EN 62270:2004

SLOVENSKI SIST EN 62270:2005
STANDARD
september 2005
Avtomatizacija hidroelektrarn – Vodilo za računalniški krmilni sistem (IEC
62270:2004)
Hydroelectric power plant automation – Guide for computer-based control (IEC
62270:2004)
ICS 27.140 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 62270
NORME EUROPÉENNE
EUROPÄISCHE NORM July 2004
ICS 27.140
English version
Hydroelectric power plant automation -
Guide for computer-based control
(IEC 62270:2004)
Automatisation  Automatisierung von Wasserkraftwerken -
de centrale hydroélectrique - Leitfaden zur computergestützten
Guide pour la commande Steuerung
à base de calculateur (IEC 62270:2004)
(CEI 62270:2004)
This European Standard was approved by CENELEC on 2004-07-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in two official versions (English, German). A version in any other language
made by translation under the responsibility of a CENELEC member into its own language and notified to the
Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2004 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 62270:2004 E
Foreword
The text of document 4/188/FDIS, future edition 1 of IEC 62270, prepared by IEC TC 4, Hydraulic
turbines, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 62270 on 2004-07-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2005-04-01
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2007-07-01
with the EN have to be withdrawn
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 62270:2004 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 62270:2004
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 61158 Series Digital data communications for EN 61158 Series
measurement and control - Fieldbus for
use in industrial control systems

ANSI C63.4 2001 Methods of Measurement of Radio-Noise - -
Emissions from Low-Voltage Electrical
and Electronic Equipment in the Range of
9 kHz - 40 GHz
IEEE Std 100 1996 The IEEE Standard Dictionary of - -
Electrical and Electronics Terms

IEEE Std 485 1997 IEEE Recommended Practice for Sizing - -
Lead-Acid Batteries for Stationary
Applications (ANSI)
IEEE Std 610 1990 IEEE Standard Glossary of Software - -
Engineering Terminology (ANSI)

IEEE Std 1010 1987 IEEE Guide for Control of Hydroelectric - -
Power Plants (ANSI)
IEEE Std 1014 1987 IEEE Standard for a Versatile Backplane - -
Bus: VMEbus
IEEE Std 1020 1988 IEEE Guide for Control of Small - -
Hydroelectric Power Plants (ANSI)

IEEE Std 1046 1991 IEEE Application Guide for Distributed - -
Digital Control and Monitoring for Power
Plants (ANSI)
IEEE Std 1147 1991 IEEE Guide for the Rehabilitation of - -
Hydroelectric Power Plants (ANSI)

IEEE Std C37.1 1994 IEEE Standard Definition, Specification, - -
and Analysis of Systems Used for
Supervisory Control, Data Acquisition,
and Automatic Control (ANSI)
IEEE Std 2002 IEEE Standard Surge Withstand - -
C37.90.1 Capability (SWC) Tests for Protective
Relays and Relay Systems (ANSI)

Publication Year Title EN/HD Year
IEEE Std 1995 IEEE Trial Use Standard for Withstand - -
C37.90.2 Capability of Relay Systems to Radiated
Electromagnetic Interference from
Transceivers (ANSI)
IEEE Std 1379 2000 IEEE Recommended Practice for Data - -
Communications Between Remote
Terminal Units and Intelligent Electronic
Devices in a Substation (ANSI)

ISO/IEC 8802-3 2001 Information technology - - -
Telecommunications and information
exchange between systems - Local and
metropolitan area networks - Specific
requirements
Part 3: Carrier sense multiple access with
collision detection (CSMA/CD) access
method and physical layer specifications

ISO/IEC 8802-4 1990 Part 4: Token-passing bus access - -
method and physical layer specifications

ISO/IEC 8802-5 1998 Part 5: Token ring access method and - -
physical layer specifications
INTERNATIONAL IEC
STANDARD 62270
First edition
2004-04
Hydroelectric power plant automation –
Guide for computer-based control

 IEC 2004  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale XB
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

– 2 – 62270  IEC:2004(E)
CONTENTS
FOREWORD.4
INTRODUCTION .6

1 Overview.7
1.1 Scope.7
1.2 Purpose.7
2 Normative references.7
3 Terms and definitions.8
4 Functional capabilities.13
4.1 General.13
4.2 Control capabilities.13
4.3 Data acquisition capabilities.22
4.4 Alarm processing and diagnostics .23
4.5 Report generation.24
4.6 Maintenance management interface.24
4.7 Data archival and retrieval .24
4.8 Operation scheduling and forecasting .24
4.9 Data access.25
4.10 Operator simulation training .25
4.11 Typical control parameters.25
5 System architecture, communications, and databases .26
5.1 General.26
5.2 System classification.27
5.3 System architecture characteristics.28
5.4 Control data networks .33
5.5 Data bases and software configuration.37
6 User and plant interfaces .39
6.1 User interfaces.39
6.2 Plant interfaces.40
7 System performance.43
7.1 General.43
7.2 Hardware.44
7.3 Communications.45
7.4 Measuring performance.46
8 System backup capabilities .47
8.1 General.47
8.2 Design principles.48
8.3 Basic functions.48
8.4 Design of equipment for backup control .48
8.5 Alarm handling.49
8.6 Protective function.50
9 Site integration and support systems.50
9.1 Interface to existing equipment .50
9.2 Environmental conditions.50
9.3 Power source.51

62270  IEC:2004(E) – 3 –
9.4 Supervision of existing contact status points .51
9.5 Supervision of existing transducers .52
9.6 Supervision of existing control output points.52
9.7 Grounding.52
9.8 Static control.52
10 Recommended test and acceptance criteria .53
10.1 Specific test requirements.53
10.2 Quality assurance.54
10.3 Acceptance.54
11 System management.54
11.1 Maintenance.54
11.2 Training.54
11.3 Documentation.55
12 Case studies.57
12.1 Automation of the Conowingo Hydroelectric Station.57
12.2 Computer-based control system at Waddell Pump-Generating Plant.59
12.3 Retrofit of TrŠngslet Hydro Power Station .63
12.4 Computer-based control system at Wynoochee Hydroelectric Project .68

Bibliography .72

Figure 1 – Relationship of local, centralized, and offsite control .15
Figure 2 – Local control configuration .15
Figure 3 – Computer communication network .28
Figure 4 – Multi-point data link versus LANs .33
Figure 5 – Star topology .35
Figure 6 – Ring topology.35
Figure 7 – Bus topology.36
Figure 8 – Conowingo control system overview.58
Figure 9 – System configuration .61
Figure 10 – Control system configuration.64
Figure 11 – Station control configuration after upgrading .67
Figure 12 – System configuration .69
Figure 13 – Local and remote interface.70

Table 1 – Summary of control hierarchy for hydroelectric power plants.14
Table 2 – Typical parameters necessary to implement automated control.25
Table 3 – Classifications of hydroelectric power plant computer control systems .27
Table 4 – Hydroplant computer control systems data communications attributes .36
Table 5 – Cable media characteristics .37
Table 6 – System performance .66

– 4 – 62270  IEC:2004(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HYDROELECTRIC POWER PLANT AUTOMATION –
GUIDE FOR COMPUTER-BASED CONTROL

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62270 has been prepared by IEC technical committee 4: Hydraulic
turbines.
The text of this standard is based on the IEEE Standard 1249 (1996) IEEE guide for computer-
based control for hydroelectric power plant automation. It was submitted to the national
committees for voting under the Fast Track procedure as the following documents:
FDIS Report on voting
4/188/FDIS 4/190/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

62270  IEC:2004(E) – 5 –
The committee has decided that the contents of this publication will remain unchanged until
2005. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
– 6 – 62270  IEC:2004(E)
INTRODUCTION
Automation of hydroelectric generating plants has been a known technology for many years.
Due to the relative simplicity of the control logic for hydroelectric power plants, the application
of computer-based control has lagged, compared to other types of generating stations, such as
fossil. Now that computer-based control can be implemented for comparable costs as relay-
based logic and can incorporate additional features, it is being applied in hydroelectric power
stations worldwide, both in new installations and in the rehabilitation of older plants.

62270  IEC:2004(E) – 7 –
HYDROELECTRIC POWER PLANT AUTOMATION –
GUIDE FOR COMPUTER-BASED CONTROL

1 Overview
1.1 Scope
This standard sets down guidelines for the application, design concepts, and implementation of
computer-based control systems for hydroelectric plant automation. It addresses functional
capabilities, performance requirements, interface requirements, hardware considerations, and
operator training. It includes recommendations for system testing and acceptance. Finally, case
studies of actual computer-based automatic control applications are presented.
The automation of control and data logging functions has relieved the plant operator of these
tasks, allowing the operator more time to concentrate on other duties. In many cases, the
plant’s operating costs can be significantly reduced by automation (primarily via staff reduction)
while still maintaining a high level of unit control reliability.
Automatic control systems for hydroelectric units based on electromechanical relay logic have
been in general use for a number of years and, in fact, were considered standard practice for
the industry. Within the last decade, microprocessor-based controllers have become available
that are suitable for operation in a power plant environment. These computer-based systems
have been applied for data logging, alarm monitoring, and unit and plant control. Advantages of
computer-based control include use of graphical user interfaces, the incorporation of sequence
of events and trending into the control system, the incorporation of artificial intelligence and
expert system capabilities, and reduced plant life cycle cost.
1.2 Purpose
This standard is directed to the practicing engineer who has some familiarity with computer-
based control systems and who is designing or implementing hydroelectric unit or plant control
systems, either in a new project or as a retrofit to an existing one. This standard assumes that
the control system logic has already been defined; therefore, its development is not covered.
For information on control sequence logic, the reader is directed to the IEEE guides for control
of hydroelectric power plants listed in Clause 2 of this standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 61158, Digital data communications for measurement and control - Fieldbus for use in
industrial control systems
ANSI C63.4-2001, Methods of Measurement of Radio-Noise Emissions from Low-Voltage
Electrical and Electronic Equipment in the Range of 9 kHz–40 GHz
IEEE Std 100-1996, The IEEE Standard Dictionary of Electrical and Electronics Terms
___________
ANSI publications are available from the Sales Department, American National Standards Institute, 11 West
42nd Street, 13th Floor, New York, NY 10036, USA.
IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O.
Box 1331, Piscataway, NJ 08855-1331, USA.

– 8 – 62270  IEC:2004(E)
IEEE Std 485-1997, IEEE Recommended Practice for Sizing Lead-Acid Batteries for Stationary
Applications (ANSI)
IEEE Std 610-1990, IEEE Standard Glossary of Software Engineering Terminology (ANSI).
IEEE Std 1010-1987 (Reaffirmed 1992), IEEE Guide for Control of Hydroelectric Power Plants
(ANSI)
IEEE Std 1014-1987 IEEE Standard for A Versatile Backplane Bus: VMEbus
IEEE Std 1020-1988 (Reaffirmed 1994), IEEE Guide for Control of Small Hydroelectric Power
Plants. (ANSI)
IEEE Std 1046-1991 (Reaffirmed 1996), IEEE Guide for Distributed Digital Control and
Monitoring for Power Plants (ANSI)
IEEE Std 1147-1991 (Reaffirmed 1996), IEEE Guide for the Rehabilitation of Hydroelectric
Power Plants (ANSI)
IEEE Std C37.1-1994, IEEE Standard Definition, Specification, and Analysis of Systems Used
for Supervisory Control, Data Acquisition, and Automation Control (ANSI)
IEEE Std C37.90.1-2002, IEEE Standard for Surge Withstand Capability (SWC) Tests for
Protective Relays and Relay Systems (ANSI)
IEEE Std C37.90.2-1995, IEEE Trial Use Standard Withstand Capability of Relay Systems to
Radiated Electromagnetic Interference from Transceivers (ANSI)
IEEE 1379: 2000, IEEE Recommended Practice for Data Communications Between Remote
Terminal Units and Intelligent Electronic Devices in a Substation (ANSI)
ISO/IEC 8802-3:2001, Information technology – Telecommunications and information exchange
between systems – Local and metropolitan area networks – Specific requirements – Part 3:
Carrier sense multiple access with collision detection (CSMA/CD) access method and physical
layer specifications (ANSI/IEEE Std 802.3, 1996 Edition)
ISO/IEC 8802-4:1990 (Reaffirmed 1995), Information processing systems – Local area
networks – Part 4: Token-passing bus access method and physical layer specifications
(ANSI/IEEE 802.4-1990 Edition)
ISO/IEC 8802-5:1998, Information technology –Telecommunications and information exchange
between systems – Local and metropolitan area networks – Specific requirements – Part 5:
Token ring access method and physical layer specifications (ANSI/IEEE Std 802.5, 1995
Edition)
3 Terms and definitions
For the purposes of this document the definitions provided here reflect common industry usage
as related to automation of hydroelectric power plants, and may not in all instances be in
accordance with IEEE Std 100-1996, or IEEE Std 610-1990, or other applicable standards. For
more rigorous definitions, or for definitions not covered herein, the reader is referred to the
appropriate IEEE standards.
___________
ISO publications are available from the ISO Central Secretariat, Case Postale 56, 1 rue de Varembé, CH-1211,
Genève 20, Switzerland/Suisse. ISO publications are also available in the United States from the Sales
Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036,
USA.
62270  IEC:2004(E) – 9 –
3.1
analog-to-digital (a/d) conversion
production of a digital output corresponding to the value of an analog input quantity
3.2
automatic control
arrangement of electrical controls that provides for switching or controlling, or both, of
equipment in a specific sequence and under predetermined conditions without operator
intervention
3.3
automatic generation control (AGC)
capability to regulate the power output of selectable units in response to total power plant
output, tie-line power flow, and power system frequency
3.4
automatic voltage control (AVC)
capability to regulate a specific power system voltage, via adjustment of unit excitation within
the limits of unit terminal voltage and VAR capability
3.5
automation hierarchy
design and implementation of automation functions in a multilevel structure, such as local level,
group level, unit level, etc.
3.6
availability
ratio of uptime (system functional) to uptime plus downtime (system not functional)
3.7
backplane
circuit board with connectors or sockets that provides a standardized method of transferring
signals between plug-in circuit cards
3.8
bridge
device that allows two networks of the same or similar technology to communicate
3.9
centralized control
control location one step removed from local control; remote from the equipment or generating
unit, but still within the confines of the plant (e.g. controls located in a plant control room)
3.10
closed loop control
type of automatic control in which control actions are based on signals fed back from the
controlled equipment or system. For example, a plant control system can control the power
output of a multi-unit hydroelectric power plant by monitoring the total plant megawatt value
and, in response, by controlling the turbine governors of each unit, change the plant power
output to meet system needs
3.11
computer-based automation
use of computer components, such as logic controllers, sequence controllers, modulating
controllers, and processors in order to bring plant equipment into operation, optimize operation
in a steady-state condition, and shut down the equipment in the proper sequence under safe
operating conditions
– 10 – 62270  IEC:2004(E)
3.12
control hierarchy
system organization incorporating multiple levels of control responsibility
3.13
control philosophy
total concept on which a power plant control system is based
3.14
data acquisition system
centralized system that receives data from one or more remote points. Data may be
transported in either analog or digital form
3.15
database
collection of stored data regarding the process variables and processing procedures
3.16
data bus
control network technology in which data stations share one single communication system
medium. Messages propagate over the entire medium and are received by all data stations
simultaneously
3.17
device (electrical equipment)
operating element such as a relay, contactor, circuit breaker, switch or valve, used to perform a
given function in the operation of electrical equipment
3.18
digital-to-analog (d/a) conversion
production of an analog signal whose magnitude is proportional to the value of a digital input
3.19
distributed processing
design in which data is processed in multiple processors. Processing functions could be shared
by the processors throughout the control system
3.20
event
discrete change of state (status) of a system or device
3.21
expert system
computer programs that embody judgmental and experimental knowledge about an application.
Expert systems are able to reach decisions from new, uncertain and incomplete information
with a specified degree of certainty. Expert system abilities include: making logical inferences
under unforeseen conditions; using subjective and formal knowledge; explaining the
procedures used to reach a conclusion; growing in effectiveness as embedded expertise is
expanded and modified
3.22
firmware
hardware used for the non-volatile storage of instructions or data that can be read only by the
computer. Stored information is not alterable by any computer program

62270  IEC:2004(E) – 11 –
3.23
gateway
device that allows two networks of differing technology to communicate
3.24
local control
for auxiliary equipment, controls that are located at the equipment itself or within sight of the
equipment. For a generating station, the controls that are located on the unit
switchboard/governor control station
3.25
logic:(control or relay logic)
predetermined sequence of operation of relays and other control devices
3.26
manual control
control in which the system or main device, whether direct or power-aided in operation, is
directly controlled by an operator
3.27
mean-time-between-failure (MTBF)
time interval (hours) that may be expected between failures of an operating equipment
3.28
mean-time-to-repair (MTTR)
time interval (hours) that may be expected to return a failed equipment to proper operation
3.29
modem
modulator/demodulator device that converts serial binary digital data to and from the signal
form appropriate for an analog communication channel
3.30
monitoring
means of providing automatic performance supervision and alarming of the status of the
process to personnel and control programs
3.31
offsite control
controls that are not resident at the plant (e.g. at a switchyard, another plant, etc.)
3.32
open loop control
form of control without feedback
3.33
proportional integral derivative (PID) [control system]
control action in which the output is proportional to a linear combination of the input, the time
integral of input, and the time rate of change of input. Commonly used in hydroelectric
applications for the control of a generator’s real power, reactive power, or flow
3.34
pixel
in image processing, the smallest element of a digital image that can be assigned a gray level

– 12 – 62270  IEC:2004(E)
3.35
programmable logic controller (PLC)
solid state control system with programming capability that performs functions similar to a relay
logic system
3.36
protocol
structured data format required to initiate and maintain communication
3.37
relay, interposing
device that enables the energy in a high-power circuit to be switched by a low-power control
signal
3.38
remote control
control of a device from a distant point
3.39
reliability
characteristic of an item or system expressed by the probability that it will perform a required
mission under stated conditions for a stated mission time
3.40
response time
elapsed time between the moment when a signal is originated in an input device until the
moment the corresponding processed signal is made available to the output device(s), under
defined system loading conditions
3.41
resistance temperature detector (RTD)
resistor for which the electrical resistivity is a known function of the temperature
3.42
scan (interrogation)
process by which a data acquisition system sequentially interrogates remote stations for data at
a specific frequency
3.43
scan cycle
time in seconds required to obtain a collection of data (for example, all data from one
controller, all data from all controllers, and all data of a particular type from all controllers)
3.44
serial communication
method of transmitting information between devices by sending digital data serially over a
single communication channel
3.45
sequential control
mode of control in which the control actions are executed consecutively
3.46
supervisory control and data acquisition (SCADA)
system operating with coded signals over communication channels so as to provide control of
remote equipment and to acquire information about the status of the remote equipment for
display or for recording functions

62270  IEC:2004(E) – 13 –
3.47
user interface
functional system used specifically to interface the computer-based control system to the
operator, maintenance personnel, engineer, etc.
4 Functional capabilities
4.1 General
Computer-based automation has enhanced hydroelectric power plant operation and
maintenance activities. Many activities previously accomplished by plant personnel can now be
performed more accurately, safely, and consistently by computer-based automation systems.
Also, new tasks are within the capabilities of computer-based systems.
Power plant operators have long been responsible for manually performing control and data
acquisition tasks. Relay logic type automatic control systems were, for many years, the only
automated control assistance for operations staff. These systems were limited to unit control
sequencing (start/stop) and were not easily changed, once installed. The quality of data
acquisition has been subject to the limitations of available staff and human error.
Computer-based control and data acquisition systems have made major changes in the way
these tasks are carried out. Power plant operator expertise has been supplemented in many
plants by the computer, which can assist with unit start/stop sequencing and data logging; in
other plants, the computer has replaced the operator altogether by performing these tasks. The
online diagnostic, corrective, and protective capabilities of these computer systems continue to
be developed.
Computer-based automation systems now allow plant owners to operate and maintain their
plants in ways not possible before. Control algorithms based on criteria such as efficiency,
automatic generation control, and voltage control allow more cost effective and safe operation
of plants and interconnected power systems. It is now possible to acquire and process more
data than in the past, so generated reports can keep operators and maintenance staff apprised
of the total plant condition. Maintenance activities are enhanced by the computer’s ability to
isolate problems, describe trends, and keep maintenance records.
Computer-based automation systems also permit operation of the power plant, switchyard, and
outlet works (spillway gates, bypass gates and valves, fishways, fish ladders, etc.) from a
single control point that can be local, centralized, or offsite. This one-point control has many
advantages, including reduced operations staff, consistent operating procedures, and the
capability to have all control and data available for reference during normal and abnormal
conditions.
Subclauses 4.2 - 4.11 outline the functional capabilities of hydroelectric plant computer-based
automation systems.
4.2 Control capabilities
4.2.1 Control hierarchy
A general hierarchy of control for hydroelectric power plants is defined in IEEE Std 1010-1987.
The combination of computer-based and noncomputer-based equipment utilized for unit, plant,
and system control should be arranged in accordance with Table 1.

– 14 – 62270  IEC:2004(E)
Table 1 – Summary of control hierarchy for hydroelectric power plants
Control category Subcategory Remarks
Location Local Control is local at the controlled equipment or within sight of the
equipment.
Centralized Control is remote from the controlled equipment, but within the
plant.
OffSite Control location is remote from the project.
Mode Manual Each operation needs a separate and discrete initiation; could
be applicable to any of the three locations.
Automatic Several operations are precipitated by a single initiation; could
be applicable to any of the three locations.
Operation Attended Operator is available at all times to initiate control action.
(supervision)
Unattended Operation staff is not normally available at the project site.

A decision is required on the extent of functions to be included in the computer-based
equipment. At one extreme, the computer-based equipment may incorporate all aspects of
local, centralized, offsite, manual, and automatic control. At the other extreme, the computer-
based equipment may handle only automatic unit sequences and data acquisition, with all other
functions, such as local manual control, handled by noncomputer-based equipment.
Manual controls are used during testing, and maintenance, and as a backup to the automatic
control equipment. Generally, manual controls are installed adjacent to the devices being
controlled, such as pumps, compressors, valves, and motor control centers. Transfer of control
to higher levels is accomplished by means of local-remote transfer switches installed at the
equipment. Often, capability to operate individual items of equipment is also provided at the
unit switchboard while in the local-manual mode. If this capability is designed to backup the
computer-based equipment, then additional interposing relays and other devices will be
required. Alternately, with the high reliability of modern computer equipment, local-manual
operation from the unit switchboard may be incorporated into the computer controls, thereby
reducing control complexity. In this case, direct manual operation will still be possible at the
equipment location. Further backup control considerations are described in 8.2.
For severe faults that require high-speed tripping of a unit, separate protective equipment is
included in the unit control system. This protective equipment comprises relay-based, solid-
state, or microprocessor-based protection for electrical and mechanical equipment and trip
logic. These high-speed protective functions are generally not incorporated into the computer-
based systems used for control.
Figure 1 illustrates the arrangement of control locations, typical functions at each location, and
typical interchange of control and operating information. Local control, centralized control, and
offsite control functions are described in 4.2.2–4.2.4.

62270  IEC:2004(E) – 15 –
IEC  496/04
Figure 1 – Relationship of local, centralized, and offsite control
4.2.2 Local control
Local control can be provided by equipment located near the generating unit itself. The local
unit computer is part of this equipment and backup manual control may be desired depending
on the operator’s design philosophy. Where there are multiple units in a plant, one computer is
typically allocated to each unit. The local unit computer interfaces to higher level plant or offsite
computers exchanging control signals and data without the need for additional wiring. Figure 2
illustrates the local control configuration.

IEC  497/04
Figure 2 – Local control configuration

– 16 – 62270  IEC:2004(E)
4.2.2.1 Start/stop sequencing
One of the most obvious uses for computer-based automation in power plants is for automating
unit start/stop control sequencing. Older designs that use electromechanical relay-based
start/stop sequential logic are being replaced with modern computer automation systems. The
computer is programmed to completely start or stop the unit when directed by higher level
control or by the operator. The computer system controls the generator’s electrical and
electrical/mechanical auxiliary systems to start or stop the unit. Inputs to the computer are unit
and plant status points that are constantly monitored for change during the sequence. The
computer can continuously monitor and display more status information than an operator can
assimilate so that control actions, such as abort sequences, can be initiated immediately,
without operator reaction time. Because the computer is programmable, modifications to the
sequence control can be made relatively simply, even after the plant is operational. Computer-
based start/stop sequencing is cost-effective, reliable, and easy to maintain, compared to older
electromechanical relay systems. Some owners of hydroelectric plants may not be comfortable
with full computer automation of the start/stop sequencing. In these cases, the start/stop
sequencing can be made more conservative by containing breakpoints in the sequencing to
allow for operator intervention or permissive action.
The computer system can also monitor the control sequence an
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