The recent progress of simulation techniques for the current interruption in high-voltage gas circuit breakers (GCBs). GCB is one of the key components for a stable supply of electricity in the electric power system. Japanese manufacturers have been kept technologically strong position with the highest voltage and current rating. The simulation techniques for current interruptions in GCB have contributed to their advancements. This paper reviews the simulations related to current interruption, including recent efforts to apply for the development of SF6-alternative GCBs.
Conventional synchronous generators have been replaced by renewable energy source such as photovoltaics generation and wind turbine generation interconnected through inverters. As the capacity of synchronous generators interconnected to the power system decrease, the power system stability can be gradually jeopardized. Therefore, these inverters may be required to have some control functions in grid-interconnection code to support power system stabilization. On the other hand, it is known that the response of some control functions become unstable and undesired oscillatory behavior appears depending on the power system conditions such as low short circuit ratio. In consequence, not only the expected power system stabilization is not obtained, but also the power quality may be degraded. In this paper, the mechanism of these instabilities is clarified by using a simplified root mean square model, and a damping controller applicable to grid-following (GFL) inverter is developed. It is shown that the damping of the oscillatory behavior could be improved by applying the proposed controller using eigenvalue analysis and time domain simulation. This contribution is useful for the appropriate operation of the control function installed to GFL inverter.
In order to improve the insulation diagnosis of C-GIS, we developed the four-terminal surface current sensor and the method to estimate an occurrence direction of partial discharges. In this method, the accuracy of the direction estimation is improved by referring only the direct wave, and the error caused by noise can be suppressed by calculating the outputs of four terminals. As the experimental result, it was confirmed that the detection characteristics of the sensor agreed well with the theoretical ones derived from the detection principle. Using the sensor and method, we have conducted the experiment to detect the surface current generated by PD occurred in a rectangular enclosure. As a result, it was confirmed that the occurrence direction could be estimated even for a rectangular enclosure. It was also found that the propagation attenuation of the surface current at the corners of the enclosure is large, and thus the installation position of the sensor needs to be optimized.
In order to protect electrical equipment from lightning, it is important to learn about the actual situation of electrical equipment damages due to lightning. We are continuously investigating lightning damage from 2011, and we conducted lightning damage field surveys 17 times (151 locations) in the Tohoku region. As a result of the investigation, we confirmed that 753 electrical equipment were damaged due to lightning in houses and enterprise places. The number of lightning damages on low-voltage equipment is more than high-voltage equipment, 668 low-voltage equipment such as telephones, televisions, water heaters, personal computers and lighting equipment were damaged due to lightning, accounting for about 85% of the total. In this paper, we described the actual situation and cases of lightning damage to low-voltage equipment, and also described the comparison with the past results of lightning damage investigations.
Quasi-two-dimensional magnetohydrodynamic (MHD) numerical simulation was conducted to clarify the power generation characteristics of a co-axial MHD energy conversion device under laminar flow. The numerical results were compared with one-dimensional theoretical results in the radial direction. For a fixed load resistance, the dependence of output power and efficiency on Hartmann number, which is proportional to the magnetic flux density, was investigated. We found the decrease in mean velocity and the increase in viscous wall shear stress owing to upper and lower walls, the increase in viscous wall shear stress owing to Taylor vortex cells, and the increase in Joule heating owing to eddy current in the MHD numerical simulation compared to those in the one-dimensional theoretical analysis.
Lightning current to a radar tower near the coast of the Sea of Japan has been observed since 2014. Positive current pulses exceeding +140kA and negative single pulses exceeding -30kA were observed. The characteristics of the current pulses are different from those of ordinary return strokes. Based on the observation of lightning current and electric field, their sources are inferred to be current pulses travelling down paths of upward leaders associated with upward lightning. This result validates the electromagnetic model of high current pulses associated with upward lightning.