Difficult situation
The most difficult problem of Power Transmission Company 3 (PTC3) is that most of the transmission lines managed by the Company passes through jungle terrain, high mountains, deep and muddy stream, no pathways or pathways already destroyed by floods, natural disasters or landslides. There are a lots of mountainous areas with difficult access such as Phuong Hoang mountain pass, Doc cao mountain pass of Khanh Hoa province, 52 mountain pass of Krongno under Daknong province, EaHleo, Krongbuk, CuMgar areas in DakLak province, Mang Giang mountain pass of Binh Dinh province, An Khe, Iaphang mountain passes of Gia Lai province. These are areas with harsh climates and usually occurs winds, storms, floods and dusts in rainy season, and lots of red soil with strong whirlwind, which made the fog insulators are contaminated very quickly. The 500kV right of way mostly passes through the cultivated coffee area, rubber plantation, le tree forests, straw grass… which thrives fastly in the wet season and easily fired in the dry season. There have been many causes of forest fire spreading from outside to the right of way and caused insulator discharge which led to faults on transmission lines.
All these situations had a significant impact on operation management, especially the night inspection, fault testing and correcting, particularly during the rainy season.
In addition to the climate, the central region is very hot and humid so middle cubicle of outdoor devices are often infected with humidity to cause electrical leakage.
Moreover there are also faults occurred due to human mistakes such as: inappropriately selection for level of environmental contamination level by consultants in some transmission line sections. Conductor insulator string lacks of lightening equipment for protection. So, when fault occurred, it usually caused insulator damages and unsuccessfully reclosing. Some projects have earth system are constructed not in accordance with technical requirements.
As a result, despite PTC3’s best efforts, in 2012, transmission lines manages by PTC3 still occurred 31 faults. In which, faults are caused by protective forest fire, sugarcane fire (5/31 times), sticking in transmission lines of objects such as trees, canvases, dumper trucks…. by whirlwind (4/31 times), lightning strike (21/31 times) and 1 time unidentified cause. For substation fault, the problems mainly come from: secondary circuit leakage, relay’s wrong impact
unusual damage of equipment; relay’s configuration setting is not consistent with reality; etc. Reached substation faults were less than assigned plan (0.029 / 0.050).
Prevention is the main solution
To ensure transmission grid operation safely and continuously, PTC3 has directed its units to conduct solutions for preventing faults in transmission lines and substation as follows:
On transmission lines:
Periodic, daily, nightly inspection, and unexpected inspection, faults and technical inspection ... are carrying out in accordance with process and regulations. Strengthening night inspections at specific sections which are frequently contaminated or having much fog to discover and promptly handle the unusual phenomenon of insulators; To examine, thoroughly handle cases of earth fail to meet the standard, lost, or point where the earth contact of the column bar not guaranteed. Reviewing and controlling the right of way to ensure right of way of high voltage transmission, especially clearing trees and dried grass out of the right of way, creating fire safety right of way during dry season in the major sugarcane planting regions such as Iaphang, Krongno, DakNong, Mang Giang, An Khe, Ninh Hoa, where forest fires happened easily. Strengthening inspection the right of way, high trees outside the right of way which have compensation and cutting down trees in accordance with the regulations to prevent trees from falling into the transmission lines; correcting damaged foundations, dredging slime in drainage before rainy and storm season. To coordinate with the functional agencies to conduct inspection and propaganda for the local people who live in and near by transmission lines about the dangers of high-voltage grid when breaching discharge safe distance for accident and fault prevention. To remind the local citizens do not use canvas to dry agricultural products; do not carry any tools which breach safe distance, motor vehicle breaching safe distance; burn fields; using threshing machines in the right of way; or let children fly kites in these areas. Combining with periodical inspection of substations for transmission maintenance such as cleaning insulators (technical inspection at regularly discharged points together with cutting power), inspecting earth contact and simulation distance … To assign workers to totally tackle shortcomings to ensure the 220 and 500 kV grid operating safely, continuously and stably, especially on major holidays, New Year, Lunar New Year. To carry out night inspections on transmission lines at sections that have insulator hygiene activities to re-evaluate the effect after maintenance work before and after each power cutting.
At the substation:
Check automatic re-strike of transmission line circuit breaker to ensure uninterrupted power supply when momentary fault occurred on transmission lines. However, this was driven by a number of power plants in the region which did not coordinate well reclosing relay so once momentary fault occurred, they cannot reclose successfully, which affected the power system operation method. So, periodically testing of substations in combination with soon detecting and correcting defects in devices such as controlling, protecting circuits to avoid the wrong impact. Regular inspects bulps, jumper bulps on the transmission line, at the substation in order to timely detect and handle remaining defects to ensure the transmission grid operating safely and continuously (especially pay attention on transmission lines, transformers which are operating under full load, overload or high capacity transition). Design a plan and regular rehearse fault situations or using the KEMA’s emergency trouble shooting column. At PTC3 and its branches, operation employees are always set to capture and mobilize forces to quickly handle serious faults and avoid power supply disruption. After fault occurred, identify causes and propose remedial measures to eliminate repeated faults.
And recommendations
According to PTC3’s leaders, the 220kV Di Linh - Bao Loc transmission line was constructed and put into operation in 1965 has been regularly operates at full load and overload situations, even some periods, it has reached up to 15%. That’s why, PTC3 expects to soon upgrade and renovate the transmission line into 02 circuits on the basis of the existing routes as approved by the Master Plan 7. The National Load Dispatch Centre and regional Load Dispatch Centers are requested to schedule power cutting of the 500kv transmission line sin dry season at least 2 times so that PTC3 can clean dirty porcelain, concurrently with timely inspecting, detecting and replacing discharge insulator strings during operation in polluted areas. To propose alternative solution for replacing glass insulator which have been declined insulated function due to operation in polluted areas, thereby enhancing the level of contamination of the line passing through the insulation. To limit the use of earth bolt with a length of over 80m for newly constructed projects, and at the same time assign PTCs to monitor the newly constructed projects in the area to ensure the quality of the project when putting into operation.