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GB/T 40588-2021: Technical provisions for automatic under-voltage load shedding in electric power systems
GB/T 40588-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 29.020
CCS F 21
Technical provisions for automatic under-voltage load
shedding in electric power systems
ISSUED ON. OCTOBER 11, 2021
IMPLEMENTED ON. MAY 01, 2022
Issued by. State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword... 3 
1 Scope... 4 
2 Normative references... 4 
3 Terms and definitions... 4 
4 General requirements... 5 
5 Basic principles of automatic under-voltage load shedding... 6 
6 Setting and configuration of automatic under-voltage load shedding measures... 8 
Annex A (informative) General steps for setting and configuring automatic under-
voltage load shedding measures... 10 
Bibliography... 11 
Technical provisions for automatic under-voltage load
shedding in electric power systems
1 Scope
This document specifies general requirements, basic principles, setting and
configuration methods for automatic under-voltage load shedding in electric power
systems.
This document applies to the technical measures for automatic under-voltage load
shedding in electric power systems involved in power system planning and design,
production operation, and scientific research and manufacturing.
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.
GB/T 156, Standard voltages
GB/T 14285, Technical code for relaying protection and security automatic
equipment
GB/T 31464, The grid operation code
GB 38755-2019, Code on security and stability for power system
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB 38755-2019
as well as the followings apply.
3.1 voltage stability
The ability that after the power system is subjected to small or large disturbances, the
system voltage can be maintained or recovered to the allowable range without voltage
collapse.
[Source. GB 38755-2019, 2.2.2]
3.2 transient voltage stability
The ability that after the power system is subjected to a large disturbance, all the busbars
of the system maintain a stable voltage.
[Source. GB 38755-2019, 2.2.2.2]
3.3 long-term voltage stability
The ability that after the power system is greatly disturbed, all the busbars of the system
maintain a stable voltage in the long-term process.
3.4 voltage collapse
The process that when the system is in a state of voltage instability, the load continues
to try to increase the current to obtain more active or reactive power, resulting in a large-
scale voltage drop in the system.
[Source. DL/T 1172-2013, 3.3, modified]
4 General requirements
4.1 According to the requirements for automatic under-voltage load shedding in GB
38755-2019, according to the safety requirements of the power system, users shall
cooperate with the implementation of under-voltage load shedding measures. In areas
where the load is concentrated, it shall be considered that when the operating voltage is
reduced, automatic or manual removal of part of the load shall be considered to prevent
voltage collapse. In addition, in areas (or some busbars) where there may be voltage
safety and stability problems, the automatic under-voltage load shedding device shall
also be equipped.
4.2 The automatic under-voltage load shedding measures shall be able to adapt to the
requirements of maintaining the safety and stability of the voltage in this area (or busbar)
under different operating modes.
4.3 The automatic under-voltage load shedding measures shall meet the requirements
of the power system for maintaining the transient voltage stability and long-term
voltage stability of the system.
4.4 The preparation and implementation of the automatic under-voltage load shedding
scheme shall be carried out according to the requirements of GB/T 31464.The setting
and configuration of the automatic under-voltage load shedding scheme shall be
coordinated and completed by the dispatching departments at all levels. The automatic
under-voltage load shedding scheme shall be reviewed periodically and when there are
significant changes in system conditions. After each serious failure of the system, the
analysis and summary work shall be done well.
4.5 The recovery of the load removed by the automatic under-voltage load shedding
device shall be carried out according to the dispatch order. Automatic investment means
such as self-preparation shall not be used.
5 Basic principles of automatic under-voltage load shedding
5.1 When a fault occurs in the power system, the automatic under-voltage load shedding
measures shall be able to avoid the under-voltage process that may exist during the
normal fault removal time. Prevent load loss due to device malfunction. The automatic
under-voltage load shedding measures shall also be able to avoid the action time of the
safety and stability control device of the second line of defense. Reasonably set the
action voltage and delay time of automatic under-voltage load shedding measures.
When the voltage stability criterion is met after the fault, the automatic under-voltage
load shedding device does not act.
5.2 The automatic under-voltage load shedding measures shall be divided into rounds
according to the operating voltage. Consider the delay time. They are mainly divided
into basic rounds and special rounds. Basic rounds and special rounds shall meet the
following requirements.
a) According to the requirements of GB/T 14285, the automatic under-voltage load
shedding measures can be divided into several rounds (levels) according to the
operating voltage and delay. The operating voltage value of the first round of the
basic rounds shall be lower than the minimum voltage allowed by the system for
a long time. The operating voltage value of the last round shall be higher than the
critical voltage of the steady-state voltage instability of the system.
b) The configuration of automatic under-voltage load shedding measures shall
follow the principle of stratification and zoning. Solve the problem of local grid
voltage stability. According to the specific situation of the voltage stability
problem in different areas, reasonably set the operating voltage and delay time of
each round. There shall be no skipping moves in each round. Considering some
unpredictable situations, special action rounds with long delay shall be added, so
that the voltage of certain areas (busbars) in the power grid will not be suspended
at a low level for a long time. The action voltage of the additional long-delay
special round can be repeated with the basic round or slightly higher than the
basic round.
c) Aiming at the problem of transient voltage stability, the basic number of rounds
of the automatic under-voltage load shedding device set in the system can be set
to 2~5.There is also a special round with long delay. For the long-term voltage
stability problem, the rounds and action delays can be appropriately increased. It
is recommended that the basic round voltage level difference is (2%~5%) UN,
(where UN is the nominal voltage of the system, and its value conforms to the
specified value of GB/T 156). The action delay of each round is 0.2s~5s. The
analyzed.
5.9 The device with automati...