Article 233. Installation of Cables in Special Structures

1. Bridge

When power cable linesgo along the bridges made of stone,reinforced concrete or steel, the lines shall be arranged under the pedestrian ways of the bridges and be installed in troughs or cable pipes made of flame-resistant materials. These cable pipes shall have protections minimizeto the direct rain on them. In addition, power cable lines installed along bridges made of reinforced concrete or steel shall be insulated from metallic parts on bridges.

When power cable lines traverse expansion of bridge and places between structures and abutment, the lines shall be protected from mechanical damage.

Oil filled cables are prohibited to be installed along bridges.

2. Wooden structure

Power cable lines along wooden structures (bridge, berths, jetties, etc) shall be installed in cable pipes made of steel or flame-resistant materials.

3. Dam, dyke, wharf

Power cable lines installed along dams, dykes, wharves, jetties or directly in soil channels shall be covered with soil layers with the thickness not less than 1m.

Chapter 3-3 Overhead Power Line Systems with Voltage up to 500kV

Chapter 3-3-1 Power Conductors and Lightning Conductors

Article 234. Requirements of Conductors with Voltage up to 1kV

The cross-sectional area of conductors of overhead power lines with voltage up to1kV shall not be less than the values shown in Table 234 in this article in Technical RegulationVol.1.

Article 235. Conductor Connections

1. Strength of connection

The mechanical tensile strength of conductor connections shall not be less than %90of traction breaking strength of conductors.

2. Connection to post-type insulator

Conductor shall be connected to post-type insulators by fasten wires or dedicated locks.

For the exceptional regulations of conductor connections, refer to article271, 275, 278, 290, 292and 298 in Technical RegulationVol.1 and this Guideline.

Article 236. Condition of Sag

The sag of conductors of overhead power lines shall be determined according to theconditions shown in this article in Technical RegulationVol.1.

123

Article 237. Requirements for Conductors with Voltage exceeding 1kV

1. Multiple conductors

The phases of overhead power lines with voltage exceeding1kV are permitted to be used with single or multiple conductors. The cross-sectional area, the number of multipleconductors and the distance between multiple conductors shall be determined by the followings condition.

-Cross-sectional area: Mechanical strength according to condition around the lines and transmission capacity

-Number of multiple conductors: Transmission capacity and corona noise.

-Distance between multiple conductors: Electromagnetic force inthe event of short circuit and size of spacers

2.Additional requirement

(1) Corona loss

Corona loss is calculated by the following formula.

P : Power loss of one conductor with the length of 1 km (kW) E : Effective value of voltage to ground (kV)

d : Diameter of conductor (cm)

D : Distance between multiple conductors (cm)

f: Frequency (Hz)

δ= 0.2892 p 273 +t

δ: Relative density of air

p : Barometric pressure (hPa) t : Temperature of air (oC)

E0 = 302 δ 23 (1+ 0.301rδ ) (kV/cm)

E0 : Corona critical voltage (kV) r :Radius of conductor (cm)

(2) High frequency interference and wireless radiobroadcast

For igh frequency interference and wireless radiobroadcast, refer to article288 in Technical RegulationVol.1 and this Guideline.

(3) Impact of elector-magnetic field

For impact of electro-magnetic field, refers to article 287 in Technical RegulationVol.1 and this Guideline.

124

(4) Calculation for conductor and lightning conductor

Calculations for conductors and lightning conductors of overhead power lines shall be donebased on the specification for them or existing standards.

Article 238. The Selection of Lightning Conductors

1.Check for thermal stability of lightning conductor

For the check for thermal stability of lightning conductors, refers to Annex II.2.3

2.OPGW (Composite fiber-optic ground wire)

OPGW shall be selected based on mechanical strength and thermal stability as it applied to normal lightning conductors.

Article 239. Calculation Condition for Conductors and Lightning Conductors

Permissible stress of conductors and lightning conductors shall not be more than the values shown in the following table.

However, the stress at the highest fixed point including large crossing spans shall notbe more than 110% of the values shown inthe following table for aluminum conductor steel reinforced and 105% of ones for other conductors.

Table 239 Ratio of tensile permissible stress to tensile breaking stress of conductor and lightning conductor

Note : *1 The above values can be applied to overhead power lines which cross other structures in the populated areas.

*2 The above values can be applied to overhead power lines which are calculated by wind pressure that is not less than 1,000N/m2.

125

Article 240. Requirements against Rust

1.Places where may be exposed to rust

The places where may be exposed to rust means coastal areas, salty rivers and lakes, chemical manufacturers, etc.

2.Anti-rust safety distance

The distance from overhead power lines with voltage exceeding1kV to the place where may be exposed to rust shall not be less than 5 km for coastal areas and 1.5km for chemical manufacturers.

Article 241. Protection against Vibration

Conductors and lightning conductors of overhead power lines with voltage exceeding 1kV whose stress at annual mean temperature are not less than the values shown inthe following table shall be protected from vibration,. However, the sections of overhead power lines with voltage exceeding1kV which are protected from horizontal action by wind are excepted (along the valleys or through the forests).

Overhead power lines with multiple conductors not less than three in one phase are not required to be protected from vibrationin the cases that the stress at annual mean temperature is not more than 67.5N/mm2 ,and the distance between spaces is not more than 60m, and the spanlengthis not more than 500 m.

Article 242. Phase Divided Conductors (Multiple Phase)

Multiple conductors within the span or at jumper parts shall be appropriately secured the distance between the conductors by spacers which the distance between the spaces in the span does not exceed 75m.

Chapter 3-3-2 Arrangement of Power Conductors and Lightning

Conductors

Article 243. Arrangement of Conductors, Neutral Conductors and Equipment

Conductors of overhead power lines on poles are permitted to be arranged at any configure.

126

Article 244. Distance between Conductors in the Same Line

1. Minimum distance between conductors with voltage up to 1kV

The distance between conductors of overhead power lines with voltage up to1kV shall not be less than the values shown in the following table.

2. Minimum distance between conductors with voltage exceeding 1kV

The distance betweenconductors of overhead power lines with voltage exceeding1kV shall be determined in consideration of the operating conditions (refer 128)to in the span and permissible insulation distance (refer to 254) between the conductor and parts of the poles.

3.Distance between conductors with suspension-type insulators with voltage not less than 35kV

(1)Horizontal distance

The horizontal distance between conductors of overhead power lines with suspensiontypeinsulators with voltage not less than35kV shall not be less than the values calculated bythe following formula according to operating conditions in the span.

D = 110U + 0.65 f + λ (m)

D : Horizontal distance between conductors (m)

U : Nominal voltage (kV)

f : Calculated maximum sag (m) λ : Length of insulator string (m)

(2)Vertical distance

The vertical distance betweenconductors shall not be less than the values calculated by the following formula.

The symbols mean the same as above

(3) Not horizontal or vertical distance

If two conductors are installed neitherhorizontally nor vertically, the distance between them shall not be less than the values calculated by the following formulas.

127

At overhead power lines with post-type insulators with voltage of 35kVand lines with voltage of 22kV, the distance between conductors shall not be less than the values calculatedythe b following formula.

D = 110U + 0.45 f (m) Symbols mean the same as above

Article 245. Distance between the Nearest Conductors of Multiple Circuits

The distance between the nearest conductors of double circuits on the pole shall comply withthe requirements in this article in Technical RegulationVol.1.

Article 246. Distance from Live Parts on Poles

If independent power station is connected to overhead power lines with voltage not less than110kV, the structures of poles shall complywith the requirements in this article in Technical RegulationVol.1 so that repairing works can be carried out without interrupting of the lines.

Article 247. Installation of Conductors with Different Voltages

1. Installation of overhead power lines with different voltages on the same pole

Overhead power lines with voltage up to 35kV and those with voltage up to1kV are permitted to be installed on the same pole in compliance with all of the following requirements.

-Overhead power lines with voltage up 1kVto shall follow the conditions of mechanical calculations as applied to lines with higher voltage.

-Overhead power lines with voltage up to 35kV shall be arranged at higher than lines with voltage up to 1kV. Also, the distance between two lines with different voltage shall be exceeding 2 m for bare conductors and exceeding 1 m for insulated conductors and cables.

-Double post-type insulators shall be applied for overhead power lines with higher voltage at each fixed position.

2.Limitation of inducted voltage on the same pole

The isolated or not directlygrounded neutral voltage of overhead power lines with voltage up to 35kV due to electro-static and electro-magnetic induction under normal operation shall not be more than 15% of the voltage of the lines with lower voltage, within the section where overhead power lines with voltage up to 35kV are installed at the same pole with higher voltage lines. There is no requirement on overhead power lines directly grounded being inducted by lines with higher voltage.

128