-Power cable lines in the area of power station withcapacity up to 25MW are permitted to be arranged in cable canals.
3.Arrangement in industrial enterprise
Power cable lines in the area of industrial enterprise shall be installed in underground cable canals, tunnels, blocks, troughs, bridges, corridors or on walls of buildings.
4.Arrangement in substation or distribution station
Power cable lines in the area of substation or distribution station shall be arranged in cable tunnels, canals, bridges, corridors, troughs or tubes.
5.Arrangement in urban or rural area
Power cable lines using singlestrandcables in urban or rural areas shall be arranged in underground cable canals under pavements, near right-of-ways or parks expect roads with vehicle traffic.
6.Arrangement under street or square
Power cable lines with 10 and more cables under streets or squares with utilizable underground
structures shall be arranged in cable tunnels or blocks. Powercable lines at intersection with heavy traffic on the streets or squares shall be arranged in cable blocks or tubes, and surface of the intersection shall be completely paved.
7.Arrangement in building
Power cable lines in buildings shall be permitted toarrange directly and openly or in boxes or
tubes in accordance with the structures, as well as in cable tunnels, troughs, pipes, under compartments and cable storey, and under floor and foundation of equipment.
8.Arrangement for oil-filled cable
Oil-filled cables shall be arranged in cable tunnels, corridors and underground cable canals and the arrangement method shall be specified by the design.
Chapter 2-3-3 Overhead Power Line Systems with voltage up to 500kV
Article 115. Consideration Requirements and Conditions
To take into consideration the most stringent requirements means to select the largest crosssectionalarea or the highest height of conductors, etc.
To take into consideration the least favorablecondition means to select the largest load or the nearest situation, etc.
Article 116. Calculation Method
Calculation method shall comply with the contents in this article in Technical RegulationVol.1.
Article 117. Installation Condition for Poles
The location of poles shall be selected to where poles do not obstruct pedestrian, traffic,danwhere poles do not collided by vehicles.
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Article 118. Protection and Signal against Vehicles
Concrete walls or crash barriers shall be installed around poles which might be collided by vehicles.
Additionally, signs or fences shall be installed by such poles, for drivers of vehicles can recognize the poles easily.
Article 119. Transposition
The transposition shall be implemented so that the length of one phase in each step transpositionof cycle is identical as much as possible.
Overhead power lines with voltage from110kV to 500kV and with the length of 100km and more shall have transposition.
Overhead power lines with voltage from110kV to 500kV and with many sections less than 100km long are permitted to have transposition at substations (at busbars in a substation, in the spanbetween the edge of the lines and the gantry in a substation).
Overhead power lines with two circuits with the same voltage on the same pole shall have transposition equally.
Article 120. Access for management and maintenance
1.Road to access overhead power lines for management and maintenance:
For overhead power lines with voltage of 500kV, the width of access roads shall not be less than 2.5m, and the location shall be within 1 km from the route of the lines.
Overhead power lines voltage from 110 to 220kV must have a way to be as close a route of the power lines and pole.
2.Operation management station
Operation management station is constructed as below.
- The location is in the area where many overhead power lines are convergthed and transportation is convenient.
-The architecture is simple and compact. (It is preferable to utilize existing architecture.)
-Communication lines are connected to regional power network and repairing units of the lines. The station should be designed based on the requirements of power management agencies, the scale of overhead power lines and existing regulations.
Article 121. Installation of Poles near Areas with Water
Possibility of erosion shall be carefully investigated in riparian land, lake side, hill, basalt areas, and especially primary forest.
Possibility of erosion shall be less than the values shown in the following table.
If above-mentioned data are not available, the highest level of historical flood shall be applied. In this case, poles shall have measures for protecting from flood(special. foundation, dyke, embankment, drainage trench, additional pole, etc.)
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Furthermore, |
poles arranged at the following areas shall have mentionedabove- |
measures for |
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preventing the flood. |
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- The area where often struck by flood. |
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- The slopes of hills or mountains where possibly eroded by flood |
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Table 121 |
Erosion possibility |
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Voltage (kV) |
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Erosion possibility |
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Exceeding 1 to 35 |
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5% and less (Once in 20 years) |
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110 and 220 |
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2% and less (Once in 50 years) |
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500 |
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1% and less (Once in 100 years) |
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Article 122. |
Pole Signs |
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Pole signs shall be installed before the operation of overhead power lines start
Arrangement of pole signs shall be at the approximate height from 2.0 to 2.5m and at the position to be seen easily.
For the pole of overhead power lines withmany circuits, they must have clear signs with stating pole number and the name of each circuit.
Figure 122 |
Pole sign |
Article 123. Protection against Corrosion of Poles
Metal parts of poles shall be galvanized with zinc or painted by anti-corrosion paint for protecting corrosion. (Zinc galvanization is the most effective protection method against corrosion.)
Corrosion protection shall comply with Article 57.
Article 124. Warning Signs and Signal Lamps
Warning signs (Painted sign) and signal lamps are shown in the following figure as reference.
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Painted Sign |
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Signal Lamp |
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Figure 124 Painted signs and signal lamps
Article 125. Fault Locating Equipment
It should install fault locating equipment for overhead power lines with voltage110kV and more according to importance and traversing route of the lines, if necessary.
Summary of fault locating equipment is shown in the following table.
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Table 125 |
Fault locating equipment |
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Type |
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Principle |
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Pulse radar |
High-frequency impulse is sent to overhead power lines after seizing signal |
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from relay. Fault location is rated by measured period of time from the start |
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(Type-C) |
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of impulse to the return to fault point. |
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Impedance calculation |
Fault location is rated by measured voltage and current values at an edge of |
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overhead power line and calculated impedance of the section from the edge |
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to fault point. |
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Article 126. The Selection of Alternative Routes
The areas with disadvantageous surrounding conditions means the areas with strong wind, |
land |
collapse, swamps, stone rolling, etc., and the areas where need to be considered in the |
design |
particularly. |
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When overhead power lines traverse the above areas, the route of them must be considered to avoid |
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going through in the areas, to calculate and to compare economic efficiency and technical assurance to |
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determine choosing the route |
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Article 127. Determination of Climate Conditions
Combinations of temperature and wind pressure in calculations of overhead power lines with voltage up to 1kV shall be taken into account the combinations in the following table.
Besides, the natural conditions mean the conditions of bumpy topography, altitude, large lake side, wind directions, etc.
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Table 127 |
Combination of temperature and wind pressure |
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Number |
Temperature |
Wind pressure |
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1 |
Maximum Tmax |
q=0 (No wind) |
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2 |
Minimum Tmin |
q=0 (No wind) |
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3 |
Average of annual Ttb |
q=0 (No wind) |
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4 |
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25°C |
Maximum qmax |
Article 128. Calculation and Consideration of Wind
1. Wind pressure
Standard wind pressure, wind pressures by region and factors increasing or reducing wind pressure for overhead power lines with voltage exceeding 1kV shall be adopted the values in TCVN-2735-1995. However, standard wind pressure of the lines with voltage of110kV and more shall not be less than 600N/m2.
Assumed time of use shall be adopted the values in the following table.
Table 128-1 Assumption time of use
Voltage (kV) |
Assumed time of use (year) |
Exceeding 1 to 35 |
15 |
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110 |
20 |
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220 |
30 |
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500 |
40 |
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2. Standard wind pressure
Standard wind pressure applied to conductors and lightning conductors of overhead power lines with voltage exceeding 1kV shall be calculated by the following formula.
P= a ×Cx × K1 ×q × F ×sin2 ϕ
P: Standard wind pressure (N)
a : Coefficient for unequal wind pressure in the span (Refer to Table 128-2)
Table 128-2 Coefficient for unequal wind pressure
Wind Pressure (N/m2) |
Coefficient for unequal wind pressure* |
270 |
1.00 |
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400 |
0.85 |
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550 |
0.75 |
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760 and more |
0.70 |
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*Note: Intermediary values are interpolated.
Cx : Aerodynamic coefficient
-1.1: The diameter of conductors or lightning conductors is 20mm and more.
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- 1.2: The diameter of conductors or lightning conductors is less than 20mm.
K1 : Conversion factor in consideration of impact of span on wind pressure (Refer to Table 128-3)
Table 128-3 Conversion factor in consideration of impact of span on wind pressure
Span-length (m) |
Conversion factor* |
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Up to 50 |
1.20 |
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100 |
1.10 |
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150 |
1.05 |
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200 and more |
1.00 |
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*Note: Intermediary values are interpolated.
q: Standard wind pressure by regions specified in TCVN-2737-1995 (This coefficient is calculated to the provisions of above-mentioned standard wind pressure of item 1 in this article.)
F: Area of conductor or lightning conductor interrupting wind (m2) φ: Angle between wind direction and the axis of the route of the lines 3. Special requirements of standard wind pressure
Standard wind pressure of overhead powerlines with voltage exceeding1kV to 22kV on conductors lower than 12mhigh is permitted to be reduced %,15 except the case that factors reduce wind pressure in the area where the wind are interrupted have already be appl ied.
Maximum standard wind pressure of overhead power lines which traverse at the following places with strong wind in the mountains shall follow the current standards, if observed data are not available.
- The places higher than the surrounding area (peaks, passes, etc.) -Valleys and canyons
4. Wind pressure at the converted height of conductors and lightning conductors
(1) Conductors at normal span
Wind pressure acting on conductors shall be determined at the height converted to gravity point of all conductors. The converted height is calculated by the following formula.
hqd = htb − 23 f
hqd : The height converted to gravity point of all conductors (m) htb : The average height of conductors installed on insulators (m)
f : The maximum sag of conductors (the maximum temperature) (m)
(2) Lightning conductors at normal span
Wind pressure acting |
onlightning conductors shall be determined by the height of lightning |
conductors at the centre. |
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(3) Conductors and lighting conductors at large overcrossing span
Wind pressure acting on conductors and lightning conductors shall be determined by requirements of item 1 in this article and comply with the additional requirements as below in this article.
1) In the case of only one large overcrossing span, the height converted to gravity point of conductors and lightning conductors shall be calculated by the following formula.
hqd = h1 +2 h2 − 23 f
hqd : The height converted to gravity point of conductors and lightning conductors at large overcrossing span (m)
h1 , h2 : The height from ordinary water level of river, bays, etc. or ground surface to the installation point of conductors or lightning conductors (m)
f : The maximum sag of conductors (the maximum temperature) (m)
2) In the case of many large overcrossing spans, the height converted to gravity point of conductors
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lightning conductors at whole large overcrossing span (between 2 anchor poles) shall be |
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calculated by the following formula. |
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= hqd1l1 + hqd 2l2 + + hqdnln |
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hqd1 , hqd 2 , hqdn : The height converted to gravity point of conductors and lightning conductors at each large overcrossing span (m)
l1 ,l2 , ln : Each span-length (m)
5. Wind pressure of poles
Wind pressure acting on poles shall be determined according to the height from the ground surface to poles.
Wind pressure of poles shall be which at average height of poles in each range whose length is not more than 15 m, and wind pressure in each range shall be adopted the same values.
6. Climate condition
(1) Design
Climate condition on designing overhead power lines with voltage exceeding1kV shall be complied with the contents in Table128-4.
Table 128-4 Air temperature and wind pressure on design
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Condition |
Air temperature |
Wind pressure |
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Maximum Tmax |
q=0 (No wind) |
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Normal |
Minimum Tmin |
q=0 (No wind) |
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condition |
Average of annual Ttb |
q=0 (No wind) |
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25°C |
Maximum qmax |
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Condition |
Air temperature |
Wind pressure |
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Fault |
Minimum Tmin |
q=0 (No wind) |
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Average of annual Ttb |
q=0 (No wind) |
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condition |
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25°C |
Maximum qmax* |
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*Note: Maximum wind pressure in fault condition is allowed to be adopted the values in TCVN -2737- 1995.
(2) Poles
Poles shall be checked by the calculation according to the installation condition at air temperature 15°C and wind pressure q=62.5 N/m2.
(3) Distance from live parts to structures
The distance from live parts of overhead power lines with voltage exceeding1kV to non-live parts of structures of the lines or other structures shall be checked by the calculation under climate conditions in the following table and as below.
Table 128-5 Air temperature and wind pressure on checking the distance
Voltage |
Air temperature |
Wind pressure |
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Operating Voltage |
25°C |
Maximum qmax |
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Atmospheric |
20°C |
q=0.1qmax |
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over-voltage |
(not less than 62.5N/m2) |
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Internal |
20°C |
q=0.1qmax |
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over-voltage |
(not less than 62.5N/m2) |
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The angle to vertical direction of deflecting suspension insulator strings by wind shall be calculated by the following formula.
tan γ = KP2 Gd + 0.5Gc
γ : Angle to vertical direction of deflecting suspension insulator strings by wind action
K : Coefficient of oscillation of conductors. The value depending on wind pressurethein following table shall be adopted.
P2 : Wind pressure acting on conductors in consideration of horizontal force by tension in case of supporting angle (N/m2)
Gd : Load of conductors acting on insulator strings (N)
Gc : Weight of insulator strings (N)
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