1 Introduction
Cable tunnel refers to a fully enclosed cable structure that accommodates a large number of cables, has a convenient passage for installation and inspection. With the development of electric power technology and the needs of urban modernization, more and more tunnels are used to lay power cables in urban power projects. And with the increase of the number of cable circuits in the tunnel, the improvement of safety requirements also requires the continuous improvement of the setting of auxiliary facilities in the tunnel. Combined with our design practice, this paper briefly summarizes the relevant contents that need to be considered in the design of auxiliary facilities of cable tunnels.
2 Power system
The power supply system of the cable tunnel is the most basic system of the auxiliary facilities of the cable tunnel, which will provide power support for the auxiliary facilities system of the entire cable tunnel.
2.1 Supply voltage.
The power supply of the auxiliary facilities of the cable tunnel is generally AC 380 220V, and the power supply radius is about 500 meters.
2.2 Configuration Requirements.
The power supply of the tunnel power supply system can be taken directly from the mains low-voltage power grid or from the dedicated power distribution system. The distribution transformer of the special distribution system can be placed above the ground, such as the sidewalk, in the green belt and other places that do not affect municipal traffic; And in harmony with the municipal landscape. If there is a large space and dry conditions in the tunnel, the distribution transformer can also be placed in the tunnel, but the dry-type transformer must be used.
The capacity of each power supply inlet of the cable tunnel should meet the power demand of all equipment in the power supply range when it is put into operation at the same time. The cable tunnel should be equipped with an incoming power distribution box, a low-voltage power distribution box, and a maintenance power distribution box. The incoming power distribution box should be located near the entrance and exit of personnel.
The feeder lines of auxiliary facilities should be laid in flame-retardant or flame-retardant pipes or fireproof groove boxes.
3 Lighting system
The lighting system includes normal lighting and emergency lighting. The lighting line should be a dual control line, and the cross-section of the line wire should not be less than 15mm2；The line switch should be a dual-control switch. The design of the lighting system should consider the humanized design, such as the photoelectric display of the switch position, emergency evacuation indication, etc., so as to facilitate the use of operation and maintenance personnel.
The lighting fixtures in the cable tunnel should be energy-saving moisture-proof lamps, and the average illumination of the pedestrian passage in the tunnel should not be less than 10lx. The emergency lighting in the tunnel is mainly used for lighting in the event of power failure or accident in the tunnel and guiding the evacuation of personnel. The illuminance of emergency lighting on the main passage should not be less than 05lx。
4 Anti-drainage system
The cable tunnel anti-drainage system is divided into two parts: waterproof and drainage, and waterproof is the premise of drainage, the cable tunnel is mainly an underground closed system, and the design principle should be to prevent the first and then the row, and the anti-drainage is set up. Try to make sure the tunnel is dry and free of standing water.
4.1 Waterproof.
The waterproof design of the cable tunnel is mainly based on structural self-waterproofing (waterproof concrete is selected) and an external waterproof layer; Inside, do a good job of plugging and repairing leaks at the water seepage site. And by the professional waterproof construction technicians to ensure the waterproof effect.
4.2 Drainage.
The drainage design in the cable tunnel is to provide a catchment and drainage system. The cable tunnel is a structural slope, and the drainage slope is not less than 05%, and set up a water collection well at the low part of the drainage slope. The setting of the collection well should also comprehensively consider the site topography and the location of the inspection well of the urban drainage system. Drainage pumps and drainage pipes are provided at the collection wells. The discharge volume and head of the drainage pump are determined by the size and depth of the sump well; The start-up mode can be automatic or manual according to the actual situation. The drainage capacity of the drainage pump should be determined according to the amount of water in the tunnel and the discharge head. The drainage pipe must be set up with reverse logging and connected to the nearby urban drainage system.
5 Ventilation system
The ventilation system of the cable tunnel can be in the form of natural ventilation and mechanical ventilation.
5.1 Natural ventilation.
Natural ventilation is the movement of air driven by a differential pressure. According to the mechanism of pressure difference, it can be divided into natural ventilation under wind pressure and natural ventilation under hot pressure. When the cable tunnel is deep, the differential pressure can be used to set up natural ventilation, which saves energy and has a better ventilation effect. However, since the cable tunnel is mainly built underground in the city, its application will be limited by the environment.
5.2 Mechanical ventilation.
In the absence of natural ventilation, cable tunnels are generally mechanically ventilated. If mechanical ventilation is used, the following conditions should be met: the ventilation volume should be selected according to the cross-section of the tunnel and the exhaust wind speed, and the wind speed should not be greater than 5m s. The inlet and exhaust fans or inlet and exhaust holes should be able to close automatically when a fire alarm is raised in the tunnel. The noise emitted by the inlet and exhaust fans should not be greater than the environmental protection requirements. The starting control mode of the inlet and exhaust fans can be controlled by remote synchronous remote control or decentralized manual control according to actual needs.
The design of the length of the ventilation section should be considered in conjunction with the length of the fire partition.
5.3 Vent location.
The location of the vent can be set in combination with the location of the entrance and exit of personnel, or it can be set in combination with the green belt, urban landscape, etc., and can also be located on the sidewalk and other locations that do not affect the municipal landscape.
6 Fire protection system
The design of the fire protection system in the cable tunnel is generally considered from two aspects: one is to prevent the occurrence and spread of fire in the tunnel; The second is to configure relevant fire-fighting facilities.
6.1 Fire protection system design.
6.1.1. The transmission and distribution cables laid in the tunnel must be flame retardant cables; The insulation and outer sheath material should be cross-linked polyethylene type (PVC), fire rating: class C. It is forbidden to use cables made of polyethylene (PE).
6.1.2Measures to reduce the spread of fire in the tunnel:
1) Install the cable in the fireproof groove box, or install the cable intermediate head in the fireproof groove box;
2) A fireproof partition should be set between the transmission cable and the distribution cable laid in the tunnel;
3) Set up a fireproof partition to divide the tunnel into several fireproof sections. The fireproof partition is composed of fireproof board, fireproof mud, fireproof door, fireproof coating, fireproof tape, etc. The fire protection section is generally 100 to 150 m long.
6.1.3. A fire alarm system and management platform should be set up in the tunnel.
The operator can monitor the operation of the system at any time, and find the location of abnormal temperature in the tunnel, temperature change and abnormal situation in time, so that the operator can find the cause of the abnormality and eliminate the fire danger in time; When the temperature changes suddenly, an alarm will be issued, which is convenient for the operator to start the plan to extinguish the fire in time. At present, the commonly used fire alarm systems in domestic cable tunnels include distributed optical fiber fire alarm system, temperature sensing cable fire alarm system, etc.
6.2 Fire fighting facilities.
A certain number of dry powder fire extinguishers should be configured in the tunnel according to the fire protection regulations. Choose a location with a moderate location and a moderate space to configure a mobile medium-sized dry powder fire extinguisher; Configure small dry powder fire extinguishers, such as portable dry powder fire extinguishers or hexafluoropropane hanging fire extinguishing devices, etc., in key fire prevention areas (such as the two sides of fire partitions, cable "T" joints, cable intermediate joints, etc.).
6.3 Evacuation Instructions.
The fire protection system in the tunnel should also consider setting up evacuation instructions, combined with the emergency lighting design of the accident, and set up the fire emergency evacuation and escape indication signs at the appropriate position to guide the operation and maintenance personnel to choose the correct escape direction when the fire is out of control.
7 Communication systems
The communication system in the tunnel is mainly concerned with ensuring that they can communicate with each other in the tunnel; The staff inside the tunnel are able to communicate with the people outside the tunnel to ensure personal safety. There are generally two ways to set up the communication system in the tunnel:
7.1 Wired communication.
The terminal switching equipment of the wired network is set up at the tunnel entrance, and the wired line is introduced into the cable tunnel. Set up a fixed ** landline at about 500m in the cable tunnel; The wellhead (spacing of about 100m) where each person enters and exits is provided with a fixed socket for the active machine carried by the staff in the tunnel.
7.2 Wireless Communication.
Using wireless communication technology (telecommunications, mobile, Unicom, etc.), a wireless receiver is set up at the appropriate location of the tunnel and the outside world, the wireless signal is introduced into the tunnel, and the entire tunnel is covered, so as to ensure that the staff can use wireless communication equipment such as mobile phones to contact each other or the outside world in the tunnel.
9 Conclusion
To sum up: the power supply system, lighting system, anti-drainage system, ventilation system, fire protection system, communication system and other six systems are the most basic configuration of tunnel auxiliary facilities.
In the future, the design of cable tunnel auxiliary facilities will be continuously supplemented, improved and developed in construction and operation to better meet the needs of power grid development.