeling is practical tool for voltage regulation analysis in distribution system.】

A Novel Tuning Method for Advanced Line Drop Compensator and its application to Response Coordination of Distributed Generation with Voltage Regulating Devices

Nowadays, the integration of small-scale electricity generators, known as distributed generation (DG), into distribution networks has become increasingly popular. This tendency, together with the falling price of DG units, has a great potential in giving the DG a better chance to participate in the voltage regulation process, in parallel with other regulating devices already available in the distribution systems. The voltage control issue turns out to be a very challenging problem for distribution engineers since existing control coordination schemes need to be reconsidered to take into account the DG operation. In this paper, a new tuning method for the line drop compensator has been proposed, and it is applied for the control coordination of DG with other regulating devices in the network, which is able to utilize the ability of the DG as a voltage regulator and, at the same time, minimize the interaction of DG with another DG or other active devices such as the on-load tap changing transformer (OLTC). The proposed coordination technique has been developed based on the concepts of protection principles (magnitude grading and time grading) for the response coordination of OLTC, DG unit, and other regulating devices. A distribution feeder with a tap changing transformer and DG unit has been extracted from a practical system to test the proposed control technique. The results show that the proposed method provides an effective solution for coordination between OLTC and DG, DG-DG, or DG and voltage regulating devices, and the integration of protection principles has considerably reduced the control interaction to achieve the desired voltage correction.

분산전원이 연계된 배전계통에 있어서 선로전압조정장치(SVR)의 전압제어 개선방안

This paper presents the novel voltage control method in power distribution system with distributed generators. The voltage in distribution systems is regulated by Under Load Tap Changer(ULTC) of substation and pole transformer of primary feeders. Recently, Step Voltage Regulator(SVR) is getting located at distribution feeders to regulate effectively voltage of primary feeders. But the effectiveness of SVR decreases due to independent operation between SVR and ULTC, and also the existing Line Drop Compensator(LDC) method considering the distributed generators may be not able to regulate the proper voltage in a permissible range. Thus, this paper presents a optimal voltage control algorithm of SVR by using the secondary voltage data of main transformer in substation.

General and Simple Decision Method for DG Penetration Level in View of Voltage Regulation at Distribution Substation Transformers

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems of the on-load tap changer (OLTC) transformer, local voltage rise, protection coordination, exceeding short-circuit capacity, and harmonic distortion. In view of voltage regulation, the intermittent fluctuation of the DG output power results in frequent tap changing operations of the OLTC transformer. Thus, many utilities limit the penetration level of DG and are eager to find the reasonable penetration limits of DG in the distribution system. To overcome this technical problem, utilities have developed a new voltage regulation method in the distribution system with a large DG penetration level. In this paper, the impact of DG on the OLTC operations controlled by the line drop compensation (LDC) method is analyzed. In addition, a generalized determination methodology for the DG penetration limits in a distribution substation transformer is proposed. The proposed DG penetration limits could be adopted for a simplified interconnection process in DG interconnection guidelines.

The Effect of Reactive Compensators and Coordination With Volts/Hertz Limiting

It is important to evaluate all of the variables necessary in the setup and commissioning of the generator excitation system to ensure predictable behavior of the synchronous machine during all conditions of operation. The digital voltage regulator has several programmable features that enable setup for proper operation. A few of the many controls include reactive droop compensation, line drop compensation, and volts/hertz limiting. Often, for reactive sharing, reactive droop compensation is utilized with either a small percentage of droop or no droop when connected to a large step-up transformer. Line drop compensation regulates the terminal voltage to a point beyond the generator terminals into a step-up transformer by using a small percentage of terminal voltage rise at the generator output. The benefit of line drop compensation is its greater reactive contribution from the generator during a disturbance. Volts/hertz limiting ensures safe operation of the synchronous machine for either underfrequency operation or generator overvoltage. Whereas the use of reactive droop compensation is fairly predictable with volts/hertz limiting, line drop compensation also needs to be coordinated with volts/hertz limiting. In this case, it is necessary to carefully examine the settings of the line drop compensator versus the setting of the volts/hertz limiter. If unchecked, the two settings may overlap unfavorably. For example, if the volts/hertz limiter set point were lower than the line drop compensation setting, there could be undesired reduction in excitation. This paper discusses the two types of reactive compensators and the volts/hertz limiter to provide a better understanding of their effect on the generator excitation system.

분산전원이 연계된 배전계통에서 ULTC와 분산전원의 전압제어

LDC(Line Drop Compensation) is widely used in controlling ULTC(Under Load Tap Changer) output voltage at distribution substation. However, LDC may experience some difficulties in voltage control due to renewable energy resources and distributed generations. Therefore, more advanced voltage control algorithm is necessary to deal with these problems. In this paper, a modified voltage control algorithm for ULTC and DG is suggested. ULTC is operated with the voltages measured at various points in distribution system and prevents overvoltage and undervoltage in the distribution feeders. Reactive power controller in DG compensates the voltage drop in each distribution feeders. By these algorithms, the voltage unbalance between feeders and voltage limit violation will be reduced and the voltage profile in each feeder will become more flat.

AI Applications to Distribution System with Distributed Generation

ABSTRACT In this paper, Artificial Neural Network, one of the Artificial Intelligence (AI) techniques, for the Volt / Var control in power distribution systems with dispersed generation (DG) is proposed. Artificial neural networks have been considered due to their ability for real time control, simpler calculations and adaptability to different operating conditions. Neuro-controllers are much more effective, fast acting than conventional controllers. Neural network for controlling Step voltage regulator (SVR) with line rise compensation (LRC) /line drop compensation (LDC) function has been presented. The neural network based controller has been simulated for a radial distribution system with DG and the neuro-controller shows promising results after testing. Keywords Artificial Intelligence, Artificial neural network, Dispersed generation, Distribution system, Line drop compensation, Line rise compensation, Step Voltage regulator, Voltage / Reactive power control.

다수 PV 시스템 배전계통 연계 시 개선된 전압조정 방법

현재의 배전계통의 전압은 변전소에서 단방향 조류를 고려하여 LDC에 의한 전압조정방법으로 ULTC 변압기의 랩을 변환하여 공급전압을 적정범위 내에서 유지되도록 운전하고 있다. 그러나 현재의 배전계통 운용은 소용량에서 대규모 용량에 이르기까지 다양한 용량의 PV 시스템이 배전계동에 연계되어 운전되는 것을 반영하지 못하고 있는 실정이다. 때문에 다수의 PV 시스템이 계통에 연계되어 양방향 조류가 발생하고 이로 인해 연계점의 전압변동이 발생하여도 이를 효과적으로 조정하지 못하여 계통의 전압이 적정범위 내에서 운용되지 못하는 경우가 발생할 수 있다.<BR> 따라서 본 논문에서는 다수 PV 시스템의 연계에 따른 양방향 조류의 발생을 고려하고 연계점의 전압변동에 따른 계통의 전압을 효과적으로 제어할 수 있도록 실시간 감시가 이루어지는 PV 시스템의 특정을 이용하고 기존의 LDC 전압조정방법을 개선하여 PV 시스템 연계 시에도 변전소에서 계통의 전압을 적정범위 내에서 조정할 수 있는 개선된 전압조정방법을 제안하였다.

Studying the Effects of Distributed Generation on Voltage Regulation

The focus of this work is to introduce the power distribution community to the effects distributed generation has on distribution systems. Specifically, changes in the voltage profiles and operation of voltage regulation are studied. A distribution system model equipped with Line Drop Compensation is developed and integrated into the PSCAD/EMTDC™ simulation environment. Distributed generation is added to the simulation environment to observe its effects on the traditional voltage regulation scheme. An algorithm from previous research that mitigates these effects is analysed and sample calculations are performed in MATLAB™ for validation.

COMBINATION OF REACTIVE CURRENT DROOP COMPENSATION AND LINE DROP COMPENSATION FOR IMPROVING VOLTAGE STABILITY

Recent power system events have shown that voltage collapse can be a root cause of some widespread outages. The thrust of this paper is to discuss some means of mitigating system voltage depressions that are available through the scheme which utilizes both Reactive Current droop Compensation (RCC) and Line Drop Compensation (LDC). The point that the voltage regulator controls can be acquired by a new method which is based on a widely accepted voltage stability analysis tool. This tool can determine which generators will have an impact on the maximum permissible loading of a bus and which will not. The dynamic analyses were carried out on the CIGRE Nordic test system to study the impact of control point location on time to collapse and prove that the new scheme can improve the voltage stability.

Applying protection principles for controlling distributed generation

In a distribution system, it is essential to maintain the voltage variation within a specified limit for satisfactory operation of connected customers' equipment. Normally, this goal is achieved by controlling the operation of compensating devices, such as load tap changing transformers, shunt capacitors, series capacitors, shunt reactors and static VAr compensators. However, technical and regulatory developments are encouraging a greater number of small generator units, known as distributed generation (DG), and this has the potential to significantly affect voltage control systems. This paper presents an adaptive voltage control technique that incorporates DG systems into the voltage control system. The control scheme uses on-load tap changing transformer (OLTC) and DG for voltage corrections, both are driven by advanced line drop compensators (LDC). At the substation, the LDC is employed to control step-up or step-down decisions of the OLTC, while another LDC will be used at the DG connection point to set DG parameters. Also, for a more cost-effective system, voltage control action coordination is proposed using magnitude and time grading. The control approach is tested on a modified distribution system with load variations that are stochastic in time and location. The results show that the integration of these magnitude and time grading protection principles have considerably reduced the DG energy required to achieve the desired control.

Voltage control with on-load tap changers in medium voltage feeders in presence of distributed generation

This paper discusses voltage regulation on medium-voltage feeders with distributed generation (DG) using on-load tap changer (LTC) and line drop compensation (LDC). The analysis shows that LTC is robust against DG, whereas DG can affect the effectiveness of the voltage regulation provided by LDC. However, with proper coordination between DG and LDC, it is possible to ensure voltage regulation without unnecessarily restricting the integration of DG. It is shown that, while lowering the LTC setting can increase the DG integration limit, even higher increase can be obtained by activating the LDC feature, which is present in most LTCs, but often not used. LDC regulation is also compared with other alternatives such as using a DG unit with voltage control capability and installing a line voltage regulator.

Discussion of “The Coordinated Automatic Voltage Control of the Italian Transmission Grid—Part I: Reasons of the Choice and Overview of the Consolidated Hierarchical System”

interaction, combined line-drop compensation and cross-current compensation has been developed at BPA [7] and by a major manufacturer of excitation equipment. Combined line drop and cross-current compensation are now installed at a large hydroelectric plant comprising 16 generators, with a similar installation planned at a plant with 22 generators. While the amount of line-drop compensation must be limited to avoid adverse interaction with parallel generators, advanced line-drop compensation (high-speed high side voltage control with cross-current compensation) has been developed and tested at a hydro plant [8]. Adjustable droop prevents interaction. An override feature can keep terminal voltage within desired limits. Regarding Section VI, the comparison of SVR with the SVC solution is informative from a network loss viewpoint. For clarity, please state the assumed installed SVC cost in Euros/kVAr. Rather than SVCs, the majority of shunt compensation would realistically be mechanically switched capacitor banks, which are perhaps only 20% of the cost of SVCs. Compared to SVCs, shunt capacitor banks have virtually zero losses and low maintenance. Where SVCs are needed for high-speed control with unrestricted switching, smaller SVCs are typically used, with the SVCs’ controlling mechanically switched capacitor/reactor banks. Also, portions of SVCs may have short-time ratings to reduce cost. Could the authors adjust the Table II numbers for use of mechanically switched equipment?

Design, installation, and initial operating experience with line drop compensation at John Day powerhouse

This paper describes design, installation, testing, and initial operating experience with line drop compensation (LDC) at John Day powerhouse. The voltage stability analysis is performed to quantify the system benefit provided by John Day LDC, transient stability studies are performed to determine target levels for LDC settings. The design, which utilizes both reactive current droop compensation and line drop compensation, is described. LDC installation and testing are presented. Operating experience is discussed, and LDC benefit for system disturbances is demonstrated.

Advanced voltage regulation method of power distribution systems interconnected with dispersed storage and generation systems

This paper deals with an issue of voltage regulation for power distribution systems interconnected with dispersed storage and generation (DSG) systems. Since DSGs within power distribution systems impact on the conventional voltage regulation method, there is a possibility that customers' voltages violate the permissible limits. A multiple line drop compensation (MLDC) voltage regulation method that determines tap positions of under-load tap changer (ULTC) transformers is proposed to maintain the customers' voltages within the permissible limits. Several case studies indicate that the proposed MLDC voltage regulation method can be applied well to practical power distribution systems having DSGs and/or severely unbalanced load diversity on different feeders.