Marek Fulczyk

Accurate Noniterative Fault-Location Algorithm Utilizing Two-End Unsynchronized Measurements

This paper presents a new two-terminal impedance-based fault-location algorithm, which takes into account the distributed parameter line model. The algorithm utilizes unsynchronized measurements of voltages and currents from two ends of a line and is formulated in terms of the fundamental frequency phasors of symmetrical components of the measured signals. First, an analytical synchronization of the unsynchronized measurements is performed with use of the determined synchronization operator. Then, the distance to fault is calculated as for the synchronized measurements. Simultaneous usage of two kinds of symmetrical components for determining the synchronization operator makes that the calculations are simple, noniterative, and at the same time highly accurate. The developed fault-location algorithm has been thoroughly tested using signals of Alternate Transients Program-Electromagnetic Transients Program versatile simulations of faults on a transmission line. The presented evaluation shows the validity of the developed fault-location algorithm and its high accuracy.

A Fault-Location Method for Application With Current Differential Relays of Three-Terminal Lines

This paper presents a new method for locating faults on three-terminal power lines. Estimation of a distance to fault and indication of a faulted section is performed using three-phase current from all three terminals and additionally three-phase voltage from the terminal at which a fault locator is installed. Such a set of synchronized measurements has been taken into consideration with the aim of developing a fault-location algorithm for applications with current differential relays of three-terminal lines. The delivered fault-location algorithm consists of three subroutines designated for locating faults within particular line sections and a procedure for indicating the faulted line section. Testing and evaluation of the algorithm has been performed with fault data obtained from versatile Alternate Transients Program-Electromagnetic Transients Program simulations. The sample results of the evaluation are reported and discussed.

Mitigating Ferroresonance in Voltage Transformers in Ungrounded MV Networks

In this paper, it is shown that ferroresonant oscillations involving voltage transformers (VTs) may be initiated by switching transients in ungrounded medium-voltage networks. It was demonstrated that various modes of ferroresonant oscillations may exist for the same VT type depending on the initial conditions and on the network capacitance. As the ferroresonant oscillations pose a risk to the VTs due to large overcurrents in the primary windings, the VTs operating in ungrounded networks should be protected against this phenomenon. The analysis of the classic method of protecting the VTs by means of connecting the damping resistor to the open-delta-arranged auxiliary winding has shown that often a very low ohmic value of the resistor is required to provide reliable protection. A new method of protecting the VTs against ferroresonance with a compact active load was thus developed.

Fault Location on Double-Circuit Series-Compensated Lines Using Two-End Unsynchronized Measurements

This paper presents an accurate fault-location algorithm for double-circuit series-compensated lines. Use of two-end current and voltage signals is taken into account and a more general case of unsynchronized measurements is studied. Different options for analytical synchronization of the measurements are considered. The algorithm applies two subroutines, designated for locating faults on particular line sections, and in addition, the procedure for selecting the valid subroutine. The subroutines are formulated with the use of the generalized fault-loop model, leading to compact formulas. Consideration of the distributed parameter line model ensures high accuracy of the fault location. The proposed selection procedure allows for reliable selection of the valid subroutine. The developed fault-location algorithm has been thoroughly tested using signals taken from Alternate Transients Program-Electromagnetic Transients Program versatile simulations of faults on a double-circuit series-compensated transmission line. The presented fault-location evaluation shows the validity of the derived fault-location algorithm and its high accuracy.

Two-end unsynchronized fault location algorithm for double-circuit series compensated lines

This paper presents an accurate fault location algorithm for double-circuit series compensated lines. Use of two-end current and voltage signals with taken into account a more general case of unsynchronized measurements is studied. Different options for analytical synchronization of the measurements are considered. The algorithm applies two subroutines, designated for locating faults on particular line sections, and the procedure for selecting the valid subroutine. The subroutines are formulated with use of the generalized fault loop model, leading to compact formulae. Taking into account the distributed parameter line model assures high accuracy of fault location. Application of the proposed selection procedure allows for reliable selection of the valid subroutine. The developed fault location algorithm has been thoroughly tested using signals taken from ATP-EMTP versatile simulations of faults on a double-circuit series compensated transmission line. The presented fault location example shows the validity of the derived fault location algorithm and its high accuracy.

Using bus impedance and bus P-Q curve for voltage stability control

Voltage control and voltage stability problems are not new in the operation of electric power networks but are now receiving special attention in many countries because of a greater need for improving efficiency of usage of transmission capacity in the competitive electric energy market. Practically, the idea of P-V and Q-V curves is used to determine the maximal reactive margin at load buses to avoid voltage collapse. In this paper, the idea of bus P-Q curve is proposed for the assessment of such a reactive margin. The P-Q curve for bus load is created on the basis of bus impedance. To assess on-line the bus voltage stability margin the measurements of the bus voltage and bus current are needed. First of all, the mathematical background of the proposed idea is given. Then numerical analysis of the example power system is presented. The bus reactive margins calculated on the basis of the bus impedance are compared with the relevant margins obtained from Q-V curve.

Wind Turbine Transformers Protection Method Against High-Frequency Transients

A new wind turbine transformers protection method against high du/dt switching transients taking place during a wind turbine operation is described. High-frequency transients, characterized by a high rate of voltage rise (du/dt) and overvoltage at the wind turbine transformer high-voltage terminals may be a result of operations of the turbine switchgear typically comprising a vacuum circuit breaker. The protection concept described in this paper is a follow up of research activities on a transients suppressing method dedicated for distribution transformers. The principle of operation of the protective device proposed and parameters optimization procedures for windmill transformers are provided in this paper. The performance of the device was verified by means of Alternative Transients Program-Electromagnetic Transients Program simulations. The physical device was built and experimentally verified by full-scale functional tests reflecting a real wind turbine power network.

Centralized substation level protection for determination of faulty feeder in distribution network

This paper presents a novel approach to design of a centralized substation level protection aimed at determining the faulty feeder in a distribution network. In opposite to phase-to-ground faults in the transmission networks (HV), impedance of phase-to-ground fault-loops in MV distribution networks is usually high. From all of these reasons, detection of ground-fault and determination of a faulty feeder at a bus-bar with many outgoing feeders arises as serious problem. However, during the ground-fault the transient component which provides important information about the disturbance in the system appears. Such signals consist of different frequency components, which result from charging or discharging of the network capacitances. In this paper new approach which is based on checking a phase displacement between a fundamental frequency component of zero sequence current and a voltage directly after the fault inception is presented. Provided simulation experiments in ATP/EMTP software package confirm the effectiveness of the proposed technique for selection of a faulty feeder during phase-to-ground fault in different and under different fault scenarios-different fault inception angles, including random mechanism and high resistance faults.

SmartChoke - protecting power equipment from fast transients

Fast transients in power systems can damage cables, motors, transformers, instrument transformers, reactors, and other equipment in both distribution and transmission networks. They are generated not only by lightning, but also by system switching operations or even by power electronics. As discovered more recently, the interaction between devices with specific high- frequency characteristics can lead to abnormal and harmful surges with steep fronts and high frequency components. Often, the existing means of surge protection, like surge capacitors, ZnO arresters, and even RC snubbers are not sufficient or are too cumbersome to be installed effectively against these surges. SmartChoke is a new type of device that can provide a better way of protecting the system. This paper presents some experimental verifications of the effectiveness of the device. Subsequent publications will also describe the device technology and more detailed application examples in the distribution networks.

New approach towards protecting electrical equipment insulation systems against Very Fast Transients

Very high frequency components in the power networks may result from events such as lightning surges and switching or fault transients. Such transients can destroy motors, transformers and other electrical equipment due internal resonant phenomena resulting in local amplification of voltage. Overstressing the insulation system reduces significantly the equipment lifetime and often leads to internal short-circuit. At very high frequencies wave propagation phenomena must be taken into account and thus wave impedance matching between particular components becomes important. The use of low-loss cables of wave impedance not matching the impedance of the equipment results in wave reflections generating repetitive HF overvoltages. A typical method of protecting the equipment against very fast transient (VFT) phenomena is the use of surge capacitors or RC-snubbers. The size and cost of installation of these devices are significant and thus they are rarely used in practice, especially for protecting MV equipment. In the present article a new approach towards suppressing VFTs with the use of compact series impedance element combined with a dedicated surge capacitor is presented. The approach developed enables one to construct a compact protective device introducing a series impedance already at significantly lower frequencies. The device is particularly suitable for protecting transformers connected to low loss cable lines with the use of a vacuum circuit breaker (VCB).