Anti-islanding Protection Research Articles

Islanding protection of active distribution networks with renewable distributed generators: A comprehensive survey

Anti-islanding protection schemes currently enforce the renewable distributed generators (RDGs) to disconnect immediately and stop generation for grid faults through loss of grid (LOG) protection system. This greatly reduces the benefits of RDG deployment. For preventing disconnection of RDGs during LOG, several islanding operation, control and protection schemes are being developed. Their main objectives are to detect LOG and disconnect the RDGs from the utility. This allows the RDGs to operate as power islands suitable for maintaining uninterruptible power supply to critical loads. A major challenge for the islanding operation and control schemes is the protection coordination of distribution systems with bi-directional flows of fault current. This is unlike the conventional overcurrent protection for radial systems with unidirectional flow of fault current. This paper presents a comprehensive survey of various islanding protection schemes that are being developed, tested and validated through extensive research activities across the globe. The present trends of research in islanding operation of RDGs are also detailed in this paper.

An Investigation on the Nondetection Zones of Synchronous Distributed Generation Anti-Islanding Protection

Anti-islanding protection is an important technical requirement when interconnecting distributed generators. Unfortunately, most anti-islanding protection schemes cannot detect islanding situations under certain system operating conditions - there are nondetection zones within which anti-islanding protection schemes are ineffective. This paper investigates these nondetection zones associated with the common anti-islanding protection schemes of synchronous distributed generators: frequency and voltage-based relays. Moreover, the characteristics of the nondetection zones and the key factors that influence them are analyzed. The results are useful for utility companies and distributed generators owners to design and to evaluate the effectiveness of anti-islanding protection schemes proposed for various distributed generation interconnection projects.

A Power Line Signaling Based Scheme for Anti-Islanding Protection of Distributed Generators—Part II: Field Test Results

Anti-islanding protection of distributed generators (DG) is a significant technical barrier to the emerging DG industry. In response to this challenge, a power line signaling based anti-islanding protection scheme has been proposed in a companion paper. The scheme broadcasts a signal from a substation to the DG sites using the distribution feeders as signal paths. A DG is considered as islanded from the upstream system if the signal is not detected at the DG site. This paper presents extensive field test results and experiences obtained for the proposed scheme. The results confirm that the proposed scheme is a very promising and economical method to satisfy anti-islanding protection requirements for synchronous DG interconnections.

A Power Line Signaling Based Technique for Anti-Islanding Protection of Distributed Generators—Part I: Scheme and Analysis

Anti-islanding protection of distributed generators (DG) is a significant technical barrier to the emerging DG industry. This paper presents an innovative power line signaling based anti-islanding scheme developed in response to the challenge. The scheme broadcasts a signal from a substation to the DG sites using the distribution feeders as the signal paths. A DG is considered as islanded from the upstream system if the signal cannot be detected at the DG site. The proposed scheme has been evaluated using analytical, simulation and field tests. The results are very promising. This paper presents the main ideas of the scheme and its design considerations. Methods to create and detect the signals are shown and their performances are analyzed.

Reducing unnecessary disconnection of renewable generation from the power system

Future power systems with large proportions of embedded generation could be severely affected if several loss of mains (LOM) protection systems maloperate in response to a non-islanding condition, potentially leading to generation shortfall and stability problems. Although many papers discuss methods of sensitively detecting islanded conditions (a short bibliographical survey is included), almost no papers in the literature address the problems associated with the stability of such protection methods during and after perturbations on the network to which they should not react. The aim is to highlight the shortcomings in existing power system protection practices relating to islanding detection with a view to identifying necessary areas of improvement to facilitate the ongoing proliferation of renewable sources in active distribution networks. Existing LOM techniques are described and stability-related shortcomings are demonstrated using the results of rigorous laboratory testing of several commercially available relays. The testing scenarios are developed using a UK Generic Distribution System repository, a public domain database representing typical distribution system architectures. Recommendations relating to the setting of existing LOM protection devices are provided, along with an overview of research and development activities relating to improvements in anti-islanding protection, including a discussion of both technical and economical viability.

A Novel Microcontroller for Grid-Connected Photovoltaic Systems

The purpose of this paper is to develop a novel microcontroller for grid-connected photovoltaic (PV) systems. As a prototype model, a 100-W-class module-integrated converter composed of the proposed controller and a flyback inverter has been built and tested. The prototype model is designed to satisfy the Japanese grid-connection guideline. Basic functions as those of a grid-connected PV inverter, such as the maximum-power-point tracking and the anti-islanding protection, have been confirmed in the experiments using a distribution network simulator located in a laboratory. This paper presents the description of the controller and the experimental results. A microcontroller has been developed with a 50-MHz-class microcomputer and simple interfaces. By revising the program, the proposed controller can be applied to various types of PV systems or grid-connected equipment

Islanding detection of grid connected distributed generators using TLS-ESPRIT

A critical protection requirement for grid connected distributed generators (DG) is anti-islanding protection. In this paper, a new islanding detection method is proposed based on monitoring the generator's frequency. Two new features, the frequency of oscillation and the damping factor of the generator's frequency output waveform, are extracted using the total least square-estimation of signal parameters via rotational invariance techniques (TLS-ESPRIT) algorithm. The proposed method has been tested under various scenarios such as load change, short circuit, and capacitor switching.

Performance Curves of Voltage Relays for Islanding Detection of Distributed Generators

This letter proposes a method for systematically evaluating the voltage-based relay's capability to detect islanding of distributed generators connected to distribution systems. The method is based on a set of detection time versus reactive power imbalance curves, which can be obtained through repeated dynamic simulations. With the curves, one can determine the characteristics of voltage-based anti-islanding protection systems.

Análise comparativa sobre a eficácia de relés baseados em medidas de freqüência para detecção de ilhamento de geradores distribuídos

Relés de proteção baseados em medidas de freqüência são usualmente empregados para detectar ilhamento de geradores síncronos conectados em redes de distribuição de energia elétrica. O desempenho desses relés é fortemente dependente do desbalanço de potência ativa na rede ilhada. Para avaliar diferentes tipos de relés de freqüência de forma sistemática, utiliza-se, neste trabalho, uma metodologia de análise baseada em um conjunto de curvas relacionando tempo de detecção do ilhamento e desbalanço de potência ativa. A partir dessas curvas, obtidas por meio de simulação dinâmica não-linear, o conceito de desbalanço crítico de potência ativa também é apresentado. Essa metodologia é aplicada aos relés de sub/sobrefreqüência, relés de taxa de variação da freqüência (Rate of Change of Frequency Relays - ROCOF Relays) e relés de deslocamento de fase (Vector Surge ou Vector Jump Relays).

05/01315 Modeling anti-islanding protection devices for photovoltaic systems

05/01315 Modeling anti-islanding protection devices for photovoltaic systems

Anti-islanding protection and islanding operation of grid-connected hydropower distributed generation

Salient issues associated with the connection of hydropower distributed generation (HPDG) into distribution networks include operation and voltage regulation, grid connection and control interaction, anti-islanding protection and islanding operation, and operation of protective devices. Better understanding of these issues and finding solutions to these problems are timely and important to the electricity industry. This paper has addressed islanding and anti-islanding issues of hydropower DG, and developed design criteria and solution for effective operation and control. A current control scheme based on microprocessor-based line-tracking system is proposed for HPDG operation with grid system. A technique is developed to use islanding detection and anti-islanding protection of HPDG. The paper has also proposed guidelines for islanding operation of HPDG to improve quality and reliability of power supply. Control of over- and under-generated islanded systems with hydropower DG have been explored and criteria for islanding operation and resynchronisation when mains return are discussed.

Impacts of dynamic reactive power compensation devices on the performance of wind power generators

This paper investigates the main impacts of dynamic reactive power compensation devices on the performance of induction machine-based wind power generators. The dynamic reactive power compensation devices analysed are the SVC (Static Var Compensator) and the DSTATCOM (Distributed Static Synchronous Compensator). The usage of these devices as a power factor regulator or a voltage regulator is investigated. The technical factors analysed are small-signal voltage stability, transient stability, and interactions with the anti-islanding protection system. The analyses are carried out by using a wind farm composed of 30 units of 1 MW induction generators. Such wind farm is connected to a 60 Hz, 33 kV distribution system. The results are a useful guideline to evaluate which control strategy and device are suitable for a determined application as well as to understand the dynamic interactions that can occur.

Evaluation of Anti-Islanding Schemes Based on Nondetection Zone Concept

This paper proposes a nondetection zone (NDZ) as a performance index to evaluate different anti-islanding schemes. The NDZ for three basic passive anti-islanding schemes: under/over voltage, under/over frequency, and phase jump are derived analytically and validated by simulation. Based on the NDZ, not only can the dominant factors that influence anti-islanding protection be identified, it may also support definition of optimal combined schemes that lead to a reduced NDZ. The methodology presented in the paper can be extended to the evaluation of other anti-islanding schemes.

Investigation of Anti-Islanding Protection of Power Converter Based Distributed Generators Using Frequency Domain Analysis

The anti-islanding algorithm proposed by the Sandia national laboratories is analyzed in this study because this scheme, also known as the Sandia scheme, is considered to be effective in detecting islanding of distributed generation systems. Previously, other than heuristic approaches, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the power rating and bandwidth of the distributed generation (DG) power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. This paper uses a frequency domain approach to analyze the range for the gains required by anti-islanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The analysis provides guidelines for using Sandia's national laboratory schemes under different application conditions. The results are validated using detailed time domain DG and power system simulations.

Modeling anti-islanding protection devices for photovoltaic systems

Applications of grid-connected photovoltaic systems are rapidly expanding, providing a viable technology for renewable energy resources. Such systems are utility interactive and one of the major difficulties in their efficient use is related to islanding phenomena connected with a possibility of supplying surplus power back to the utility grid. In detecting and preventing such situations, anti-islanding protection devices play a paramount role. In this paper, we analyze the existing techniques in order to identify a methodology with an optimum combination of characteristics. We implement the chosen methodologies in SIMULINK. Major attention is given to the phase jump detection method (PJD), and to the slip mode frequency shift method (SMS) for which we provide a detailed description of our SIMULINK implementations and their evaluations performed on the basis of their non-detection zones. We develop an experimental iterative scheme to validate the results of computational experiments obtained with the developed models, and report the results of several computational tests.

Predicting islanding operation of grid connected PV inverters

Increasing numbers of photovoltaic arrays are being connected to the power utility through power electronic inverters. This has raised potential problems of network protection. If, due to the action of the inverter or inverters, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. Many methods to prevent this have been proposed and a SPICE-based model and analysis of the system are presented. Specifically aimed at predicting the effectiveness of two of these. These are: active frequency drift, which causes the inverter current to be generated slightly lower or higher in frequency than the frequency of the terminal voltage; and slip mode frequency shift, which controls the phase angle of the inverter current as a function of the frequency deviation of the terminal voltage from that of the normal network frequency. Experimental verification of the model is provided. Active frequency drift using frequency speed-up rather than speed-down is shown to be preferable for inductive loads, but conditions that resulted in islanding could be predicted. Slip mode frequency shift proved to be a more robust anti-islanding protection technique.