Showing papers on "Islanding published in 1991"

Method for preventing islanding phenomenon on utility grid with a number of small scale PV systems

Abstract: Tests and a study for preventing the islanding phenomenon have been conducted. Several islanding methods applicable to both PV power systems and utility grids were designed, and the validity of those methods is being evaluated. As a result, the validity of the harmonic voltage monitoring method was demonstrated. The power output variation method is also likely to be applicable. As for a prevention method applied to a utility grid, the validity of the method of unbalancing reactive power by connecting a capacitor load to the grid on islanding was confirmed. Results of demonstration tests for prevention of the islanding phenomenon are described. >

Digital modeling of an induction generator

Abstract: An induction generator mathematical model in the arbitrary reference frame is presented. With this model, short circuits, lines open at the terminals of an induction generator connected to an infinite bus are simulated. The transformed equations, especially the constraints for lines open for an induction generator with the neutral grounded through an impedance, are derived for the first time. The simulation results revealed some unknown transient characteristics of the small induction generator, such as the stator frequency following the rotor speed quickly during islanding, the nonfaulted phase current is larger than the faulted phase current for a line-to-line fault, and moderately large nonthree phase short circuit currents are sustained. These not only show that the conventional method for short circuit current calculation is not valid for small induction generators, but also suggest a scheme of protecting induction generators, including islanding, using only the local intelligence. >

The parallel operation of generating plant within a regional electricity company's distribution network

Abstract: The Energy Act (1983) established a right for persons or companies to use the public electricity supply systems to transmit energy from one location to another or to third parties. The publishing in October 1988 of the revised Electricity Supply Regulations set out the statutory requirements for those wishing to operate private generating plant. This has led to a considerable increase in generation embedded in distribution networks ranging in size from about 15 kW to 10 MW or more. Connections can be at a voltage level ranging from 1 V through to 33 kV or even 132 kV and typical energy sources used are water, waste heat from chemical processes, combined heat and power units and gas from refuse disposal plant or tips. The author addresses the effect of the growing numbers and sizes of relatively small embedded generators on the operation and performance of distribution networks. The author concentrates on technical issues and not on the regulatory or operational procedures. The issues discussed include voltage regulation, fault currents, islanding, system stability, earthing and protection of the interface between the network and embedded generator.

Prevention of Islanding Operation in Utility Interactive Photovoltaic Systems

Abstract: A new method to prevent the islanding mode of utility interactive inverters has been introduced. By properly choosing the inverter feedback control loop construction and parameters, the inverter frequency can be moved out of the limit after the islanding occurs. The reason to cause the inverter frequency response changing has been discussed in some detail.