The document discusses Thailand's Blackout Prevention Plan, which was implemented by EGAT (Electricity Generating Authority of Thailand) to enhance the stability, reliability, and security of Thailand's power grid. The plan includes power system simulations and studies to identify vulnerabilities. It also details several short-term and long-term measures to strengthen the grid, including special protection schemes, construction of new transmission lines and generators, and installation of FACTS equipment. Specific schemes discussed are under-frequency load shedding, under-voltage load shedding, generation shedding, and rapid load shedding to maintain stability in case of contingencies.

1. Abstract--The stability, reliability and security of power
system are the concerned issues in Thailand due to the lessons
from the blackout around the world in 2003. Electricity
Generating Authority of Thailand (EGAT), which is responsible
on the generation and transmission system in Thailand, has
considered the measures to avoid the major power failure in
Thailand so-called the blackout prevention plan. The blackout
prevention plan is used as a tool for managing and operating the
system efficiently.
The blackout prevention plan is the preventive plan to
minimize the chance of the failure in the power system in
Thailand as possible. To identify the system vulnerability in the
network, the power system simulations are performed as the
important methodology. The power system analysis is not only
examined on the N-1 criteria but also the events from the past
experience and the potential events that can occur in the
Thailand power grid. Many aspects are analyzed to understand
the constraint on system and select the appropriate methods to
solve the problems efficiently. The investment and maintenance
cost of the solution also are taken into the account to optimize the
security of the system and economics.
This paper presents the blackout prevention plan for
Thailand system. It is also addressed the power system analysis
on the load flow study as well as the dynamic simulation. The
enhancement of system strength is divided into the long term and
short term duration. The construction of the new transmission
lines and generators as well as the installation of new
technologies equipment will be suggested to reinforce the system
for the long term planning. As the short terms planning, the
special protection schemes generally played the important role to
maintain the system stability. The use of the special protection
systems and the existing FACTS equipment in the system such as
HVDC and SVC are expected to mitigate problems associated
with the blackout in Thailand system. The implementation of
special protection schemes and FACTS devices to increase the
power system stability, reliability and security are represented in
this paper.
Applying the blackout prevention plan will be beneficial to
Thailand power grid as a whole. This paper is the case study for
the power system study and implementation on the blackout
prevention plan to enhance the stability, reliability and security
of the power system in Thailand.
Index Terms-- Blackout Prevention Plan, Power System
Stability, Power System Security, Power System Simulation,
Blackout, Special Protection Scheme
I. INTRODUCTION
The Electricity Generating Authority of Thailand (EGAT)
is a state enterprise organization responsible on the electric
generation and transmission for the whole country of
Thailand. EGAT transmits the bulk electric energy directly to
two distribution authorities, namely the Metropolitan
Electricity Authority (MEA) and the Provincial Electricity
Authority (PEA). The voltage level of the transmission system
is range from 115 kV, 230 kV and 500 kV. The system peak
demand reached 19,748 MW, as of March 2005. The more
complex power system changes, the more complicated tasks in
managing the power system with high security are. Therefore,
it is a challenge for EGAT to operate the system maintaining
the high security and reliability with the lowest costs of
operation and investment.
The power system needs the planning and operating system
to manage the power system efficiently. Even though, there is
the excellent system management but the error can occur in
the power system. In some conditions, the system disturbance
such as a fault on transmission facilities, loss of generation,
and loss of a large load may cause system vulnerability and
lead to system instability. Finally, it may lead to total or
partial power system blackout. EGAT as the system operator
which is responsible on generation and transmission system in
Thailand introduced the blackout prevention plan to enhance
the system stability, reliability and security efficiently.
Fig. 1. Blackout prevention plan diagrams and detailed issues
The blackout prevention plan is the operation plan
describes the weak point in the system and offers the best
planning and other alternative solutions. It also can
Witchaya Pimjaipong Tormit Junrussameevilai Natthakorn Maneerat
Electricity Generating Authority of Thailand
Blackout Prevention Plan – The Stability,
Reliability and Security Enhancement in
Thailand Power Grid

2. demonstrate the scope of work and problems in the power
system in Thailand. The main purpose of the blackout
prevention plan is to prevent the major blackout event in
Thailand power system. The other advantages are improving
the system stability, reliability and security of the system.
EGAT separated the blackout prevention plan into several
sections as the following.
A. The preventive measures
The preventive measures are the plan to prevent the
interruption in the power system due to several causes such as
animal or fire under the transmission system. Human error and
computer failure also includes in this section.
B. The inspection procedures
The inspection procedures are the process plan for
maintenance of the equipment in the substation. The high
voltage equipments, protection and control equipment,
transmission facilities as well as communication system are
the importance components in the power system. This topic is
covered on the procedure and duration of the maintenance on
the equipment in the substation.
C. Power System Study
The power system study is the issues focusing in this paper.
Load flow analysis and transient stability is the method to
understand the problems and define the alternative solutions
for Thailand power system.
The special protection schemes are implemented as the tool
to preventive plan to protect the system from major power
failure. It is the final system protection before the blackout
occurs. The special protection schemes offer the alternative
solution to prevent the major power failure. It will detect the
problems in the power system and send the command to shed
the load or trigger the FACTS equipment to operate depending
on the problems in the power system.
EGAT also established another plan related to the blackout
so-called the blackout restoration plan. It is the master plan to
restore the power system back to normal conditions within the
shortest duration as possible.
The investment budget in the transmission system is
limited due to the deregulated and privatized environment. By
constructing new facilities such as new transmission lines or
new generating sites, the blackout can be avoided.
Nevertheless, there are many problems on the construction of
the new facilities. High investment cost for new facilities and
environmental concern are the most common obstructions.
Thus, the special protection scheme is one favorite of the
blackout prevention plans for the low investment cost and
high efficiency. Even though, other measures is trying to
prevent the system before the events happen such as human
error or fault via animals, the fault in power system still can
occur. The fault and error cannot be avoidable completely.
This paper will focus on the power system study section –
the conceptual design and methodology of the special
protection scheme as the blackout prevention plan. The
problems in the Thailand power system are classified and the
implementations of the special protection schemes are also
described in this paper.
II. POWER SYSTEM STUDY - CONCEPTUAL DESIGN
AND METHODOLOGY
Power system simulation is the major process to design the
special protection scheme. The concept for the system study is
to prevent the system from the contingency N-1 and
contingency N-2 in case of the parallel equipments such as
transmission line and transformer. The past experience power
failure events are also introduced to consider on prevention
the recurring events. Several scenarios have to be considered
and studied to find the best solution of each specific problem,
which usually called special protection schemes. The SPS
would then be designed and implemented in the system. When
such a predetermined disturbance occurred, the designed SPS
will detect and operate immediately to save the system. The
main purpose of the SPS is to prevent the power system from
instability and splitting up, as well as limit the power system
problem within the small area and minimize the effect of the
problems in the power system.
The power system study carried out by EGAT for blackout
prevention plan will be divided into 2 major studies.
1. Load Flow Study
Load flow study is the study on the characteristics of the
power system on the steady state behavior. It uses for the daily
operation plan to considers the problem on voltage profiles
and overload equipments.
2. Transient Stability Study
The transient stability study is the study related to the
response of the system due to the large disturbance in the
system. The study will consider in the time domain within the
scope of seconds to minutes. The equipment in the system
such as generator, governor, excitation system, Turbine –
generation controller and FACTS devices will have the
different response on the different time frame. The study will
focus mostly on voltages, frequency and angle of the
generators.
For the power system analysis results, it will lead us to
understand the system problems as overviews and classified
the problem according to the characteristics of the events.
These results will be the direction to select the appropriate
solutions for each problem.
Fig. 2. Example of the transient stability simulation: the angle of the southern
generators when power plants trip and power flow exceeded the stability limit.

3. The vulnerability in Thailand power grid can be classified
into 4 major types which depended on the characteristics of
the phenomena – Frequency stability, transient stability,
voltage stability and overload on the equipment.
III. IMPLEMENTATION OF THE SPECIAL PROTECTION
SCHEMES IN THAILAND
The problems of the power system have to be considered to
find the optimized solution. The design of the special
protection system should consider in reliability, simplicity and
selectivity. The main objective of the special protections
scheme is to prevent the corruption of the power system and to
control the damage in the power system in limited area. The
special protection scheme in the blackout prevention plan is
divided as following.
A. Under Frequency Load Shedding
Automatic under-frequency load shedding is the most
effective method to balance load and generation thus restoring
the system frequency back to normal. Under-frequency relays
need to be installed at all designed load points. Power system
analysis is carried out to determine amount of load needed to
be shed at each frequency step.
EGAT’s under-frequency load shedding scheme is being
designed for the maximum of 50 percents loss of the total
generation. The starting frequency to shed load is considered
for the ability of the system to recover from the loss of
generation. There are also the other frequency controllers in
EGAT system to be considered such as HVDC frequency limit
control function and under frequency relay for pump storage.
Thus, the starting frequency to shed load is set at 49 Hz.
Number of steps and sizes depending on the maximum load
that needed to be shed, the upper and lower limits and speed
of the operation of relay and breaker have to be considered.
When a disturbance occurs in the system, the frequency
oscillation may occur and cause the frequency to be different
at buses in the system. This effect needs to be taken into
account when coordinating the operation between steps.
Fig. 3. The design of the under-frequency load shedding
The result of the power system analysis study assuming the
generation loss of 10%, 20%, 30%, 40%, and 50% and the
recovery frequency following the operation of the under
frequency load shedding scheme are shown in Figure 3. The
setting of the under frequency load shedding scheme is shown
in table 1.
TABLE1. Setting for under-frequency load shedding schemes
Step Setting RelayTime BreakerTime %LoadShed
(Hz) (msec) (msec) (%)
1 49 150 100 10
2 48.8 150 100 10
3 48.6 150 100 10
4 48.3 150 100 10
5 47.9 150 100 10
The scheme is applied for all load location in the country.
The total amount of load shed is divided between the two
distribution utilities equally - 50 % for the Metropolitan
Electricity Authority (MEA) and 50 % for the Provincial
Electricity Authority (PEA). The distribution utilities can
select their own load to be shed depending on the priority.
B. Under Voltage Load Shedding
In some cases, the transmission lines are tripped and cause
the voltage drop in some area. The voltage drop in some point
of the system may cause the problem in the surrounded area
and eventually bring the voltage collapse. The simply solution
is shedding the load at the lowest voltage point to minimize
the damage. If the system is normal, the load will be restored
back in the system with the short time.
C. Generation Shedding Scheme
Generally, the generation is located in the distant area from
load area and transfers bulk power via the transmission lines.
The congestion line problems have become the common
problems in the transmission systems around the world. If the
significant lines were tripped from the system, the remaining
transmission system capability may not be enough to transfer
the energy through the power system. The power swing may
occur and cause the separating system which may leads to
total power system failure.
There are many alternative ways to avoid the transient
stability problem. Either by building additional transmission
lines or controlling the generation output below stability limits
can mitigate the stability problem. However, it would require
high initial investment cost or increase of the production cost.
Generation shedding scheme is the most effective and
economical method compared to the above two solutions. It is
provably very powerful method to protect the system from
instability. [3]
The power system simulations were performed to analyze
all variables related to stability factors. Numbers of the
generators, power flows on the concerned lines, disturbances
in the system, patterns of generating unit dispatched, and load

4. conditions are the parameters to be considered for the
acceptable amount of generation to be disconnected or shed.
Fig. 4. The implementation of generation shedding scheme
An example of this type of scheme is the generation
shedding scheme for Ratchaburi power plant. From the power
system study, it was found that the western system of
Thailand’s network will be unstable due to the double circuit
lines 500 kV Ratchburi3-Chom Bung tripped. The western
system will be separated from the central and southern
systems and become isolated. The large generators in the
western system itself will lose the synchronism and finally trip
out from the system. The blackout will occur in the western
system while the rest of the system will suffer in the severe
lack of generation. The generation shedding scheme is
implemented to solve the stability problem at Ratchaburi
power plant in the western system. The power system study
also tries to optimize the amount of generation unit trip
enough to maintain the system stability. Several scenarios of
system conditions have been considered and studied. The
results of the study were programmed into the control box,
which is a programmable logic controller, installed at
Ratchburi3 substation. Figure 4 shows the implementation and
operation of the generation shedding scheme for Ratchaburi
power plant in Thailand.
D. Rapid Load Shedding Scheme
The southern system of Thailand has long been
encountered with the problem lacking generation supply to the
demand in the area itself. Thus, the southern system needs to
rely on the power transferred from the central system via the
tie transmission lines. Unfortunately, the tie lines have the
stability limit around 570 MW. The power transfer near the
stability limit has the high risk against the loss of generation in
the southern system. The power flow between the central
system and the southern system will increase over the stability
limit. In such a case, the power oscillation will occur and
cause the tie lines to trip and isolate the southern system from
the central system. Either partial or total blackout could occur
in the southern system due to severe lack of generation. From
the power system analysis study, when generators in the
southern system trip during the high power flow on the tie
lines. The power oscillation will occur on the tie lines and
causes the remaining generator units in the southern system as
well as the tie lines to trip. It is suggested to minimize the
effect on the southern system by preventing the tie lines from
tripping so that the power transfer from the central system to
the southern system can continue to supply most of the load.
One of the solution known as the transient stability
enhancement is the direct load shedding method. The scheme
will detect the tripping of generating units in the southern
system and operate immediately to disconnect some
predetermined load points in order to prevent the power flow
exceeds the stability limits. This direct load shedding scheme
has to operate fast enough to avoid the stability problems on
the tie lines. Thus, the tele-protection signals have to be
utilized in the scheme. This scheme is so-called the rapid load
shedding scheme. [4]
Fig. 5. Rapid load shedding scheme for the southern Thailand system.
The power system study was performed both in steady state
and dynamic simulations. The study focuses on Khanom (KN)
power plant tripped as the KN power plant is the largest power
plant in the southern system. The study covers all load
conditions and all patterns of KN power plant generating units
dispatched. The result of the study was programmed into the
control box, which is a programmable logic controller,
installed at Khanom substation. Figure 5 shows the
implementation of rapid load shedding scheme for KN power
plant.
E. HVDC Stability Functions
HVDC has the special control for increasing the stability
of the power system. The stability functions consist of 4 sub-
functions as following. [5]
1. Power Run-Up Function - It will send the signal to
increase the HVDC power level to the required power set
point. The increasing power follows the pre-programmable
ramp rate.
2. Power Run-Back Function - Normally, power runback
function will be used together with the power run-up function.
It will reduce the HVDC power transfer to the setting power
level with the designed ramp rate. The run-back function also
comes with the alternative function – Fast Power Reversal.

5. The fast power reversal function can change the power
direction of HVDC system immediately.
3. Power Swing Damping Function - Basically, power
swing damping function or dual frequency modulation
function will be used as the solution for the power oscillation
problem in the AC system. If the power oscillation appears in
one side of the power system and the power swing damping
function enabled, the HVDC system will adjust the power
transfer to counter the oscillation so as to stop or diminish the
oscillation.
4. Frequency Limit Control Function - This function will
operate when the system frequency is out of the normal range.
It will compare the frequencies of the networks on both sides
and find the frequency difference. If the frequency of either
system is lower than the setting range by any reasons, this
function will operate to increase the DC power to compensate
for the loss of power of the system. If the frequency is higher
than the set frequency, the DC power will be decreased to
lower the frequency of the system. The duration of operation
varied with the frequency deviation.
Fig. 6. Control block diagram for HVDC stability functions
F. Other Special Protection Schemes
There are also several other protection scheme such as
overload line protection and automatic switching capacitor.
The overload line protection will protect the line to overload
especially the major lines that can lead to the cascade trip of
the lines. The automatic switching capacitor will use to close
the circuit breaker of the capacitor into the system when the
voltage dropped for some duration.
The combination of the special protection schemes is also
the other alternative that can be useful. Figure 6 shows the
example of the integration of HVDC stability function and
rapid load shedding scheme to reduce the amount of the shed
load.
IV. CHALLENGES AND SUGGESTIONS
The complexity of the special protection scheme is problem
during the implement. The special protection scheme should
apply in the simple concept and easy to understand for the
operator.
In some conditions, the dispatches of generation can cause
the constraint in the power system. The low cost generation
such as hydropower plant will produce the power transfer
through some constrain link and may cause the overload in the
system.
The modification of the network can also cause the
difficulty of the special protection scheme implementation and
the error in the operation of the special protection scheme.
Thus, the power system analysis has to be carried out to verify
the correction of the special protection scheme when the
power grid is changed.
Fig. 7. The combination of HVDC stability functions and rapid load shedding
scheme.
V. CONCLUSIONS
The electricity supply industry is a high investment
business and yet has a direct impact to the overall country
economy as well as a good living of the people. Therefore,
operating and managing the power system with high security,
quality, and economics play the most important role in
developing the country.
Limited budget on new investments, environmental
concerns, and widely scattered national resources increase the
risk of major system failure. It is a challenge for EGAT to
minimize the investment while operating the system to the
high security and quality with the lowest costs. Special
protection scheme can be a low cost alternative compared to
constructing new transmission facilities to maintain the system
security. New transmission lines and new generation projects
are needed to meet with the long-term power development
plan. While special protection scheme can be used as an
interim measure until those projects are completed as it
permits the maximum utilization of the existing transmission
system.
The stability, reliability and security of the Thailand power
grid are considered as one of the major issues due to the
blackout around the world. The blackout events in power
system in the past few years are motivated EGAT as the
Thailand power grid operator to be alert and ready for the
unexpected events in the power system. EGAT is considered
the blackout prevention plan to enhance the stability,
reliability and security of the Thailand power system.

6. Blackout prevent plan is the preventive plan to minimize
the chance of power system failure and limit the loss in the
controllable area. Many factors can cause the blackout in
power system. Thus, the blackout prevention plan is separated
into many items such line maintenance or human error control.
The special protection scheme is a measure in blackout
prevention plan which are represent in this paper. This paper
refers to special protection schemes as the standard protection
schemes used in various utilities around the world. From
EGAT’s actual experiences, these schemes achieve the
satisfactory purposes.
The generation shedding scheme is the typical solution for
the power system to solve the transient stability problems. The
implement of the special function of FACTS device is also
one solution that is always efficiently. The integration of the
special protection scheme is the splendid strategy in
application on the power system.
The load shedding scheme is the last option to use in case
of other options cannot provide. The load shedding will shed
some amount of load to maintain the whole system from
blackout and it will take less time to manage the system and
put the customer back into the service.
Although, the blackout prevention plan has been
implemented, other measures also bring into the practice to
increase the system stability. Blackout restoration plan is also
another preparation plan in case of the blackout occurs in the
Thailand power grid.
VI. REFERENCES
[1] Phabha Kundur,” Power System Stability and Control”, Electrical Power
Research Institute, 1993
[2] Jan Machowski, Janusz W. Bialek, James R. Bumby, “Power System
Dynamics and Stability”, John Wiley & Sons, 1997
[3] Witchaya Pimjaipong, Luechai Surapongpan, Patai Phuyodying, “
Ensuring Stability of Southern Thailand Network by New Generation
Shedding Scheme”, CAFEO2000, Hanoi, VIETNAM
[4] Witchaya Pimjaipong, Natthakorn Maneerat, Patai Phuyodying, “Ensuring
Stability of Southern Thailand by Rapid Load Shedding Scheme” ,CEPSI
2004, CHINA
[5] Witchaya Pimjaipong, Luechai Surapongpan, Chanin Choniratisai,
“HVDC Stability Functions and Implementation in Thailand”, CEPSI 2004,
CHINA
[6] Robert H. Miller, James H. Malinowski, ”Power System Operation”,
Third edition, McGraw-Hill, Inc. 1993
[7] PTI, “PSS/E 26 Program Application Guide: Volume I”, Power
Technologies, Inc., 1998
VII. BIOGRAPHIES
Witchaya Pimjaipong received his B.E. degree
from Kasetsart University, Thailand in 1994 and
M.Sc. degree from University of Southern
California, Los Angeles, US. He is currently
power system analyst with EGAT (Electricity
Generating Authority of Thailand). His areas of
research interest are power system protection,
power system simulation including digital
simulation of electromagnetic transients in power
systems and HVDC transmission.
Tormit Junrussameevilai received his Electrical
Engineering degree from King Mongkut Institue
of Technology North Bangkok in 1997. He has
join Electricity Generating Authority of Thailand
(EGAT) since 1998. He is presently working in
Power System Analysis Division. His current role
is to provide technical service in the power system
analysis area and equipment implementation.
Natthakorn Maneerat graduated in Electrical
Engineering from Kasetsart University, Thailand
in 2000. Since 2001, she has been employed by
Electricity Generating Authority of Thailand
(EGAT) where she is currently power system
analyst. She has involved in various power system
stability studies including small signal simulation.