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Development of an Advanced Switching System for Distribution Networks
TAKAMU GENJI and OSAMU NAKAMURAThe Kansai Electric Power Co, Inc., Japan
MASAO SHIMAMOTO and KOICHI KISHIDADaihen Corporation, Japan
SUMMARY
This paper describes a high-speed switching system
for distribution networks that was developed with the aim
of improving power supply reliability (reducing the number
of supply interruptions) of distribution systems. When a
fault occurs in conventional distribution systems, the fault
section is isolated using a sequential time-out control
scheme that requires the reclosing and re-reclosing of the
entire system. A major drawback of such systems is that
normal sections are also subjected to unnecessary power
supply interruptions. In order to resolve this problem, we
have developed a high-speed switching system that isolates
only the fault section without interrupting the power supply
to normal sections. This new system can fully restore power
to the normal sections and can completely isolate the fault
section within 500 ms in the case of a ground fault. © 1998
Scripta Technica, Electr Eng Jpn, 125(3): 1�10, 1998
Key words: High speed switching system; distribu-
tion network; power supply reliability; fault detection.
1. Introduction
The highly information and technology oriented so-
ciety of today is steadily increasing its dependence on
electric power. At the same time, the requirement for high-
quality, highly reliable power supplies is also increasing as
the demand for power increases.
In response to this requirement, conventional distri-
bution systems have used an automatic switching system
with a sequential time-out control scheme that allows the
isolation of fault sections and normal sections by automat-
ically opening and closing the switching system at the
source side of the fault section.
In recent years the duration of power interruptions
between a fault section and the end of load side sections has
been significantly reduced by controlling the power supply,
after separating the sections, through the introduction of a
remote control switching system into the automated distri-
bution system. Even with this automated system, a mini-
mum of two power interruptions are unavoidable at the fault
feeder. Taking into account the greater complexity and
diversity of activities in metropolitan areas, the advent of
the information oriented society, advances in electric equip-
ment, and other factors, demand for less frequent power
interruptions is expected to grow in the near future.
In this context, the authors have developed a high-
speed switching system for distribution networks that offers
fewer and briefer power interruptions than existing switch-
ing control systems. The new system is intended to quickly
obtain fault data and isolate a fault section, while maintain-
ing uninterrupted power supply to other normal sections
without the need to operate a substation circuit breaker.
Since the high-speed switching system requires faster
switching operations as well as interruption of fault current,
the authors have also developed a switching control algo-
rithm and a high-speed circuit breaker. This paper outlines
the high-speed switching system and the test results, with
emphasis on the fault detection method and the section
identification algorithm.
2. Conventional Distribution Line Fault
Sectionalizing System
Existing distribution systems are divided into sec-
tions by automatic sectionalizing switches. If a fault occurs,
these automatic sectionalizing switches and the sequential
time-out control system are coordinated with the reclosing
system of a substation circuit breaker, so that the automatic
switches are successively closed to isolate the fault section
while continuing to supply power to the normal sections.
The supply of power to the normal sections located
beyond the fault section is achieved through remote control
of the switching systems linked to other distribution lines,
CCC0424-7760/98/030001-10
© 1998 Scripta Technica
Electrical Engineering in Japan, Vol. 125, No. 3, 1998Translated from Denki Gakkai Ronbunshi, Vol. 117-B, No. 10, October 1997, pp. 1353�1359
1
based on operation procedures prepared using system in-
formation stored in an office computer database.
The operation of the components of the system
shown in Fig. 1 when a fault occurs at point A is explained
below.
1) A fault is detected at the substation and the
circuit breaker (FCB) is tripped.
2) Automatic sectionalizing switches SW1-SW3
are no-voltage opening type and they open simultaneously
after the delay time limit has elapsed. SW4 is a connecting
switch linked to other distribution lines.
3) After the reclosing time has elapsed (normally
one minute) the FCB is reclosed.
4) SW1 is charged and closes automatically after
the closing time limit has elapsed.
5) Similarly, SW2 closes automatically after the
closing time limit has elapsed.
6) FCB is reopened once the fault section is
charged. After SW2 has closed, it is locked open by a power
interruption within the detection time limit.
7) After the second reclosing time limit has elapsed
(normally three minutes), the FCB is reclosed.
8) As with the reclosing above, SW1 is closed and
power is supplied up to SW2 (SW2 is locked open).
9) The office computer system automatically pre-
pares operation procedures for power supply redirection,
using system information.
10) Following the operation procedures, the con-
necting breaker (SW4) is closed and SW3 is opened via
remote control.
As the above operation shows, power interruptions
are unavoidable with conventional systems: two power
interruptions (1 min. and 3 min.) before the completion of
the fault section isolation and another 5 to 6 min. power
interruption required to prepare the operation procedures in
normal sections located beyond the fault section. Such
conventional systems can perform automatic fault section-
alizing only on predetermined system configurations and
take a long time to determine operation procedures for
redirection.
3. Objective and Target Performance of the High
Speed Switching System
3.1 Objectives of the system
In response to the anticipated requirement for more
reliable power supplies, further reduction in the areas af-
fected by a fault is expected to become necessary, as well
as reduction of the duration of the power interruption.
This high-speed switching system has the following
functions to eliminate the drawbacks of conventional sys-
tems and to reduce both the duration and the area affected
by power interruptions.
a. In principle, power supply to normal sections
continues uninterrupted and only the fault section is iso-
lated.
b. Isolation of the fault section and load redirection
to normal sections are performed regardless of the changes
made in the system configuration.
c. Isolation of fault sections, load redirection, re-
supply procedures (determination of the appropriate con-
necting switches and the re-supplied sections) and
processing of overloads (overloading of normal feeders
caused by load redirection) are made faster through simpli-
fication of the management and monitoring of distribution
network status information.
3.2 System configuration
The system configuration is based on the existing
automated distribution system and, as shown in Fig. 2, is
composed of the central station (1) in the office, a terminal
(2) installed at the substation, and a pole-mounted terminal
(3) and pole-mounted circuit breaker (4) connected to the
terminal. Fault information from the sensor (CT, ZCT)
installed in the pole-mounted circuit breaker is detected by
the pole-mounted terminal and obtained at the substation
terminal.
The substation terminal recognizes the current con-
figuration of the distribution system using system configu-
ration information preset by the central station, and
Fig. 1. Automatic sectionalizing system for a distribution network.
2
performs the fault section isolation, load redirection and
re-supply procedures, together with the fault information
obtained above.
Major Functions of Main Components
· Central Station: Responsible for sending system
configuration information to the substation terminals, as
well as to the standard central station functions of CRT
display of distribution line and switch status, and transmis-
sion of the system database information and remote com-
mands.
· Substation Terminal: The most highly functional
component in the system is responsible for detecting feeder
faults, recognizing the system configuration, high-speed
communication, troubleshooting (fault section identifica-
tion, isolation and re-supply, overload processing), in addi-
tion to the standard functions of relaying monitor and
control signals and transmitting substation status informa-
tion.
These functions are designed to speed up fault proc-
essing by assigning some of the standard central station
functions to the substation terminal, thus eliminating the
transmission delay between the substation terminal and the
central station.
· Pole-Mounted Terminal: Responsible for high-
speed communication, fault processing (sensor information
processing; opening when short-circuit currents are de-
tected) and identifying the direction of ground faults, in
addition to the standard functions of transmitting distri-
bution line and switch status information to the office,
and controlling the switch using signals from the substa-
tion.
· Pole-Mounted Circuit Breaker: Capable of faster
switching than conventional automatic switches, also re-
sponsible for interrupting short-circuit currents.
3.3 Performance requirement
3.3.1 Constraints
In the course of developing this system, the following
goals were set, taking into account the ease of migrating
from automated distribution systems already in use, and
developing as highly functional a system as possible.
(1) In the event of ground and short-circuit faults,
the fault section is isolated without operating the substation
circuit breaker.
Since the substation circuit breaker operates in the
event of ground and short-circuit faults for intervals of 0.5
s and 0.1 s, respectively, the system must complete isolation
of the fault section within these intervals.
(2) The system promptly recognizes the system
configuration, which changes frequently.
Even when the normal system configuration tempo-
rarily changes for some reason (e.g., distribution line work),
the system is able to accurately recognize the system status
information required for fault processing. Therefore, pole-
mounted breaker operation procedures for all system con-
figurations must be determined to permit fault isolation and
power supply redirection within the intervals specified
above.
Fig. 2. System block diagram.
3
(3) A maximum of 30 breakers controlled per dis-
tribution line is assumed.
Thirty controlled breakers are assumed to be installed
per distribution line, taking into account the number of
breakers necessary to sectionalize long-span distribution
lines plus those for customer drop wires.
(4) Existing communication lines are affected as
little as possible and their reliability must not be affected
even if additional hardware is introduced.
(5) The operation time limit of the substation circuit
breaker remains unchanged and the substation components
(e.g., relays) must not require modification.
3.3.2 Function of the algorithm
To implement high-speed isolation of a fault section
and power supply redirection, it is essential to identify a
fault section and determine breaker operation procedures
within an extremely short time.
One method to achieve this is to predetermine the
operation procedures for each potential fault section in a
fixed system configuration and tabulate them for quick
reference. This method, however, cannot handle situations
where system configurations differ from those tabulated, or
where there are multiple faults. Consequently, easy-to-use
methods that support complex and constantly changing
system configurations were required, together with a uni-
versal algorithm capable of identifying a fault section while
allowing sectional re-supply based on the system informa-
tion. The basic functions of the algorithm developed are
described below. The details of the algorithm and commu-
nication speed are described in the next section.
(1) System Configuration Recognition Logic
Each breaker is assigned a unique breaker number
(e.g., pole number). In addition, the breaker numbers con-
nected to the source side of the breaker (side 1) and load
side (side 2), and the breaker on/off status are also stored in
the substation terminal. By using this data, connections
between the breakers are identified and the overall configu-
ration is recognized.
(2) Universal Identification Logic
A fault distribution line is identified through the
substation relay information and the fault information is
then obtained via high-speed communication (polling) of
the pole-mounted terminal installed on that line. This is a
general-purpose technique for identifying a fault section
using the fault information detected at each breaker, to-
gether with the system configuration information obtained
in (1) above (identified using the breaker numbers on the
source side and load side of the fault section).
(3) Determination Logic for Sectionalizing and Re-
supply Procedures
The connection between individual breakers is iden-
tified by using the system configuration information ob-
tained in (1), with the breaker number on the load side of
the fault section identified in (2) as the origin. After power
supply on the load side of the fault section is ensured by
closing the appropriate breakers to connect the fault distri-
bution line with other normal lines, the load-side breaker is
opened together with the breaker on the source side of the
fault section.
Following the procedures in this order, it is possible
to sectionalize the fault section while maintaining an unin-
terrupted power supply to the normal sections.
(4) Coping with Various Types of Fault
The occurrence of faults at multiple points can be
classified as simultaneous or sequential. In either case,
identification, isolation of the fault section, and resupply
must be performed properly.
Based on the fail-safe principle, the system configu-
ration must ensure that the area affected by a power inter-
ruption is minimized and normal sections are never affected
by the power interruption, even if the fault section cannot
be properly isolated.
3.3.3 Performance of the communication
system
Conventional systems use distribution line carrier
systems and communication lines (pair, coaxial, and optical
cables) with low communication speeds of several hundred
bps and 1200 bps, respectively. The polling transfer method
is used, with the area within which information is collected
defined by the central station. This type of system requires
considerable time to collect information from its terminals
and does not meet the time requirements for high-speed
switching system. For this reason, a higher system commu-
nication speed must be used. The communication system
adopted is described below.
(1) Communication Speed
As a criterion for determining the communication
speed and based on the assumption mentioned previously
of 30 control breakers per distribution line, the processing
time for each procedure was calculated in the following
sequence: fault detection, data collection, fault section
identification, connecting breaker closing, and opening of
the breaker on the source side of the fault section. The
4
results showed that the communication speed must be 64
kbps or higher. Since a communication speed of 64 kbps
cannot be achieved currently using pair cables, coaxial and
optical cables were adopted as the communication media.
(2) Communication Mode
Communication is normally performed using polling
(half-duplex mode) as in conventional systems. In the event
of a fault, full-duplex mode is used to save time.
For error detection, a parity word was used since the
conventional collation of reverse communication data in-
creases the length of communication data.
3.3.4 Operation time
In case of a ground fault the delay from the occur-
rence of the fault to the time when the breaking signal is
sent to the FCB by the substation relay is 500 ms. Therefore,
target performance in terms of system operation time must
meet the requirement of opening the breaker on the source
side of the fault section within 500 ms of the time of fault
detection in the sequence: fault detection, data collection,
fault section identification, connecting breaker closing,
opening the breaker on the source side of the fault section,
opening the breaker on the load side of the fault section.
The results of estimating the respective processing
times are described below.
(1) Fault Circuit Identification Time
A maximum detection time of 60 ms is the estimated
requirement for a substation terminal supporting the relay
function to identify a fault by inputting the fault current and
voltage data for each distribution line.
(2) Data Collection Time
All data can be obtained within 170 ms, assuming a
full-duplex polling mode of 30 units is operated at a com-
munication speed of 64 kbps.
(3) Fault Section Identification Time
The substation terminal recognizes the system con-
figuration of a distribution line fault and identifies a fault
section using the collected data. The CPU processing time
required for this is estimated to be approximately 10 ms.
(4) Connecting Breaker Closing Time
To save time, the control step was changed from the
usual two actions (selection and control) to one action
(control only). This change is expected to result in an
operation time of approximately 100 ms at each point.
(5) Open Time of the Breaker on the Source Side of
the Fault Section
Approximately 90 ms is estimated by assuming a
breaker operation time is at most 50 ms.
The overall time required for the above steps is 430
ms to satisfy the target operation time of less than 500 ms.
In the event of a short-circuit fault, the breaker on the
source side of the fault section must open within 100 ms of
the fault being detected. However, as shown above, data
collection alone takes more than 100 ms.
For this reason, the following system configuration
was implemented to handle short-circuit faults. The pole-
mounted terminal is responsible for autonomous opening
when a short-circuit fault occurs (i.e., the pole-mounted
terminal makes its own decision and gives instructions for
opening). In the event of a fault, therefore, the pole-
mounted terminal that has detected a short-circuit current
on the source side of the fault section opens the breaker on
its own initiative, collects data on the side of the power
interruption, identifies and sectionalizes the fault section,
and thus controls the system.
4. Fault Detection Procedure
4.1 Ground fault
The substation terminal identifies a faulty feeder
using a combination of the zero-phase voltage of the trans-
former bus bar and the zero-phase current of each feeder.
The terminal also recognizes a pole-mounted terminal used
for polling to obtain fault information. The continued ex-
istence of the fault is confirmed by the presence of zero-
phase voltage.
Detection by breakers that sectionalize a distribution
line is performed by calculating the phase difference (Io-
Vca) between the zero-phase current of the pole-mounted
terminal input from the ZCT contained within the breaker
and the voltage Vca supplied from the PT (control power
transformer) also contained within the breaker. The pole-
mounted terminal detects the ground fault phase informa-
tion (detected at the substation terminal) contained in the
polling signal from the substation terminal, and compares
it with reference data and the above phase difference data
to determine the direction of ground fault occurrence. The
result is returned as the polling response.
The substation terminal identifies a faulty section
according to the universal identification algorithm using the
fault information obtained above.
5
4.2 Short-circuit fault
In the event of detection by each feeder at the substa-
tion, a short-circuit fault is identified when each feeder fault
current exceeds the detection level. In the event of detection
at the breaker sectionalizing a distribution line, the value of
the current running the distribution line is input to the
pole-mounted terminal from the CT built into the breaker
and is taken to indicate a short-circuit fault when the current
exceeds the detection level. The pole-mounted terminal that
has detected a short-circuit fault controls the breakers after
the time limit determined from the input current has
elapsed. The terminal responds to fault polling from the
substation terminal by indicating the detection of a short
circuit. The substation terminal that has collected fault
information from the breaker connected to the faulty feeder
thus identifies a faulty section according to the universal
identification algorithm.
5. Developed Algorithm
To meet the above performance requirement, an al-
gorithm for recognizing the system configuration and iden-
tifying fault sections using indexes representing
connections has been developed.
The overall basic flowchart for fault occurrence is
shown in Figure 3.
5.1 System configuration recognition method
For each of the breakers sectionalizing a distribution
line, the following information is recorded: breaker num-
ber; address number; open/close status; the numbers of the
breakers connected to the power source and load sides; and
the operation mode. In addition, the open/close status and
operation mode are refreshed by regular polling and re-
sponse to instructions. The latest system configuration can
thus easily be recognized by checking the connections and
the open/close status of the breakers using this information.
Examples of a system configuration and its configuration
information are shown in Figure 4 and Table 1, respectively.
5.2 Fault section identification and load
redirection algorithm
When a fault has occurred, fault information is ob-
tained from all breakers connected to the faulty feeder and
the information from the breakers connected to the faulty
FCB is checked successively. Based on this information and
according to the universal identification logic, a search for
the fault section is made. Following the universal identifi-
cation logic, at that point the system configuration is inter-
preted as a tree-like structure as shown in Fig. 5.
Identification of a faulty section is made from the terminal
polling response information in the order indicated by the
arrows. At this point, the breakers connected to one branch
point in the system are grouped by their index (n-value). A
Fig. 3. Flowchart for ground fault.
Fig. 4. System configuration example.
6
faulty section among the circuit breakers is identified as
shown in Fig. 6. One circuit breaker is set as a reference
point and if no fault polling response is received from any
of the circuit breakers (ground circuit breakers) connected
beyond the reference breaker, the faulty section is identified
as the section immediately following the reference breaker.
Conversely, if a fault response is received from any of the
breakers, the next group of polling responses are examined
using this breaker as a new reference breaker. The polling
responses are thus examined continuously until a faulty
section is identified. On the other hand, the open/close
status of the breakers is updated through regular polling and
this algorithm is designed to examine the on routes succes-
sively while recognizing the above-mentioned status ac-
cording to the system configuration information.
Consequently, since the substation terminal has the latest
information, faulty sections can be identified within any
system configuration, even if the system configuration has
changed.
In order to perform load redirection, a search is made
for connection points with normal feeders on the load side
of a faulty section according to the sectionalizing and
re-supply procedures and redirected sections are recog-
nized by closing the connecting breakers. Consequently, as
Fig. 7 shows, the system configuration is interpreted as a
tree-like structure starting from the faulty section and link
points beyond the faulty section are examined based on the
system configuration information shown in Table 1. After
confirming that the circuit breaker is connected to the FCB
of the normal feeder, the breaker is closed. From this point
the redirected section can be recognized by tracing the on
breakers back to the faulty section. The same procedures
are performed for all the breakers recognized as being in
the second level group to check whether redirection has
been performed in all the sections beyond the fault point.
As previously mentioned, an algorithm with the fol-
lowing features was obtained by grouping the connections
at the system branch point using their indexes.
· Simple data structure and a small amount of data
allow recognition of various system configura-
tions.
· Real-time recognition of changes in the system
configuration is possible.
· Identification of a faulty section and determina-
tion of re-supply procedures can be performed in
less than 10 ms.
6. Demonstration Test Results
A simulated system using a prototype apparatus (one
substation terminal, four pole-mounted terminals, four
pole-mounted breakers) was constructed at the Yamazaki
experiment center of the Kansai Electric Power Co., Inc.,
Table 1. Data indicating distribution network structure
Fig. 5. Procedures for fault section identification search.
Fig. 6. Fault section identification procedure.
Fig. 7. Sectional re-supply procedures.
7
which has full-scale voltage (6 Kv) systems, to demonstrate
the operation of the algorithm and the system operation
time and synthetic performance evaluation.
6.1 Test conditions
The simulated system shown in Fig. 8 was con-
structed using four high-speed circuit breakers. The system
reservation is described below.
(1) Capacitors connected between the lines and
earth: 1 mF
(2) Ground fault resistance: 100 W
(3) Short-circuit fault: ground faults of each resis-
tance 20 W occurs at two points F11, SW1, SW2, and SW4
in Fig. 8 compose a single distribution line, which was taken
as the faulty distribution line. F11 and SW3 were taken as
normal distribution lines and were assigned the role of load
redirection.
6.2 Test results
(1) Operation at Ground Fault Occurrence
Figure 9 shows the operational status of each section
when a fault occurs at section 2. The results show that the
following procedures were performed.
Closing of normally open point (SW4), 400 ms delay
for natural decay. Fault point power source side (SW1)
opening, fault point load side (SW2) opening, reclosing
timer (5S) delay, reclosing (SW1 closing), fault continu-
ation, SW1 opening.
The times required for each step, measured from Fig.
9, are shown in Table 2.
(2) Operation for Short-Circuit Fault
Figure 10 shows the operational status of each section
when a short circuit occurs at section 2. The results show
that the following procedures were performed.
Local opening (SW1), fault polling, fault section
identification, fault point source side (SW1) opening, fault
point load side (SW2) opening, closing of normally open
point (SW4), reclosing timer (5S) delay, reclosing (SW1
closing), fault continuation, SW1 opening (local opening).
The times required for each step, measured from Fig.
10, are shown in Table 3.
(3) Observation
a. As seen from the above results, it has been con-
firmed that for a ground fault occurring at a single point,
the operation from identification of the fault section to
supply of power to the normal sections can be performed
within the planned procedures and time limits. Further-
more, we regard the controlled breakers as totaling 30 units
for the target of this system. However, the test was con-
ducted using four breakers. As a result of this experiment,
the self-decay counter indicated 385 ms (Table 2, Ä).
Therefore, it is effective to use 310 ms as the time for
pole-mounted terminal data collection, even though we
deduct the time for ground fault detection, completion of
isolation, and re-supply procedure from this. The data of all
30 pole-mounted terminals can be obtained within 170 ms
at a communication speed of 64 kbps, and thus it is possible
Fig. 8. Simulated test circuit.
Fig. 9 Output of test for ground fault.
Table 2. The time required for each step
8
to complete the data collection from 30 pole-mounted
terminals within the countup of the self-decay counter.
Further, breaker operation after fault section identification
involves only three units: one is on the source side, another
is on the load side, and the third is a connecting breaker.
Even though the number of these units per distribution line
will change, the condition is always changed. Therefore, it
is possible for the system performance to be completed
within the target time in the case of 30 controlled breakers.
b. The cumulative time up to breaking of the ground
fault current in Table 2 is 467 ms, within the target system
operation time of 500 ms.
c. It was confirmed that even if another fault oc-
curred in the system after a faulty section had been section-
alized, isolation of the fault section was possible. From this
fact, it was verified that faulty sections can be correctly
identified even if a system configuration change has been
necessary.
However, when there are ground faults at multiple
points, especially at the same branchpoint, the direction of
the fault current is determined by the earth capacity in the
fault section. This fact results in sections where faults
cannot be identified, and thus the substation circuit breakers
must be tripped.
If a faulty section can be identified normally, it was
confirmed that isolation and re-supply processing was pos-
sible even if multiple faults had occurred.
d. Since the elapsed time until breaking of the short-
circuit fault current in Table 3 is 48 ms, it was confirmed
that the pole-mounted terminal was able to open the breaker
within the target system time of 100 ms.
7. Conclusions
The authors have developed an advanced switching
system for distribution networks and have successfully
demonstrated its operation for actual voltage systems. This
system collects fault information about the distribution
lines at high speed and can isolate just the faulty sections
while maintaining uninterrupted power supply to the nor-
mal sections, without the need to operate circuit breakers at
the substations.
· This system is more advanced than conventional
systems in the following respects.
· Even if the system distribution line configuration
changes, this can be recognized almost immedi-
ately and a faulty section can be identified.
· Load redirection breakers can be identified
quickly, according to the identification of the
faulty section.
Reclosing is performed only in faulty sections within
a brief five-second period, thus avoiding the reclosing or
re-reclosing of an entire distribution network.
The authors intend to conduct performance evalu-
ation tests designed for actual applications, including dem-
onstrations using universal algorithms for more
complicated system configurations.
REFERENCES
1. Sekine. Power Distribution Technology Annual.
Ohm Press [no date].
2. Mastumoto. How far can enhanced information tech-
nology improve power distribution? 1996 Annual
Meeting of IEE Japan. S 24-25.
3. Genji, et al. Development of a high-performance
switching system for power distribution. 1995 An-
nual Meeting of Power and Energy Division.
Fig. 10 Output test for short circuit.
Table 3. The time required for each step
9
AUTHORS (from left to right)
Takamu Genji (member) received his B.S. and M.S. degrees in electrical engineering from Okayama University, Okayama,
Japan, in 1973 and 1975, respectively. In 1975 he joined the Kansai Electric Power Co., Inc. From 1978 to 1983 he was engaged
in development of distribution systems and equipment in the Distribution Department. Since 1985 he has been engaged mainly
in the development of distribution control systems using a two-way communication system at the Technical Research Center.
Mr. Genji is a member of the Institute of Electrical Engineers of Japan.
Osamu Nakamura (nonmember) received his B.S. and M.S. degrees in electrical engineering from Kyoto University,
Kyoto, Japan, in 1968 and 1970, respectively. In 1970 he joined the Kansai Electric Power Co., Inc. From 1991 to 1995 he was
engaged mainly in the development of distribution control systems at the Technical Research Center. Mr. Nakamura is a member
of the Institute of Electrical Engineers of Japan.
Masao Shimamoto (member) received his B.S. degree in electronic engineering from Himeji Institute of Technology,
Hyogo, Japan, in 1987. In 1987 he joined Daihen Corporation. Since 1987 he has been engaged in the development of distribution
equipment. Mr. Shimamoto is a member of the Institute of Electrical Engineers of Japan.
Koichi Kishida (member) received his B.S. degree in electrical engineering from Kansai University, Osaka, Japan, in
1975. In 1975 he joined Daihen Corporation. Since 1975 he has been engaged in the development of distribution equipment.
Mr. Kishida is a member of the Institute of Electrical Engineers of Japan.
10