Update：6/18/2021
Promote Fair, Equitable and Efficient Use of Transmission/Distribution Facilities
Streamline the fair usage environment of electricity systems in Japan by formulating guidelines on transmission/distribution operations,accepting system impact studies, and managing use of interconnection lines.
Formulate rules for all electricity companies to comply
OCCTO formulated the Network Codes, a set of rules to be followed by transmission operators and users in accordance with the Electricity Business Act and revises these guidelines where necessary in an effort to ensure the proper and smooth operations of consigned supply operations and operations pertaining to the transmission and distribution of electricity.
Reviewing the method by which interconnection lines are used
Considering the deliberation results of the System Review Working Group o n Electricity and Gas Basic Policy Subcommittee (3rd), as well as from the viewpoint of utilizing fair and equitable and efficient use of interconnection lines and developing a market environment, OCCTO changed the interconnection lines u sage method to “implicit auction ” in October 2018.
Accept system impact studies of generation facilities
OCCTO will accept applications for preliminary consultations and system impact studies from those who wish to connect power generation facilities to the network and verify the results of studies conducted by general transmission and distribution companies. A collective study process for generator connection led by general transmission and distribution companies was begun in October 2020 as a mechanism for systematically developing the network with a push-type approach that takes future power supply potential into account.
Make efforts to maximize utilization of existing network
Against the background of progress in electricity liberalization and the Feed-in Tariff Scheme (FIT Scheme) of renewable energy, power stations with variable renewable energy such as photovoltaic as well as projects to build new thermal power stations are increasing and the needs of interconnection for new power sources are expanding.
In formulating a long-term policy on cross-regional network, OCCTO decided to aim to facilitate and render more affordable use of the electric power network by maximizing the use of the existing network in light of these environmental changes. To this end, OCCTO has been conducting “Probabilistic evaluation of power flow” *1 and engaged in connect and manage efforts (N-1 inter-tripping scheme and non-firm access connections). Further, we continue studying new network operation rules such as re-dispatching method*2.
*1 Probabilistic evaluation of power flow is a methodology to increase available transmission capacity by assumed power flow given the actual situation and assessing network, such as by reviewing practical output based on historical data of variable renewable energy and by practical generator dispatches in accordance with demand (applied on April 2018)
*2 Re-dispatching method is a methodology to manage congestion which general transmission and distribution company implement utilizing balancing capacity when it judges that congestion of network occurs, or likely to occur, without specifying congested line.
Japanese Connect and Manage
N-1 Inter-Trip scheme
In Japan, from the viewpoint of network reliability, etc., power system development is conducted to secure stable and adequate transfer capacity even if an N-1 contingency (e.g. single line fault) occurs. N-1 Inter-trip scheme is a measure to utilize this capacity under no contingency situation by inter-tripping a generator when N-1 contingency occurs (curtailment of the generator output immediately with the relay system).
The N-1 inter-tripping scheme began to be applied to new power sources to be connected to a special high-voltage network in October 2018 (prior application). System design work is being carried out to enable the N-1 inter-tripping scheme to be applicable to new power sources to be connected to the high-voltage network sometime during fiscal year 2022
Non-firm access
A non-firm access connection is an initiative to enable new power sources to come online and be operated within the scope of available capacity without having to increase facilities on the assumption that output curtailment will be implemented if operational capacity is expected to be exceeded during normal times. In January 2021, it became possible to apply a non-firm access connection to a backbone grid network in any area lacking available capacity. We will also look into applying non-firm access connections to local grid networks.
