The 500kV North – South transmission line (circuit 1) put into operation from 1994 is the 1st 500kV transmission line in Vietnam. It has a total length of 1,462.5 km, starting from Hoa Binh Hydropower Plant and ending in Ho Chi Minh city. Together with it, the circuit 2 transmission line put into operation in 2005 connecting from South to North has the responsibility of transfering power from the North to the South and vice versa. Since its operation, the 500kV North-South transmission line has effectively brought into play, transfered a huge capacity of power from the North to the South and Central area to supply for the socio-economic development demands, increasing considerably the reliability of the system and ensuring quality of power voltage, playing the role of power transmission “highway”. Therefore, it optimizes the power transfer of generation plants in the system, creating a large economic benefit for the country.
The transmission operators work day and night to keep smooth operation of transmission lines
Silent efforts have not been mentioned
EVNNPT is responsible for managing and operating 98 substations, 4,848 km and 11,313 km of the 500kV and 220kV transmission line. Over the last time, EVNNPT has applied many new technologies in the management and operation of the 500kV and 220kV transmission lines, such as equipping with Corocam for recording the electric corona in insulators to prevent the failures caused by electric discharge; using composite insulators instead of glass ones for the sections of line running through the contaminated areas; using the emergency restoration towers (KEMA) transfered by Holland for failures repair; applying the online oil monitoring and transformer partial discharge technologies for early recognizing the dangers of failures; reparing optical cables using helicopters, etc. Many scientific themes have been recognized and applied effectively in the operation of the 500kV North-South transmission line (circuit 1), including clearing hot-line insulators done by Power Transmission Company No. 3 (PTC3); Maintenance of transformers and formulation of procedures on maintenance of the 500kV transformers done by PTC2. In order to increase the operational efficiency of power system, in general and the 500kV North-South transmission line (circuit 1), in particular, EVNNPT has replaced the 500kV transformers in the 500kV substations of Hoa Binh, Da Nang, Pleiku, Phu Lam, upgraded the series capacitors of 500kV transmission lines from 1000 A to 2000 A… Besides, the regular repair including maintenance, consolidation of foundations, conductors, optical cable, strengthening of grounding wire, right of way (RoW) protection are implemented well by the PTCs.
It is impossible not to mention the transmission operators who silently overcome difficulties, wander up hills and down dale, go through high mountains and deep forests to stay close to transmission lines and towers to keep them in smooth operation. For them, the highest attention is to maintain well the national power grid, ensuring the energy security for the country. Many technical solutions on minimizing power losses and failures occurred to the transmission lines have been carried out, including improvement of grounding wire; increasing the number of direct grounding access of the lightning arresters in some locations; increasing porcelain bowls in insulators in the high mountainous areas; installing the surge arresters for transmission lines; regularly clearing RoW; strengthening the cooperation with local authorities, polices, social unions, propagandizing and encouraging people to protect RoW; Coordinating with the load dispatch centers to set out appropriate operation scheduling to avoid the transmission line overload; strengthening the inspection light-up of equipment and joint heating to ensure the secure operation of equipment; establishing the regional testing and repairing units to respond quickly any failures; organizing the training courses on increase of knowledge and skills for the testers; Monitoring and responding timely the upgrade of capacity of the overloaded substations; implementing periodically and intensively tests of substation equipment as planned and carrying out tests whenever failures occurred; Organizing training courses on power safety; pushing up the application of information technologies in operational management, technical management and management of substations’ equipment; Applying the automation technologies to simplify the manipulation and control the manipulation orders for the operators; Strengthening the inspection, monitoring in all aspects of operational management, inspection, repair, management of materials and equipment.
Engineers are working in control centre of substation
Foreseeable difficulties
The fact shown that together with the efforts by power sector, in general and the transmission operators, in particular, after nearly 20 years of operation of the 500kV transmission line (circuit 1) and 10 years of operation of the one (circuit 2), they operate safely, without any serious failures. Both transmission lines have been transfering over 3,000MW power capacity from the North to the South, supplementing the South’s power shortage in dry season. However, the biggest difficulties for EVNNPT are that the 500kV North-South transmission line and the 220kV ones do not ensure the secure requirements at n-1 standard, regularly are in the full-load and overload operation, making the transmission system tense. Due to the power shortage, load consumption increases quickly and unevenly in different localities so the operation scheduling of power system changes continuously, the substations’ diagram of operation must be changed sometimes, making the quality of operation affected.
Apart from being in danger due to the overloaded operation, the high voltage power grid is very tense because the RoW violation occurs frequently. Mentioning again the development of 500kV transmission line (circuit 1), after the construction completion, Ministry of Energy has issued the norms on secure protection of transmission lines and substations, the 500kV transmission line RoW has a profile of 40m, running from the North to the South, the sag from transmission line to ground is constructed in accordance with topography to ensure a secure distance. The regulations on right of way (RoW) are stipulated in Decree No. 106/2005/ND-CP on August 17th 2005 by the Government guiding the implementation of some articles of Law on Electricity on secure protection of high voltage power grid projects. In which stipulating that the RoW width (limited by 2 verticals toward 2 directions of transmission line, parallel with transmission line, with the distance from the outer line toward each direction when conductor is at maximum sag regulated ≥ 7m). The actual distance of trees planted at failure point which is 14 m from outer phase C vertically, outside the RoW. The second regulation is on the RoW height (defined from ground to the highest point of project plus the vertical secure distance regulated ≥6m). The distance between phase – ground (meaning the lowest sag of conductor from ground) of the 500kV transmission line at the failured tower distance regulated > 10m, while the actual distance of transmission line at the time of failure at 19 m – can be in conformity with the regulation.
However, the power grid security is always in danger because of people’s consciousness. In 2012 alone, the 220kV Northern transmission grid had 4 failures causing a break of ground cable, electric discharge in the transmission line, or the electric discharge due to the kite stucked in transmission line. In the Central Highland transmission line system, 31 failures occurred, mainly due to the protection forest fire, slash and burn fire, while 22 failures occurred in the Southern system, in which failures caused by RoW violations account for 36.4%.
Involvement by entire society is required
The failure occurred in 22nd May in Tan Dinh area of Binh Duong shown that the protection system of transmission lines and substations operate well, therefore, after only 3 hours, with the high efforts by EVNNPT staff, the failure has been repaired, power system has been restored in time and started to operate normally in all affected provinces. However, to limit such a failure, many solutions must be carried out as well as involvement by the whole society from local level, relevant sectors and Departments and especially the people’s consciousness on the Right of Way (RoW) security. In addition, the strict and clear legislations, with severe sanctions are very needed so that dangers of failures to transmission grid can be reduced.
In order to have a secure and sustainable power system, the power generation and transmission projects need to be implemented in accordance with the National Power Development Plan for period of 2011 – 2020, with consideration to 2030 (Master Plan 7) which has been approved by the Prime Minister. Under direction by EVN, the investment in construction of the 500kV and 220kV transmission lines and substations have been carried out by EVNNPT in many areas, including the expansion of 500kV Phu Lam substation and others, completion of the 500kV transmission line connecting Son La Hydropower Plant to Hanoi and the 500kV North-South transmission line. Besides, the power sector is desploying construction of 500kV transmission line (circuit 3) transfering power from Pleiku, while EVNNPT is promptly completing the 500kV Pleiku- My Phuoc – Cau Bong transmission line, with a length of 437 km to ensure the power supply to the South. However, the construction of 500kV, 220kV transmission lines and lower voltage level ones has to face with many difficulties on investment capital, especially in compensation and site clearance. This requires the support by the relevant local authorities, Ministries, sectors to push up the progress of projects which are important for the national power energy security.