Soji Kojima

Potential distributions of metal oxide surge arresters under various environmental conditions

A semi-analytical approach is proposed for potential distribution of metal-oxide surge arresters under normal condition. Conventional approaches like the finite-element method are also applicable. The authors suggest that the proposed method is more appropriate for a general approach; an analysis in combination with lumped constants of R, L and C is possible. Environmental conditions like pollution of snow-covering on the surface of insulators may disturb the potential distribution at normal condition. Potential distributions were experimentally measured in an artificial pollution test, naturally polluted and snow-covering conditions, whose major characteristics are shown. >

Transient impedance of GIS grounding grid

The transient impedance of a grounding grid for a commercial 550 kV gas-insulated substation (GIS) was measured on site using steep front currents with rise time from 100 ns to 2 /spl mu/s. From the measured results, it was found that the transient impedance of the measured grid for those currents is simulated by a series circuit with an inductance 1 /spl mu/H and a resistance 3 /spl Omega/. Applying the obtained impedance to the lightning surge analysis, it is pointed out that the grounding condition at an arrester tank end has a remarkable influence on the protecting performance of a surge arrester. >

Life Performance of Zinc-Oxide Elements Under DC Voltage

The voltage-current, watt loss, and characteristics of three kinds of ZnO elements were compared when subjected to ac and dc voltages.

Surge Discharge Capability and Thermal Stability of a Metal Oxide Surge Arrester

The surge discharge capability and the thermal stability of a metal oxide surge arrester were examined experimentally.

Lightning Surge Analysis in a Multi-Conductor System for Substation Insulation Design

Analysis of back flashover lightning surges coming into a substation is important to understanding of substation insulation co-ordination. These surges are usually analyzed for a single conductor system, but in this paper, they were analyzed with EMTP for a multi-conductor UHV system consisting of two ground wires and six phase conductors. It was clarified that lightning surge voltages on the phase conductor decreased due to negative reflection of the lightning surge at a tower, and the electrical coupling between the ground wire and phase conductor. The multi-conductor system was applied to surge analysis for the line entrance circuit of a gas insulated substation.

Temporary overvoltage duty of surge arresters in noneffectively grounded systems

Important characteristics of metal oxide surge arresters depend on the specified temporary overvoltage duty requirement due to the volt–ampere characteristics. However, there are few reports on the duty of surge arresters in noneffectively grounded systems. The temporary overvoltages of 1.43 pu proposed in effectively grounded systems is too low compared with nearly pu in a line-to-ground fault. The overvoltages due to a combination of a line-to-ground and load rejection, where not only the main power circuits but also control systems such as AVRs participate, is rare but probably the severest case. Here the overvoltage duty of surger arresters is clarified for various residual voltage levels and system conditions. The severest condition is that in a system including a cable line because of operation of the UEL of the AVR.

Development of an interrupting chamber for 1000-kV high-speed grounding switches

In Japan, construction of 1000 kV (UHV) transmission lines is planned in order to deal with the expected increase of electric power demand. On the line, after the fault current is interrupted by circuit breakers, the arc caused by electrostatic induction current remains for a long time because of its high voltage. To re-energize the fault line after arc extinction, a new circuit breaker reclosing system which has high-speed grounding switches (HSGS) installed at both ends of the line is employed. If, while the HSGS is interrupting an electromagnetic induction current, a ground fault takes place in another energized line, causing a shirt-circuit current including a dc component to flow, the large dc component is superimposed on the HSGS current, producing a zero shifting state with no passage through the zero point for long time. Such zero shifting durations are estimated to be up to about 80 ms. Therefore HSGS are required to interrupt this delayed zero current as a special duty. This requirement is met by a newly developed puffer interrupting chamber allowing a long pressure rise by optimizing the exhaust and residual volume of the puffer cylinder and utilizing the effect of pressure rise due to the arc.

Switching Surge Duty of Metal Oxide Surge Arresters in Multi-Phases' System and Its Equivalent Conditions in a Test

Switching surge duty test imposing the highest power dissipation on high voltage metal oxide arresters has usually been done with a single phase circuit due to the limit of test facilities, in spite of complex multi-phases in a service system. The purpose of this paper is to propose new equivalent line constants and reasonable conditions of charging voltage in a test circuit, which were derived from the application study of surge arresters on double circuits and transposed 500kV lines. So-called positive, negative, zero, self and mutual mode impedances are not equivalent. Other impedances must be used and some correctiorts for charging voltage are required in a transmission line discharge test.