IEC 63298:2024

IEC 63298 ®
Edition 1.0 2024-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Electrical power systems –
Coordination and interaction with electric grid

Centrales nucléaires – Systèmes d'alimentation électrique –
Coordination et interaction avec le réseau électrique
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IEC 63298 ®
Edition 1.0 2024-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Nuclear power plants – Electrical power systems –

Coordination and interaction with electric grid

Centrales nucléaires – Systèmes d'alimentation électrique –

Coordination et interaction avec le réseau électrique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-9376-8

– 2 – IEC 63298:2024 © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 8
1.1 General . 8
1.2 Use of this document . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Abbreviated terms . 11
5 Contractual coordination . 12
6 Technical coordination . 12
6.1 General . 12
6.2 Conceptual design of the interface of the NPP with the electric grid . 12
6.3 Exchange of technical information between the NPP operator and the
electric grid operator . 13
6.4 Connection scheme . 13
6.5 Analyses of the interface between the NPP and the electric grid . 14
6.5.1 General . 14
6.5.2 Load flow analyses . 14
6.5.3 Transient stability analyses . 14
6.5.4 Steady state stability analyses . 15
6.5.5 NPP island operation mode analyses (if applicable) . 15
6.5.6 NPP house load operation analyses (if applicable) . 15
6.5.7 NPP flexible operation analyses . 15
6.5.8 NPP electrical transients/faults analyses . 16
6.5.9 Electric grid reliability analyses . 16
6.5.10 Protection setting studies . 16
7 Electric grid – NPP operating procedures . 16
8 Commissioning and testing . 17
8.1 General . 17
8.2 Tests undertaken during commissioning/trial and run phase . 17
9 Coordination during NPP operation . 18
9.1 General . 18
9.2 Short- and long-term planning . 18
9.3 Maintenance . 18
9.4 Analyses . 19
9.5 Testing . 19
Annex A (informative) NPP and electric grid: description of specific features . 20
A.1 General . 20
A.2 NPP . 20
A.3 Electric grid . 21
Annex B (informative) Example of NPP connection schemes to electric grid . 22
Bibliography . 24

Figure B.1 – Connection scheme by 2 lines to a single substation . 22
Figure B.2 – Connection scheme considering multiple substations and lines . 22

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS – ELECTRICAL POWER SYSTEMS –
COORDINATION AND INTERACTION WITH ELECTRIC GRID

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,
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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6) All users should ensure that they have the latest edition of this publication.
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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
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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 63298 has been prepared by subcommittee 45A: Instrumentation, control and electrical
power systems of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation. It
is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
45A/1529/FDIS 45A/1545/RVD
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.

– 4 – IEC 63298:2024 © IEC 2024
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.
INTRODUCTION
a) Technical background, main issues and organization of the standard
Nuclear power plants (NPPs) need an electric grid for the dual purpose of exporting produced
energy and for a reliable power source for start-up, operation, shutdown and emergency
conditions.
Owing to the electrical size of the NPP compared to the electrical size of the electric grid, it
may be a challenge to safely integrate the NPP into the electric grid.
Coordination between the electric grid and the NPP is becoming increasingly important as more
countries adopt a liberal energy market and responsibilities are held by multiple stakeholders
(e.g., production, transmission, distribution, and trading organizations).
The purpose of this document is to define the high-level requirements and recommendations
for the coordination of NPPs and electric grids to ensure the appropriate interactions between
the two entities.
The specific features of the NPP and electric grid that are in scope for this document are
described in Annex A.
The requirement for coordination between the electric grid operators and NPP operators is
described in WANO SOER 1999-1 which focusses on significant operating experience relating
to the loss of connection to the electric grid at NPPs (this event being one of the major
contributors to NPP core damage frequency).
IAEA Nuclear Energy Series, NG-T-3.8, Electric Grid Reliability And Interface With Nuclear
Power Plants describes the characteristics of the electric grid that are required for the
connection and successful operation of an NPP, as well as the characteristics of an NPP that
are significant for the design and operation of the electric grid.
This document focuses on technical requirements, such as the data exchange between the NPP
operators and the electric grid operators, the analyses carried out by both sides and the
acceptance criteria.
This document also defines the coordination requirements to ensure that operating instructions
for the electric grid and the NPP are developed to provide a means of safe and reliable
operation.
This document also defines the requirements for the development of a framework for any
specific tests that may be deemed necessary for the electric grid and the NPP, such as testing
of NPP regulation capabilities and load rejection to house load operation tests.
Finally, this document provides guidance on the need for continuous coordination between the
electric grid and NPP during the NPP's design life, on topics such as operation and
maintenance, design modifications and changes to grid conditions.
b) Situation of this document in the structure of the SC 45A standard series
This document is a second level document specifically addressing the topic of coordination
between the NPP and electric grid.
For more details on the structure of the SC 45A standard series, see item d) of this Introduction.

– 6 – IEC 63298:2024 © IEC 2024
c) Recommendations and limitations regarding the application of this document
This document is used in conjunction with IEC 61513, IEC 62855 and IEC 63046.
d) Description of the structure of the IEC SC 45A standard series and relationships with
other IEC documents and other bodies' documents (IAEA, ISO)
The IEC SC 45A standard series comprises a hierarchy of four levels. The top-level documents
of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for instrumentation and control (I&C) systems and
equipment that are used to perform functions important to safety in nuclear power plants
(NPPs). IEC 63046 provides general requirements for electrical power systems of NPPs; it
covers power supply systems including the supply systems of the I&C systems.
IEC 61513 and IEC 63046 are considered in conjunction and at the same level. IEC 61513 and
IEC 63046 structure the IEC SC 45A standard series and shape a complete framework
establishing general requirements for instrumentation, control and electrical power systems for
nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general
requirements for specific topics, such as categorization of functions and classification of
systems, qualification, separation, defence against common cause failure, control room design,
electromagnetic compatibility, human factors engineering, cybersecurity, software and
hardware aspects for programmable digital systems, coordination of safety and security
requirements and management of ageing. The standards referenced directly at this second level
should be considered together with IEC 61513 and IEC 63046 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific requirements for specific equipment, technical methods, or
activities. Usually these documents, which make reference to second-level documents for
general requirements, can be used on their own.
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical Reports
which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the relevant
documents of the IAEA nuclear security series (NSS). In particular this includes the IAEA
requirements SSR-2/1, establishing safety requirements related to the design of nuclear power
plants (NPPs), the IAEA safety guide SSG-30 dealing with the safety classification of structures,
systems and components in NPPs, the IAEA safety guide SSG-39 dealing with the design of
instrumentation and control systems for NPPs, the IAEA safety guide SSG-34 dealing with the
design of electrical power systems for NPPs, the IAEA safety guide SSG-51 dealing with human
factors engineering in the design of NPPs and the implementing guide NSS42-G for computer
security at nuclear facilities. The safety and security terminology and definitions used by the
SC 45A standards are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application sector.
In this framework, IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3 for the
nuclear application sector.
IEC 61513 and IEC 63046 refer to ISO 9001 as well as to IAEA GSR part 2 and IAEA GS-G-3.1
and IAEA GS-G-3.5 for topics related to quality assurance (QA).

At level 2, regarding nuclear security, IEC 62645 is the entry document for the IEC SC 45A
security standards. It builds upon the valid high level principles and main concepts of the
generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it adapts them and
completes them to fit the nuclear context and coordinates with the IEC 62443 series. At level 2,
IEC 60964 is the entry document for the IEC SC 45A control rooms standards, IEC 63351 is the
entry document for the human factors engineering standards and IEC 62342 is the entry
document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions (e.g.
to address worker safety, asset protection, chemical hazards, process energy hazards) international or national
standards would be applied.
NOTE 2 IEC TR 63400 provides a more comprehensive description of the overall structure of the IEC SC 45A
standards series and of its relationship with other standards bodies and standards.

– 8 – IEC 63298:2024 © IEC 2024
NUCLEAR POWER PLANTS – ELECTRICAL POWER SYSTEMS –
COORDINATION AND INTERACTION WITH ELECTRIC GRID

1 Scope
1.1 General
The scope of this document is to provide high level requirements and recommendations for the
coordination of NPPs and the electric grid; see also item a) of the Introduction.
The specific design requirements for components and equipment are covered by other specific
IEC standards outside the scope of this document.
1.2 Use of this document
This document is intended to be used:
• for the design of new NPPs (including small modular reactors (SMRs), where applicable);
• for considering the adequacy and impact of major modifications to the electric grid for
operating NPPs;
• for periodic design reviews of operating NPPs.
Pertinent parts of this document can be used as guidance for NPP operation and in general for
nuclear facilities.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 62855:2016, Nuclear power plants – Electrical power systems – Electrical power systems
analysis
IEC 63046:2020, Nuclear power plants – Electrical power system – General requirements
3 Terms and definitions
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

3.1
defence in depth
hierarchical deployment of different levels of diverse equipment and procedures to prevent the
escalation of anticipated operational occurrences and to maintain the effectiveness of physical
barriers placed between a radiation source or radioactive material and workers, members of the
public or the environment, in operational states and, for some barriers, in accident conditions
Note 1 to entry: Five levels of defence in depth are discussed in IAEA SSR-2/1:2016:
a) The purpose of the first level of defence is to prevent deviations from normal operation and the failure of items
important to safety.
b) The purpose of the second level of defence is to detect and control deviations from normal operation in order to
prevent anticipated operational occurrences from escalating to accident conditions.
c) The purpose of the third level of defence is to prevent damage to the reactor core and releases of radioactive
material requiring off-site protective actions and to return the plant to a safe state by means of inherent and/or
engineered safety features, safety systems and procedures.
d) The purpose of the fourth level of defence is to prevent the progress of, and to mitigate the consequences of,
accidents that result from failure of the third level of defence by preventing accident sequences that lead to large
release of radioactive material or early release of radioactive material from occurring.
e) The purpose of the fifth and final level of defence is to mitigate radiological consequences of a large release of
radioactive material or an early release of radioactive material that could potentially result from an accident.
[SOURCE: IAEA Nuclear Safety and Security Glossary, 2022 edition]
3.2
distribution system operator
DSO
party responsible for providing and operating networks for distribution of electricity and
responsible for ensuring system security with a high level of reliability and quality
3.3
electric grid
network of synchronized electrical generators and consumers that are connected by electric
lines and operated by dedicated control center(s)
Note 1 to entry: The electric grid is composed of the national transmission system(s) and distribution system(s) to
which the NPP is connected; within the scope of this document this term mostly refers to the part of electric grid that
has "functional relevance to the NPP itself".
3.4
electric grid operator
organization operating the electric grid, which could be either the transmission system operator
or distribution system operator depending on the relevant part of the electric grid
3.5
fault-ride-through
ability of generating units to ride through transmission system faults and stay connected to
electric grid
3.6
frequency control
method of operating a generating unit at less than full output, under automatic control, so that
its output increases automatically if the system frequency falls, and decreases automatically if
the system frequency rises
[SOURCE: IAEA NP-T-3.23, 2018 edition, modified – The term "automatic frequency
control/automatic frequency responsive operation" is replaced with "frequency control".]

– 10 – IEC 63298:2024 © IEC 2024
3.7
grid code
document that describes the required technical characteristics, performance and operation of
the transmission system and generating units, as defined by the TSO or government agency
[SOURCE: IAEA NG-T-3.8, 2012 edition]
3.8
house load operation
operation of a nuclear power plant to supply power only to its own electrical loads
[SOURCE: IEC 62855:2016, 3.2]
3.9
island operation
independent operation of a part of the electric grid after being disconnected from the rest of the
electric grid having at least one generator supplying power and controlling the frequency and
voltage
Note 1 to entry: The terms "house load operation" and "island operation" for an NPP are similar from a functional
and control point of view, where house load operation is the smaller of the electric loads.
3.10
loss of off-site power
LOOP
simultaneous loss of electrical power to all unit safety buses, requiring the standby AC power
sources to start and supply power to the safety buses
Note 1 to entry: DC systems and uninterruptible AC systems safety buses are not included.
[SOURCE: IEC 62855:2016, 3.4, modified – The abbreviated term has been added.]
3.11
NPP operator
company or organization that is the operator of an NPP and which has the primary responsibility
for the safe operation of the plant and will have to satisfy the requirements of the nuclear
regulatory body in the country where the NPP is located
Note 1 to entry: For the scope of this document, NPP operator also includes an organization that has a license for
the design and construction of an NPP that is not yet constructed or operating
[SOURCE: IAEA NP-T-3.23, modified – The term "nuclear power plant owner/operating
organization" has been replaced with "NPP operator", the definition has been modified to form
a single phrase, "nuclear power plant" has been replaced with "NPP" and the Note to entry
added.]
3.12
probabilistic safety assessment
PSA
comprehensive, structured approach to identifying failure scenarios, constituting a conceptual
and mathematical tool for deriving numerical estimates of risk
Note 1 to entry: Three levels of probabilistic safety assessment are generally recognized:
Level 1 comprises the assessment of failures leading to determination of the frequency of fuel damage.
Level 2 includes the assessment of containment response, leading, together with Level 1 results, to the
determination of frequencies of failure of the containment and release to the environment of a given
percentage of the reactor core’s inventory of radionuclides.
Level 3 includes the assessment of off-site consequences, leading, together with the results of Level 2 analysis, to
estimates of public risks.
[SOURCE: IAEA Nuclear Safety and Security Glossary, 2022 edition]
3.13
transmission system operator
TSO
party responsible for providing and operating networks for long-distance transmission of
electricity as well as regional distribution and responsible to ensure the system security with a
high level of reliability and quality
[SOURCE: IEC 63046:2020, 3.51, modified – The abbreviated term has been added.]
4 Abbreviated terms
AC Alternating current
CDF Core damage frequency
DiD Defence in depth
DSO Distribution system operator
FCT Fault clearance time
FMEA Failure mode effect analysis
GIC Geomagnetic induced currents
HV High voltage
IAEA International Atomic Energy Agency
LOOP Loss of off-site power
NPP Nuclear power plant
OPC Open phase condition
PSA Probabilistic safety assessment
SBO Station black out
SMR Small modular reactors
TSO Transmission system operator

– 12 – IEC 63298:2024 © IEC 2024
5 Contractual coordination
The first step in developing coordination between an NPP and electric grid operator is to set up
an appropriate contractual framework or, in the initial phases, develop cooperation agreements.
The method chosen to achieve this will depend upon the rules of a specific country but generally
there should be a contract for different levels of cooperation: preliminary joint studies, grid
analyses and finally, a contract for the connection of the NPP to the electric grid and subsequent
operation of the NPP.
Contractual arrangements shall clearly define, as a minimum:
– boundaries between the NPP and the electric grid;
– mutual responsibilities;
– technical conditions for connection of the NPP;
– references to valid operating procedures.
NOTE Boundaries between the NPP and the electric grid can include physical, operating, maintenance, etc.
6 Technical coordination
6.1 General
Technical coordination should take place between the NPP operator and the electric grid
operators at all stages of operation including design, construction, operation and maintenance.
Technical coordination, based on agreed input data and analyses, should take place to check
and verify that the mutual requirements of the NPP and electric grid are satisfied in accordance
with agreed acceptance criteria.
The objective is to ensure that:
– the NPP will remain connected to the grid after disturbances, if the grid is within defined
limits;
– the functionality of the NPP electrical system should not be impacted by the electric grid.
6.2 Conceptual design of the interface of the NPP with the electric grid
The NPP and electric grid operators, from first phases of conceptual design, shall:
a) Plan the new NPP generating units according to the planned demands of electric grid
consumption and flexible operation requirements;
b) Check the electrical size of a new NPP in comparison with the available electric grid to be
confident it will be possible to dispatch the produced energy;
c) Provide an assessment of the electric grid reliability based on electric grid operator data;
d) Run a preliminary version of the power system analysis relevant to the new NPP connection,
based on electric grid operator data (power system analyses are specified in 6.5);
e) Design the scheme for connecting the NPP to the electric grid;
f) Carry out an initial assessment of the NPP compliance with electric grid parameters with
regards to frequency/voltage ranges, regulation, and load rejection capabilities. This
assessment should confirm that compliance with the electric grid requirements does not
create nuclear safety constraints.

6.3 Exchange of technical information between the NPP operator and the electric grid
operator
The input data for the NPP grid interface design should be defined by the electric grid operator
in the grid code. Additional requirements/inputs should be agreed between the electric grid
operator and the NPP operator while maintaining nuclear safety.
Input data for the NPP and electric grid interface should include:
a) Expected maximum and minimum short circuit current (three-phase and single-phase) at
the electric grid connection point under defined standards and operating conditions. In order
to correctly size equipment, information on the planned future development of these values
shall be provided;
b) Limits and rates of changes of electric grid frequency and voltage at the connection point
(including values expected during the NPP shutdown mode) and, where available, historical
data (number of events/duration) for abnormal frequency and voltage values (see 6.2 c));
c) Measurements and commands to be exchanged between the NPP and electric grid;
d) NPP and electric grid data relevant for building models for grid studies (e.g., rotating
masses, voltage regulator characteristics);
e) Frequency of LOOP and restoration time as input for the NPP probabilistic safety
assessment.
6.4 Connection scheme
The electric grid operator and NPP operator shall design the connection scheme between the
NPP and the electric grid taking account of defined input data.
The number, type and level of independence of lines connecting the NPP to the electric grid
should be determined based on the NPP design, according to the NPP safety case, reliability
of the electric grid, and the characteristics of the electric grid itself. Some examples of
connection schemes are included in Annex B.
The electric grid is the preferred source of power to the on-site power system and is also a
significant contributor to defence in depth (DiD) for the plant's safety design. The operation of
an NPP in transient and accident conditions, as well as normal shutdown, is more reliable if the
electric grid is available.
The NPP operator and electric grid operators shall technically assess the advantages and
disadvantages of alternative connection schemes after consideration of available options. The
connection scheme should include the definition of:
a) Type of HV switchyard (e.g., air or gas insulated) including functional and redundancy
requirements (refer to IEC 63046:2020);
b) Ownership and control of circuit breakers in the HV switchyard;
c) Type of electrical protection, number of channels and means of connection;
d) Arrangements for communication signals between the NPP and electric grid;
e) Dispatch control;
f) Metering.
– 14 – IEC 63298:2024 © IEC 2024
6.5 Analyses of the interface between the NPP and the electric grid
6.5.1 General
Analyses of the electrical power supply system shall be undertaken to design and verify the
connection and interface arrangements between the NPP and the electric grid.
Analyses shall be undertaken for different phases of the NPP design and operating life and
shall be updated periodically and when modifications to the NPP or electric grid are considered.
The first step is to conduct a general study (usually done by the electric grid operator) to assess
the feasibility of constructing the NPP, taking account of the expected electrical size of the plant
and the capability of the grid to operate with the NPP.
Responsibility for performing the analyses depends on the agreements between the NPP and
electric grid operators.
Specific analyses have a more defined responsibility (e.g., transient stability analysis is typically
performed by an electric grid operator, while analyses of NPP island operation mode are
typically performed by the NPP operator). It is important that both parties agree to exchange
the data needed for the given analyses.
Analyses shall also demonstrate that the electric grid and NPP have the capability to safely
respond to defined disturbances, as specified in the grid code (e.g., slow/fast voltage/frequency
variations, short circuits with relevant fault-ride-through capability, lightning and OPC).
The requirements for electrical power system analysis are detailed in IEC 62855. A summary
of the various types of analyses required specifically for the interface between the NPP and the
electric grid is provided in 6.5.2 to 6.5.10.
6.5.2 Load flow analyses
Load flow analyses shall be performed to determine the grid voltage and phase angle
distribution for a specific electric grid state given by generating sources, consumption points
and connecting transformers/lines.
As part of the assessment of the NPP grid connection, load flow analyses shall be performed
to verify the capacity and capability of the electric grid to export the power produced by the NPP
in a safe manner without violating electric grid limits, e.g., overload of equipment, violation of
n-1, n-2 criteria.
Electric grid load flow analyses shall be performed to check and verify possible maintenance
activities of electric grid during the NPP operation and to determine if some maintenance of the
electric grid can only be executed during the NPP shutdown states.
6.5.3 Transient stability analyses
Transient stability analyses shall be performed to confirm that the NPP generator(s) will
maintain stability in the event of limiting failures in the electric grid, as described in the grid
code (e.g. close 3-phase short circuits). The analyses shall be used to determine recovery
measures, where needed. In addition, the impact from grid transients on the NPP on-site
electrical systems shall be assessed.
A dynamic model of the NPP and electric grid shall be established to calculate the "fault
clearance time" (FCT) after which, if the grid failure is not cleared by protections on electric grid
side, affected generators would lose synchronism and would need to be tripped by their own
protection systems before loss of synchronism occurs.

It is preferable that generators are able to safely maintain stability during grid transients as
multiple generator trips will have a wider effect on the electric grid stability itself. In several
cases, the electric grid imposes a required minimum time for which generators are required to
maintain stability.
6.5.4 Steady state stability analyses
Steady state stability analyses shall be performed to study voltage/frequency stability of the
NPP in response to possible voltage/frequency profiles in the electric grid.
Steady state stability analyses shall also be performed to determine the capability of the NPP
generators regarding voltage (reactive power) regulation.
Analyses shall be performed to verify that the NPP has sufficient capability to withstand voltage
variations in the electric grid as defined in the grid code. Where this is not achieved, additional
measures should be implemented such as the use of on-load tap changers on the main
transformers.
Steady state analyses shall include the verification of the NPP capability (mainly auxiliaries,
reactor coolant pumps, safety systems) for degraded frequency states on the electric grid or
resulting from house load operation.
6.5.5 NPP island operation mode analyses (if applicable)
Where agreed between the NPP operator and electric grid operator, the NPP should be able to
safely operate in island operation (frequency control) where the NPP varies its own power based
on the variation of the frequency within its island. The boundary and extension of the given
island should be defined by the electric grid operator.
The scope of the analyses performed by the NPP operators should initially confirm that the NPP
is designed to safely operate in this mode.
The NPP electrical protection shall be designed to support this operation mode.
See also the requirement for flexible operation analyses in 6.5.7.
6.5.6 NPP house load operation analyses (if applicable)
Some NPPs are designed for performing house load operation (where the NPP provides power
to its own auxiliaries when disconnected from the electric grid) without tripping the reactor and
turbine-generator to minimize the reconnection time to the electric grid and to reduce transients
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