Chapter 8 Power Cable Lines

Article 323. General provisions

Power cables are usually placed in the building, and underground cable works, and less of a problem, but maintenance and overhaul to them shall be done in order to prevent corrosion of metal parts around water or underground and control panels of the associated equipment (barrels of oil and warning systems, etc.)

Power cable lines shall be maintained and overhauled as the following table.

Table 323 Sample methods of maintenance and overhaul for each equipment

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Article 324. Load cables

The maximum allowable load current of power cable lines shall be determined at the worst heat condition.

In case that additional cables are installed,the maximum allowable load current of other cables in the same section of additional cables shall be revised.

Therefore, the maximum allowable load current shall be understood in both power network management units and load dispatching units.

The maximum load current may be determined by testing results on sites which is carried out in the worst condition.

-Testing site shall be at the section of the highest cable temperature.

-Cable temperature shall be considered with the temperature of inner core based on the temperature outside cable sheath.

Article 325. Temperature in tunnels and cellars

The temperature in cable tunnel (cellar, etc.) where maintenance workers can access shall be 45deg C or below basically, as considering the following items.

- The physical condition of workers who carry out maintenance and repair.

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-The overheat of cable (Calculation condition of the maximum allowable load current may be changed as the temperature in cable tunnel increases.).

In case that the temperature in cable tunnel exceeds 45 degrees Celsius, the following items shall be carried out.

-The temperature in cable tunnel is decreased by forcing and cooling ventilation systems

-The operating current is limited not to exceed the temperature of 45deg C in cable tunnel.

Article 326. Overload of cables

It shall be prohibited to use the cable which is over permissibletemperature because it is impossible for insulation materials (insulating paper and cross-linked polyethylene) to perform expected insulation strength. Specifications of insulating paperor cross-linked polyethylene of thecable shall be confirmed sufficiently before the operation because the permissible temperature is decided by them. As the point requiring attention in particul,ablecr permission temperature is notthe surface temperature that is lower than the core but the core temperature.

Article 327. Oil pressure

Oil pressure of oil-filled cables shall comply with the value prescribed by the manufacturer.

Article 328. File documents

Related technical materials shall be referred to Article 249 in Technical Regulation as well as Article 328.

Article 329. Supervision of implementation

On cable laying works and assembling works of cable connection boxes, management unit or power company shall check the works during the construction,and confirm that suitable construction is carried out by constructors since it is difficult to check in detail after the works are completed.

Article 330. Protection of metal structures

It is necessary to paintor galvanize the support rackto protect from rustbecause cable trays, cable racks easily corrode due to be installed in cable canals or cable tunnels with very high humidity environment.

In addition, it is necessary to carry out painting or other countermeasures for the support rack to protect it from the heat in case that the support rack is exposed to sunshine, and it is damaged from the

heat by direct sunshine.

Article 331. (moved to Article 276)

Article 332. Checking power cable

It shall be referred to Chapter 6 in Technical Regulation Vol.5 to check the electrical power cable.

When the failure occurs in the cable, the patrol shall be executedto detect the failure point, confirm the facilities damage, and necessary repair or restoration means shall be taken. The patrol shall be

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executed promptly because the public may reach the danger such as electric shock and a fire, etc. by the failure cable, and the facilities damage may be expanded by unrepaired parts.

The method of patrol

-In case of oil-filled power cable lines, patroller shall check oil supplier unitfor the oil level, oil pressure and oil amount, and confirm that there is no oil leakage.

-Patroller shall confirm that there is no civil work such as excavation or pile driving which damages

underground cable lines, and there is no shortcoming cableof sections gone outfrom the underground.

-Patroller shall confirm that there is no defect near cableroom, cable cellar andcable well and invisible points of power cable lines.

Article 333. Protection of electrochemical corrosion

Electrolytic corrosion shall be protected by protective covering outer sheath or electrolytic protection.

In case of a normal cable, protective covering outer sheath made of synthetic rubber protects electrolytic corrosion. In case that pipe type cable line are placed underground, the line shall be equipped with not only protective covering outer sheath but also an electrolytic protection shown in

the following table since a corrosion of steel pipe causes a serious failure.

Article 334. Protect of power cable line attach mechanical actions

When the excavation work is done on undergroundcable, the management unit of the cableshall investigate the construction contractor to the digging depth,heavy civil machines will be used and measures for protecting the cable before carrying the work out, and confirm that the site work can not damage the cable.

The management unit shall not permit the construction work, and the construction contractor shall not carry the work out in case that the work may damage the cable.

In addition, in the permitted constructionwork, the management unit shall check the safety of the cable, and confirm thatthe actual situation of the work does not differ from the situation ofprior investigation at the construction site.

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Article 335. Construction near power cable line

The construction area affecting underground power cable lines must be supervised by the cable management unit are shown in the image. Engineer’s supervision shall be requiredwhile performing the pavement rehabilitation and the macadam road paving, etc. .. above the underground cables and offset distance to underground cables shall not be more than 1 m.

In addition, when the distance from the underground cable to the ground surfaceis 0.7 m or less,the pavement work by heavy civil machine (Iyon, etc.) is prohibited. The use of the heavy civil machine which may damage the underground cable shall beconferred between the management unit and the construction contractor.

When boring or chemical grouting work carriedis out within 1m from the cable line, engineer's presence from the management unit shall be conducted in all cases. In case that the work is carried out at more than 1mfrom the cable ine,l engineer's presencefrom management unitmay be required depends on the situation.

Figure 335 Excavation Area needs Engineer's Presence from management unit

Article 336. Proclaim Information

The power network management unitshall inform the following contents for the people and the construction organization in the region where the cable is laid underground annual, and aim to receive cooperation from the people and the construction organization.

Information content

-The name and contact information of management unit

-The fact that permission of the management unit is necessary in implementation of construction.

- The area where contact to management unit is necessary prior to the construction(The area near the underground cable)

-The contents of the construction in cable corridor informed to the management unit (Construction time, construction place, constructor name, construction outline, heavy civil machine, etc.)

Article 337. Occupational safety