Hitomi Otoguro

Digital fault location for parallel double-circuit multi-terminal transmission lines

Two new methods are proposed for fault point location in parallel double-circuit multi-terminal transmission lines by using voltages and currents information from CCVTs and CTs at all terminal. These algorithms take advantage of the fact that the sum of currents flowing into a fault section equals the sum of the currents at all terminals. Algorithm 1 employs an impedance calculation and algorithm 2 employs the current diversion ratio method. Computer simulations are carried out and applications of the proposed methods are discussed. Both algorithms can be applied to all types of fault such as phase-to-ground and phase-to-phase faults. As one equation can be used for all types of fault, classification of fault types and selection of faulted phase are not required. Phase components of the line impedance are used directly, so compensation of unbalanced line impedance is not required.

Influence of fault arc characteristics on the accuracy of digital fault locators

This paper proposes a time domain model of a fault locator with special reference to fault are nonlinearities by applying the MODELS language of the EMTP. It has been found that an impedance relay type locator is significantly influenced by the fault arc nonlinearities, while the current diversion ratio method is not influenced. This validates the advantage of the current diversion approach over the impedance approach.

An influence of voltage sag duration on nonutility generator's shaft torque

An influence of the voltage sag magnitude and duration on nonutility generators mechanical shaft torque is investigated by simulations using the Electromagnetic Transients Program (ATP-EMTP). Various types of fault are simulated, changing the fault point, the number of faulted phases and the voltage phase angle at the moment of fault occurring. From the simulation results, it becomes clear that the high-speed static switchgear is effective for the stable operation of the in-house generation systems and the critical loads, which are subjected to the voltage sag.

Digital fault location for high resistance grounded transmission lines

This paper demonstrates that the presence of multiple load taps cannot be neglected for single-phase-to-ground fault location. A new method has been developed taking this into consideration, that can be applied to correct the location error due to intermediate power sources. Then fault location methods for parallel double-circuit two-terminal transmission lines are discussed. Finally, a new fault location method is proposed for high-resistance grounded double-circuit transmission lines with three terminals.

Fault locator simulation using MODELS language

In this paper, a time domain model of a fault locator is represented using the MODELS language in the ATP version of EMTP. The fault locator model consists of five parts: input analog filter; sampling hold and digital filters; magnitude and phase calculation; fault locating algorithm; and statistical output procedure. Using different simulation cases, various fault types are modeled, considering the fault resistance to be constant or nonlinear and then considering the input device error. The calculated results are presented and discussed, and confirm the validity of representing the fault locator in a time domain simulation using MODELS.

An influence of voltage sag on nonutility generator shaft torque

An influence of the voltage sag on the shaft torque of the nonutility generator connecting to the utility system is investigated. During the oscillation of the generator electromagnetic torque, the mechanical shaft torque also oscillates according to the mechanical oscillation modes. In this situation, the shaft might be damaged. Three phase voltage sags are simulated by using ATP-EMTP, changing the fault point impedance and the short-circuit impedance of the utility system while the transformer impedance and the generator parameters are kept constant. The state equation of the generator mechanical system is investigated by using MATLAB/SIMULINK. Numerical simulation results show that the waveform of the electromagnetic torque is influenced not only by the fault point impedance but also by the short circuit impedance of the utility system, and thus a special condition of both impedances, in which the shaft torque has a maximum amplitude, could be found.

A study on overvoltages in wind tower due to direct lightning stroke

Lightning is one of the most serious problems for a wind turbine generator system. Direct lightning strokes to wind turbine generator systems sometimes cause serious damages. Power apparatuses and instruments in a wind tower as well as blades must be protected from the lightning from economical point of view. This paper discusses lightning overvoltages in apparatuses in a wind tower for direct lightning stroke to the tower. Simulations are carried out using the EMTP for such parameters as peak value of lightning current and grounding condition of metallic sheath of power cables in the tower.