1. power supply and distribution system
1.1 underground substation design should pay attention to several issues:
In addition to the existing norms in the design of underground substations should also pay attention to the following issues:
1.1.1 plane layout to be compact
Under the premise of conforming to the norms, as far as possible to do Layout should be compact, to make full use of space to properly reduce the height of the floor, reduce the depth of excavation underground. Those in a position to do so should use the upper inlet and outlet.
1.1.2 Entrance/Exit
Entrance/Exit can not be less than two, one of which is the main entrance/exit (personnel and equipment entrances/exits), the other is the security entrance/exit, another must be considered for the equipment entrances/exits, the equipment entrances/exits can be used for lifting holes, but the lifting holes must have reliable waterproof measures. Door width for the equipment width plus 200 millimeters, door height for the equipment height plus 300 millimeters, the door are fire doors, the opening direction of the inner door should meet the requirements.
1.1.3 Cable import and export
Cable import and export has been equipped with a special cable shaft, there must be waterproof flood control measures.
1.1.4 Ventilation system
Underground substation must set up a reliable air supply and exhaust system, it is appropriate to use the lower side of the upper side of the send back (air supply outlet 300 mm from the ground). Ducts can not enter the substation, it is appropriate to set the accident exhaust fan. The number of air changes in the substation for 15 times / h, specific should be calculated according to the heat generation, if the use of tunnel wind, in the entrance to the duct should be set up at the fire damper door.
1.1.5 Waterproofing measures
Underground substation should be properly selected waterproofing measures (such as commonly used waterproofing method, descending drainage method and integrated method), along the basement of the inner side of the outer wall should be equipped with drainage ditches and water collection pits.
1.1.6 Flood control measures
All entrances and exits of the underground substation should be elevated above the ground outside the station, and for the sake of safety, it is generally required to be elevated above the 100-year flood level of 0.3 meters. The indoor floor of the attached underground substation should be elevated 0.15 meters, to prevent the accumulation of water when the water sprinkler action.
1.1.7 Moisture-proofing measures
Underground substation rooms (high-voltage and low-voltage distribution room, transformer room) should be set up to dehumidify the machine power outlets, box board flush. Socket capacity depends on the dehumidifier capacity.
1.1.8 Fire prevention measures
The underground substation should be set up with safe and reliable fire prevention measures, see the relevant fire code.
1.2 Actively promote the application of D - Yn11 junction distribution transformer
1.2.1 D - Yn11 junction distribution transformer has the advantages of low loss, inhibit the high harmonic currents, the capacity can be fully utilized, the zero sequence reactance is small, and it is beneficial to the removal of single-phase faults on the low-voltage side.
1.2.2 D - Yn11 junction distribution transformer overcurrent protection should be used three-phase three-relay star wiring, can improve the sensitivity of the transformer overcurrent protection, is Y - Yn0 transformer 1.155 times. If the AC operating power supply, should be used to shunt relay protection wiring.
1.2.3 D - Yn11 junction distribution transformer according to the regulation requirements, generally set the current cut-off protection, overcurrent protection, low-voltage side of the single-phase grounded short-circuit protection, and its set value calculation with the same Y - Yn0 distribution transformer.