Hans Ove Nielsen

Control and testing of a dynamic voltage restorer (DVR) at medium voltage level

The dynamic voltage restorer (DVR) has become popular as a cost effective solution for the protection of sensitive loads from voltage sags. Implementations of the DVR have been proposed at both a low voltage (LV) level, as well as a medium voltage (MV) level; and give an opportunity to protect high power sensitive loads from voltage sags. This paper reports practical test results obtained on a medium voltage (10 kV) level using a DVR at a distribution test facility in Kyndby, Denmark. The DVR was designed to protect a 400 kVA load from a 0.5 p.u. maximum voltage sag. The reported DVR verifies the use of a combined feed-forward and feed-back technique of the controller and it obtains both good transient and steady state responses. The effect of the DVR on the system is experimentally investigated under both faulted and nonfaulted system states, for a variety of linear and nonlinear loads. Variable duration voltage sags were created using a controllable LV breaker fed by a 630 kVA distribution transformer placed upstream of the sensitive load. The fault currents in excess of 12 kA were designed and created to obtain the required voltage sags.The dynamic voltage restorer (DVR) has become popular as a cost effective solution for the protection of sensitive loads from voltage sags. Implementations of the DVR have been proposed at both a low voltage (LV) level, as well as a medium voltage (MV) level; and give an opportunity to protect high power sensitive loads from voltage sags. This paper reports practical test results obtained on a medium voltage (10 kV) level using a DVR at a distribution test facility in Kyndby, Denmark. The DVR was designed to protect a 400-kVA load from a 0.5-p.u. maximum voltage sag. The reported DVR verifies the use of a combined feed-forward and feed-back technique of the controller and it obtains both good transient and steady-state responses. The effect of the DVR on the system is experimentally investigated under both faulted and nonfaulted system states, for a variety of linear and nonlinear loads. Variable duration voltage sags were created using a controllable LV breaker fed by a 630 kVA distribution transformer placed upstream of the sensitive load. The fault currents in excess of 12 kA were designed and created to obtain the required voltage sags. It is concluded the DVR works well in all operating conditions.

Control and test of dynamic voltage restorer on the medium voltage grid

Power quality problems like voltage dips and sags are presently important issues in the utilities. Major economic losses might appear at the customers due to those failures. This paper presents a power electronic device, which keeps voltage sags away from sensitive loads. It is a dynamic voltage restorer (DVR), which creates a series injection of voltage into the medium voltage grid. Energy storage is keeping the sensitive load running in a limited time. The design and a new control method of a DVR are explained in this paper. The DVR is also tested at medium voltage level (10 kV) and methods to initiate voltage dips are described and implemented. Different test results at 10 kV level show that the DVR keep the voltage to a sensitive load fixed in the case of voltage dips. Furthermore, it is also demonstrated that in the case of a transformer failure the system also works very fine.

Full scale earth fault experiments on 10 kV laboratory network with comparative measurements on conventional CTs and VTs

In this paper, the authors present a result of a full-scale earth fault test carried out on the 10 kV research/laboratory distribution network at Kyndbyvaerket Denmark in May 2001. The network is compensated through a Petersen-Coil and current and voltage measurements were measured on conventional current transformers (CTs) and voltage transformers (VTs) by an optical link. Comparison with a similar earlier performed experiment carried out autumn 1998, where current and voltage measurements were measured with high bandwidth Rogowski coils and high voltage Tektronix probes, gave remarkable results. The necessity of high bandwidth measurement equipment for earth fault measurements on compensated distribution networks can be undermined, since it will be shown that the transient signal transfer through conventional CTs and VTs for further signal analysis is sufficient. Caused by the inadequacy three phase conductor cable models in PSCDAD/EMTDC/sup /spl reg// V3, the simulations of the whole laboratory network shows more or less good identity with the measurements.

Optimization of the compensation of a meshed MV network by a modified Genetic Algorithm

This article discusses the utilization of a modified genetic algorithm (GA) for the optimization of the shunt compensation in meshed and radial MV distribution networks. The algorithm looks for minimum costs of the network power losses and minimum capital and operating costs of applied capacitors, all of this under limitations specified by a multicriteria penalization function. The parallel evolution branches in the GA are used for the purpose of the optimization acceleration. The application of this GA has been implemented in Matlab. The evaluation part of the GA implementation is based on the steady-state analysis using a linear one-line diagram model of a power network. The results of steady-state solution are compared with the results from the DIgSILENT Power Factory program. Its practical applicability is demonstrated on examples of 22 kV radial and meshed overhead distribution networks.