EN IEC 61116:2025

SLOVENSKI STANDARD
01-januar-2026
Nadomešča:
SIST EN 61116:2001
Navodilo za elektromehansko opremo malih hidroelektrarn (IEC 61116:2025)
Electromechanical equipment guidance for small hydroelectric installations (IEC
61116:2025)
Anleitung für die elektromechanische Ausrüstung von kleinen Wasserkraftanlagen (IEC
61116:2025)
Recommandations pour l'équipement électromécanique des petits aménagements
hydroélectriques (IEC 61116:2025)
Ta slovenski standard je istoveten z: EN IEC 61116:2025
ICS:
27.140 Vodna energija Hydraulic energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61116

NORME EUROPÉENNE
EUROPÄISCHE NORM November 2025
ICS 29.160.20; 27.140 Supersedes EN 61116:1994
English Version
Electromechanical equipment guidance for small hydroelectric
installations
(IEC 61116:2025)
Recommandations pour l'équipement électromécanique Anleitung für die elektromechanische Ausrüstung von
des petits aménagements hydroélectriques kleinen Wasserkraftanlagen
(IEC 61116:2025) (IEC 61116:2025)
This European Standard was approved by CENELEC on 2025-10-30. 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 CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61116:2025 E
European foreword
The text of document 4/510/CDV, future edition 2 of IEC 61116, prepared by TC 4 "Hydraulic turbines"
was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-11-30
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-11-30
document have to be withdrawn
This document supersedes EN 61116:1994 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61116:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60034-2-1:2024 NOTE Approved as EN IEC 60034-2-1:2024 (not modified)
IEC 60034-5:2020 NOTE Approved as EN IEC 60034-5:2020 (not modified)
IEC 60041:1991 NOTE Approved as EN 60041:1994
IEC 60076-1:2011 NOTE Approved as EN 60076-1:2011 (not modified)
IEC 60193:2019 NOTE Approved as EN IEC 60193:2019 (not modified)
IEC 60308:2024 NOTE Approved as EN IEC 60308:2024 (not modified)
IEC 60545:2021 NOTE Approved as EN IEC 60545:2021 (not modified)
IEC 60609-1 NOTE Approved as EN 60609-1
IEC 60609-2:1997 NOTE Approved as EN 60609-2:1999 (not modified)
IEC 60831-1:2014 NOTE Approved as EN 60831-1:2014 (not modified)
IEC 60871-1:2014 NOTE Approved as EN 60871-1:2014 (not modified)
IEC 61362:2024 NOTE Approved as EN IEC 61362:2024 (not modified)
IEC 61869-2:2012 NOTE Approved as EN 61869-2:2012 (not modified)
IEC 61869-3:2011 NOTE Approved as EN 61869-3:2011 (not modified)
IEC 61869-5:2011 NOTE Approved as EN 61869-5:2011 (not modified)
IEC 62006:2010 NOTE Approved as EN 62006:2011 (not modified)
IEC 62256 NOTE Approved as EN 62256
IEC 62271-100:2021 NOTE Approved as EN IEC 62271-100:2021 (not modified)
IEC 62271-102:2018 NOTE Approved as EN IEC 62271-102:2018 (not modified)
IEC 62271-102:2018/AMD1:2022 NOTE Approved as EN IEC 62271-102:2018/A1:2022 (not modified)
ISO 80000-4:2019 NOTE Approved as EN ISO 80000-4:2019 (not modified)

IEC 61116 ®
Edition 2.0 2025-09
INTERNATIONAL
STANDARD
Electromechanical equipment guidance for small hydroelectric installations

ICS 29.160.20; 27.140 ISBN 978-2-8327-0635-0

IEC 61116:2025-09(en)
IEC 61116:2025 © IEC 2025
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and units . 7
3.1 General . 7
3.2 Terms and definitions . 7
3.3 Units . 9
4 Methodology . 9
5 Description of installation and operating conditions of power station . 11
5.1 General . 11
5.2 Site conditions. 11
5.3 Hydraulic conditions for plant and design criteria for the units . 16
5.4 Electrical conditions for plant operation . 18
5.4.1 General. 18
5.4.2 The plant is intended to operate in an isolated grid . 18
5.4.3 The plant is intended to operate in parallel with a grid which imposes
the frequency . 19
5.4.4 Energy transport and distribution . 19
5.5 Types of regulation and modes of operation (reference can be made to
IEC 61362 and IEC 60308) . 20
5.5.1 Frequency regulation . 20
5.5.2 Power regulation . 20
5.5.3 Level control. 20
5.5.4 Flow regulation . 20
5.5.5 Simplified governing . 20
5.6 Automation, telemetry, remote control, alarms . 20
6 Equipment specifications . 21
6.1 General . 21
6.2 Technical requirements . 21
6.3 Limits of the supply . 21
6.3.1 General. 21
6.3.2 For the hydraulic system . 21
6.3.3 For the electric system . 21
6.3.4 For the auxiliary equipment system . 21
6.3.5 Elements not normally included in the supply . 21
6.4 Specifications of the elements of the plant . 22
6.4.1 General. 22
6.4.2 Trashrack and rack cleaner . 22
6.4.3 Water-level control . 22
6.4.4 Discharge closure devices (see Figure 5) . 22
6.4.5 Penstock . 24
6.4.6 Turbine (see Figure 6) . 25
6.4.7 Generator . 29
6.4.8 Automatic control system . 31
6.4.9 Main transformers (reference can be made to IEC 60076-1) . 33
6.4.10 Auxiliary equipment . 34
6.4.11 Spare parts and special tools . 35
IEC 61116:2025 © IEC 2025
6.4.12 Mechanical handling . 35
6.4.13 Corrosion protection . 36
6.5 Guarantees . 36
6.5.1 General. 36
6.5.2 Discharge closure devices . 37
6.5.3 Turbine . 37
6.5.4 Generator . 37
6.5.5 Governor . 38
6.5.6 Speed increaser. 38
6.5.7 Excitation equipment . 38
6.5.8 Comments concerning the complete generating set . 38
6.5.9 Main transformer. 39
6.6 General conditions for tender enquiries and comparison of tenders . 39
6.6.1 General. 39
6.6.2 Instructions to tenderers . 39
6.6.3 General conditions of contract . 39
6.6.4 Technical comparison of tenders . 39
7 Inspection, delivery, operation and maintenance . 41
7.1 General . 41
7.2 Approval of the design and inspection of the work . 42
7.2.1 Approval of design documents . 42
7.2.2 Inspection of materials and sub-assemblies . 42
7.2.3 Inspection at manufacturer's works . 42
7.2.4 Delivery . 43
7.2.5 Assembly at site . 43
7.3 Commissioning . 44
7.3.1 General. 44
7.3.2 Preliminary checks before watering-up . 44
7.3.3 Watering-up . 44
7.3.4 Unit rotation . 45
7.3.5 Preliminary checks and electrical load tests . 46
7.4 Operation. 46
7.4.1 Trial operation . 46
7.4.2 Guarantee period . 46
7.4.3 Normal operation . 48
7.5 Training of personnel . 49
7.6 Checking and maintenance . 49
Bibliography . 52

Figure 1 – Example of sequence of events . 10
Figure 2 – Power station arrangements . 14
Figure 3 – Run-of-river power station arrangements . 16
Figure 4 – Flow duration curve (showing river flow and plant flow) . 17
Figure 5 – Hydraulic closure devices (examples) . 23
Figure 6 – Schematic representation of a hydraulic machine . 25
Figure 7 – Electrical single-line diagram . 33

IEC 61116:2025 © IEC 2025
Table 1 – Energy utilization for passive and active loads . 19
Table 2 – Elements of bid evaluation . 40
Table 3 – Examples of checks during normal operation . 51

IEC 61116:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Electromechanical equipment guidance for
small hydroelectric installations

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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 61116 has been prepared by IEC technical committee 4: Hydraulic turbines. It is an
International Standard.
This second edition cancels and replaces the first edition published in 1992. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) harmonization of scope with IEC 62006;
b) introduction of new technical aspects;
c) overall editorial revision.
IEC 61116:2025 © IEC 2025
The text of this International Standard is based on the following documents:
Draft Report on voting
4/510/CDV 4/521A/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC 61116:2025 © IEC 2025
1 Scope
This document is used as a guidance that applies to hydroelectric installations containing
impulse or reaction turbines with unit power up to about 15 MW and reference diameter of about
3 m. These figures do not represent absolute limits.
This document deals only with the direct relations between the purchaser or the consulting
engineer and the supplier. It does not deal with civil works, administrative conditions or
commercial conditions.
This document is intended to be used by all concerned in the installation of electromechanical
equipment for small hydroelectric plants.
This document, based essentially on practical information, aims specifically at supplying the
purchaser of the equipment with information which will assist him with the following:
– preparation of the call for tenders;
– evaluation of the tenders;
– contact with the supplier during the design and manufacture of the equipment;
– quality control during the manufacture and shop-testing;
– follow-up of site erection;
– commissioning;
– acceptance tests;
– operation and maintenance.
The document comprises the following:
a) general requirements for the electromechanical equipment of small hydroelectric
installations;
b) technical specifications for the electromechanical equipment, excluding its dimensioning
and standardization;
c) requirements for acceptance, operation and maintenance.
Bearing in mind the type of installation considered, the relevant documents are intended to be
as simple as possible but to satisfactorily define the particular operation conditions. Over-
specification is harmful to the economy of the project.
This document does not cover the initial stage of investigations, that is to say the preliminary
study and feasibility study. Neither does it deal with the economic study concerning the supply
and demand of energy.
To conclude, the document does not replace the applicable engineering studies for the
selection, design, manufacture, installation and testing of the equipment. It is intended only to
make the purchaser aware of the important points and data to be furnished, specified and kept
in due consideration in the construction of small hydroelectric plants.
2 Normative references
There are no normative references in this document.
IEC 61116:2025 © IEC 2025
3 Terms, definitions and units
3.1 General
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.2 Terms and definitions
3.2.1
power station
installation whose purpose is to generate electricity and which includes civil engineering works,
energy conversion equipment and all the necessary ancillary equipment
[SOURCE: IEC 60050-602:1983, 602-01-01]
3.2.2
hydroelectric installation
ordered arrangement of civil engineering structures, machinery and plant designed chiefly to
convert the gravitational potential energy of water into electricity
[SOURCE: IEC 60050-602:1983, 602-01-03]
3.2.3
powerhouse
central structure that houses the key electromechanical equipment required to convert the
kinetic energy of flowing water into electrical energy
3.2.4
hydroelectric power station
power station in which the gravitational energy of water is converted into electricity
[SOURCE: IEC 60050-602:1983, 602-01-04]
3.2.5
run-of-river power station
hydroelectric power station which uses the river flow as it occurs, the filling period of its own
reservoir by the cumulative water flows being practically negligible
[SOURCE: IEC 60050-602:1983, 602-01-05]
3.2.6
generating set
group of rotating machines transforming mechanical or thermal energy into electricity
[SOURCE: IEC 60050-602:1983, 602-02-01]
IEC 61116:2025 © IEC 2025
3.2.7
hydroelectric set
generating set consisting of a hydraulic turbine mechanically connected to an electrical
generator
[SOURCE: IEC 60050-602:1983, 602-02-03]
3.2.8
dam
structure to retain water inflows for specific uses
[SOURCE: IEC 60050-602:1983, 602-02-05]
3.2.9
penstock
pipeline bringing water under pressure to the turbine
[SOURCE: IEC 60050-602:1983, 602-02-09]
3.2.10
surge tank
surge shaft
open-surface reservoir of water decreasing the effects of shock pressure waves in the penstock
[SOURCE: IEC 60050-602:1983, 602-02-10]
3.2.11
impulse type turbine
turbine in which a fluid acts chiefly by its kinetic energy
[SOURCE: IEC 60050-602:1983, 602-02-11]
3.2.12
reaction type turbine
turbine in which a fluid acts both by its kinetic energy and by its pressure
[SOURCE: IEC 60050-602:1983, 602-02-12]
3.2.13
Pelton turbine
hydraulic impulse type turbine usually operated from a high head source with small flow rate
[SOURCE: IEC 60050-602:1983, 602-02-13]
3.2.14
Kaplan turbine
axial hydraulic reaction type turbine with adjustable runner blades operated with a high flow
rate
[SOURCE: IEC 60050-602:1983, 602-02-15]
IEC 61116:2025 © IEC 2025
3.2.15
crossflow turbine
action turbine with a very small degree of reaction
Note 1 to entry: The flow crosses the runner twice perpendicularly to its axis of rotation and the runner blades are
arranged cylindrically.
[SOURCE: IEC TR 61364:1999, 4.4.3]
3.3 Units
The International System of Units (SI, see ISO 80000-4) has been used throughout this
document.
All terms are given in SI Base Units or derived coherent units (for example N instead of
-2
kg m s ). The basic equations are valid using these Units. This shall be taken into account if
other than coherent SI-Units are used for certain data (for example kilowatt or megawatt instead
-1 -1
of watt for power, kilopascal or bar instead of pascal for pressure, min instead of s for
rotational speed, etc.). Temperatures should be given in degrees Celsius because
thermodynamic (absolute) temperatures (in Kelvins) are rarely required.
Any other system of units can be used, but only if agreed to in writing by the contracting parties.
4 Methodology
In the interests of clarity, the sequence of the necessary steps for the construction of a small
hydroelectric power station is represented diagrammatically in Figure 1.
It principally covers the preparation of technical specifications, the examination of tenders, the
manufacture, and finally the commercial operation and maintenance of equipment.
This sequence also shows the relationship between the different phases and areas of
responsibility of all the parties concerned (consulting engineer, chief resident engineer, and
users).
If the purchaser does not have in-house engineering capabilities or the services of a consulting
engineer he can call for, to facilitate relations with contractors, a "turn-key" supply, or at least
a leading contractor responsible for the supply of all or part of the electromechanical equipment
should be adopted (e.g. the turbine and generator package, or a "water-to-wire" package).
IEC 61116:2025 © IEC 2025
Figure 1 – Example of sequence of events
IEC 61116:2025 © IEC 2025
5 Description of installation and operating conditions of power station
5.1 General
The following data is generally required by the equipment supplier and should appear in the
enquiry. In some cases, all these data are not always readily available. Nevertheless, it shall
be emphasized that the more information that is given, the better will the project be understood
and therefore the better the technical solution which will result.
5.2 Site conditions
5.2.1 Supply a topographic survey (plan and profile) giving the altitude of the points indicated
and the position desired for the main works (see Figure 2), water intake, reservoir, channel,
surge tank or head pond, penstock, power plant, headwater, tailwater and their main
characteristics (sections, lengths, materials of the channels and penstocks, etc.). Indicate the
foundation conditions (sand, rock, soft ground, etc.).

a) High and medium head plant arrangements
IEC 61116:2025 © IEC 2025
b) Low head station (bulb unit and rim generator unit)
IEC 61116:2025 © IEC 2025
c) Low head station (vertical unit and unit with elbowed tail-race)
IEC 61116:2025 © IEC 2025
d) Low head station (siphon unit and unit with elbowed penstock)

Figure 2 – Power station arrangements
5.2.2 Attach numbered pictures with cross-references to the topographic survey described
in 5.2.1, showing the setting and location of the main works.
5.2.3 Supply the chemical analysis of the water with extremes of temperature and, if
necessary, the amount and size of sediments carried by the water in the area around the water
intake or downstream of the sand trap, if any.
Indicate the presence of any living organisms or floating debris, etc.
5.2.4 Specify the local conditions: extremes of air temperature, humidity, occurrence of
strong winds, earthquakes, etc.
IEC 61116:2025 © IEC 2025
5.2.5 Indicate any transport or access limitations.
5.2.6 Certain information mentioned in 7.2.5.1 and 7.2.5.3 (erection) should also be shown
in the tender enquiry if this reflects a particular feature of the purchaser's own country.
5.2.7 State if it is a run-of-river (see Figure 3) or a scheme with a reservoir.
Indicate if there exists any particular operational constraints: e.g. multi-purpose scheme,
environmental, fisheries, etc.
State and describe (with drawings) those elements of the plant which are part of an existing
installation which it is foreseen will eventually be put back into use.

a) Run-of-river power station
IEC 61116:2025 © IEC 2025
Key
1 Power house
2 Intake
3 Trashrack
4 Dam
5 Coarse trashrack
b) Run-of-river plant in a bypass channel

Figure 3 – Run-of-river power station arrangements
5.2.8 State if the plant will be manned or unmanned.
5.2.9 Indicate if there exists any particular operational constraints and provide any relevant
environmental regulations or permits required for the project. This could include water quality
constraints, fish passage requirements, minimum seasonal flow requirements, etc.
5.3 Hydraulic conditions for plant and design criteria for the units
5.3.1 Specify the maximum allowable up or down surges in the channels.
5.3.2 Provide a flow duration curve (see Figure 4) with an indication of the limiting flows
(guaranteed water supply, irrigation, drinking-water).
IEC 61116:2025 © IEC 2025
Key
1 + 2 = Q = Available run-of-river flow
river
1 = Q = Usable or exploitable flow
usable
2 = Q - Q = Flow losses (dotation, drainage, leakage, spilled flow)
river usable
Q = Total rated flow that can be used by the turbine
a
Figure 4 – Flow duration curve (showing river flow and plant flow)
5.3.3 Specify the chosen design flow, Q , in cubic metres per second, and the availability in
a
days per year.
5.3.4 Specify the extreme water-levels at the intake and at the tail-race in metres (m) above
sea-level, as follows.
a) headwater level max … m
min . m
b) tailwater level max . m
min . m
c) operational range allowed: . m
and give the curves for:
d) level versus discharge (headwater and tailwater)
e) level versus volume of the headwater reservoir or head pond (essential for a reservoir
scheme).
5.3.5 Specify the desired outputs and the duration of the corresponding operations. The
number of starts and stops, load rejections per year and expected runaway events in a lifetime
can also be useful. The net heads are defined as in IEC 62006. The crossflow turbines with
diffusers are considered as reaction turbines.
IEC 61116:2025 © IEC 2025
5.3.6 State the number of units suggested.
5.3.7 Define the evaluation criteria for efficiency over the full range of operation as well as
overload conditions (weighting the efficiency according to the amount of energy produced at
different heads and flows). The weight to be given to a particular efficiency or overload depends
on the time of utilization at the point of operation considered and the energy thus recovered
from the installation. For general instructions to tenderers, see 6.6.
NOTE 1 For low head plants with short intakes, the intake design can significantly affect hydraulic behavior, such
as the formation of vortices and air admission.
NOTE 2 The proper design of the waterways is essential in order to minimize the head losses (difference between
gross and net head).
5.3.8 For containerized minimum hydroelectric plants, the influence of container storage
space on the type and size of the hydroelectric units should also be considered.
5.4 Electrical conditions for plant operation
5.4.1 General
The plant electrical conditions and requirements are listed under either 5.4.2 or 5.4.3.
5.4.2 The plant is intended to operate in an isolated grid
a) Without any other energy supply on the grid
For isolated grids, black-start capability is essential.
1) Required grid voltage . V
Tolerance (under steady-state conditions) + . % - .%
2) Grid frequency . Hz
Tolerance (under steady-state conditions) + . % - . %
3) Minimum output required all year round by the grid . kW
4) Load acceptance rate of the grid
(to determine whether or not a flywheel is required) . kW/s
5) Hydraulic inertia time constant (T ) . s
w
6) Mechanical inertia time constant (T ) . s
a
7) Value of the maximum step-change in load which
the grid can accept + . kW - . kW
8) Power factor (cos φ) .
b) With permanent connection to another electrical energy supply defined as follows:
1) Hydroelectric unit: type .
min output . kW
2) Thermoelectric unit: type .
3) Generator characteristics (synchronous or asynchronous):
i) rated voltage . V
ii) rated frequency . Hz
iii) rated output . kVA
iv) inertia J of rotating parts . kg·m
v) Mechanical inertia time constant (T ) . s
a
vi) power factor (cos φ) .
IEC 61116:2025 © IEC 2025
4) Turbine governor characteristics
The grid conditions shall be defined as in 5.4.2 a), items 2) to 7).
5) Voltage regulator characteristics (distribution of reactive power).
The grid conditions shall be defined as in 5.4.2 a), items 1) and 8).
c) Energy utilization: daily and seasonal load variations, see Table 1 below.
Table 1 – Energy utilization for passive and active loads
Output (kW) Minimum Average Maximum
Passive loads
(lighting, heating, drying, …)
Active loads
(electric motors)
Total
In order to decide the method of regulation and the design of the governor, it is necessary
to give an indication of the load variations (load curve):
1) daily;
2) weekly;
3) seasonal.
Indicate the priority and non-priority loads (load shedding) as this is useful for designing the
governor.
5.4.3 The plant is intended to operate in parallel with a grid which imposes the
frequency
a) Characteristics of the grid
1) Voltage . V
Tolerance + . % - . %
2) Frequency . Hz
Tolerance + . % - . %
3) Short-circuit power
(at the point where the new scheme is linked to the grid) . kVA
4) Power factor (cos φ) .
b) Apparent output of the largest generator working on the grid . kVA
5.4.4 Energy transport and distribution
Provide the following drawings:
– a general layout drawing of the entire proposed grid, in the case of isolated load operation;
– a drawing showing the link to the grid, in the case of operation in parallel with a large grid.
The layout should also indicate the main load centres and power supply points.
Also provide information on any possible developments of the grid.
IEC 61116:2025 © IEC 2025
5.5 Types of regulation and modes of operation (reference can be made to IEC 61362
and IEC 60308)
5.5.1 Frequency regulation
If the unit or the plant operates in an isolated grid, or is an important part of the grid, a governor
is required to maintain the grid frequency during load changes.
For units with low output and where hydraulic energy is abundant, simplified governors could
also be used by producing a constant output at full load and dumping the unused power.
5.5.2 Power regulation
The operating position of the power station in the power system map and the accuracy
requirement of power regulation should be clarified.
The type of power regulation should be specified, and the load regulation curve according to
the plan should be provided when taking part in peak load or intermediate load of the system.
5.5.3 Level control
Specify if it is necessary to maintain the headwater or tailwater level constant, or within a
working range using the generating sets or some other discharge device. If this is so, the turbine
opening shall then be governed with level feedback. This is generally the case with run-of-river
plants (in the river itself or in a bypass channel) or when linked to an irrigation canal.
NOTE On isolated load, level or frequency can be controlled but not both.
5.5.4 Flow regulation
Specify the presence of any reservoirs and their respective capacity.
NOTE On isolated load, flow or frequency can be controlled but not both.
5.5.5 Simplified governing
If the plant is to operate on a large grid which imposes the frequency, its units can be fitted with
simplified governors (positioners) having level feedback or load feedback. Stability can be
affected in the case where part of a large grid becomes accidentally detached and simplified
governors are used.
5.6 Automation, telemetry, remote control, alarms
a) Indicate if staff are available for the starting and shut-down sequences or if it is required to
minimize the use of operators.
b) If the plant is unattended, unmanned or remote controlled, specify where the alarms shall
be located.
c) Specify whether the starting sequence, synchronization, loading and shut-down operations
shall be:
1) manual;
2) automatic;
3) remote controlled (in this case, indicate the location of the control centre, the carrier and
the type and method of transmission of the signals).
d) Where a scheme has a reservoir, and there are several units, specify if manual or automatic
control of the reservoir water is required (operation according to a programme).
e) Specify if the plant shall be the control centre for other energy supply sources in the grid.
IEC 61116:2025 © IEC 2025
6 Equipment specifications
6.1 General
The information given below is useful in establishing technical specifications and comparing the
technical offers for the most important items in a small hydroelectric development.
6.2 Technical requirements
In addition to supplying the equipment, the supplier should provide the following:
a) Suitability of the proposed technical solutions with regard to the hydraulic characteristics,
the operational requirements and the operating range.
b) The supplier should inform the purchaser of the necessary civil work data at an early stage
so that the civil work can be designed in accordance with the requirements of the equipment.
Verification of the compatibility between the civil work and the electro-mechanical
equipment (overall dimensions, floor loads, supply and verification of the preliminary civil
work layout drawings, etc.).
c) Information required for erecting, starting-up, operating and maintaining the equipment.
d) Results for the hydraulic transients and rotor-dynamic calculations, if included in the works.
6.3 Limits of the supply
6.3.1 General
These limits should be clearly and physically defined for each item. It should be checked that
no equipment has been excluded.
6.3.2 For the hydraulic system
On the upstream side, the limit could be trashrack and the rack cleaning machine, if installed,
or the first hydraulic closure device (stop-logs, gate or valve), or any other suitable section.
On the downstream side, the limit could be defined as the end of the draft tube or of the stop-
logs or gate, or any other suitable section.
6.3.3 For the electric system
This could include all the electrical equipment, up to the first point of connection with the grid
to be defined by the purchaser.
6.3.4 For the auxiliary equipment system
This could include all the auxiliary equipment, such as lifting equipment, oil supply system (e.g.
for governor control and bearing lubrication), water supply systems (e.g. cooling water and
lubricating water), compressed air systems, hydraulic monitoring system, etc.
6.3.5 Elements not normally included in the supply
Generally, the following are not included:
a) civil works,
b) telemetry and remote control,
c) ventilation and sanitation.
IEC 61116:2025 © IEC 2025
6.4 Specifications of the elements of the plant
6.4.1 General
Without overlooking the criterion of simplicity which this type of installation requires, the
selection of good quality materials, suitable technology and good machine characterist
...