Optimizing Power Supply Stability through ICT Utilizationin Power Systems

Tetsuo Otani

Grid and Communication Technology Division
Grid Innovation Research Laboratory
Central Research Institute of Electric Power Industry

1. Introduction

Electricity is an essential energy for daily life and industry,and sound operation of power systems for electricity supply
to consumers is directly related to stable supply of electricity.
To operate a power system in a sound state, the following
requirements must be satisfied: (i) match the amount of electricity
generated with demand constantly (supply-and-demand balance),(ii) maintain power quality such as frequency and voltage (qualitymaintenance), (iii) promptly locate and isolate a fault section of
the power grid (fault clearance), and (iv) maintain continuationof power supply to sound areas that are not affected by the fault(security of the electricity supply). Various ICT-based systems
are in operation to satisfy these requirements concerning powersystems.
In the meantime, to achieve carbon neutrality by 2050, it
will be increasingly necessary to promote renewable energy andutilization of facilities and equipment that demand electricity suchas electric vehicles (EVs). The utilization of ICT will be a crucial
factor in achieving the goal.
Considering the background, this paper describes the usage of
ICT in power systems currently in operation as well as the future
vision of such usage of ICT and expectations for it.

main protection relay and a back-up protection relay—eliminates
short circuits or earth faults that occur on transmission lines.
The main protection relay uses communication/transmission forsampled values of current and voltage, and pulse-code-modulation(PCM) current differential relays are used as the main protection
relays in 500 and 275 kV bulk power systems.
The basic configuration and operation of the PCM current
differential relay is shown in Figure 1. Protection-relay devices are
installed at substations located at both ends of the transmission
line to be protected, and sampled values of the current flowing ineach phase of the transmission line are constantly transmitted tothe other end of the line. The protection relay devices calculate thedifference of current by using the current values sampled at its own
end and those transmitted from the other end. In the case wherethe difference exceeds the setting criteria, they judge that a fault
has occurred on the transmission line, and dispatch trip signals tothe circuit breaker to isolate the fault section.
■ Figure 1: Configuration of PCM current differential relaysystem

2． Utilizing ICT for power systems

This section focuses on the utilization of ICT for stabilizing
electric power supply. So it describes the following systems
and technologies as representative examples in the following
sub-sections: a “transmission line protection relay system” insubsection 2.1 and an “online pre-calculating system stabilizing
controller (OPCSSC)” in subsection 2.2, which are responsible
for adjustment of supply and demand to maintain the supply-anddemand balance during normal times in subsection 2.3; control of
output for non-firm power sources to achieve both effective useof transmission and substation facilities and stable power supply
and quality control on the consumer side in subsection 2.4; and a"distribution feeder automation system” in subsection 2.5.
Smart meter systems also utilize various t y pes ofcommunications. However, this paper focuses on power supplystability. So please refer to other literature for communications for
smart meter systems, if necessary.
2.1 Transmission line protection relay system
A transmission line protection relay system—consisting of a

Communication systems used for the PCM current
differential relays must have low latency (i.e., 5 ms for 50 Hz
power systems and 4 ms for 60 Hz power systems) and highreliability (i.e., system-wide failure rate to operate of 1.0 ×
10 -7)[1]. To meet those requirements, microwave radio[2] andoptical ground wires (OPGW)[3] are used as communication
media, which are connected by dedicated multiplex equipment(CR-MUX). Microwave radio has two key features as a

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communication technology for the PCM current differential
relays: (i) ease of assuring low-latency transmission because thetransmitting and receiving points are connected over the shortest
possible distance and (ii) reliability even in the event of large-scaledisasters because physical media are not used (only robust towers
are used)[4].
2.2 Online pre-calculation system stabilizing controller
Online pre-calculation system stabilizing controllers(OPSSCs) are operated for purposes such as maintenanceof frequency during severe accidents, and they play a role inpreventing fault cascading[5]. During the large-scale power
outages that occurred in recent years, they also operated to prevent
blackouts from occurring[6].
Figure 2 shows a basic configuration of OPSSC —[7]. The
processing device constantly receives measured values related to
power flows at important points within the power system, and it
repeatedly identifies circuit breakers to be tripped for all patterns
related to transmission route faults in a bulk power system, loss ofgeneration, etc. at regular intervals. In the event of a fault causinga system disturbance, the relevant monitoring devices notify thefault occurrence to the processing device, which then sends trip
signals to the power/load shedding devices responsible for thecontrol target at that time. The power/load shedding devices
receiving the trip signals, they trip the designated circuit breakers.
The transmissions of fault notifications and trip signals
necessitates ICT that achieves low latency and high reliability;
therefore, as in the case of PCM current differential relays,
microwave radio, OPGW, etc. are used as the communication
media.
■ Figure 2: A basic configuration of OPSSC

2.3 Supply and demand balance control
To maintain the balance between power supply and demand,

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the output of generators and other equipment is controlled by“load frequency control” (LFC) and “economic load dispatchingcontrol” (EDC). Figure 3 illustrates the basic configuration ofthe system used for LFC and EDC. The load dispatching centersystem receives measured values such as output and current flow
and status values such as breaker open/close status from power
plants, etc., and it sends control signals for LFC and EDC to thetarget power plants every few seconds and every few minutes,respectively. Since the communication used for LFC and EDC(especially in the case of the LFC command) requires low latency
and high reliability, microwave-radio and OPGW are mainly used
for the transmission path.
■ Figure 3: Basic configuration of the system for balancing
supply and demand2.4	Curtailing the output from non-firm connected powersupplies
Non-f irm connection is a method of connecting thepower supply with the upper limit of the available capacity oftransmission and substation facilities, and the output of thepower supply is controlled according to the available capacity.
Specifically, this control is achieved by transmitting the upperoutput-limit schedule for each 30-minute time frame as apercentage of the generator’s rating in advance via communication.
In some cases, the upper output limit value in the 30-minute
frame during operation is changed on demand according to thesituation.
Two different systems are operated for this output curtailment,
and the one chosen depends on the voltage level with which thepower supply is interconnected. For power supplies connected tomedium- and low-voltage (less than 66 kV) grids, a system basedon the Internet and HTTP is used. As for this system, a serveris installed on the side of the distribution system operator, andthe output-upper-limit schedule is periodically obtained from thegenerator side via HTTP and Internet VPN. On the contrary, forpower supplies connected to high-voltage (66 kV or higher) grids,
the output-upper-limit schedule is distributed by cyclic digitaltransfer (CDT) via a dedicated communication network. Via thededicated network, commands can be issued at any time, so output
can be controlled in real time according to the actual supply anddemand of the day.
2.5 Feeder automation system
A feeder automation system in Japan is mainly for mediumvoltage feeders (6.6 kV), and they are responsible for distribution
grid switching, regulating voltage, and quick restoration of soundsections by isolating a trouble section[8]. This system is almost
100% adopted in Japan, where it is contributing to optimizing
voltage and shortening power-outage times. Figure 4 illustrates
the basic configuration of a feeder automation system. The system
consists of a master unit which is responsible for monitoring andcontrol as well as fault location, isolation, and service restoration,and field controllers. Some of the field controllers are responsible
for control of sectionalizer and measurement of current andvoltage, and others are used to monitor and control voltagecontrol equipment (e.g. a step voltage regulator) installed on themedium-voltage feeders. The master unit is also linked to othersystem such as distribution management systems and control
and protection systems for transmission power systems. For
communication between the master unit and field controllers,
power line communication, metal cables, and optical cables areused as dedicated communication paths. Whichever is used,
they are basically mounted to distribution poles and laid along
medium-voltage feeders.

“real-time smart digital twin” (RSDT) proposed by the Central
Research Institute of Electric Power Industry as one kind ofdigital twin, as shown in Figure 5, remote devices installed in
power plants and substations synchronize their times with highprecision and transmit measured values with time stamp to theprimary device at 10 ms intervals. The primary device ascertains
the degree of system stability in a few minutes according to thereceived values measured at the same time, and it could perform
preventive control, as necessary[9].
■ Figure 5: Illustration of communication relationship in
RSDT (transmission of measurement and statusvalues only)■ Figure 4: Basic configuration of feeder automation
system

3.2 Cooperation between power system and EVs
EVs are one of the major changes in future electricity
usage compared to today’s one. Numerous projects are alreadyconducting field trials to utilize the charging and discharging
functions of EV storage batteries as a service for operation ofpower systems[10]. These field trials include transmitting control
setpoints to EVs to supply services for replacement reserve forfeed-in-tariff. In the future, the utilization of telematics data isanticipated to foster a synergy between the power system and EVs,
serving as a key component of a broader range of services tailoredto EVs.

3．Future vision of utilizing ICT in powersystems

3.3 Utilization of flexibility
Alongside the synergy between power systems and EVs
outlined in the previous section, there is increasing focus on
power system operations – such as congestion management andvoltage regulation – that capitalize on the flexibility provided by
distributed energy resources (DERs), including controllable loads,
to adapt power output or demand.[11]. When utilizing flexibility,
power system operators and aggregators exchange data related toFour future visions of the use of ICT that are considered todiffer significantly from the conventional use of ICT in powersystems are described in this section.
3.1 Utilization of ICT for digital twins
Utilizing ICT is essential to create a digital twin. As for theNew Breeze Spring 2024

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■ Figure 6: Platformfor utilizing flexibility (cited from reference[11])service transactions and operations of DERs through a platform
such as that shown in Figure 6.
3.4 Collection of equipment-maintenance dataTo stabilize power supply, it is necessary to maintain not only
the operation and protection of the power system as describedabove but also the soundness of facilities such as transformers
and transmission lines. Until now, the soundness of facilities has
basically been maintained through periodic inspections; however,in the future, methods that actively utilize ICT for appropriate
inspections and repairs while monitoring the condition of facilities
are expected to become mainstream[12]. That is, in addition totemperature, liquid level, vibration, and other data that are widelyused in other fields, data characteristic of the electric-power field(such as partial discharge) is expected to be collected through theInternet of Things (IoT) and other means, and the state of thesystem will be analyzed by using AI and other methods.

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4．Expectations for ICT

Expectations for ICT are described hereafter from theperspective of realizing the above-described future vision of ICT
utilization and enabling the stable power supply in the future.
4.1 Ensuring openness through international standards
As for coordination with EVs and utilization of flexibility,
parties outside of the electric-power sector are involvedin the operations of the power system. And as for ICT usedin such environments, “openness” is expected to be ensured.
One way to ensure openness is to create international standards
for coordination between the electric-power field and otherfields. That standardization should be led by the International
Electrotechnical Commission (IEC), which creates international
standards for electric power-related communications. For
example, regarding IEC 61850, the international standard forcommunications for monitoring and controlling power systems,the IEC has published a technical report for communications
related to the sector coupling between power systems and thermalenergy systems. In addition, another document for “power to gas”
(P2G) technology is under development.
4.2 Expanding the scope of wireless communications
Wireless communications are already used in the PCM
current differential relays for transmission line protection andsmart meters. In addition, it is anticipated that its application incollecting facility-maintenance data will increase. At that time,
it is expected that the power supply for wireless-communication
terminals will also become wireless or independent. Moreover, theapplications of wireless communication in fields such as protectionand control are expected to simplify removal of communication
cables and testing at substations.
4.3 Utilization of all-photonic communication network
To create digital twins, it is necessary to implement highspeed broadband communications. As one of the communication
networks to meet that need, the “all-photonic communication
network” is expected to be used in combination with high-speed
wireless communication. It has already been presented by NTT
in the form of their concept known as the “Innovative Opticaland Wireless Network” (IOWN), and domestic and international
companies are participating in the IOWN forum[13]. It is hopedthat IOWN technologies will contribute to the realization ofdigital twins.
4.4 Assuring cybersecurity
Assuring cybersecurity is required in all fields. The design ofcybersecurity measures for ICT in power systems should ensure
the uninterrupted continuity of power system operations. For
example, if communication is cut off immediately when a security
certificate expires, the power system may be unable to operate,
and a large-scale power outage may occur. For that reason, it
is expected that an appropriate security policy—tailored to thecharacteristics of the electric-power sector—will be established,
and that power systems will be operated in accordance with thepolicy.

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Cover Art
Shinagawa, Tokaido

5．Conclusion

This article has described how various ICTs are utilizedin power systems and contribute to stable power supply. It also
outlines future visions for ICT utilization in power systems,
including digital twins, EV integration, flexibility use, and facility
maintenance data collection, along with the expected role of ICTin achieving these visions.

Utagawa Toyokuni(III)(1786-1864)
Source: National Diet Library,NDL Image Bank(https://rnavi.ndl.go.jp/imagebank/)

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