Showing papers on "Islanding published in 2002"

Evaluation of Islanding Detection Methods for Utility-Interactive Inverters in Photovoltaic Systems

Abstract: This report describes the various methods and circuits that have been developed to detect an islanding condition for photovoltaic applications and presents three methods that have been developed to test those methods and circuits. Passive methods for detecting an islanding condition basically monitor parameters such as voltage and frequency and/or their characteristics and cause the inverter to cease converting power when there is sufficient transition from normal specified conditions. Active methods for detecting the island introduce deliberate changes or disturbances to the connected circuit and then monitor the response to determine if the utility grid with its stable frequency, voltage and impedance is still connected. If the small perturbation is able to affect the parameters of the load connection within prescribed requirements, the active circuit causes the inverter to cease power conversion and delivery of power to the loads. The methods not resident in the inverter are generally controlled by the utility or have communications between the inverter and the utility to affect an inverter shut down when necessary. This report also describes several test methods that may be used for determining whether the anti-islanding method is effective. The test circuits and methodologies used in the U.S. have been chosenmore » to limit the number of tests by measuring the reaction of a single or small number of inverters under a set of consensus-based worst-case conditions.« less

Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

Abstract: The traditional frequency-shift methods for islanding detection of grid connected PV inverters (the active frequency-drift method and the slip mode frequency-shift method) become ineffective under certain paralleled RLC loads. The automatic phase-shift method is proposed in this paper to alleviate this problem. The method is based on the phase shift of the sinusoidal inverter output current. When the utility malfunctions, the phase-shift algorithm keeps the frequency of the inverter terminal voltage deviating until the protection circuit is triggered. Simulation and experiments are performed for verification.

Self-healing in power systems: an approach using islanding and rate of frequency decline-based load shedding

Abstract: This paper provides a self-healing strategy to deal with catastrophic events when power system vulnerability analysis indicates that the system is approaching an extreme emergency state. In the authors' approach, the system is adaptively divided into smaller islands with consideration of quick restoration. Then, a load shedding scheme based on the rate of frequency decline is applied. The proposed scheme is tested on a 179-bus, 20-generator sample system and shows very good performance.

Distributed generation islanding-implications on power system dynamic performance

Abstract: Distributed generation can potentially support unintentional system islands, isolated from the remainder of the system. These islands pose a significant risk to safety and equipment, and need to be quickly detected and eliminated. Islands are detected by sensitive under- and over-voltage and frequency functions, sometimes aided by active island destabilization techniques. Both the passive voltage and frequency trip point and active destabilization measures to counter islanding, however, can also adversely impact system dynamic performance. As DG penetration grows, attention will need to be directed to the balance between the need to eliminate Islands, and the impact of measures used to detect and eliminate islands on system performance when no islanding occurs.

Anti-islanding techniques for distributed power generation

Abstract: Techniques for detecting an island in a system including a node that is operatively coupled to a primary power source (e.g., grid) and one or more distributed power generation sources are disclosed. In one embodiment, a current pulse is included in the output of a distributed power source. The grid voltage is monitored at the node to determine if a pulse-related disturbance occurs. If the grid is present, no pulse-related disturbance will manifest. If grid is down, then a pulse-related disturbance will manifest. Detection of the pulse-related disturbance is used to signal island detection.

Implementation and testing of anti-islanding algorithms for IEEE 929-2000 compliance of single phase photovoltaic inverters

Abstract: Electrical system islanding occurs when the utility grid is removed but local sources continue to operate and provide power to local loads. This can present safety hazards and the possibility of damage to other electric equipment. Anti-islanding functionality is a key requirement for grid-interactive inverters used in PV systems that function as distributed generation sources. The IEEE Std. 929-2000 "Recommended Practice for Utility Interface of Photovoltaic (PV) Systems" (IEEE 929) sets testing requirements for these systems which includes an anti-islanding requirement. UL has adopted this practice in UL-1741. This paper provides a description of Xantrex anti-islanding algorithms and examples of inverter testing. Inverters tested were the Xantrex SW with GTI and ST models. Testing was performed at the Sandia National Laboratories Distributed Energy Technologies Laboratory. Data is provided for single and multiple units with additional data on power quality.

Development of a logical rule-based islanding detection method for distributed resources

Abstract: The islanding protection for distributed resources (DR) becomes an important and emerging issue in power system protection since the distributed resources installations are rapidly increasing and most of the installed systems are interconnected with distribution network In order to avoid the negative impacts from islanding operations of DR to protection, operation, and management of distribution system, it is necessary to effectively detect the islanding operations of DR and disconnect it from distribution network rapidly Generally, it is difficult to detect islanding operation by monitoring only single system parameter This paper presents a new logic based islanding detection algorithm for distributed resources that is interconnected with distribution network The proposed islanding detection algorithm utilizes four system parameters that include the conventionally used ones of voltage magnitude, phase, and frequency and the newly proposed one in this paper of total harmonic distortion (THD) of current The method monitors changes in four parameters and detects the islanding operations by logical rules The authors verified the efficiency of the proposed method using the radial distribution network of IEEE 34 bus model

A scheme for controlled islanding to prevent subsequent blackout

Abstract: The power systems operated by the utilities in developing countries suffer from a large gap between demand and generation, inadequate transmission capacity, and nonuniform location of the load centers and generating stations. Occurrences of faults in such systems, in most of the cases, end up with the worst consequences (i.e., complete blackout). This paper illustrates the way a blackout can be prevented in real time through controlled segregation of a system into a number of viable islands together with generation and/or load shedding. The nature and location of any fault that warrants such islanding can be ascertained in real time through monitoring the active-power (megawatt) flows at both ends of a number of prespecified lines. The blackout of June 20, 1998 in the Bangladesh Power Development Board system has been used as an example in the illustration. The philosophy of the proposed islanding scheme may be considered for implementation in other power systems also.

Devices and methods for detecting islanding operation of a static power source

Abstract: Devices and methods for detecting islanding operation of a static power source involve injection of a non-harmonic error on the phase angle of the static power source in regular steps to introduce a very small intentional phase shift for the output voltage of the static power source in every voltage cycle which is corrected in each cycle in synchronization with the grid voltage in normal operation of the grid. In abnormal operation of a grid loss, this intentional small phase shift or error causes an intentional small frequency drift in each voltage cycle that continues in one cycle after another cycle. When the intentional frequency drift is over a preset level, a detection circuit starts to isolate the static power source from the grid to prevent islanding operation.

Islanding behaviour of grid-connected PV inverters operating under different control schemes

Abstract: This paper compares the islanding behaviour of different inverter implementations, which have current source or voltage source characteristics. Measurements were made on a number of commercially available inverters, and simulation models were developed to enable further investigation of the influence of the type of control system on islanding operation. Additionally, a modified active-frequency-drift detection method is presented which reduces the amount of distortion introduced to the grid compared with the conventional approach often described in the literature.

System islanding considerations for improving power system restoration at Manitoba Hydro

Abstract: System islanding and load shedding concepts have been discussed throughout the industry and considered for years at Manitoba Hydro. The aim is to preserve stable areas of load and generation to aid in system restoration following a major outage. If the islanding scheme operates correctly system restoration may be less complex and overall restoration time reduced by one hour or more. This paper documents studies pertaining to the islanding scheme currently in service. Following a total loss of Manitoba Hydro HVDC, considered to be one of the more significant outages that can be experienced on the power system, the system naturally forms an island due to existing relays. Due to severe undervoltages, the island may disintegrate almost Immediately after its formation. Results show that if high speed under-frequency relays are installed at the natural islanding locations, forcing the island to form at a predetermined system frequency of 59.0 Hz, and prior to its natural formation, a relatively stable northern island can be formed and preserved. The integrity of this island is sensitive to the chosen islanding frequency and speed at which separation can occur in forming the island, TRVs across associated circuit breakers must be considered.

A new power stabilization control system based on making use of mechanical inertia of a variable-speed wind-turbine for stand-alone wind-diesel applications

Abstract: In this paper is described the development of a new wind-diesel generator system which is based on standard diesel generators connected to MADE AE-56 wind turbines. Such wind-turbines have variable-speed, variable-pitch operation and they are regulated under a special patented control algorithm, devoted to stabilization of grid frequency. One of the most important advantages deduced from the behaviour of the complete system is the continous improvement of the power quality, in terms of frequency and voltage stabilisation as it is shown from the exposed results. This is a required feature in islanding power systems, which is achieved with the presented stand-alone generation system. The control algorithm is being based in DSP operation and the complete system is being built with MADE's technology.

Emergency-stability controls through HVDC links

Abstract: The paper deals with some power modulation controls achievable by using the high voltage direct current (HVDC) interconnections between different grids or subnetworks. HVDC links can be in fact effectively used for damping electromechanical oscillations, stabilizing power swings, reducing the life-fatigue effects of sub-synchronous resonance (SSR), etc. The development of voltage source converter (VSC) technology (used for instance in HVDC Light interconnections) can improve also the network voltage compensation and the transmission grid load-ability, reducing the risks of voltage instability and collapse. The paper mainly focuses on the power modulation strategies designed for two Italian HVDC links, the Sardinia-Corsica-Italy link (SACOI), with more than ten years of commercial operation after refurbishment by ENEL and EDF, and the Italy-Greece link (GRITA), more recently put in service by ENEL and PPC. These mono-polar links with sea return (rated voltage 300 kV and 400 kV respectively, rated current 1500 A and 1250 A respectively, rated power 300 MW and 500 MW respectively) are based on conventional grid commuted double thyristor bridges. The permanent or transient critical conditions of network islanding are faced by high speed and low droop frequency regulators, characterized by flexible and effective control operations.

Power system modeling requirements for rotating machine interfaced distributed resources

Abstract: Rotating machine interfaced power generation equipment today constitute the majority of interconnected distributed resources (DR). Even though new electronically interfaced DR devices, such as fuel cells, photovoltaics and microturbines are rapidly emerging, rotating machines are expected to continue to represent a major sector of interconnected DR capacity for the foreseeable future. To simulate and predict the impacts of these machines on power system control, protection and power quality conditions, it is crucial for the industry to have reasonable model representations of these devices. Machine models must characterize the prime mover response and generator electrical response behavior including its exciter. Critical types of analysis will include short circuit calculations (fault contributions), harmonic contributions, dynamic response of the generator to load steps and during islanding, voltage regulation, and stability. This paper is a starting point for discussing the modeling needs for rotating machine interfaced DR and potential sources of data for these models.

The development of a scaled-down simulator for distribution grids and its application for verifying interference behavior among a number of module integrated converters (MIC)

Abstract: Islanding is one of the serious problems in an electric power system connected with dispersed power sources. To secure the power system from islanding, it is quite important to verify the ability of islanding detection for the individual power sources in advance. The authors have been developing a scaled-down, simulated distribution network including a distribution substation, 6.6 kV distribution line, pole transformers, low-voltage lines, customer loads and a number of PV systems. This paper describes the development of the scaled-down simulator and the experimental results about the interference phenomena among multiple module integrated converters (MIC).

A two-phase method based on OBDD for searching for splitting strategies of large-scale power systems

Abstract: System splitting problem, also known as controlled system separation problem, is to determine proper splitting points to split the entire interconnected transmission network into islands of load with matched generation when islanding operation of system is unavoidable. It is very difficult because of combinatorial explosion of searching space with the size of power network increasing. This paper proposes a two-phase method to find proper splitting strategies in real time by introducing the graph-model of system splitting problem. The method can narrow down the strategy space by highly efficient OBDD-based algorithm in the first phase and give all proper splitting strategies by power-flow calculation in the second phase. Simulation results on IEEE 30-bus test network shows that this method can quickly (in several seconds) give all proper splitting strategies guaranteeing synchronization, power balance and satisfaction to capacity constraints of transmission lines and other facilities in each island.

The costs and benefits of embedded generation islanding operation

Abstract: This report describes the results of a study commissioned by the UK Department of Trade and Industry to identify the technical, legal and commercial issues of islanded embedded generation and to quantify the costs and benefits. Technical considerations affecting island mode operation include security of supply requirements, the licence duty of distribution network operators (DNOs) to comply with 'group demand' restoration times, 'guaranteed standards' licence requirements governing restoration of supplies to customers, and frequency and voltage control. The economics of islanded embedded generation are discussed and key factors noted.

Sandia Smart Anti-Islanding Project; Summer 2001: Task II Investigation of the Impact of Single-Phase Induction Machines in Islanded Loads: Summary of Results

Abstract: Islanding, the supply of energy to a disconnected portion of the grid, is a phenomenon that could result in personnel hazard, interfere with reclosure, or damage hardware. Considerable effort has been expended on the development of IEEE 929, a document that defines unacceptable islanding and a method for evaluating energy sources. The worst expected loads for an islanded inverter are defined in IEEE 929 as being composed of passive resistance, inductance, and capacitance. However, a controversy continues concerning the possibility that a capacitively compensated, single-phase induction motor with a very lightly damped mechanical load having a large rotational inertia would be a significantly more difficult load to shed during an island. This report documents the result of a study that shows such a motor is not a more severe case, simply a special case of the RLC network.

Diffusion-induced islanding in heteroepitaxial systems

Abstract: A microscopic lattice gas model for ultra-thin film dynamics is developed and applied to the case of heteroepitaxial growth. A set of non-linear kinetic equations for average occupations of adsorption sites in 3D lattice is studied analytically in a continual limit. It is found that within a range of parameters of heteroepitaxial system space-uniform state becomes unstable in critical thickness range and system undergoes spontaneous islanding. Space-ordered quasistationary solutions to the model equations describe the dynamics of 3D islanding induced by the uphill diffusion in the field of deposit–deposit and deposit–substrate interactions. Lateral size of islands depends on material constants of the system, surface temperature and deposition rate. Initial discrete system of non-linear kinetic equations is studied numerically; results for surface morphology describe dense arrays of 3D nanoislands.

Investigation of the Impact of Single-phase Induction Machines in Islanded Loads Summary of Results

Abstract: Islanding, the supply of energy to a disconnected portion of the grid, is a phenomenon that could result in personnel hazard, interfere with reclosure, or damage hardware. Considerable effort has been expended on the development of IEEE 929, a document that defines unacceptable islanding and a method for evaluating energy sources. The worst expected loads for an islanded inverter are defined in IEEE 929 as being composed of passive resistance, inductance, and capacitance. However, a controversy continues concerning the possibility that a capacitively compensated, single-phase induction motor with a very lightly damped mechanical load having a large rotational inertia would be a significantly more difficult load to shed during an island. This report documents the result of a study that shows such a motor is not a more severe case, simply a special case of the RLC network.