Thailand and Malaysia have long enjoyed close cooperation,particularly  in the energy sector,which has significantly contributed to the enjoy security and development of both nations.Among those cooporative efforts is the interconnection of transmission networks.The 300 MW Thailand Malaysia High Voltage Direct Current (HVDC) Interconnection System is the second stage of the grid interconnection between EGAT of  Thailand and TNB of Malaysia.The new interconnection,which represents of the first cross-border DC link in the ASEAN region.is an important stepping stone to the realization of the ASEAN Power Grid which will significant  enhance the greater energy security and economic integration of the region.
























       The 300 MW Thailand Malaysia HVDC interconnection system consits of  Khlong Ngae  converter station on the Thai border and Gurun converter station on the Malaysia border.Both stations are linked by a 300 KV DC overhead transmission line of 110 km. EGATs Khlong Ngae converter  station is situated at Sadao district in Southern  Songkhla province ,about 24 km.from Thai-Malaysia border. TNBs Gurun converter station  is located in Kedah,about 86 km. from Malaysias northern boder.
























Power Supply System of Southern Thailand


         The southern part of Thailand  covering  14 provinces is currently connected to the nation  grid system via the 115 kv. and  230 kv.transmission  lines with an approximate  transfer capacity of 350 MW.Major generation facilities in this part of the country provide a total capacity  of 1,380 MW,including EGATs 240 MW Rajjaprabha  hydropower,72 MW Bang Lang  hydropower and 240 MW Surat Thani gas turbine power plants and EGATs  privatized 824 MW Kanom power plants. A new 300 MW Krabi thermal power plant   is due for operation soon.

         Demand in southern province has previously been met by generation  from the above mentioned power sources,the power transfer via the 115 kv and 230 kv central southern tie lines,and the power exchange with Malaysia.In 2002 ,maximum power demand of Thailandsouthern  system amounted  to 1,356.20 MW.According  to the recent load forecast, the demand is projected  to increase to 3,547 MW by the year 2016,or an average annual growth of 7% over the next 15 year period.Although EGAT  plans to upgrade to central-southern  tie line with the addition of 500 kv system,no power generating facilities will be put into the system after  the oil-fired  Krabi power plant.Thus  the new HVDC interconnection  system will help improve reliability of the power system of Southern Thailand.







Historical Background of EGAT TNB Interconnection


          A concept of  interconnection the electric power  networks of Thailand  and  Malaysia was  first the conceived  in the early 1970s  with the prime objective of emergency assistance and economic power exchange  due to the time difference in peak demand of the two systems.The first alternating current (AC) interconnection between EGATs Sadao substation and TNBs Bukit Keteri(Chuping) substation became operation since February 1981,allowing  a power of up to 80 MW via a 115/132 kv transmission line of 24.5 km length.























              However ,the existing interconnection was too small to tie the two system for synchronous operation.As a result ,during the power exchange , the power system had to be operated in such a way that EGATs  southern system  or  TNBs  northern system had to be isolated from their own main grid in order to be connected  to the network of the other system. Due to the capacity and stability restriction of the existing  AC interconnection, in  1988 EGAT and TNB explored the feasibility  of upgrading the interconnection to future  expand  the power transfer capability. Following the studies, and HVDC interconnection was adopted by the two utilities as the HVDC system could provide solutions to the synchronization problem. It also allows full bi-directional control of power interchange and improves reliability and dynamic performance of  both AC transmission systems.



Sophisticated  Transmission Technology for the 21st  Century


           The Thailand Malaysia HVDC interconnection project establishes a new efficient interconnection between Khlong Ngae  converter  station  in  southern  Thailand and Gurun  converter station in northern  Malaysia.Both  converter stations are linked  by a 300 kv DC overhead line of 110 km (approximately 24 km on the Thai border and 86 km on the Malaysian border). Initially,the converter station is configured as a  monopolar converter with the power transfer capacity of 300 MW.Provision  has also been made for adding  a  second 300 MW  pole in the future to extend the system into a bipolar configuration with a total transfer capability 600 MW.

        Project implementation started in August 1997.A joint implementation Committee  was set up by EGAT and TNB to oversee  and ensure the consistent  project implementation by both utilities. Each of the utilities is responsible for the HVDC station and the DC transmission line  in the respective  country.On Thailands side , the project involves the construction of a new DC transmission system and the reinforcement of the existing high voltage AC transmission system.











         The new  DC  transmission system includes the contruction of a new Khlong Ngae converter station and a 300 kv bipolar DC  line  of 24 km linking  Khlong Ngae  station with the HVDC system  on the Malaysian  border.The  converter  station features major components  including smoothing reactor.converter transformers,thyrister valves.DC  hybrid filters, AC filter banks, DC measuring device as well as state -of - the art decentralized control and protection system.


       The reinforcement of EGATs existing AC transmission system involves the construction of the following  transmission facilities :

·       A 230 kv AC substation  at the side of Khlong  Ngae  station

·       A 230 kv AC double  circuit line of 30 km linking Khlong Ngae  station with Hat Yai 2 substation

·       A 230 kv AC double  circuit line of  210  km linking Khlong Ngae  station with  Thung Song substation

·       A 230/115/33 kv AC Thung Song  substation,and

·       The reinforcement of the existing 230 kv AC Hat Yai 2 substation.

  Construction of the 300  MW Thailand Malaysia HVDC Interconnection  on the Thai side  was  completed  in September 2001 at a total cost 4,980 millions baht.A new HVDC system  interconnection Agreement was sign between EGAT and TNB on May 14,2002.Commercial  operation of the new HVDC interconnection officially started  on June 3,2002.

    The DC monopolar  converter station is currently capable of transmitting  a full rated power of 300 MW(300 kv,1,000 A) in either direction up to a maximum  ambient temperature of 39° C.The DC transmission line also permits a 10-minutes overload of 450 MW  of power once per day.According to the  agreement, both EGAT and TNB agreed to initially generate and deliver 30 MW power as an obligatory  energy to enable the continuous  operation of the HVDC interconnection .Commercial energy is the energy sold and purchased at any time request by either utility.




Enhancing Mutual Energy Security


        The Thailand Malaysia HVDC interconnection system provides various benefits including:

·       Economic exchange of power between two different networks

·       Enhancing system  reliability

·       Reduction of reserve capacity  of both countriespower systems  by sharing spinning reserve

·       Sharing of HVDC system operational and maintenance experience

·       Closer cooperation  between Thailand and  Malaysia


















A  Stepping stone to the Integrated ASEAN Power  Grid


       The  HVDC interconnection system marks another successful cooperation effort between Thailand and Malaysia in future building up mutual  energy security.The project will not only benefit  the two nations,but also all ASEAN  countries as a whole.As the first cross-border  DC link in the region,the Thailand Malaysia HVDC interconnection system has been included in the ASEAN Interconnection Master Plan Study as part of the ASEAN Power Grid.The success of the Thailand Malaysia interconnection will greatly help accelerate the integration of the ASEAN power networks which will significantly  enhance the regions sustainability  and security of energy supply  for the benefit of the people of all countries  in the  region.






















Key Data


Smoothing  reactor

     100 mh,single core

Converter transformers

3 x 116 MVA, 1 phase 3 winding

230/122.24/122.24 kv

Thyristor  valves

T 1501 N75T-S34

12  group valves  indoor air insulation suspension type

No. of  thyristor  per valve : 48,

Blocking voltage : 8 kv /1550 A

DC  hybrid filters

Passive part filter (12/24 harmonics)

Active part filter (6/15/21/24/27/33/36/42/48 harmonics)

Transmission line


DC, 110 km (24 km  on Thailands  border and 86 km on Malaysias boder)

Pole conductor : 546 mm2 (ASCR Cardinal)

Neutral  conductor :298 mm2 (ASCR Hen)

Main contractor

Siemens AG ,Germany


Teshmont  Consultants Inc..,Canada