Matthias Kereit

Proper detection and treatment of power swing to reduce the risk of blackouts

Any sudden load change in a power system, such as a fault, line switching etc. causes the systems generators to adjust to the new condition. In that case a power swing may occur. This paper describes a zero-setting power-swing detection method that is independent of network parameters. Power swing can be detected up to 10 Hz swing frequency, also during open pole condition and during asymmetrical operation. A blocking logic prevents unselective trips by the distance protection. For unstable power swings a flexible out of step tripping function will be proposed. The coordination of power swing detection, distance protection and out of step protection provides a reliable system protection. The risk of unwanted trips and cascading effects in the power system will be reduced.

Usage of phasor measurement units for industrial applications

The number of phasor measurement unit installation is growing, especially in Europe since a few years. The collected experience of installation requirements and operation conditions as well as their behavior provides much important information about the possible usage of these measurement devices in real power system applications already. Generally, the phasor measurement technology is used to montoring the high voltage level of the power system, especially transmission system already and/or sometimes distribution system as well. This paper describes the investigations made inside of the industrial network to provide the information about possible contribution of the PMUs in such power system operating area.

Experience with PMUs in industrial distribution networks

Phasor measurement units (PMUs) were installed in an industrial distribution network and synchronized measurements taken from the PMU at medium and low voltage during different system states were analyzed. Two cases of system operation were investigated, normal and abnormal operation. Results from up to six PMUs were compared and analyzed for each case.

Fault direction method in compensated network using the zero sequence active energy signal

In medium voltage distribution network, a coil might be placed in the transformer neutral to compensate the zero sequence capacitance of the network. This creates a zero sequence system with very high impedance fault. In case of single phase earth fault, the consequence is a very small faulty current which allows continuous operation even in faulty condition. Several protection devices exist to indicate the fault direction using the transient signal. A new method has been developed by computation of the zero sequence active energy signal to increase the sensitivity of the device regarding the fault impedance. The energy comes from the charging of the zero sequence capacitance of the sound feeder and the imperfection of the Petersen coil. This paper describes the phenomenon behind the algorithm of direction determination and followed by the explanation of the algorithm with simulation tests and recordings from a German DSO.

Automated test procedures for accuracy verification of Phasor Measurement Units

The continuous development of electric power systems characterized by an increasing potential of decentralized energy generation requires high precision measurement technologies for an effective and reliable network monitoring and system state assessment to ensure the high level of present and future security of energy supply. One possibility to capture system parameters, which has been established primarily within transmission networks, is the use of Phasor Measurement Units (PMU). Taking Smart Grid discussions into account, PMU usage in distribution systems, under particular conditions regarding observability aspects should also be considered [2]. The goal of this paper is to introduce the new requirements for PMU measurement accuracy testing according to IEEE standard C37.118.1 [1]. This publication focuses on two things: the development of automated procedures for a certified PMU test bench, and a way to extend an existing test concept according to the new testing regulations. Based on these investigations, exemplary and representative measurements, which were made with this automated test bench are presented and analyzed for one proposed static test scenario.

Analysis of High-Speed-Distance protection

The modern power system often operates at its performance limit. Therefore, uncontrolled events, e.g. short circuits, can quite rapidly cause thermal stress of system components as well as instability of the entire power system with the risk of longer energy interruption. In order to maintain the reliability and security of the power system at good level, the reaction to such undesirable events must be very quick. This task is undertaken by protection equipment. One such fast protection function is the High-Speed-Distance (HSD) line protection, which provides selective tripping of the line within half of the fundamental cycle after short circuit beginning. In this paper, the High-Speed-Distance protection function is systematic analyzed.

Precise impedance based fault location algorithm with fault resistance separation

The reactance method with fault resistance separation has been developed in order to determine as precisely as possible the impedance of a fault loop in a transmission or distribution power system line. This method has commonly been used for impedance calculation in case of a single phase-to-earth fault in diverse power system protection applications. New developments in this area have shown that the extension of the method to multi-phase faults is not only possible but also of practical relevance. However, all previous investigations focused on impedance calculation using data from one single side of the power system line. Due to missing data from the remote end, the determined impedance value can deviate from its real value. This research consists in an improvement of this calculation method using data from both the own and the remote line end. This approach uses communication between two measurement units e.g. protection relays, which have the advantage of not requiring a precise synchronization with each other. The additional time invariant parameters of the power system, acquired by each device and transferred to the remote end, allow an exact computation of the fault reactance and fault resistance. In this paper, the derivation of this novel approach as well as experimental results in a fault location application are presented.

Fault locator comparison tool and designer for distribution network

Fault location research in compensated network has led to several ideas; from the classic use of the steady state to the use of the charging transient. This paper treats the steady state signal and several algorithms to get the best accuracy for a specific feeder in this kind of network. A tool to compare the different algorithm is presented. Regarding the different topologies available in a distribution networks, the radial, the loop and distributed loads are compared and the sensitivity of each algorithm is computed using Monte Carlo simulations and linearization of the error. The algorithms studied use one or several measurements and can estimate the load consumption by using the pre fault signal. General conclusions are taken about the classic topology with the algorithms using steady state for fault location in compensated network.