VOL. 95/SEP. 2001 - Mitsubishi Electric · 2020. 2. 18. · ISSN 1345-3041 VOL. 95/SEP. 2001...

ISSN 1345-3041

VOL. 95/SEP. 2001

MITSUBISHIELECTRIC

Power-System Control/Protection & Radiation-Monitoring Edition

● Vol. 95/September 2001 Mitsubishi Electric ADVANCE

A Quarterly Survey of New Products, Systems, and Technology

TECHNICAL REPORTS ON POWER-SYSTEMCONTROL/PROTECTIONOverview ............................................................................................. 1by Shin-ichi Azuma

Introducing the MELPRO-C Series ..................................................... 2by Norimasa Kusano and Hideo Noguchi

MELPRO-C Series Protection Relays and Their Basic TechnologicalElements ............................................................................................. 5by Toshio Anzai and Takashi Oosono

Applying Relay Protection to a 500kV Transmission Line with SeriesCapacitors .......................................................................................... 8by Shigeto Oda and Takashi Hattori

MELPRO-C Digital Relay System for Feeder Protection in OutdoorInstallations ....................................................................................... 10by Susumu Fujita and Yasuhiro Tsunoi

MELPRO-D Series Protective Relays for PowerReceiving/Distribution Systems....................................................... 14Kazuyoshi Fujita and Toyoki Ueda

TECHNICAL REPORTS ON RADIATION MONITORINGOverview ........................................................................................... 17by Keiichi Matsuo

A New Radiation-Management System ........................................... 18by Kenichi Moteki and Kazuhiko Fuzita

Semiconductor Radiation Sensor .................................................... 22by Seisaku Imagawa and Hiroshi Nishizawa

Radiation Sensing System Using an Optical Fiber .......................... 25by Ryuichi Nishiura and Nobuyuki Izumi

CONTENTS

Mitsubishi Electric Advance is published online quarterly (in March, June, September,and December) by Mitsubishi ElectricCorporation.Copyright © 2001 by Mitsubishi ElectricCorporation; all rights reserved.Printed in Japan.

Our cover story reflects the dual emphasisof Vol. 95, on power-system control andprotection, and on trends in radiationmonitoring. In the center is a typical controlpanel for a MELPRO-C protection relay, aseries with major advantages described inseveral of the articles. At the lower left is anillustration of the DPR03 radiation detectorfor medical linear accelerators (LINACs)and at the upper right is a surfacecontamination monitor using scintillationdetectors and optical fibers, readilytransportable to the scene of any nuclearmishap.

Kiyoshi Ide

Haruki NakamuraKoji KuwaharaKeizo HamaKatsuto NakajimaMasao HatayaHiroshi MuramatsuMasaki YasufukuMasatoshi ArakiHiroaki KawachiHiroshi YamakiTakao YoshiharaOsamu MatsumotoKazuharu Nishitani

Yuji HasegawaKeiichi Matsuo

Keizo HamaCorporate Total Productivity Management& Environmental ProgramsMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-2465

Yasuhiko KaseGlobal Strategic Planning Dept.Corporate Marketing GroupMitsubishi Electric Corporation2-2-3 MarunouchiChiyoda-ku, Tokyo 100-8310, JapanFax 03-3218-3455

Editor-in-Chief

Editorial Advisors

Vol. 95 Feature Articles Editor

Editorial Inquiries

Product Inquiries

Power-System Control/Protection &Radiation-Monitoring Edition

· 1September 2001

TECHNICAL REPORTS

*Shin-ichi Azuma is with Transmission & Distribution, Transportation Systems Center.

OverviewPower-System Protection and Control in the Network Age

by Shin-ichi Azuma*

In recent electric power-supply systems, society’s demands for fur-ther deregulation and privatization have led to a primary concern overcutting costs without compromising system reliability, making the effi-cient functioning of the protective and control systems that form thepower grid’s central nervous system more important. Mitsubishi ElectricCorporation has developed two new product series for protective and con-trol systems in the network age: the MELPRO-C series for power genera-tion and distribution systems and the MELPRO-D series for user systems.

Both series provide for interconnection using the networks inside powerstations and the intranets and realtime networks of utility companies.They facilitate the remote operation of equipment, supporting remotemaintenance, monitoring, and other new functions and services. Theytherefore also support increases in the effective utilization of equipment,the slimming down of facilities, and the rationalization of operations.

The MELPRO-C series centers around high-performance CPUs, andthe individual products are significantly smaller than previous compa-rable models. They can be built up into systems that meet the specificneeds of particular system characteristics with flexible hardware andsoftware options.

Again, the MELPRO-D series uses general factory automation networksto provide for simplification and integrated protection, monitoring andcontrol, enabling low-cost implementation of systems that reduce thelabor requirements of power management. ❑

TECHNICAL REPORTS

Mitsubishi Electric ADVANCE2 ·

*Norimasa Kusano and Hideo Noguchi are with Transmission and Distribution, Transportation Systems Center.

by Norimasa Kusano and Hideo Noguchi*

Introducing the MELPRO-C Series

As part of our continuing efforts to build economi-cally attractive and environmentally friendly elec-tric power network systems, Mitsubishi ElectricCorp. has developed MELPRO-C, a shared plat-form with an architecture that ties together theprotection and control systems, linked by a com-munications network.

Protection Control Systems—The BusinessEnvironment and System RequirementsElectric power is an ideal form of environmentallyfriendly energy, and more efficient generation andtransmission of electric power contribute to envi-ronmental protection by, for example, reducingcarbon dioxide emissions. On the other hand, asvarious countries deregulate electric power utili-ties, the drive for higher profits from power distri-bution puts the highest priority on efficient systemoperations. This has led to increasing demands forslimming down equipment and high-efficiency op-erations while maintaining power-system reliabil-ity. Protection control systems, as the centralnervous system in the power systems, are calledupon to provide increasingly sophisticated intelli-gent functions and communication functions asshown in Fig. 1. In order to fulfill these needs,Mitsubishi Electric Corp. has developed MELPRO-C, a new intelligent electronic device (IED) plat-form for protection and control (see Fig. 2, 3).

Design Rules for the New PlatformThe MELPRO-C applies two design rules.

DESIGN RULE 1. The intelligence to perform mea-surement, protection, control, monitoring, andcommunications functions must be capable ofdistribution to the vicinity of the primary equip-ment.

DESIGN RULE 2. This distributed intelligencemust be linked by an open de facto protocol.

Fig. 1 Integrated protection and control system with IEDs

Fig. 2 External appearance of MELPRO-C

Powerutilities /IPP

Largedemand industrial

plants

Consumer

Communicationnetwork

Power station

Consumer side

Ry

Ry

Ry

Ry

Ry Ry Ry Ry

S/S : Sub station . Primary . Secondary

PC

S/S

S/S

S/S

S/S Remotesupervisingoffice/center

TECHNICAL REPORTS

· 3September 2001

The six letters of the acronym “ CHARGE”stand for the design concepts upon which theplatform was built.

The Design Concept “ CHARGE”

COMPACT. Taking advantage of high-perfor-mance processors and high-density mountingtechnology, the corporation has succeeded in cre-ating a compact unit with a body and a requiredinstallation space only one-half that of previousunits. In addition to standard models equippedwith a 19-inch rack and control board, modelsthat use an IP 65-level sealed case makes it pos-sible to locate the equipment outdoors, near theprimary equipment.

HUMAN FRIENDLY. User-friendly computer displaysallow the user to determine remotely the optimalsettings for the power system, and to access re-motely details such as measurement information,waveform information, and event logs. The mea-surement information is collected in 48/96 sam-pling/cycles, using 16-bit resolution, therebyproviding data for detailed analyses.

ADAPTIVE. The MELPRO-C has been designed sothat it can be connected to upstream systems andsystems from other companies using de facto stan-dard protocols. The protection control unit adjust-ment values have been stored as multidimensionaltables, allowing the program to be changed flexiblyto match the relay output conditions and the condi-tions of use (programmable DO).

RYC card

CPU

CPU

MPX

MPX

PCM

DI

FD card

DO card

TR card

DI card

COM card

PCM card

GPSI/F

DI...

Communicationport PCM

CX

CX

COMI/F

RS-485RS-232C

IRIG-Bdigital

AI...

(V, I)S/H

S/HF

FDSPA/D

CPUA/D

Option

Option

CPU

DO

DO FD

M

HMI card

DC DC

S/HF

S/HF

Power sourceDC

Bus

Fig. 3 Hardware block diagram

RELIABLE. The final trip output of the protectionrelay can be provided after a two-level check hasbeen performed. This two-level check uses twotypes of independent CPUs, a standard CPU andan optional CPU, each using a different calcula-tion algorithm, where the trip output is the resultof a logical AND calculation on the results of theindividual calculations performed, see Fig. 4. Highlevels of reliability are assured by the self-diagnos-tic functions performed on each of the individualfunctional modules built into the protection relays,see Fig. 5. Additionally, at its maximum applica-tion, four levels of password protection provide se-cure access to the protection/control system.

The software can be generated by the selectionand configuration of modules from a module li-brary. The results are a virtual machine runningon a PC, with the same functions as the actualequipment, thus making it possible to perform re-

KEYTR Input transformer DO Digital outputRYC Main CPU HMI Human machine interfaceDI Digital input

TR RYC card

FD card

DI HMI

DO card

X

X

Fig. 4 Hardware-independent fail-safe function

TECHNICAL REPORTS


sponse analyses on the virtual machine. Thismakes it possible to perform evaluations more ef-ficiently under a variety of conditions before thebuilding of the actual power network.

GROWING. In this system, both the hardware andthe software are modular, allowing functions tobe added as necessary using a building-blockmethod.

The circuit reclosing function, back-up function,the number of feeder lines under protection, andthe capacity of the event log are optionally avail-able with additional hardware options. The prod-uct lineup is shown in Table 1.

ENVIRONMENTALLY FRIENDLY. The power con-sumed by the unit is one half of that of previousunits. Also, batteries have been eliminatedthrough the use of non-volatile memory. Effortshave been made to eliminate the use of plasticswhenever possible.

MELPRO-C can be placed near primary equip-ment, so it is possible to greatly reduce the cablethat used to be necessary between the primaryequipment and the protection/control equipment.

Through the use of tried-and-true algorithms toprevent current transformer saturation, the

RYC card

TR

TR card

PS

PS card

DSP

KeyCPU Central processing unit AI Analog input S/H Sample and hold RYC Main CPUDI Digital input TR Input transformer A/D Analog to digital converter HMI Human interfaceDO Digital output F Filter DSP Digital signal processor PS DC power supply

PS check

AI check

CPU and DSP check HMI check

DO check DI check

F S/H A/D

CPU

HMI card

Direct HMI

Do card

DO DI

DI card

Fig. 5 Self diagnosis

noitacilppA emehcS tcudorP

senilnoissimsnarTnoitcetorp

laitnereffidtnerrucMCP H-DCM

yalerecnatsiD H-TDM

noitcetorprabsuBlaitnereffidtnerruC H-PBM

laitnereffidecnadepmihgiH 3H-PBM

noitcetorperuliafBC COdeepshgiH H-FBM

noitcetorprefsnarT laitnereffidoitaR H-PTM

noitcetorpenilredeeFlanoitceridGVO/VU,GCO/CO

tluafhtraeH-PFM

enilredeeFtnemeganam

lanoitceridGVO/VU,GCO/COlortnoc,tluafhtrae

UTF

noitcetorprotareneG COevitagen,laitnereffidoitaR H-PGM

Table 1 MELPRO-C Series Product Line

MELPRO-C can be applied to existing primary sys-tems, and can contribute to the reuse of exis-ting systems. On the secondary side, MitsubishiElectric Corp. has developed an input conversionmodule with low loads and high linearity usingair-core coils. This module is one-sixth the size ofprevious modules. A module has also been pre-pared that can be used when an air-core currenttransformer is used as the current transformer onthe primary side.

In the future, we can anticipate advances in powersystems based on the introduction of, for example,distributed power supplies. Mitsubishi ElectricCorp. intends to continue its contributions to to-tal system solutions for high-efficiency operationwhile still maintaining high levels of reliability andenhancing compatibility with primary systems. ❑

Reference1. Arun G. Phadke and James S. Thorp, 1988, Computer Relaying for

Power Systems.2. H. Sato, T. Takano, S. Inoue, S.Oda, T. Anzai, N. Kusano, 2001, A

Comprehensive Approach for Numerical Relay System Evaluationand Test, IEE DPSP 2001.

TECHNICAL REPORTS

· 5September 2001

The authors have developed a new *MELPRO-C series of protection relays using the latest 32-bit RISC processors and high-density componentmounting techniques. The series combines ex-cellent performance with a reduction in size toone-half that of the corporation’s preceding types.The adoption of intranet technology enableshighly “open” networks to be configured, whilethe associated software provides high produc-tivity and reliability.*MELPRO is currently undergoing registration as atrademark of Mitsubishi Electric Corporation.

The Basic Technological ElementsThe basic technological elements of MELPRO-Cprotection relays are shown in Fig. 1. Supportingthe upstream application software suite for moni-toring, control and protection are the technolo-gies for microprocessor application, equipmenthardware, software productivity and network ap-plications.

As shown in Fig.1, of these basic technologicalelements, software is divided into two layers, abasic layer and and an application layer. Thismeans that as and when new technological de-velopments result in changes to the external speci-fications of hardware, their influence can be

*Toshio Anzai and Takashi Oosono are with Transmission & Distribution, Transportation Systems Center.

by Toshio Anzai and Takashi Oosono*

MELPRO-C Series Protection Relays andTheir Basic Technological Elements

Table 1 A Comparison Between MELPRO-C andthe Preceding Hardware

Item Preceding type MELPRO-C

Cards used Analog Main Main input CPU CPU

Card size (mm) 290.8 x 233.35 160 x 233.5

(two) (one)

Processors 32-bit CISC 32-bit RISC(one each) 16-bit CISC 32-bit DSP

Performance ratio 1 1.5 (standard)4.0 (large scale)

MELPRO-SAVE produces software code

SO

FT

WA

RE

MainCPU

FailsafeCPU

Digital I/O(embedded, remote)

Transmission and communication

Embeddedweb server

HA

RD

WA

RE

Application software layer

Technological elements layer

Basic software layer

Hardware layer

MonitoringRelay

elementControl

Sequenceprocessing

Measure-ment

Network

Real-time task scheduling Control of system bus Self diagnostics

De-facto standards High-performance microprocessor High-density implementationLow-power design Radiation System bus Network applications ReliabilityNoise immunity Plug-in

Standardized design

Human/machineinterface

Fig. 1 Architecture of basic technological elements used in MELPRO-C relays

handled entirely within the basic layer, exertingno influence on the application layer.

MiniaturizationBy adopting an LSI implementation of the mi-croprocessor peripheral circuitry and applyinghybrid IC technology, the component count hasbeen significantly reduced. This, combined withthe latest high-density mounting technology, hasreduced the size of the relays to about one-halfof the corporation’s preceding models, as shownin Table 1.

Again, by using a serial I/O bus to connectthe processor and the input/output sections, the

TECHNICAL REPORTS


space previously needed for wiring within therelay panel has been reduced.

NetworksWe have provided MELPRO-C relays with thefollowing two network functions:

● A network operating at the substation level(to provide high-level system operation andeffective maintenance) that can interconnectwith supervisory control and data acquisition(SCADA) systems, so that the relays can func-tion as data terminals for supervision, con-trol and protection within electric powersystems.

● A process-level network linking monitoring,control and protection equipment and con-trolled-system equipment (to reduce the costof building substations by eliminating metalcables).

The network interface specification are shownin Table 2. The network protocols chosen sat-isfy international standards to ensure “ open”(non-proprietary) operation and low costs.

Fig. 2 Typical display on the human/machine interface

Menu view

System state view

Adoption of Intranet TechnologiesThe adoption of intranet technologies forMELPRO-C relays provides remote monitoringfunctions that make it possible to remotely con-firm the information of monitoring, control andprotection equipment and operate a setting. Thegeneral intranet technology base has beensupplemented to ensure the necessary operabil-ity and reliability. As a result, monitoring, con-trol and protection equipment with the remoteoperation maintenance function can be config-ured at low cost and with outstanding ease ofoperation.

A typical display for a remote maintenance sys-tem is shown in Fig. 2. The human-machine in-terface continuously displays the names and statesof the equipment, giving the operator a continu-

Table 2 Network Interface Specifications

Item Specification

Substation level network DNP3.0, UCA2.0, IEC-StandardElectrical/optical

Process level networkcc-Link, Lon, IEC61850Electrical/optical

TECHNICAL REPORTS

· 7September 2001

ous grasp of the condition of the various items ofequipment, including abnormalities and the stateof TRIP. Again, remote operations that would havea major effect on equipment functions are sub-jected to restrictions.

Adoption of Software TechnologyThe application of previously developed softwaretechnology has enabled us to develop a revolu-tionary engineering tool, MELPRO-SAVE. Theoutline of this tool is shown in Fig. 3.

This software tool has three main character-istics:1. It does not require programming.2. It guards against human error.3. It provides enhanced system verification functions.

To render the tool free of programming, wefirst created standard software components forall relay elements, sequential logic, etc., thenperformed selection of components, setting ofparameters, and allocation of the input and out-put signals by a graphic user interface. This issufficient to generate the required software.

We implemented human-error prevention bya function that establishes a parameter auto-matically, maintaining consistency between

Menu-based input of assignment of I/O channels

Logic design

Component selection

System configuration

System simulation

Component library

Central server (Windows NT)

Re-use for routine

Configuration information

library

Simulation condition

library

System model library

Re-use ofsimulationcondition

PC-basedcluster

Easy custom-made logicusing block-diagram format

System simulation on PC provides for dynamic characteristics test

Set

sim

ulat

ion

cond

ition

Tes

t com

plet

e

R

egis

trat

ion

Fig. 3 Outline of the MELPRO-SAVE engineering tool

parameters. For this function, we assigned theattributes beforehand to the components and theparameters.

For enhanced verification, we build not onlythe software provided with the product but alsothe model of analog input circuits and the digi-tal input/output circuits of the hardware and thepower system itself in this tool so as to makepossible overall simulation on a PC.

The application of this tool reduces the cycletime for planning, design, production and verifi-cation, improves the quality of the software, andincreases the flexibility of the monitoring, con-trol and protection equipment of the power sys-tems in which it is used.

MELPRO-C and MELPRO-SAVE offer significanttotal cost savings for electric power systems andtheir operational maintenance systems. Theyalso facilitate flexible monitoring, control andprotection systems applicable to a wide range ofpower systems, ideally meeting their specialcharacteristics and operating requirements. ❑

Reference1. H. Sato, T. Takano, S. Inoue, S.Oda, T. Anzai, N. Kusano, 2001, A

Comprehensive Approach for Numerical Relay System Evaluationand Test, IEE DPSP 2001.

TECHNICAL REPORTS


*Shigeto Oda and Takashi Hattori are with Transmission & Distribution, Transportation Systems Center.

by Shigeto Oda and Takashi Hattori*

Applying Relay Protection to a 500kVTransmission Line with Series Capacitors

The MELPRO-C Series MCD-H (a PCM carrierrelay with a distance-relay function) has beenadopted for a system in the Peoples Republic ofChina that includes series capacitors. The au-thors simulated a transmission system in whichseries capacitors have been installed, using areal-time digital simulator to verify the effectson the MCD-H relay of transient voltage andcurrent phenomena when there is a system fail-ure, allowing appropriate countermeasures to beimplemented. This article reports on the tran-sient current and voltage phenomena and on so-lutions for their effects on the relay.

The Application SystemThe MCD-H relay was ordered and installed toprotect the parallel transmission line betweenthe 500kV Datong and the Fangshan substationsby the North China Power Group. In order toprevent transmission losses (and reductions inthe amount of electrical energy that can be trans-mitted) due to increases in transmission linereactance over the long-distance transmissionlines in this system, series capacitors were in-stalled in the transmission path to reduce thereactance. The Datong and Fangshan substa-tions are 288km apart, and the series capacitorsare installed 151km from the Fangshan substa-tion. The series capacitors provide 35% compen-sation for the transmission-line reactance. Notethat a gap is provided in the series capacitor toallow it to short when the voltage across thecapacitor exceeds a certain level. This is to pro-tect the series capacitor when there are highvoltages during failures.

Static Effect on RelaysPCM carrier current differential relays are unaf-fected by the installation of series capacitors inthe transmission path, as the currents passingthrough the relays when there is an externalfault do so without generating a differential cur-rent. However, with internal faults, the faultcurrent itself is a differential current, so no prob-lems arise with relay operation.

In distance relays, the impedance seen by therelays, as shown in Fig. 1, as affected by theseries capacitors (with the compensation ratio

of 35%), depends on whether there is a seriescapacitance (point B in Fig. 1) or whether thecapacitor is shorted (point B’ in Fig. 1). In Zone1, the Zone of immediate operation, point Bserves as the far end where the length of theoperating region is shortened due to the influ-ence of the series capacitors, so it is establishedat between 80 and 90% of point B. OperatingZone 2, which covers the far end, must be es-tablished as a Zone that is able to cover point B’at the far end, which is established envisioningthe case where the gap circuit operates to causea short when the voltage across the capacitorrises due to a fault current on the far end.

The Impact of the Relays on OperationsThe maximum deviation in voltage and currentthat can be anticipated due to the resonance inthe series capacitors and the system reactancewhen there is a fault or when the circuit breakertrips was observed at around 130 to 140ms. Fig.2 shows the electric current and the voltage thatwas saved by the relay when there was a 3ΦSfault at the far end. (In this case, the series ca-pacitors did not short.)

A description follows of the impact on the re-lays when there are transitory fluctuations in

Zone2

B'S/S (at short-circuit of series capacitor)

BS/S

R

Fast operating zone

Slow opearting zone for stable operation Zone 1

Fig. 1 Operating zone setting of AS/S distancerelay element

TECHNICAL REPORTS

· 9September 2001

current and voltage whenever the circuitbreaker operates, as described above, or whenthere is a fault, along with countermeasures forthis impact.

A circuit that reduces the relay operating sen-sitivity (the differential current operating sensi-tivity) for a specific period of time when thecircuit breaker is turned on is installed in thecurrent differential PCM carrier relay. We haveconfirmed that this circuit is able to absorb theimpact of the transitory differential currentswhen the circuit breaker is turned on.

Fig. 3 shows the impedance trajectory analy-sis of AS/S relay “ save” data in the distance re-

Fig. 2 Fault waveform of voltage and currentsaved on the AS/S relay (at F1 3ΦS faultof Fig. 4)

Fault Ocurrence

VA

VB

VC

V0

VB1

VB2

IA

IB

IC

I0

Fig. 3 Impedance locus at A S/S relay(at F1 3ΦS fault of Fig. 4)

Fault occurrence time: 195ms (time in figure by ms unit)

have also confirmed that, at this time, the faultimpedance transitionally goes into the Zone 1operating region. The Zone 1 operating regionis broadly divided into two parts; a low-speedregion (for obtaining stable operation withlengthy operating checks) and a high-speed re-gion (where one can expect high-speed opera-tion, and the operating checks are shorter). Amethod has been used to prevent unnecessaryresponses due to transient incursions, as shownin Fig. 3, by setting the region wherein theseincursions can take place as a low-speed region.

At the same time, in systems where there isno series capacitor, even if there is a transitoryincursion into Zone 1 in this way, the fault im-pedance moves rapidly to the fault point fromthe load current status (within several millisec-onds), obviating the need for any broad low-speedregion such as shown above.

The use of the real-time dynamic simulator asdescribed above has made it possible to under-stand precisely the transient relay response in asystem with series capacitors, and after appro-priate countermeasures were put in place, themeasures also passed verification tests using adifferent type of dynamic system simulation atthe Chinese Electric Power Research Institute.The dynamic simulation tests at the Institutewere artificial transmission line (ATL) simulatortests using a power generator, a transformer anda simulated transmission line system to performactual testing on a simulation of the substationsthat are used at Datong and Fangshan, and witha dummy system transmission line at 500kV for400km. Both simulation systems confirmed thecorrect operation of the relays, providing the nec-essary verification. At present, final on-site ad-justment tests are underway for the relays, withthe start of actual operations scheduled for June,2001.❑

Fig. 4 Line system diagram between Datong andFangshan

lays, when there is a fault outside of Zone 1,shown by the F1 point in Fig. 4, in the case wherethe serial capacitors do not short. In this case,there will be transient fluctuations in voltageand current when the fault occurs, and we haveconfirmed that the fault impedance rotatesaround the fault point before reaching it. We

Datong (AS/S)

127km 161km Line2

Fangshan (BS/S)

127km 161km Line1

F1(3ΦS)

Line length : 288kmSeries capacitor location : 161km from Fangshan S/SCT ratio : 2500A/1APT ratio : 500kV/100V

TECHNICAL REPORTS


*Susumu Fujita and Yasuhiro Tsunoi are with Transmission and Distribution, Transportation Systems Center.

by Susumu Fujita and Yasuhiro Tsunoi*

MELPRO-C Digital Relay System for FeederProtection in Outdoor Installations

Mitsubishi Electric Corporation’s MELPRO-CSeries of digital relay systems apply a consis-tent architecture to bus protection and distribu-tion feeder protection. In equipment providingfeeder protection on power distribution systems,there is a growing need for integration of themetering, control and protection functions, andfor outdoor installation. The feeder terminal unit(FTU) introduced here is an example ofMELPRO-C application to a new feeder protec-tion system that functions as a pole-mountedterminal.

Main FeaturesThe role of the FTU in feeder protection is illus-trated in the system block diagram in Fig. 1. Theappearance of the FTU is shown in Fig. 2.

The FTU implements metering, supervision,control and communications functions. It is usedto detect short circuit faults and phase-to-groundfaults. To withstand outdoor installation it adoptsa highly rugged enclosure (IP65), with a compactsize of 330mm (D) by 330mm (W) by 380mm (H).

The unit is accessible from a remote or localhost for referencing or changing settings and fordownloading programs. Communication with aremote terminal unit makes use of twisted-pair

Fig. 1 System block diagram

Substation

FTUFTU

SAS

FTU

Communication from Master-Station to RTUs

- WAN/Point-to-Point- Micro-wave/Optical fiber/Metallic- 1,200/2,400/4,800/9,600/19,200bps- DNP3.0/IEC870-5-101/TCP/IP

Master Master

WAN

RTUDAS

RTU

Substation

SAS+DAS

Communication from RTUs to FTUs

- Optical fiber/Metallic- 1,200/2,400/4,800/9,600/19,200bps- DNP3.0/IEC870-5-101- Polling from RTUs

FTU

FTU

LBS

TR

Battery box

Fig. 2 Appearance of FTU

TECHNICAL REPORTS

· 11September

cable or single-mode optical fiber cable. Inter-national standard communication protocols aresupported, including IEC60870-5-101 andDNP3.0 (Level 2/3). A multi-drop topology andstar configuration are used for the network, oneither optical fiber or metallic cable. Communi-cation speeds of 1200, 2400, 4800, 9600 and 19,200bits per second are supported.

The FTU implements self-closing processing,described below. Using a phase transistor for itspower supply, it requires no external power source.

FunctionsThe data flow between FTU functions is shownin Fig. 3, while the control functions and meter-ing functions are listed in Table 1.

The main processing functions of the FTU aredescribed here.

LOAD BREAK SWITCH MONITOR INFORMATIONTRANSMISSION. Requests from the RTU gener-ate transmission of LBS monitor information,fault detection information, and FTU status in-formation.

LOAD BREAK SWITCH CONTROL INFORMATIONRECEIPT. Load break switch (LBS) control infor-mation is received from the remote terminal unitand is output to digital output (DO).

FAULT DATA TRANSMISSION. Detailed fault in-formation and fault data are sent on request froma remote terminal unit.

PROGRAM DOWNLOAD AND SETTINGS UPDATE.Program data and settings in the FTU are up-dated on request from a remote terminal unit.

MONITOR DATA TRANSMISSION. Requests fromthe RTU generate transmission of the latestmonitor data.

SELF-CLOSING PROCESSING. An explanation ofself-closing processing is given below.

FTU STATUS MONITORING. The FTU status ismonitored, and the result is passed as “ FTU sta-tus” in load break switch monitor informationtransmission.

Fig. 3 Data flow

LBS

FTU

DI

FTU StatusLBS information transmission processing

LBS information

LBS control information receive processing

DO

RTU

LBS controlinformation

AI

CT data

Monitor data processing

Monitor datatransmission processing

Request from RTU

Fault detection processing

Fault datatransmission processing

Self closing process

Down line load andsetting value processing

PT

PT

PT data

TECHNICAL REPORTS


Table 1 FTU Functions

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rebmunUTFgnittes)rebmunelop(

.032ot1morftessi)elop(UTFforebmunnoitacifitnedI

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Fig. 4 Self-closing diagram

CB status

SECTION#1

SECTION#2= LBS#1 status

SECTION#3= LBS#2 status

Fault

X time X time

X time

Y time Y time

Y time

CBtrip #1

CB close #1

LBS#1close #1

LBS#2close #1

CBtrip #2

CBclose#2

LBS#1close#2

Lock

Not closebecause of lock

Substation Distribution line

FTU2 FTU1

LBS2 LBS1 CB

X time

Y time

FTU

X time

Y time

1 12 22 4

FTU

TECHNICAL REPORTS

· 13September

MONITOR DATA PROCESSING. Monitor data (ef-fective values and power factor) is calculated from30-degree sampling data at analog input (AI).

FAULT DETECTION PROCESSING. Short circuitfaults and phase-to-ground faults are detectedfrom the 30-degree sampling data.

If a fault is detected, the monitor data is savedas fault data.

Protection Function (Self-Closing Processing)The self-closing processing function, which isone of the FTU feeder protection functions, isexplained here with reference to Fig. 4.

Feeder protection by self-closing processing isused in a distribution system with no remoteterminal unit or in which remote terminal unitpolling is stopped.

1. When a fault occurs, the FTU detects a volt-age drop on the source side and opens theload break switch.

2. If the source-side voltage is restored after thefault occurs, the load break switch is closedafter (time interval X) has passed.

3. If the load-side voltage is restored after thefault occurs, lock state is set and the loadbreak switch is not closed until the lock statehas been cleared.

4. If there is a recurrence of the fault within(time interval Y) after load break switch clos-ing control, lock state is set and the load breakswitch is not closed until the lock state hasbeen cleared.

5. When the voltage on both the source and loadsides is restored by forcibly closing the loadbreak switch, the lock state is cleared after(time interval Y) has passed.

Among the likely demands for feeder protectionsystems in the future are increased meteringinformation and shorter control times. To meetthese needs, Mitsubishi Electric is planning todevelop systems with faster communicationspeeds and more advanced functions, includingthe application of international standardIEC61850 and UCA2.0. ❑

TECHNICAL REPORTS


The MELPRO-D series of protective relays, withcomplex functions and communication capabili-ties, go beyond the fault isolation provided byconventional protective relays. Their advancedcombination of control, measurement, faultrecord and monitoring functions is comple-mented by their ability to transfer informationto manned control centers. They are humanfriendly and cost effective.

The Development ConceptsIn recent years, protective relays are required todo much more than their original task of isolat-ing faults from the distribution system. Theymust employ information-processing, communi-cations and semiconductor technologies to in-crease the sophistication and reliability of theprotection they provide, while at the same timecontributing to labor savings by convenient andlargely service-free operation, and to lower costs(not only of their complex functions but the to-tal cost throughout the product life cycle). Thedesign concepts behind the new series are (1)exploiting digital technology to provide moresophisticated functions; (2) reducing labor andpower requirements by exploiting network tech-nology; and (3) reducing costs by including mul-tiple, complex functions. Two members of thenew series are shown in Fig. 1.

Characteristics of the New Series

IMPROVED PERFORMANCE. Relay operation pro-vides multiple functions, digital filters reducethe effect of high harmonics, and digital process-ing has been adopted for high-speed sampling.

SOPHISTICATION AND COMPLEXITY. The seriesis compatible with advanced communicationnetworks and provides enriched metering func-tions with fault record functions.

SIMPLER MAINTENANCE. Detailed data acqui-sition is possible using a PC interface, datasaving functions enhance self diagnostic capa-bilities, digital processing ensures stable oper-ating characteristics, and resistance to hostileoperating environments has been increased.

*Kazuyoshi Fujita and Toyoki Ueda are with the Transmission & Distribution Systems Center.

by Kazuyoshi Fujita and Toyoki Ueda*

MELPRO-D Series Protective Relays forPower Receiving/Distribution Systems

CUSTOMER ORIENTED. Programmable contactsprovide flexible response to customer needs, avery wide range of settings is possible, consis-tent installation dimensions are designed to fa-cilitate replacement, and the series conforms tointernational standards (IEC, BS, etc).

USES ESTABLISHED RELAY TECHNOLOGY. The se-ries embodies the corporation’s traditional ex-pertise, dating back to the analog era, andpower-distribution system technology up to andincluding UHV systems.

EXHAUSTIVE VERIFICATION FACILITIES. The com-plete test facilities for verification enable simu-lation of the full range of power-system faults,and automated testing can be provided to expe-dite customer acceptance testing.

Fig. 1 Two typical members of the MELPRO-Dseries of protective relays for powerreceiving and distribution systems

TECHNICAL REPORTS

· 15September

System ConfigurationThe analog input and CPU cards and the previ-ously separate digital output card have all beenintegrated onto a single relay card with an in-ternal high-speed serial communication bus fordata transfer, forming a system with high expan-dability, see Fig. 2.

Again, the adoption of a serial bus for communi-cations enables a reduction in the amount of wiringrequired and makes for efficient (i.e., more compact)mounting, with the human-machine interface (HMI)now integrated with the motherboard.

HIGHER RELIABILITY. This is achieved by the sig-nificantly reduced component count (to approx.50% of the previous series), and by dispensingwith wiring.

EXPANDABILITY. Additional relay cards can be in-serted to expand capabilities (not only relays butalso digital input/output cards, etc.); optional com-munication cards are also available.

STANDARDIZATION. Despite the very wide rangeof products available in the series, the same ba-sic hardware configuration has been adoptedthroughout, from those with few internal ele-ments to those with very many.

Fig. 2 Internal block diagrams of former and MELPRO-D relays

METAL/PLASTIC HYBRID CASE. A design thatmakes the best use of the different characteris-tics of metal and of plastic moldings helps thepackaging to contribute to overall reliability, seeFig. 3 and Table 1.

Molded plastic is used for the case, cover,frame and other structural elements, designedto ensure the necessary strength and advantagesin installation.

Comm. card (Option)EMI sealed

Plastic goodsMetal processing

Cover

Sub-unit

Case

Fig. 3 Typical unit structure

<A/I>

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rnal

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us

X

X

TECHNICAL REPORTS


Concerns over electromagnetic interference(EMI) with the adoption of plastic casing havebeen addressed by providing a metal shieldaround the internal components.

The MELPRO-D series provides all the elementsnecessary for protection of extremely high voltageand high voltage receiving and distribution sys-tems and parallel running systems, and includesover-current, voltage, feeder, motor, and trans-former protection.

With MELPRO-D protective relays, MitsubishiElectric Corporation is writing a new chapter inthe long story of corporate achievements in help-ing to protect the world’s electric power systems.These sophisticated, flexible and highly cost-ef-fective units are alrady finding widespread appli-cations around the world. ❑

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Table 1 Factors Behind Selection of Materials, Metal or Plastic.

· 17September 2001

TECHNICAL REPORTS

*Keiichi Matsuo is with the Nuclear Power Department.

OverviewCurrent and Future Trends in Radiation Monitoring Technology

by Keiichi Matsuo*

Mitsubishi Electric Corporation has been supplying radiation monitoring systemsfor all pressurized water reactor (PWR) nuclear power plants in Japan since 1969. Recently,the medical uses of radiation have been attracting attention, as heavy particle beams andproton beams have been used in the treatment of cancer and unsealed radiation sourceshave found applications in medical diagnostics. This has led to a marked increase in thenumber of facilities where radiation levels must be monitored. The large quantitative in-crease in the demand for monitoring equipment has been accompanied by a major departurefrom traditional methods of measuring radiation levels. Previously, it was sufficient if themeasurements were reliable, and the external appearance and physical form of the equip-ment making up the system were largely immaterial. Now, however, particularly wheninstalled at locations in the public eye, such as at hospitals, radiation measuring equipmentthat is both compact and good to look at is called for. Again, in the absence of any on-siteradiation specialists, there is a very strong need for minimal maintenance. In this marketenvironment, the corporation has supplemented its conventional detectors by developingnew products that use the following key technologies: semiconductor radiation detectorswith characteristically small size and long working life, and radiation monitors that useoptical fibers to achieve outstanding resistance to interference and noise.

In the future, the customer will be linked to the service center responsible for maintainingthe workplace over public telephone lines, so that abnormalities at the monitored installa-tion can be diagnosed and the information on the situation being monitored can be trans-ferred, with a centralized monitoring service being performed at the workplace. To achievethis, the technology for monitoring the status of the semiconductor detectors has beenestablished (providing diagnostics for performance degradation) and will be used to configurea system that provides continuous monitoring of the health of on-site monitors and measur-ing equipment and can do so remotely.

The corporation’s long experience in providing radiation monitoring systems for nuclearpower plants and its advanced expertise in computers and communications will be dedi-cated to producing an enhanced product lineup for hospitals and research laboratories. Thecorporation is committed to providing systems that will offer clear advantages over thecompetition to its customers. ❑

TECHNICAL REPORTS


*Kenichi Moteki and Kazuhiko Fuzita are with the Energy & Industrial Systems Center.

by Kenichi Moteki and Kazuhiko Fuzita*

A New Radiation-Management System

A radiation-management system is a compre-hensive system for measuring and keeping trackof radiation levels in and around nuclear powerplants and other facilities where radioactivematerials are present. Mitsubishi Electric Cor-poration now provides a radiation-managementsystem based on a new approach, with the ad-vantages of fast response, high reliability andeasy maintenance.

System ConfigurationThe radiation-management system consists ofseveral subsystems. These include a system formanaging the exposure of individuals to radia-tion, a system for controlling room entry and exit,a radiation-monitoring system, and a radiation-

Fig. 1 Radiation-management computer system

ITV system in guardroom, etc.

Control system for accelerator, etc.

Lighting control equipment

Main console

ITV system

Radiation monitoring

system

Inte

rlo

ck

Radiation exposure

management system

Room entry/exit

controlsystem

Outdoor multifunction camera unit

Supervision room

Terminal

Camera Indoor multifunctioncamera unit

Camera

General-purpose network

Entry card

reader

Entry card

readerEntry card

reader

Entry card

reader

Exit card reader Exit card

readerExit card

readerExit card

reader

Automatic door

Automatic door

Display screen Display screen Display screen Display screen

Hand, feet and

clothingmonitor

Electroniclock Electronic

lock

Emergency stop switch

Emergency stop switch

Personal key panel

Personal key panel

Speaker

Neutron radiation area monitoring

systemWater monitor

Gas monitorSampling

panel

Optical fiber-based radiation detector

Gamma radiation areamonitoring system

Measures gammaradiation distribution

Statusindicator

lamps

Room entry/exit management system




management computer system for overall con-trol of these systems. The total system configu-ration is shown in Fig. 1.

System Design ApproachThe radiation-management system is designedbased on the following approach.

1. Processing response is improved by separat-ing the computer processing for radiation-exposure management from that for radiationmonitoring.

2. The system is designed so that individual com-puters serve as backups to each other, in or-der to prevent local failures from causing aloss of total system function.

TECHNICAL REPORTS

· 19September

3. Industry standard equipment and equipmentinterfaces are adopted for ease of mainte-nance.

System Functions

RADIATION-MANAGEMENT COMPUTER. The roleof the radiation-management computer in theoverall system is to perform real-time online pro-cessing of the radiation-measurement data fromeach of the subsystems, and to display and man-age the resulting data. A conventional systemwith one computer responsible for all the man-agement tasks puts an excessive processing loadon that computer and risks the complete loss ofsystem function in case of a computer failure.Distributing the processing to separate serversfor each function has raised the level of reliabil-ity as well as improving system operability andmaintenance.

Table 1 Main Specifications of Components Making Up the Radiation-Management System

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The functions of the components making upthe radiation-management computer are outlinedbelow. The main specifications of each compo-nent are given in Table 1.

1. Radiation-management server. This servergathers and manages data from the systemas a whole. It is also used for maintenance ofmanagement information.

2. Information-management system (for room en-try/exit control). Information on individuals isgathered by this system, including their jobclassification and type of work, radiation ex-posure, etc. Typical screen shots are theworker registration screen (Fig. 2), list of work-ers (Fig. 3), and room entry/exit log (Fig. 4).This system stores the gathered informationin the radiation-management server. In caseof trouble with this system, backup can beimplemented by switching to the information-

Fig. 2 Worker registration screen Fig. 3 List of workers

TECHNICAL REPORTS


management system for radiation monitoring.3. Information-management system (for radia-

tion monitoring). Over a local network, thissystem gathers and stores the settings andmeasurement values from the instrumentsused to monitor radiation levels. The basicscreens include the radiation monitoring andtrend graph screen (Fig. 5) and constants set-ting screen (Fig. 6). This system periodicallystores the gathered radiation-monitoringinformation in the radiation-managementserver. In case of trouble in this system, datacollection is continued by switching to theinformation-management system for roomentry/exit control.

4. Remote administration terminal. Informationis displayed and changes in settings are madeusing this system. For security, the authorityto display and change settings is restrictedby password control.

Fig. 4 Entry/exit log screen

ROOM ENTRY/EXIT CONTROL SYSTEM. The partof the radiation-exposure management systemthat controls room entry and exit is outlined here.It makes use of card-reader door controllers atthe entry/exit points to each of several radia-tion controlled areas, monitoring and restrict-ing movement through these points. Since thesedoor controllers store the minimum necessarymanagement information for entry into the area,they support a standalone operation mode in caseof a server crash or network failure, etc., allow-ing them to perform an ID card check and openand close doors as necessary. The componentsof the entry/exit control system are describedbelow.

1. Entry/exit control terminals. The card read-ers used to control movement through check-points provide information such as personalidentity, job objective, and location. This IDcard information input at a card reader ischecked by the information-managementsystem for entry/exit control, and the door isopened and closed accordingly. It can performthis checking on its own if necessary, basedon a minimum amount of stored information,in case it cannot connect to the information-management system.

2. Card readers. The card readers are a non-contact type, and are used to check informa-tion on people entering the controlled area.Card information is sent through the entry/exit controller to the entry/exit control sys-tem for checking. Since the ID card uses ra-dio waves from the card reader for emittingsignals, it does not require a battery.

3. People sensors. The counting of people en-tering and leaving the area is monitored bypeople sensors in addition to the ID cards. TheFig. 5 Radiation monitoring and trend graph

Fig. 6 Constants setting screen

TECHNICAL REPORTS

· 21September

people sensors monitor people entering orleaving the area by CCD camera, and canissue an alarm as necessary, to prevent some-one without an ID card from going through adoor at the same time as a card holder.

RADIATION-MONITORING SYSTEM. Radiation-monitoring equipment measures and monitorsthe dose rate of radiation within the controlledarea, as well as the levels of radioactive materi-als in the air, exhaust and wastewater, etc. Itsounds an alarm if the level exceeds a presetvalue. This equipment incorporates a highlycompact controller inside the detector signal-processing unit, equipped with computing andcommunication functions. Signals from the ra-diation detectors are input to this controller forprocessing, then the digital data is sent over alocal network to the information-managementsystem for radiation monitoring. The local net-work can be connected as necessary to a sam-pler or other radiation-measurement instrumentor to a control device or I/O device for data dis-play, etc., enabling on-site equipment to be in-terconnected over the local network. In addition,there is environmental radiation-monitoringequipment for measuring the dose rate of radia-tion in a given area, detectors for detecting lowlevels of NaI, and ionization chambers for de-tecting high levels. For the monitoring equip-ment there are temperature controllers to keepdetector temperature constant, display units toshow dose rates graphically, and recording equip-ment. Output specifications (pulse and contactoutput) are also available for telemetry output.

The new radiation management system, as de-scribed above, applies the latest in hardware,package software and general-purpose LANtechnology to realize a total system that incor-porates a variety of user-requested functions forradiation management. ❑

TECHNICAL REPORTS


*Seisaku Imagawa is with the Energy & Industrial Systems Center and Hiroshi Nishizawa is with the IndustrialElectronics & Systems Laboratory.

by Seisaku Imagawa and Hiroshi Nishizawa*

Semiconductor Radiation Sensor

A novel radiation measurement system has beendeveloped using semiconductor radiation detectorsto improve the life expectancy, reliability, main-tainability, and miniaturization of detector equip-ment in radiation measurement systems forpressurized water reactor (PWR) nuclear powerplants. This article will present a summary of thesemiconductor-type radiation monitor technology.

Mitsubishi Electric Corp. handles measurementand control systems for PWR nuclear powerplants within Japan. As part of this measurementand control, radiation monitoring equipment hasthe function of constantly monitoring the radia-tion levels in the air and in fluids, so as to moni-tor releases of radioactivity into the environment,protect human workers and provide early warn-ing of problems with equipment. Note that bothγ radiation and β radiation are monitored whenperforming the radiation measurements.

Benefits of Semiconductor DetectorsSemiconductor detectors detect radiation takingadvantage of the generation of electron/hole pairscaused by the radiation (along with the drift of theelectron/hole pairs). The semiconductors used inthese detectors include silicon (Si), germanium(Ge), cadmium tellurium (CdTe), zinc cadmiumtellurium (CdZnTe), and mercury diiodide (HgI2).

Physical Principals of the MeasurementSystemIonizing radiation such as X-rays and gamma raysdo not directly ionize atoms, but rather some orall of the energy is deposited on electrons due tothe photoelectric effect, the Compton effect, andpair production, and the ionizing power of the elec-trons causes an ionizing effect. On the other hand,α and β particles have a direct ionization effect.The electrodes of semiconductor detectors collectthe electrons and holes generated by this ionizingeffect, and output a radiation detection signal.

The Benefits of the Semiconductor ElementsAt present, GM counter tubes, scintillation de-tectors and ionization chambers, etc., are gen-erally used as the radiation detectors in nuclearpower plants; however, the following advantages

can be obtained by the use of semiconductor sen-sors as the detectors.

LONG LIFE EXPECTANCY. GM counter tubes andscintillation detectors deteriorate over time, re-quiring replacement every year or every fewyears; however, because of the stability of thematerials in semiconductor detectors, the inter-val between replacements of semiconductor de-tectors is over ten years, making it possible toreduce maintenance costs.

IMPROVED RELIABILITY. In GM counter tubes,the gas deteriorates, and in scintillation detec-tors, the photomultiplier tube wears out overtime, which can cause the readings to drift; how-ever, fundamentally these problems do not oc-cur with semiconductor detectors, and even inthe test equipment the readings were stable.

IMPROVED MAINTAINABILITY. In scintillationdetectors, the applied voltage must be adjustedor otherwise maintained periodically; but be-cause semiconductor detectors operate at a fixedlow voltage, the need for work in adjusting thedetectors is greatly reduced.

MINIATURIZATION. Because semiconductor de-tectors are small—even when they still have thesame detection capabilities as conventional de-tectors—the use of the semiconductor elementsmakes it possible to reduce the size of the de-tector equipment and the samplers (lead-shieldedvessels), thereby both saving space and reduc-ing costs.

A Comparison of the Characteristics ofSemiconductor ElementsThe semiconductor elements currently in useare as shown in Table 1. Based on this table, thespecifications of the semiconductor elementsused in the various radiation monitors installedin nuclear power plants were selected and usedin the detectors. Detector elements with supe-rior energy characteristics are required in areamonitors and the primary steam-duct monitors,and Si semiconductor monitors were selectedbecause they fulfill these requirements. Because

TECHNICAL REPORTS

· 23September 2001

Table 1 Main Characteristics of the Semiconductor Detectors

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the primary steam duct monitor must be oper-ated at high temperatures (up to 90°C), the high-temperature type Si semiconductor monitors,which can measure at up to 90°C were selected.

Because the gas monitors require high sensi-tivity to the β-rays that are emitted from thenuclei (which is what is measured by the detec-tors), the CdTe semiconductor detector, with itssuperior sensitivity to β-rays, was selected. Al-though the sensitivity to β-rays is about the samefor CdTe semiconductor detectors and CdZnTesemiconductor detectors, the CdTe semiconduc-tor detectors have a longer mean path lengthfor the charge carriers (producing superior sig-nal-to-noise ratios), so the CdTe semiconductordetectors were selected.

As with the gas monitors, the high range gasmonitors also require high sensitivity to β-rays ;however, because this also requires operationat high temperatures (up to 100°C), the CdZnTesemiconductor detectors, which have good ther-mal characteristics up to such high tempera-tures, can also measure β-rays.

Examples of Applications of SemiconductorDetectorsOf the monitors that use semiconductor detec-tors, two types of monitors (area monitors andhigh-range β-ray gas monitors) are describedbelow as examples.

AREA MONITORS. Area monitors are fitted tomeasure the amount of radiation within a spe-cific space established in the nuclear powerplant. Conventionally, GM counters have beenused in area monitor detectors. Because of the

extended life expectancy and improved reliabil-ity of Si semiconductor detectors, area monitorshave been developed using the Si semiconduc-tor detectors. These detectors have a wide deple-tion region, which is the sensitive part that hasa reverse bias at the PN junction, and by plac-ing an appropriate filter in front of the detector,the energy characteristics can be flat. Fig. 1 is aphotograph of an area monitor. Along with thedetector element and the pre-amplifier, the moni-tor also includes a check source for performingperiodic calibrations. This monitor is designedto provide stable measurements even given ad-verse environmental conditions in terms of tem-perature and humidity.

β-RAY GAS MONITORS. β-ray gas monitors haveconventionally used plastic scintillators.CdZnTe, with its high band-gap energy, was se-lected for this application of semiconductor

Fig. 1 External view of the area monitor

TECHNICAL REPORTS


detectors because it can withstand use in high-temperature environments. The semiconductor-type β-ray gas monitors have exactly the samecharacteristics as the conventional detectors.The use of semiconductor detectors can, in prac-tice, greatly reduce the size of the detectionequipment because the semiconductor detectorsdo not require the light guide and photomulti-plier tubes required in conventional scintillator-based equipment. However, because they willreplace equipment in existing plants, the exter-nal dimensions have been set to be exactly thesame as those of the conventional detectors; asshown in Fig. 2, to ensure compatibility.

Fig. 2 Semiconductor beta-ray gas monitor

Sensor Pre-amplifier

In CdZnTe semiconductor detectors, the poormobility-lifetime product of the carriers (espe-cially of the holes) cause the carrier trappingphenomenon to be a problem. However, whenmeasuring β-rays, the location of the interac-tion position is limited to the vicinity of the sur-face, and thus if the incident surface side is usedas the cathode, there is little influence on thehole-trapping effect, making it possible to ob-tain an accurate amplitude output. Fig. 3 showsthe T1-204 (β−ray maximum energy: 764keV) en-

ergy spectrum near the main regions of appli-cable energy.

Additionally, the temperatures over which thismonitor can be used range from – 15 to +80°C,and Fig. 4 shows the measurement results ofthe thermal characteristics of this monitor (thegross count ratios of energy above 100keV).Because the temperature characteristic over therange from – 15 to +80°C causes fluctuations ofless than ±10%, there is no need for compensa-tion as a function of temperature.

Fig. 3 Beta-ray gas monitor energy spectrum

The research regarding gas monitors, high-rangegas monitors, and mainsteam duct monitors inthis report, and the current research regardingtheir applicability to nuclear power, is the re-sult of joint research with:• Kansai Electric Power Co., Inc.• Hokkaido Electric Power Co., Inc.• Shikoku Electric Power Co., Inc.• Kyushu Electric Power Co., Inc.• The Japan Atomic Power Company,and we are deeply grateful for the wide range ofadvice and guidance we have received.❑

Fig. 4 Beta-ray gas monitor temperaturecharacteristics

Beta-ray gas monitor (CZT)

Temperature [oC]

-20 0 20 40 60 80 100 120

120

110

100

90

80

70

60

50

Cou

nt r

ate

(a.u

) [%

]

TECHNICAL REPORTS

· 25September 2001

*Ryuichi Nishiura is with the Industrial Electronics & Systems Laboratory and Nobuyuki Izumi is with the Energy &Industrial Systems Center.

by Ryuichi Nishiura and Nobuyuki Izumi*

Radiation Sensing System Using anOptical Fiber

The authors have developed a radiation detec-tor using a plastic scintillation optical fiber (PSF)doped with a radiofluorescent material (or scin-tillator) as the detector.

This article introduces and gives the basic per-formance characteristics of an optical fiberradiation sensing system and a portable scintil-lation-type optical fiber body-surface contami-nation monitor.

Fiber-Optic Radiation Sensing SystemAn optical-fiber sensing system is a device thatdetects the distribution of radiation intensityalong an optical fiber in a single operation. Fig. 1is a photograph of the detector.

A linear type optical fiber radiation sensingsystem can be quickly installed in, and removedfrom, the work area, thus helping to reduce theexposure of workers to radiation. It can also beinstalled in any convenient space within a com-plex system of pipelines.

Principle Of Measurement Using Fiber-OpticRadiation Sensing SystemThe radiation detector of the optical fiber sens-ing system consists of a cable containing a scin-tillation fiber (an optical fiber doped with ascintillator, see Fig.1). A scintillator is a mate-rial that generates a fluorescent pulse when itreceives radiation energy under irradiation by γrays, for example. This fluorescent pulse propa-gates to both ends of the optical fiber (see Fig.2).The times at which these two pulses arrive atthe detectors connected to each end of the fiberdiffer depending upon the location of the inci-dent radiation. By measuring the difference inthe arrival times, the location of the incidentradiation can be determined, and by countingthe total number of light pulses, the intensity ofthe radiation can be determined.

This method is called the “time of flight” (TOF)method. Fig. 3 shows an outline of the opticalfiber radiation sensing system monitor.

The light-pulse signal emitted from the scin-tillation fiber (PSF) is converted into an electri-

Fig. 1 Detector of the fiber-optic radiation sensingsystem

Fig. 2 Principle of detection

Radiation detector (scintillator)

Optical transmission(optical fiber)

Core

Cladding

Cladding

g light pulseTransmitting

Core

Radiation

Radiation

Light

Light emission

TECHNICAL REPORTS


cal pulse signal in a photomultiplier tube (PMT).This electrical pulse signal is passed through awave-shaping circuit to a time-difference mea-surement circuit. The time-difference measure-ment circuit has a START side and a STOP side.The STOP side has a delay circuit that ensuresthat the STOP side always operates after theSTART side. The basic specifications of this sys-tem are shown in Table 1.

Features of the Fiber-Optic Radiation SensingSystemA description of the features of the optical fiberradiation sensing system follows:

1. Permits measurement of radiation-intensitydistribution over a wide range.This sensing system permits measurement ofcontinuous radiation intensity along the de-

Fig. 3 Principle of measurement

MCA

Delay

TAC

Stop

Start

CFD 2FastPre-amp 2PMT 2

CFD 1FastPre-amp 1PMT 1

Radiation source

PSFKeyCFD Constant-fraction discriminatorMCA Multi-channel analyzerTAC Time-to-amplitude converterPSF Plastic-scintillation fiberPMT Photo-multiplier

Light pulse

Table 1 Basic Specifications of the Optical FiberRadiation Sensing System

Type of radiation γ rays

Measurement distance 20m (max. possible with onesystem)

Length 30m

Range of energies 350keV~1.3MeV

Locational accuracy ±30cm

Operating Temperature -15 ~ +50°C

Measuring range 1 ~ 104µSv/h

tection cable in contrast to the single pointmeasurements made by a conventional areamonitor.

2. The radiation-intensity distribution can bedisplayed visibly.Fig. 4 shows a typical display screen on theoptical fiber radiation monitor. The lower left

Fig. 4 Example of display screen

Upper right - Radiation intensity distribution measurement results.Upper left - Trend graph consisting of the graph at top right to which a time axis has been added.Lower right - Peak position and peak value.Lower left - Installed condition of the detection cable, and the peak display.

of the figure shows the installed condition ofthe cable. At the upper right, a colored markedis displayed at each position where the inten-sity is at least a certain value (this value canbe set freely). The table at the lower rightshows where the radiation intensity exceedsa certain value and also the radiation inten-sity at those points. The graph at the upperleft shows the time change at arbitrary points.

3. Freedom from electromagnetic interference– Intrinsic noise countermeasures are

possible.The detector consists of a cable that has atotal length of 30m. Measurement can beperformed at a point remote from the detec-tion zone. Also, detection of radiation and sig-

TECHNICAL REPORTS

· 27September 2001

Fig. 5 Example of a screen showing theradioactive waste resin being transferred

.

nal transmission use optical signals, hencemeasurement can be performed without anyadverse effects from electromagnetic noise.

Example of Application of the Fiber-OpticRadiation Sensing SystemOne system using an optical fiber radiation moni-tor is a radioactive waste resin transportationmonitoring system.

Used resin is passed through a transfer pipe tothe waste resin storage tank. Sometimes duringthis process, resin collects at bends in the pipe,valves, etc., making it necessary to monitor andevaluate the situation. The use of the opticalfiber radiation sensing system makes this workmore efficient, and can reduce the exposure ofthe workers to radiation. Fig. 5 shows an ex-ample of a display indicating the transfer condi-tion of this radioactive waste resin.

Portable Scintillation Fiber-Optic Body-SurfaceContamination MonitorAfter the JCO atomic power disaster, more than500 radiation control officers from electric powercompanies and elsewhere gathered at the siteof the accident and checked the local residentsfor radiation contamination using survey meters.The problems with this method included theneed for a specialist radiation control officer tooperate each meter, the time-consuming mea-

surements themselves, their cost, and the timetaken for the entire operation. To overcome theseproblems, we developed a body-surface contami-nation monitor usable by anyone, that performsmeasurements quickly, can identify the part ofthe body contaminated by radiation, and can bereadily transported to the required location.

Basic Specifications of the PortableScintillation Fiber-Optic Body-SurfaceContamination MonitorThe specifications of the monitor are shown inTable 2. Its performance is the same as that of apermanently installed body-surface contamina-tion monitor. To ensure monitor mobility, wedesigned it for easy disassembly and reassembly.

Table 2 Basic Specifications of the Body-SurfaceContamination Monitor

Radiation detected β/γ radiation

Sensitivity β: =0.4Bq/cm2 (10s)γ: =4Bq/cm2 (10s)

Effective detection area 40,000cm2

Accuracy ±20% (measurement error forirradiation with plane-wavesource )

Structure Readily assembled.

EffectivenessMeasurements can be made much quicker thanwith the conventional method that detects ra-diation using a survey meter (5min. per person).

Technological DevelopmentIn a conventional detector, the light-emittingsurface of the conventional plastic scintillatoris combined with a large number of photomulti-pliers, resulting in a detector at least 10cm thickand fairly massive. To facilitate monitor port-ability and rapid assembly, we adopted scintilla-tion-type optical fiber technology and succeededin developing the slim, light detector shown inFig.6. Conventional scintillation optical fiber isdesigned to measure γ radiation. The new opti-cal fiber was modified by reducing the claddingthickness so that it could measure β radiation.

TECHNICAL REPORTS


Fiber-optic radiation sensing system

Portable scintillation-type fiber-optic body-surface contamination monitor

Fig. 7 External appearance of products usingoptical fiber

In view of the vital importance of rapid, conve-nient and reliable measurements of radioac-tivity, Mitsubishi Electric is confident that theproducts and systems introduced, and the fluo-rescent optical fiber sensor systems upon whichthey are based, will have an important role incontributing to human health and safety.❑

Fig. 6 Scintillation fiber plate

MITSUBISHI ELECTRIC CORPORATIONHEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310, FAX 03-3218-3455

VOL. 95/SEP. 2001 - Mitsubishi Electric · 2020. 2. 18. · ISSN 1345-3041 VOL. 95/SEP. 2001...

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Transcript of VOL. 95/SEP. 2001 - Mitsubishi Electric · 2020. 2. 18. · ISSN 1345-3041 VOL. 95/SEP. 2001...