IEC TS 63384-2:2026

IEC TS 63384-2 ®
Edition 1.0 2026-01
TECHNICAL
SPECIFICATION
Power System Stability Control -
Part 2: Guideline for quantitative assessment of power system stability and
security
ICS 91.140.50  ISBN 978-2-8327-0932-0

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CONTENTS
FOREWORD . 2
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Classification of power system stability and security . 6
4.1 Classification of power system stability . 6
4.2 Classification of power system security . 6
5 Objective and general requirements of power system stability and security
quantitative assessment . 7
5.1 Objective . 7
5.2 General requirements. 8
6 Quantitative assessment . 8
6.1 Selecting appropriate assessment indices . 8
6.2 Data and models requirements . 9
6.3 Quantitative assessment via state-based indices . 9
6.4 Quantitative assessment via distance-based indices . 10
6.5 Quantitative assessment via control-based indices . 11
6.6 Quantitative assessment via risk-based indices . 11
6.7 Strategies for improving assessment efficiency . 12
7 Applications of quantitative assessment . 12
7.1 General . 12
7.2 Power system planning . 13
7.3 Stability control system engineering design . 13
7.4 System operation planning . 13
7.5 Off-line control decision planning . 13
7.6 System operation . 13
7.7 On-line control decision planning . 14
Annex A (informative) Exemplars of quantitative indices . 15
A.1 Exemplars of state-based indices . 15
A.2 Exemplars of distance-based indices . 17
A.3 Exemplars of control-based indices . 18
A.4 Exemplars of risk-based indices . 19
Bibliography . 20

Figure 1 – Classification of stability in power system with high penetration of power
electronic interfaced technologies [1], [2] . 6

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Power System Stability Control -
Part 2: Guideline for quantitative assessment of power system stability
and security
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced
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IEC TS 63384-2 has been prepared by subcommittee 8C: Network management in
interconnected electric power systems, of IEC technical committee 8: System aspects of
electrical energy supply. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
8C/136/DTS 8C/156/RVDTS
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 Technical Specification 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.
A list of all parts in the IEC 63384 series, published under the general title Power system
stability control, can be found on the IEC website.
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.
1 Scope
This Technical Specification (TS) addresses the quantitative assessment of power system
stability and security. Its purpose is to provide guidelines encompassing the use of terms and
definitions, as well as the objectives and general requirements for conducting quantitative
assessments. The TS includes the classification of stability and security, classification of
quantitative indices, and key considerations for implementing quantitative assessments. These
considerations involve selecting appropriate assessment indices, methods for obtaining these
indices, model and data requirements, and strategies for improving assessment efficiency.
Examples of quantitative indices are also provided (see informative Annex A).
The application of a stability and security quantitative assessment serves several purposes.
Firstly, it establishes an adequate margin to ensure the synchronous operation of the power
system and the safety of primary equipment under both normal and abnormal conditions.
Additionally, it helps improve the cost-benefit ratio of power system operations. The TS is
applicable to various domains, including system planning, operation planning, operation control,
stability control system design, and stability control decision planning, as well as software,
equipment, and systems for the secure and stable operation of the power system. By using
quantitative assessment of stability and security, it is possible to identify key factors that
contribute to instability and to develop mitigating methods for enhancing stable operation.
The stability and security quantitative assessment techniques specified in IEC TS 63384-2 are
independent of any specific software, equipment, or systems used for the secure and stable
operation of the power system.
2 Normative references
There are no normative references in this document.
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
stability
ability of an electric power system, for a given initial operating
condition, to regain a state of operating equilibrium after being subjected to a physical
disturbance, with most system variables bounded, so that practically the entire system remains
intact
Note 1 to entry: If following a disturbance the power system is stable, it will reach a new equilibrium state with the
system integrity preserved, i.e., with practically all generators and loads connected through a single contiguous
transmission system.
3.2
security
ability of an electric power system to operate in such a way that
credible events do not give rise to loss of load, disruption of physical integrity of equipment,
stresses of system components beyond their ratings, bus voltages or system frequency outside
tolerances, instability, voltage collapse, or cascade tripping
Note 1 to entry: This ability can be measured by one or several appropriate indices.
Note 2 to entry: This concept is normally applied to bulk power systems.
Note 3 to entry: In North America, this concept is usually defined with reference to instability, voltage collapse and
cascade tripping only.
[SOURCE: IEC 60050-617:2009, 617-01-02, modified – The words "disruption of physical
integrity of equipment" have been added.]
3.3
stability and security assessment
assessment that judges and analyses whether the requirements
of power system stability and security are satisfied
Note 1 to entry: Stability and security assessment includes: verifying that the operating conditions are met, checking
the system's ability to withstand disturbances, and determining a margin for which the deviation of selected variables
or parameters that can be tolerated without causing the system to become unstable or insecure.
3.4
stability and security quantitative assessment
assessment that judges and analyzes quantitatively whether the
requirements of power system stability and security are satisfied
Note 1 to entry: Stability and security quantitative assessment includes: providing the degree to which the power
system meets these requirements or identifying the differences (margin) between the actual values and the critical
values for instability or insecurity.
3.5
state-based index
quantitative index of stability
and security, which exclusively considers the given power system state based on the
characteristic and theoretical critical values that indicate instability or insecurity
Note 1 to entry: Power system state refers to: (1) steady state, the initial operating condition(point) of the power
system subjected to a disturbance; (2) dynamic state, the response (variables variation) of the power system to a
disturbance.
3.6
distance-based index
quantitative index of stability
and security, which considers the margins of power system operation parameters (based on
power flow) constrained by stability and security, such as margins of load, generation amount,
transfer power, and other relevant factors
Note 1 to entry: Here, the distance means the deviation (gap) from the given power system operation parameters
(point) to the boundary of power system operation parameters (point) constrained by stability and security.
3.7
control-based index
quantitative index of stability
and security, which considers the control parameters constrained by stability and security, such
as the critical clear time (CCT) of faults and the necessary (indispensable) control action to
maintain stability and security
3.8
risk-based index
quantitative index of stability
and security, which accounts for the risk associated with stability and security
3.9
risk
combination of the probability of contingency occurrence and its
impact
Note 1 to entry: Risk assessment may take into account the likelihood of implementing stability control measures
and their associated costs in response to the contingency, especially if the impact of the contingency cannot be
quantified directly.
3.10
rotor angle stability
ability of interconnected synchronous machines in a power
system to maintain synchronism under normal operating conditions and to re-establish
synchronism after experiencing disturbances
3.11
voltage stability
ability of a power system to sustain steady state voltages across
all buses within the system following disturbances
4 Classification of power system stability and security
4.1 Classification of power system stability
The classification of power system stability should consider the following factors:
– the physical manifestation of instability, as indicated by the power system variables where
instability is observable;
– the size of the disturbance to be analyzed, which affects the approach for calculating and
predicting stability;
– the devices, processes, and timeframe required for stability assessment.
Figure 1 illustrates the classification of stability in power systems with a high penetration of
power electronic interfaced technologies, delineating categories and subcategories.

Figure 1 – Classification of stability in power system with high penetration of power
electronic interfaced technologies
4.2 Classification of power system security
The classification of power system security is determined by the following criteria:
a) capability to withstand disturbance(s): the system's ability to endure disturbances and return
to an acceptable state following a contingency;
b) satisfaction of operational constraints: ensuring that all operational constraints are met
under the new state following a contingency, including adherence to equipment ratings, bus
voltage, and frequency limits;
c) physical integrity of equipment: verification that all equipment, including power electronics
interfaced devices, remains within its physical capabilities during system operation and
transient evolution post-contingency;
Power quality issues are excluded, such as harmonic distortion, flicker, impulse transients,
voltage surges, etc., from considerations related to power system security.
The types of power system security can be classified as follows:
– system stability;
– thermal overload;
– steady voltage, including under voltage and over voltage;
– steady frequency, including under frequency and over frequency;
– transient voltage, including under voltage and over voltage;
– transient frequency, including rate of change of frequency (RoCoF), under frequency and
over frequency;
– short circuit current;
– power electronics interfaced devices (such as nonsynchronous generator, HVDC, etc.) fault
ride-through.
5 Objective and general requirements of power system stability and security
quantitative assessment
5.1 Objective
The overarching goal of power system stability and security quantitative assessment is to
establish a reliable numerical margin, ensuring the synchronous operation of the power system
and the safety of primary equipment, including power electronics interfaced devices, under both
normal operating conditions and disturbances. This assessment is essential to ensure:
– proper system design: verification that the system is adequately designed with stability and
security margins;
– continuous margin evaluation: continuous monitoring to confirm the presence of sufficient
stability and security margins across all operational scenarios, encompassing system
operation parameters and stability control parameters;
– risk management: assessing and managing the risk associated with power system stability
and security to ensure it remains within acceptable limits.
When assessing multiple scenarios, power system stability and security quantitative
assessment serves to:
– identify weaknesses: detect areas of vulnerability that could compromise stable and secure
operation;
– analyze instability factors: identify key factors contributing to instability and insecurity;
– develop control strategies: devise strategies to enhance stable and secure operation based
on the findings of the assessment.
Moreover, stability and security quantitative assessment enhances the cost-benefit ratio of
power system operation and control. Operating the power system based on risk necessitates
the use of stability and security quantitative assessment.
Additionally, implementing the same stability and security requirements across different areas
of interconnected power systems can be facilitated through quantitative assessment
methodologies.
5.2 General requirements
Power system stability and security quantitative assessment shall take into account the
following aspects:
– assessment results: ensure that the results of the assessment are reasonable, accurate,
and comprehensive;
– application goals: tailor the assessment to meet the objectives of system planning, operation
planning, operation control, stability control system design, or stability control decision-
making;
– characteristics of the power system: consider the specific attributes of the power system
under evaluation;
– operational and control performance requirements: address the performance requirements
unique to the particular power system;
– application environment: adapt the assessment methodology to suit the online or offline
environment in which it will be utilized.
When applied in an online environment, the assessment should prioritize dependability and
rapid response to ensure real-time monitoring and decision-making capabilities.
6 Quantitative assessment
6.1 Selecting appropriate assessment indices
The quantitative indices utilized in power system stability and security assessment shall meet
the following criteria:
a) numerical representation of system state: the indices should digitally describe the power
system state in terms of its adherence to stability and security requirements. They should
reflect changes in both primary and secondary system variables, accurately capturing their
impacts on stability and security;
b) qualitative judgment: The indices should allow for qualitative assessment of the power
system's stability and security state. If the index falls within acceptable ranges for stability
and security, the system is deemed to meet the requirements. Otherwise, it indicates
instability or insecurity.
The selection of appropriate quantitative assessment indices should consider several factors:
– type of stability and security concerned: tailor the selection to address the specific types of
stability and security issues relevant to the power system;
– information requirement: determine the type of information needed from the indices to
effectively assess stability and security;
– availability and affordability: choose indices that can be obtained using existing resources
and at a reasonable cost;
– model and input data accessibility: ensure that the required models and input data can be
obtained using available resources.
Different types of quantitative assessment indices are utilized
...