IEEE Power & Energy Magazine - March/April 2021 - 77

Overload Detector

The overload detector has a specification that enables it to
minimize the number of intertripping generators by intertripping an appropriate amount of power output based on
the extent of overload. The number of systems for overload
detection is determined by the degree of importance of the
target facility (e.g., a bulk power system needs two systems,
a regular use plus a spare).
Communication Device and Communication Route

The telecommunication system and number of routes of the communication lines are determined by the degree of importance of
the target facility (e.g., bulk power system) and the installation
environment (e.g., mountain area, remote area, and so on).
Controlling Device

The control device receives data from the overload detector
and needs to be able to ensure reliable control. Since the controlling devices belong to the generation entities, the maintenance (including expenses) of the devices falls under their
responsibility.

A Demonstration Case Study for the
N−1 Intertrip Scheme
Table 4 displays the result of a demonstration case study
made for the power system illustrated in Figure 6 to examine
the effect of the N−1 intertrip scheme. Operational capacity is expanded by the implementation of the N−1 intertrip
scheme, and transmission bottlenecks are eliminated.

The assumptions in the case study analysis are as follows:
✔ The N−1 intertrip scheme is applied to the bulk power system, which is radial, considering the impact on reliability.
✔ The maximum intertripping amount by the N−1 intertrip scheme allowed for a single transmission line
is 500 MW.
✔ The operational capacity is doubled by the N−1 intertrip scheme.
✔ All generators are eligible for the N−1 intertrip scheme.
✔ The available capacity is calculated assuming that interconnection is made from the lower to the upper system.
The actual applicability of the N−1 intertrip scheme and
additional available capacity, which are calculated by the
transmission and distribution utility companies in each area,
can be found on each company's website (Table 5).

Future Work
In this article, we reviewed the application of the N−1 intertrip scheme in Japan. The initiatives brought about through
the Japanese version of connect and manage were established as rules after the consensus of concerned parties and
deliberation by the Cross-Regional System Development
Committee, an advisory committee of the OCCTO. Future
work includes the following.

The Application of the N−1 Intertrip
Scheme to Distribution Generators
With the start of the first-step application of the N−1 intertrip scheme, it becomes possible for new transmission-level

Loop Bulk Power System
500 kV
2,540 ← 1,930

275 kV
1,000 → 1,270
Point F

Point B
400 400 270

400 →510
Point D

Point A
77 kV
130

77 kV

154 kV

200 ←130

100 → 260

400 → 510

500
200←130
77 kV

500 kV

System H

930 →1,270
275 kV

500 kV

Point C

100 → 260

154 kV

Point E

300 10
100 → 200

100 160

Legend
100 : Existing Generator

100 : New Generator (After Application of N -1 Intertrip Scheme)

Numbers in Red: Power Flow After Application of the N -1 Intertrip Scheme

figure 6. A demonstration case study of the effect of N−1 intertrip scheme (i.e., a simulated system).
march/april 2021

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