Yoshiharu Okumoto

An application of robust power system security to power system operation for high-penetration of PV

This paper proposes a method of analyzing the N-1 security under the circumstances of PV penetration. The concept of Robust Power System Security (RS) proposed by the authors is used to evaluate the N-1 security quantitatively. It is shown that (1) the relationship between PV penetration and the N-1 security results in a clear trade-off, (2) installation of storage batteries is effective to enhance the N-1 security and (3) power system operators will be able to monitor the N-1 security condition directly by visualizing the security regions gained from the concept of RS. The effectiveness of the proposed method is demonstrated through simulations using a three machine system.

Dynamic load dispatch for power system robust security against uncertainties

The rapid growth in the electricity demand and expansion of renewable energy (RE) generation are presenting serious challenges for the optimal network operation. The future perspective of the dramatic increase in renewable generation, such as wind and solar energy will lead to severe problems related to the load dispatch. Power system security is threatened due to increase in the uncertainties of RE outputs and the reduction of controllable resources. This paper investigates power system “robust security” in relation with the increase in the uncertainties and the decrease in system control ability. A new concept of robust security and its security regions is defined and then a new technique for real-time dynamic ELD is proposed. It is guaranteed secure operation in the security region and mitigating the irregularity associated with renewable power generation. Key issue is an effective treatment of uncertainties caused by RE forecast and an efficient solution for real-time management over the limited control resources of a power system. The flexible operational outcome of the proposed approach satisfies the economical requirements and reliability against uncertainties. The proposed method is also useful to investigate the limitation of RE under given ability of real-time generation control. Critical problems anticipated in the future are further investigated from the point of view of robust security concerned with the load dispatch. Robust security for West Japan system is also investigated from the present up to 2030 concerned with the transient stability.

A Method of Suppressing Fault Currents and Improving the Ground Level Electric Field in a Novel Six-Phase Power Transmission System

In this paper, it is shown that the maxnuma electric field under the six-phase line with a modified phase arrangement becomes as low as that under the three-phase double-circuit ( conventional ) line. Then, a method is proposed for limiting line-to-ground fault currents and short-circuit currents without causing the fall in unfaulted phase voltages in the six- phase system with its neutrals solidly grounded. The fault analysis and the experimental result demanstrate that for a single line-to-ground fault at the sending end, the fault current in the proposed system is half that in the conventional system. As for the three-phase short-circuit fault at the sending end, the fault current in the proposed system is about 60% of that in the conventional system. It is concluded that the proposed six-phase system is superior in the system transient stability to the conventional system.In this paper, it is shown that the maxnuma electric field under the six-phase line with a modified phase arrangement becomes as low as that under the three-phase double-circuit ( conventional ) line. Then, a method is proposed for limiting line-to-ground fault currents and short-circuit currents without causing the fall in unfaulted phase voltages in the six- phase system with its neutrals solidly grounded. The fault analysis and the experimental result demanstrate that for a single line-to-ground fault at the sending end, the fault current in the proposed system is half that in the conventional system. As for the three-phase short-circuit fault at the sending end, the fault current in the proposed system is about 60% of that in the conventional system. It is concluded that the proposed six-phase system is superior in the system transient stability to the conventional system.

A concept of Robust Power System Security and its application under renewable energy sources penetration

Penetration of large amount of renewable energy sources (RES) may introduce considerable uncertainties in power systems making difficult the planning and operation tasks. This paper proposes a new concept named “Robust Power System Security (RS)” in order to investigate power system security in the presence of uncertainties. RS region is defined as an area of power system operation in which the system is secure regardless of uncertainties in parameters such as RES outputs. When the size of the uncertainties is specified, RS region is identified. It is observed that the region tends to shrink and disappear as the uncertainty increases. Emerging problems concerned with security issues in future power systems are investigated. Simulations under large RES penetration are carried out using a three generators test system. Possible applications of the proposed concept toward real-time operation problems are discussed for keeping up the security.

Closure of dynamic load dispatch for power system robust security against uncertainties

We would like to thank the discussers for their valuable discussions. They raised an important issue concerned with the treatment of extreme perturbations of low probable scenarios. Therefore, we would like to discuss how the system security is achieved against such uncertainties in real power system. Hereof, our policy of risk management is presented.