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Owing to several advantages over traditional phase shifters, applications of hexagonal phase-shifting transformers (PSTs) keep expanding. These transformers are built with unique connections of their windings, neither delta nor wye. Modeling and protection methods are not yet fully established for hexagonal phase shifters. This work is divided in two parts. In Part I, a digital model of a hexagonal PST has been developed and validated. This part presents protection techniques for hexagonal PSTs. Several novel protection schemes have been developed based on ampere-turn balance equations of a hexagonal PST. These schemes include linear and nonlinear current-based protection methods, a power-based technique, and a phase comparison method. Protection schemes that require position of the tap changer for maximum sensitivity as well as a method to work without this extra information are presented. The developed techniques have been validated with digital and physical made-to-scale transformer models, and implemented on a general-purpose microprocessor-based relay platform. This material is of value to protection engineers facing the problem of protecting hexagonal PSTs. Index Terms--Differential power protection, differential protection, hexagonal winding connection, phase comparison protection, phase shifting transformer (PST), short-circuit protection.

Owing to several advantages over traditional phase shifters, applications of hexagonal phase-shifting transformers (PSTs) keep expanding. These transformers are built with unique connections of their windings, neither delta nor wye. Short-circuit modeling and analysis methods are not yet fully established for hexagonal phase shifters. This work is divided into two parts. In this part, a digital model of a hexagonal PST is developed and validated. This original material is of assistance when performing short-circuit system studies, relay setting calculations, as well as when modeling internal faults and developing protection techniques for the transformer itself. This paper explains construction of hexagonal PSTs, deriving their sequence impedances under varying taps and compares the model with manufacturer test data and a physical made-to-scale model developed specifically for this study. The transient model introduced in this paper can easily be integrated into the commonly used Alternate Transients Program and real-time digital simulator modeling environments. Part H of this work presents original protection methods for hexagonal PSTs. Index Terms--Hexagonal winding connection, phase-shifting transformer (PST), short-circuit studies, transient simulation.

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. Index Terms--Alternate Transients Program (ATP)-Electromagnetic Transients Program (EMTP), current differential relay, fault location, simulation, synchronized phasor measurement, three-terminal line.

This paper deals with the postfault analysis of the operation of distance protective relays from the line terminals. The signals of the digital distance relays are processed in the offline regime with the aim of evaluating the particular relay operation case. First, the program enables imitating the fault-loop impedance measurements of the distance relays. Second, the two-end unsynchronized measurements of the relays are considered. The unknown synchronization angle is determined by using the developed noniterative procedure. Then, the distance to fault is calculated. It is applied for calculating the actual values of impedance for the line sections. Comparing the results of these two ways performs analysis of operation of the relays under resistive fault cases. The described postfault analysis algorithm has been tested with the fault data obtained from versatile Alternative Transients Program-Electromagnetic Transients Program simulations. The examples are reported and discussed. Index Terms--Algorithms, distance protection, fault analysis, power transmission line, simulation, two-end measurement.

This paper presents a new algorithm for locating faults on two-terminal power transmission lines. Unsynchronized two-end voltages and currents are processed for determining the sought distance to fault and the synchronization angle. The calculations are performed initially for the lumped model of a transmission line. Then, these results are used as the initial data for the Newton--Raphson method-based iterative calculations, in which the distributed parameter line model is utilized. The delivered fault location algorithm has been tested and evaluated with the fault data obtained from versatile ATP-EMTP simulations. The sample results of the evaluation are reported and discussed. Index Terms--ATP-EMTP, fault location, simulation, transmission line, two-end unsynchronized phasor measurement.

One of the important operational conditions of a single-circuit ultra-high-voltage transmission line is the power transmission by two phases during the clearance of a temporary single-phase short circuit. Such a condition may be sustained for an interval of 1 s without losing the dynamic stability of the system. The influence of the arc on the single-phase reclosing time of an ultra-high-voltage power transmission line is investigated on the basis of the primary and the secondary arc models incorporated into the transient program EMTP. The validity of the models used is proven by comparison with field test results on an actual 1150-kV power transmission line from Ekibastuz to Kokchetav in Northern Kazakhstan. The processes of this power transmission in the 'dead time' of the single-phase reclosing cycle arc simulated. It is shown in the paper that simplified short-circuit simulation without the incorporation of the dynamic arc model leads to erroneous results. Mathematical analysis and field experiments show that natural secondary arc extinguishing in a highly compensated 1150-kV power transmission line cannot be reached in a reasonable time (e.g., less than 1 s). It is shown in the paper that this problem can be solved by automatic phase shunting (APS) of the faulted phase. Index Terms--Arc discharges, modeling, reclosing devices, transient analysis, UHV transmission.

This paper presents a new first zone algorithm for distance protection of series compensated lines. The algorithm detects faults with the reach of 75-85% of the line length by measuring two distinctive impedances, using three adequate regions on the impedance plane and applying appropriate logic functions. The algorithm estimates instantaneous values of the voltage drop across the series capacitors on-line, and compensates for this signal when calculating the impedance valid for faults behind the series capacitors. The other impedance (without compensation) is calculated for faults in front of the series capacitors. An explicit selecting procedure for the two impedances is not required since the presented relaying method asserts directly the fault within or outside the first zone. The algorithm is presented in detail and extensively tested using the EMTP model of a 400 kV 300 km transmission line. The enclosed results demonstrate high speed, dependability and security of the new algorithm. Index Terms--Distance protection, first zone element, numerical relaying, series compensated line.

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