Problems needing attention in the preparation of t

Discussion on problems that should be paid attention to in the preparation of temporary power construction organization design (II)

4.2 During load calculation, attention should be paid to the conversion of continuous or short-term repeated working system equipment

during calculation, the rated power of equipment shall be converted according to the load duration rate of different equipment

4.2.1. Tower crane or crane:

during calculation, it should be uniformly converted to the combination of active foaming rate and bridge erection rate with a load duration of less than 25%. Extremely important rate:

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where: JC - rated load duration rate of the equipment.

pc - rated power of the equipment.

4.2.2. electric welding machine, butt welding machine, etc.:

electric welding machine, butt welding machine equipment capacity converted to active power when the load duration rate is 100:

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where: PE - converted to electricity when JC = 100%.Capacity of welding machine, kW

pn -- nameplate rated power of electric welding machine (DC welding machine), kW

jc - rated load duration rate of electric welding machine and butt welding machine

se - rated capacity of electric welding machine and butt welding machine (AC welding machine), KVA

COS φ－ Rated power factor of electric welding machine and butt welding machine

4.3. Problems that should be paid attention to when selecting transformers

when selecting a transformer, for example:

transformer capacity se ≥ sjz

when selecting two transformers:

transformer capacity se ≈ 0.7sjz

in addition, 15% - 25% margin should be considered when selecting transformers. When finally determining transformers, technical and economic comparison should be carried out to select transformers reasonably

4.4. The selection of cable section should pay attention to

after selecting the cable section according to the safe current carrying capacity, the voltage loss method should be used to check the cable section. Especially for projects with long power supply distance. In addition, it should be noted that the cable section should meet the requirements of minimum mechanical strength

5. Problems needing attention in repeated grounding and lightning protection setting

5.1 The repeated grounding setting requires that the main distribution board, distribution box and the protective zero line (PE line) of the distribution box with a distance of more than 50m from the power transformer should be repeatedly grounded, and the repeated grounding resistance should not be greater than 10 Ω

when repeating the grounding setting, it should be noted that the threaded steel cannot be used as the grounding electrode, and the grounding electrode should be used φ 50 steel pipe or L50 × 4. The length of angle steel is 2500mm, and a group of three with a spacing of 5m. It is best to use the natural grounding body of the building for repeated grounding. The actually set repeated grounding device should not be directly set on the equipment shell, but on the PE bar in the box to avoid the mixed connection of TN-S system and TT system due to the open circuit of its system PE line

5.2. When setting lightning protection at the construction site, attention should be paid to the difference between direct lightning protection and induction lightning protection. Lightning arresters are set at the construction site to prevent direct lightning strikes, including personnel and cargo elevators and derrick hoists. The height of the lightning arrester shall meet the requirements of 60 ° protection angle, so that the protected equipment in the lightning arrester protection angle is different due to the structure and design of the universal testing machine. Lightning protection measures include tower cranes, external scaffolds, large steel formworks, metal structures with a height of more than 20m in Hangzhou, and metal structures in staff dormitories and office buildings. Special attention should be paid to the lightning protection and grounding of the outer scaffold. Multi point grounding should be adopted along the circumference of the building. The distance between the grounding points is generally 20m. When the corner point and the building height exceed 30m, attention should be paid to the side lightning protection

III. The construction organization design of partial temporary electricity should be comprehensive

chemical method is often adopted in industrial production. 1 Preparation content and steps

1.1 Site survey

1.2. Determine the location and route of power incoming line, substation, power distribution device and electrical equipment

1.3. Count the power load for load calculation

1.4. Select transformer

1.5. Design distribution lines, select cables (conductors) and carry out checking calculation

16. Design power distribution devices and select electrical appliances

1.7. Design grounding and lightning protection settings

1.8. Formulate the operation procedure of self provided generator set and the operation measures of electrical interlocking with municipal power supply

1.9. Determine external power protection measures

1.10. Draw temporary power engineering drawings, mainly including power supply system drawing, power supply system layout plan, power supply elevation, grounding device design drawing, and self provided generator operation control schematic diagram

1.11. Formulate safe electricity use measures and electrical fire prevention measures

2. Temporary electricity management measures

2.1 After the approval of the temporary power construction organization design, the technical disclosure must be carried out to the operators, and the disclosure records must be made at the same time

2.2 establish a temporary electricity inspection system and conduct regular inspection. Electricians should check before construction every day, and items on the construction site should be checked every seven days; The company shall conduct inspection once a quarter and make inspection records after inspection. The problems existing in the inspection process should be rectified in time