Kazuhiro Horikoshi

Fault current limiter based on series active compensator

Series active compensator (SAC) is a custom compensator utilized in power distribution network, however, due to connected in series with distribution line then SAC would suffer from large current flows due to downstream faults. To limit the flow those fault currents and protect SAC itself as well, a fault current limiting (FCL) function is proposed. Fault current limiting function of SAC will be activated by protection system and then SAC will start injecting a series voltage to the line in such a way to limit fault current to an appropriate level. The contribution of this proposal is the utilization of signals from existing feeder protection system to activate and terminate the FCL. This control simplifies the structure of SAC because the extra build-in fault detection module is not required. Moreover, it will ensure proper coordination between SAC and existing protection systems. Other benefits could be the voltage sag mitigation effect for upstream buses in case fault occurs at downstream section.

An adapted control strategy for dynamic voltage restorer to work as series active power filter

This paper presents an adapted control strategy based on Instantaneous Power Theory for a conventional dynamic voltage restorer. By employing this control method the dynamic voltage restorer is inherently able to operate as a series active power filter to block the propagation of harmonic current from the power grid into the important load and vice versa. The advantage of the control algorithm is its ability to extract only harmonic component from supply current even this current is distorted and unbalanced. Numerical simulation results show that this control strategy not only enhances the utilization factor of the existing dynamic voltage restorer but also help the DVR to has a better performance in mitigating harmonics.

Experimental study on short circuit phenomena in air switch of distribution line due to lightning overvoltage on which one surge arrester of the three ones is omitted

We experimentally examined the possibility of the internal short circuit of an air switch due to the sparkover between different poles under the condition that no surge arrester exists in neighboring poles and one of three surge arresters is omitted at the pole with an air switch. Experiments at Shiobara Testing Yard and Akagi Testing Center of CRIEPI clarified the following. Fault current may flow via the grounding point of a pole with an air switch and that of the next pole on a different phase from grounded phase of the pole with an air switch. If the low-voltage wire, overhead ground wire or communication wire forms a short circuit between them, ultimately the air switch may burn out. Moreover Fault current continues even if the length of the short circuit between different poles is increased. Although the increase of the short-circuit length results in the increase of wire impedance, the amount of increase is still small compared with source impedance.

Phase loading balancing by shunt passive compensator

This paper presents a proposal to deal with imbalance phase loading phenomenon in power distribution system. Discrete switched passive shunt compensators are considered as the means to help balancing phase loading. Discrete switched passive compensator offers advantages in term of installation cost and simplifies the maintenance process. A new algorithm is developed to calculate the size of those compensators, this algorithm consists of the unbalance power flow calculation module and discrete optimal sizing module. In addition, the algorithm is written in MATLAB language and tested on actual data of a distribution feeder. All the tests have proven the effectiveness of the proposal and shown the advantages of proposal over others. Moreover, this proposal can be utilized as an useful tool for any electrical utilities.