10
Development of an Advanced Switching System for Distribution Networks TAKAMU GENJI and OSAMU NAKAMURA The Kansai Electric Power Co, Inc., Japan MASAO SHIMAMOTO and KOICHI KISHIDA Daihen 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): 110, 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, 1998 Translated from Denki Gakkai Ronbunshi, Vol. 117-B, No. 10, October 1997, pp. 13531359 1

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Page 1: Development of an advanced switching system for distribution networks

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

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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.

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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.

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(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

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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.

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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.

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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.

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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

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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

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Page 10: Development of an advanced switching system for distribution networks

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.

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