Yoshibumi Yamagata

Development of optical current transformers and application to fault location systems for substations

The authors report on an optical current transformer (CT) based on the principle of the Faraday effect. The information measured by the optical CT is transmitted to the ground side through optical fibers contained in an insulator. An application of the optical CT, a new fault location system, is described. >

Study on a field data of secondary arc extinction time for large-sized transmission lines

Secondary arc extinction time is an important factor, which influences system stability because it directly affects the reclosing time. However, few reports exist on a field data of the secondary arc extinction time on transmission lines. This paper describes the investigation results of secondary arc extinction characteristics by analyzing voltage wave shapes during the lightning faults on 550 kV transmission lines. Recovery voltages and secondary arc currents on each transmission line during faults were calculated to consider correlation with the secondary arc extinction time. The secondary arc extinction time is estimated by the existing formula, the secondary arc current and the recovery voltage required for one second reclosing are evaluated.

Very fast transients in 1000 kV gas insulated switchgear

For 1000 kV transmission system, disconnecting switches (DSs) fitted with resistors and high-speed grounding switches (HSGSs) were developed. At the UHV Equipment Test site, DS surge and HSGS closing surge tests were conducted. Then, the very fast transient overvoltage (VFTO) controlling performance of the DS and the surge voltage level due to HSGS closing were confirmed. In the same tests, the surge level transferred into the protecting and controlling components were confirmed to be low enough for them to operate properly. The transferring mechanism was clarified by an electromagnetic wave propagation analysis.

Study on Transient Recovery Voltages for Transformer-Limited Faults

Severe transient recovery voltage (TRV) after current interruption may appear when a fault occurs in the immediate vicinity of a power transformer without any appreciable capacitance between the transformer and the circuit breaker. These faults are called transformer-limited faults (TLFs), that may cause higher rate of rise of TRV than the standard values specified for terminal fault test duties T10 and T30 of IEC 62271-100 and IEEE standard C37.06. TRVs for TLF conditions with large capacity and high-voltage shell-type power transformer were measured by the capacitor current injection method. The impedance frequency response were also measured by the frequency-response analysis (FRA) and then TRVs were reproduced by the simplified transformer model with a series connection of parallel circuit of inductance, capacitance, and resistance evaluated by the FRA measurements. The reproduced TRV showed good agreement with the measured TRV even though deformation from a sinusoidal waveshape was observed due to superposition of higher frequency components on the TRV.

Measurement and computation of transient recovery voltage of transformer limited fault in 525kV–1500MVA three-phase transformer

Transient recovery voltage (TRV) in a 525kV-1500 MVA transformer of the three-phase-in-one-tank type was measured. It was proved that TRV can be measured by interrupting the current generated by discharging a capacitor of low voltage through the transformer. The current was interrupted at its zero point by a semiconductor diode at a low voltage. To compute the TRV, a transformer equivalent model composed of an L-C multi-mesh circuit was developed. The TRV waveform computed using the transformer equivalent model agreed well with the measured TRV waveform. The difference among the TRV of the first, second and third pole interruption was explained by the computation with the circuits of symmetrical component method. The transformer inductance that determines the TRV did not have frequency dependency up to the rage of about 20 kHz of the TRV frequency.

Field tests on current carrying performances of 1000 kV GIS

Field tests on 1000 kV (UHV) gas insulated switchgear (GIS) substation equipment have been conducted. This paper presents mainly the results of a temperature rise test which demonstrates the mechanical reliability of the GIS. The specified value of induced current of the enclosure and shunt bars among phases is set as much as 100% of rated normal current. The average temperature of four points defined on GIS enclosure surface is adopted as the base temperature for evaluation of thermal expansion and thermal stress of the enclosure. The limit of temperature rise for the GIS enclosure is as high as 65 K according to the revised specification.

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.