A. Makinen

A practical approach for estimating future outage costs in power distribution networks

Quantitative reliability analysis is integrated as a part of a distribution network information and design system. The outage rates, outage durations and costs of outages are evaluated using the data included in the network database together with the reliability data for network components and the per unit values for the energy not supplied. Using the reliability calculation program together with other programs, optimum development plans for each network can be studied. In these studies, both the technical restrictions and the total costs, including the costs of investments, losses, and outages, must be included. >

An Anti-islanding protection method based on reactive power injection and ROCOF

All distributed-generation units need to be equipped with an anti-islanding protection (AIP) scheme in order to avoid unintentional islanding. Unfortunately, most AIP methods fail to detect islanding if the demand in the islanded circuit matches the production in the island. Another concern is that many active AIP schemes cause power-quality problems. This paper proposes an AIP method which is based on the combination of a reactive power versus frequency droop and rate of change of frequency (ROCOF). The method is designed so that the injection of reactive power is of minor scale during normal operating conditions. Yet, the method can rapidly detect islanding which is verified by PSCAD/EMTDC simulations.

Power hardware in-the-loop laboratory test environment for small scale wind turbine prototype

This paper presents power hardware-in-the-loop (PHIL) laboratory test environment for wind turbine (WT) prototype. The environment utilizes dSPACE and RTDS real time simulators, converter controlled grid emulator (GE) and the prototype. The analysis is carried out using frequency response measurements. The main contribution is the detailed analysis of the grid emulator performance. The main performance limitations are revealed and it is shown that the performance of the GE is dependent on the hardware of the WT prototype in addition to the design of the emulator itself. The comparison of the operation of the GE with open loop and closed loop control modes is carried out. It is shown that the accuracy of the environment is clearly sufficient for symmetrical voltage dips when closed loop control system is used. However, the open loop controlled GE cannot execute correct point of common coupling voltages independent on the operation point of the WT which is relative to the wind conditions. If the GE is controlled at open loop or at closed loop, the network asymmetrical voltage dips are not generated accurately. The reason is that the system bandwidth is not wide enough to execute negative sequence 50 Hz component without gain and phase error. However, the accuracy of the PHIL environment is clearly enough for testing the operation of WT control functionalities under asymmetrical network voltages. These functionalities may include PCC voltage balancing or positive sequence reactive power injection.

Influence of DFIG reactive current injection during a voltage dip on the operation of wind turbine circuit breaker

This paper deals with an issue that has not received much attention in literature. The aim of the study is to investigate the influence of doubly fed induction generator (DFIG) reactive current injection during a voltage dip on the operation of a wind turbine circuit breaker. The study is done using a novel hardware-in-the-loop test environment constructed using two real time simulators (dSPACE and RTDS) and commercial protection relay. It is found in this study that the reactive current injection enhances the operation of wind turbine protection since the zero crossing of the circuit breaker currents is achieved earlier. This action may prevent from failed auto reclosing and other safety hazards.