Showing papers on "Islanding published in 1994"

Performance evaluation of static security analysis methods

Abstract: This paper describes a method for static security analysis based on a coordinated combination of PI methods, subnetwork solutions, compensation methods and sparse vector methods. The method is hybrid utilizing PI methods and contingency screening/analysis methods. This paper focuses on the contingency screening/analysis method. It is capable of efficiently handling PV/PQ bus type conversions and islanding conditions caused by contingencies. It also features an "optimal" combination of computational procedures which yields the least execution time for a specified level of accuracy. The performance of the method is statistically evaluated on large power systems. The results clearly illustrate the superior performance of the method. >

Islanding phenomenon elimination study at Rokko test center

Abstract: When a certain part of the utility grid, with a substantial number of interconnected PVs, gets cut off from the grid, islanding phenomenon may occur. There are two ways to suppress the islanding phenomenon, one of them is performed on the utility side, the other one on the PV side. On the utility side the reactor insertion method and the capacitor insertion method are advocated. The islanding phenomenon suppression characteristics of these two methods are compared in tests. Further, it is proved that the process, leading to the suppression of islanding phenomena, can be described in general power supply theory.

Statistical evaluation of optimum islanding preventing method for utility interactive small scale dispersed PV systems

Abstract: The optimum islanding preventing method for the small scale dispersed PV system were evaluated, based on a simulation analysis concerning the occurrence probability of islanding phenomenon in actual operation. As a result, it is sufficient to adopt only one developed measure when the PV penetration ratio to distribution line capacity is less than 20% to 30%. It is necessary to adopt a combination method consisting of 2 or more developed measures when the penetration ratio is more than 40%. The harmonic monitoring method is effective in the case of using it in a combination method.

An AGC implementation for system islanding and restoration conditions

Abstract: An island AGC function has been implemented in a large-scale power system, Virginia Power Company (VP), to assist in system emergency and restoration situations. It is the first time that the conventional AGC function has been enhanced to be utilized, rather than to be suspended, under such circumstances. The island AGC function is designed to be implemented in both the real-time and the dispatcher training simulator (DTS) environments. The latter provides a realistic closed-loop simulation environment that mimics the real system behavior, offering an excellent opportunity for operators to be well-trained, aware and prepared for abnormal situations. This implementation has been tested on the VP system model, which consists of 4400 buses and 775 generators. It has successfully completed custom factory tests, and it is the user's opinion that the island AGC will provide a valuable additional capability for use during system restoration. >

Protection of dispersed storage and generation units against islanding

Abstract: This paper deals with islanding protection which is the most important protection requirement of dispersed storage and generation units (DSGs). A power based digital algorithm has been developed for the protection of DSG units against islanding. Computer simulation results show that, in addition to effectively detecting the islanding, the new algorithm trips for the load changes that occur during the islanding operation but remains unstable for the load fluctuations while the DSG unit is operating in parallel with the utility network. The algorithm also detects the condition when the utility supply is reconnected to the power island while the two supplies are out of phase. >

Development of a new utility-connected photovoltaic inverter LINE BACK

Abstract: A new utility-connected photovoltaic inverter called "LINE BACK", which is suited to small-scale photovoltaic generation systems for use in private households, has been developed. The inverter converts DC power generated by rooftop photovoltaic cells into AC power, and provides it to house loads connected to the utility line. When photovoltaic power is greater than the loads, the excess power is fed to the utility line through a reverse power flow. The inverter has several special functions such as a utility protection relay, maximum power point tracking (MPPT) control, automatic operation with photovoltaic power, detection of islanding operation, and utility voltage compensation for reverse power flow. These functions and characteristics conform to the "Utility-Connected System Technical Guidelines" revised by Japan's Ministry of International Trade and Industry in March 1993. >

A development of compact and reliable protective control unit for grid connected small residential PV systems

Abstract: In the future, serious problems may arise with the maintenance of power quality, stability and safety of electric utility grids interconnected with low quality private PV power systems, without adequate protection measures being taken. The safety problem is the most important factor for electric utilities in Japan and therefore the reliability of islanding protection of such power systems must be checked because the phenomenon will directly affect the safety of personnel and utility facilities. In order to solve this problem, a reliable and compact protective control unit for residential PV power system application was developed by CRIEPI. It is confirmed that the unit shows excellent reliability for interconnected power system islanding protection.

Kinetic suppression of islanding in impurity‐mediated heteroepitaxial growth of germanium on silicon

Abstract: The impurity‐mediated suppression of islanding in molecular beam epitaxy growth experiments of Ge on Si(100) can be understood by a kinetic reduction of surface diffusion. Besides the energy barrier for surface diffusion, an energy barrier for a site exchange mechanism between Ge adatoms and the impurity atoms also has to be considered in a simple phenomenological approach that describes this effect. We found satisfactory agreement with different experimental results, like dependence of kinetic suppression of islanding on temperature and/or submonolayer coverage with impurities and germanium flux density.

Anti-islanding protection using a twin-peak band-pass filter in interconnected PV systems, and substantiating evaluations

Abstract: The authors have successfully developed and industrialized a new frequency-shift anti-islanding protection method using a twin-peak band-pass filter (BPF) for grid-interconnected photovoltaic (PV) power systems. In this method, the power conditioner has a twin-peak BPF in a current feedback loop in place of the normal BPF. This new method works perfectly for various kinds of loads such as resistance, inductive and capacitive loads connected to the PV system. Furthermore, because there are no mis-detections, the system enables the most effective generation of electric energy from solar cells. A power conditioner equipped with this protection was officially certified as suitable for grid-interconnection.

Protector for system interconnection

Abstract: PURPOSE:To detect an islanding condition surely and to stop the operation of an inverter by comparing the line voltages of a single-phase 3-line type AC system and detecting a malfunctioning condition, concerning a device having an inverter which converts DC power to AC power and interconnects to the single-phase 3-line type AC system. CONSTITUTION:A difference voltage detecting circuit 22 detects the voltage difference between the two line voltages of a single-phase 3-line type, i.e., between L1 and a midpoint and between L2 and the midpoint, and a level detector 23 performs level judgment. And if it exceeds a set value, it is judged that malfunctioning occurs, and a time function circuit 24 produces output V24. A value V25 obtained by multiplying this output V24 by the output V11 of an amplifier 11 for amplifying the voltage difference between a voltage reference 10 and a DC power source 1 through the working of a multiplier circuit 25 is inputted to a current reference circuit 12, and the magnitude of an AC current reference V12 is varied. As a result of this, the output current of an inverter 2 varies, and balance with loads 9a, 9b, and 9c is lost, and the voltage and frequency of a distribution line change swiftly. These are detected with a malfunction detecting circuit 19 through a voltage relay 17 and a frequency relay 18, and the inverter 2 is stopped.

Issues in utility-interactive photovoltaic generation

Abstract: This article examines factors affecting the application of solar Photovoltaic Power Plants to their power grid. A utility considering the use of solar photovoltaic generation should consider the following issues: power conditioning, protection, islanding, intermittent output, and installation. PV generation, like many advanced electrical technologies, will at times require improved performance from the utility system. Operating and protection practices may have to change to accommodate PV. However, operating experience and studies show that PV generation will operate well with existing electric utility systems.

A Novel Islanding Protection System for Photovoltaic Inverters

Abstract: It is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power. This is because a sufficiently large voltage or frequency change cannot be expected at such a balanced state. Many studies have been reported so far to complement dead bands in combination of active and passive methods to prevent the islanding, but none of them has been successful. This paper presents the principle of a new active method called slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionally to cause the frequency to shift as if it slips down a slide. The performance when the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.

Cogeneration in distribution system : planning, operation, transients

Abstract: This thesis relates to a study of abnormal conditions on a threephase distribution feeder of industry like State Electricity Commission of Victoria (SECV) with several loads and a capacitor bank. An induction generator, which plays the role of a dispersed storage and generation unit, driven by a hydraulic turbine, which is a common form of renewable energy scheme, is connected to the distribution feeder through a Δ/Y transformer. Transients caused switching of the induction generator, by single line-to-ground fault, double line-to-ground fault through contact resistances, broken conductor touching the ground through a small resistance, isolating the induction generator to form its own supply domain (islanding) etc are investigated and interesting conclusions of practical importance are derived. The IBM PC version 4 of the Electro-Magnetic-Transient Program - Alternative Transient Program (ATP), was used to solve this problem. The program also gives output results for automatic plotting in time domain. Accordingly, transient voltages at several nodes and transient currents at interesting points were plotted from the output results. Planning and operational aspects like voltage control, reliability, harmonics, earthing, and contractual matters between the private generator and the utility are also considered. Technical aspects interconnections between the private generation and the utility has been considered. Interesting conclusions, valuable for insulation co-ordination, interrupting duty on circuit breakers, effect on response of protective relays and automatic control systems are pointed out. It also considers security to personnel and protection of metering equipment. The thesis also offers guide for contractual matters between the utility and the private generation.

Islanding phenomenon elimination study at rokko test center (characteristics comparison of the reactor method and capacitor method)

Abstract: When a certain part of the utility grid, with substantial number of interconnected PVs, gets cut off from the grid islanding phenomenon may occur. There are two ways to suppress the islanding phenomenon, one of them is performed on the utility side, the other one on the PV side. On the utility side the reactor insertion method and the capacitor insertion method are advocated. The islanding phenomenon suppression characteristics of these two methods are compared in tests. Further, it is proved that the process, leading to the suppression of islanding phenomena, can be described in general power supply theory.