Yilmaz Yelgin

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.

Novel impedance determination method for phase-to-phase loops

In this paper a novel impedance determination method for the phase-to-phase loops is described. This approach promises a better accuracy of the reactance calculation of the faulty loops. Thus, better selectivity and security in operation of the distance element applied for the protection of transmission and distribution lines is guaranteed. Moreover, with this new method the separation of the fault resistance from load condition is achieved. Due to this fact, special measures for load encroachment are not necessary. It contributes to simplification of distance protection settings.

Adaptive autoreclosure to increase system stability and reduce stress to circuit breakers

Automatic reclosure is a key element in the concept of self-healing grids. According to statistics, a large amount of faults in transmission and distribution networks are temporary faults. These faults disappear a certain time after deenergization of the faulted sections of the network. Automatic reclosure is used to recover the original status of the network without any human interaction. Automatic reclosure can be done as a three pole autoreclosure or a single pole autoreclosure. During a three pole autoreclosure the line will be de-energized completely for all three phases even for a single phase to ground fault. A single pole autoreclosure only de-energizes the faulted phase of a single phase to ground fault. Single pole autoreclosure increases the system stability because during the single pole dead time energy can be transmitted through the two healthy phases. Another advantage is that a single pole autoreclosure does not require a synchrocheck before reclosing because both ends of the line are still synchronized through the two healthy phases. If the voltage transformers are located on the line side of the circuit breaker, autoreclosure with an adaptive dead time can be used. In this case autoreclosure with a fixed dead time is executed at one end of the line only. The other end only gives a close command to the breaker if the voltage measurements indicate that the line was successfully re-energized from the remote end. Otherwise if the fault persists the circuit breaker at this position is not reclosed and is not unnecessarily stressed as a result. Single pole autoreclosure can lead to the occurrence of a secondary arc. During the single pole dead time capacitive and inductive coupling induces a voltage into the open phase conductor and feeds the secondary arc. The success of the single pole autoreclosure depends on the extinction of this secondary arc. This paper reviews methods to detect the extinction of a secondary arc by monitoring the voltages based on a set of real faults that occured at a German TSO. If the secondary arc disappears, an auto reclose command will be issued. Thereby the dead time can be reduced. If a permanent fault occurs, auto reclosure will be blocked and a three pole trip will be initiated to reduce stress to the circuit breaker. Under extreme weather conditions line swinging can cause an increasing number of phase to phase faults. These faults are mostly flash-arcs between two wires. This paper also describes an approach used in Germany, Poland and Austria to clear such phase to phase faults without ground by the means of a single pole autoreclosure. Also in this case voltage measurements during the single pole dead time can predict whether or not a reclosure will be successful.

Accurate impedance based fault location algorithm using communication between protective relays

The reactance method with fault resistance separation has been developed in order to determine the impedance of a fault loop as precisely as possible in a transmission or distribution power system line. This method has commonly been used for impedance calculation in the 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. This research consists of an improvement in the calculation method using data from both the own and the remote end of the line. This approach uses a communication link 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 for an exact computation of the fault reactance and fault resistance. In this paper, the derivation of this novel approach, as well as the experimental results in a fault location application are presented.

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.

Power Swing during fault conditions - blackout analysis and avoidance

Power Swings are a major reason for many of the latest blackouts all around the world. Regardless of cause, once a system has a blackout it often needs several hours to re-establish the system. This has a huge economical impact and has to be prevented in a modern smart grid.