l Chapter 1: Common Terms and Codes
l Chapter 2: Temporary Power Distribution Systems and Configurations
l Chapter 3: Summary of Safety Technical Code for Temporary Electricity on Construction Sites
l Chapter 4: Temporary Power Distribution Programs and Organizational Designs for Construction
l Chapter 5: Common Diseases in Temporary Power Distribution and Prevention and Control
l Chapter 6: Management Measures of Temporary Power Distribution
Chapter 1: Common Terms and Codes
★Terms
1. Low Voltage: AC Rated Voltage of 1kv and Above
2. Outside Power Lines: Power Lines Outside of the Distribution Lines of Temporary Electricity Works in the Construction Site
3. Work Grounding: The grounding is work grounding for the purpose of the circuits or equipments to meet the operational requirements. To achieve the operational requirements of the grounding for the work of grounding
4. Repeated grounding: equipment grounding line in one or more places through the grounding device and the earth again connected to the ground
5. Earthing body: buried in the ground and directly in contact with the earth's metal conductors
6. Earthing device: the sum of the grounding body and grounding wire
7. Electrical connection: between the conductor and the conductor to provide direct electrical pathway connection
7. Electrical connection: the connection between conductor and conductor that directly provides electrical access
8. Distribution box: a power distribution device used to distribute electricity, including the main distribution box and sub-distribution box
9. Switch box: a common name for the last level of power distribution device, can also be used as a control device for electrical equipment
★Designation
DK- Power isolation switch; H - illuminator;
L1, L2, L3 - three-phase phase line; M - motor;
N --neutral point, line, working zero line; PE -- protective zero line;
RCD -- earth leakage protector, earth leakage circuit breaker; T -- transformer;
TN -- power neutral point directly grounded when the leakage of conductive parts of electrical equipment through the zero line grounding zero protection system;
TN-C- - the working zero line and protective zero line combined with the installation of the zero protection system;
TN-C-S - the working zero line and the protective zero line of the former part of the combination of a separate part of the installation of the zero protection system;
TN-S - the working zero line and the protective zero line of the first part of the combination of a separate part of the installation of the zero protection system;
TN- -Zero protection system in which the working zero wire and the protective zero wire are set separately;
W--Welding machine
Chapter 2 Temporary power distribution system and configuration
◆Temporary power distribution system:
Internationally and nationally, major design institutes commonly use The form of system specified by International Electrotechnical Commission (IEC) standard. According to IEC regulations, the low voltage distribution grounding and zeroing system is divided into IT mode, TT mode, TN mode, three kinds of basic form system.TN mode can be subdivided into TN-C, TN-S and TN-C-S these three kinds of mode.
In the "construction site temporary power safety technical specifications" in Article 4.1.1 clearly stipulates that the construction site dedicated neutral point directly grounded power lines must be used to zero protection system, that is, the TN system. At present, the construction site is commonly used three-phase five-wire system, that is, TN-S mode. As shown in the figure:
1-work grounding; 2-repeat grounding; 3-equipment exposed conductive part; L1 L2 L3-phase line; N-work grounding; PE-protection zero
advantages and disadvantages and measures:
TN-S system due to the separation of the line and the PE line, the three-phase imbalance current no longer flows through the PE line, to avoid the potential rise of the shell of the electrical equipment. TN-S system can be used residual current action protection, this protection directly reflects the ground fault current, high sensitivity, the action current can be adjusted to a very small, to the extent that it can protect the non-metallic ground faults, adjust the current as long as it is greater than the normal leakage current of the line electrical equipment. However, because of the inherent disadvantages of the system, the transformer neutral to the potential (transformer low voltage side neutral grounding resistance Ro on the voltage drop) will still be through the PE line so that the electrical equipment enclosure has current and voltage. Therefore, to reduce the grounding resistance, the realization of the entire site of all construction equipment metal casing and a variety of metal components (including tower cranes, construction elevators, lifting frames and new building foundation grounding network), such as a reliable total equipotential connection, to improve the safety of the entire system is particularly important.
The main measures to reduce the contact voltage are to reduce the protective devices, cut off the time of the fault, repeated grounding, equipotential connection.
The choice of the main switch of the distribution room (total distribution box):
In the construction site, the main switch of the distribution room (total distribution box) is generally used for the automatic air switch or automatic air switch with leakage protection.DW10 universal switch has the functions of overload, loss of voltage, short-circuit protection and phase sequence protection, and it is the best choice of the main switch of the distribution room (total distribution box). As shown in the figure:
XJ-phase break and phase sequence protection relay; K-DW10 switch loss of voltage coil; L1 L2 L3-phase line
Distribution box, switch box and leakage switch configuration options:
In accordance with the standard requirements, the construction site should be carried out, "three-level distribution, two-level protection," that is, the main distribution box set up on the main switching box, the switch box and leakage switch. That is, in the total distribution box on the sub-distribution box, sub-distribution box below the switch box, switch box is the last level, the following is the power equipment, so the formation of the three-level power distribution. Two-level protection means that in addition to the last level (switch box) set leakage protection, but also in the upper level (sub-distribution box) set leakage protection open, the overall formation of two levels of protection, the two levels of leakage protector has a hierarchical segmentation between the protection function.
The distribution box should be made of iron box, choose the outdoor rain type, the box should be set up to protect the zero line terminal row, depending on the need to set up the work of the zero line terminal row. The electrical installation board in the box is made of iron plate, and the protective zero line terminal rows are well connected. The door of the box also needs to use yellow and green two-color wire to make a good connection with the protective zero line terminal and lock. Box with red paint for "electric danger" and other warning signs.
The main switch of the power supply in the switch box should be a disconnect switch instead of an automatic air switch. Isolation switch can cut off the power supply under normal circumstances, play a role in isolating the power supply and facilitate maintenance, can save a level of protection between the selective requirements, so that the last level of power distribution box is easier to protect the selectivity. Switch box box within the selection of electrical appliances must adhere to the "one machine, one gate, one drain, one box" principle.
To ensure the selectivity of the leakage switch, we must carefully select the upper and lower levels of rated leakage action current and the upper and lower levels of leakage action time. When selecting, the following principles should be followed: the end of the line leakage protector rated leakage action current I Δn value selection 30mA; superior leakage protection appliances I Δn1 value must be the lower I Δn2 double or more than double, that is, I Δn1 ≥ 2I Δn2; direct contact with the protection of the leakage protector for the maximum breaking time for the 0.1s, indirect contact with the protection of leakage protectors with maximum breaking time for the 0.2s. The maximum breaking time of the leakage protector for indirect contact protection is 0.2s. Therefore, the leakage protector for end protection should be selected for direct contact protection, and the rated action time should be ≤ 0.2s. It is best to use the leakage protector for hierarchical protection for two levels, and it will be difficult to get selective protection for a large number of levels.
Chapter III "construction site temporary power safety technical specifications" summary
Transformer installation
① capacity of 400KVA and a transformer, can be used on the pole (column) installation, and the bottom of the transformer from the ground height should not be less than 2.5m; 400KVA transformer should be used to install the ground.
② ground transformer should be installed around the fence, wall, height of not less than 1.7m.
③ transformer indoor installation, should pay attention to the wall is not less than 0.8m, from the door is not less than 1.0m.
▼ high and low distribution panel (box, cabinet, switch box) installation
① distribution cabinet base channel steel is generally 8 ~ 10 steel, channel steel should be straightened and descaling. And descaling.
② indoor switchgear front operating channel width of a single arrangement of not less than 1.5m, double face-to-face arrangement of not less than 2.0m.
③ indoor switchgear behind the maintenance of the channel width of a single and double (cotton opposite) columns of the arrangement is not less than 0.8m, double columns of the arrangement of back-to-back is not less than 1.5m.
④ indoor switchgear side of the maintenance of the channel width of not less than 1.0m; the roof should be straightened and rusted first. 1.0m; the distance between the ceiling and the ground is not less than 3.0m; the upper end of the distribution device is not less than 0.5m from the ceiling.
⑤ The distance between the sub-distribution box and the switch box shall not be more than 30m, and the horizontal distance between the switch box and its control of the fixed electrical equipment shall not be more than 3.0m.
6 The rated action current of the leakage protector in the switch box shall not be more than 30mA, and the rated action time shall not be more than 0.1mA, and the rated action time shall not be more than 0.1s. Action time should not be greater than 0.1s; total distribution box leakage protector rated action current should be greater than 30mA rated leakage action time should be greater than 0.1s, but its rated leakage action current and rated leakage action time of the product should not be greater than 30mA -s.
▼ Distribution line installation
① overhead line cross-section according to the requirements of the mechanical strength of the insulated copper wire no less than 10m ㎡, aluminum wire not less than 16m ㎡.
② overhead line spacing shall not be less than 0.3m, near the pole of the two wire spacing shall not be less than 0.5m.
③ When there is a line crossing, the minimum vertical distance between the wires of different lines should be met: a low-voltage and low-pressure lines between not less than 1m; b high-voltage and low-voltage lines between not less than 2m.
④ cable line must be used for five-core cable, and must include blue Cable lines must be five-core cable, and must contain blue, green/yellow two insulated core wire.
5 cable directly buried depth should not be less than 0.7m; buried cable from the ground 2.0m high to 0.2m underground must be added to protect the casing, and the inner diameter should not be less than 1.5 times the outer diameter.
6 indoor non-buried trunk line from the ground height shall not be less than 2.5m; indoor wire or cable cross-section requirements: copper wire not less than 1.5m ㎡, aluminum wire not less than 2.5 m ㎡.
▼Grounding and lightning protection
①Power distribution devices and electric machinery connected to the PE line should be insulated multi-stranded copper wire with a cross-section of not less than 2.5m ㎡; hand-held power tools should be insulated multi-stranded copper wire with a cross-section of not less than 1.5m ㎡ PE line.
② L1 (A) ﹑ L2 (B) ﹑ L3 (C) ﹑ N ﹑ PE wire insulation color is yellow, green, red, light blue, green / yellow color.
③ single capacity of more than 100KVA or use the same grounding device running in parallel and the total capacity of more than 100KVA power transformers or generators shall not be greater than 4 ohms; single capacity of not more than 100KVA or the use of the same grounding device running in parallel and the total capacity of not more than 100KVA power transformers or generators shall not be greater than 10 ohms; in TT, the power transformers or generators shall not be greater than 10 ohms; in the TT, the power transformer or generator insulation color. 10 ohms; in the TN system, the protective zero line each repeated grounding device grounding resistance should not be greater than 10 ohms.
4 mechanical equipment on the lightning rod (flashover) length should be 1 ~ 2m; construction site of all lightning protection device impact grounding resistance shall not be greater than 30 ohms.
Chapter IV temporary power distribution and construction design
Temporary power distribution and construction design of the construction site includes: project electricity profile, preparation basis, construction of electricity layout and drawing of electricity system diagram, load calculation and transformer selection, selection of cables and electrical switches, safe use of electricity, lightning protection and grounding, safety and technical briefings, and other organizational measures.
A ﹑ project electricity profile
On the construction scale, production environment, construction progress and so on for a brief description; on the power load design considerations, power equipment in the field distribution of the use of electricity, different construction period of electricity consumption statistics and analysis of the power load, power supply lead location, especially important construction equipment and various construction stages of the reliability of the power requirements and so on. The power supply lead-in point location, especially the important construction equipment and each construction stage of the power supply reliability requirements, etc. are briefly described.
Basis for the preparation of two
a construction project in the construction organization of the general design (construction plan, equipment list and layout plans, etc.);
b "Construction Site Temporary Electricity Safety Technical Specification" (J GJ46O88);
c "construction site construction site power supply safety code" (GB50194O93);
d local power supply in the construction site, and so on.
Three ﹑ construction power layout and drawing power system map
Construction power layout should be based on the general layout of the construction site in the distribution of electrical equipment, taking into full account the changes in different construction period of electrical equipment and major electrical load equipment, to meet the safety distance of the power lines and other circumstances, the correct and reasonable layout of power distribution lines.
Drawing the power system map mainly consider the site of temporary power distribution mode selection. Usually the total power box to the distribution box using trunk distribution, distribution box to the switch box using radial distribution. It should be noted that the load distribution should be considered in the three-phase load balancing principle, balanced single-phase load equipment on the site is connected to different phase sequence.
Four ﹑ load calculation and transformer selection
Ⅰ. Load calculation
According to the construction of electricity layout and power system diagram, load calculation should be from the switch box, sub-distribution box, the total power box step by step, load calculation is usually used in the need for coefficient method, the load calculation of each group of electrical equipment
Active power calculation PjS=kxPe; reactive power calculation QjS=PjStgθ;
apparent power calculation SjS=
where Pjs-active calculated load kW of the group of electrical equipment;
Qjs-reactive calculated load kVar of the group of electrical equipment;
SjS-apparent calculated load kVA of the group of electrical equipment;
Kx-need factor of the group of electrical equipment .
Ⅱ. Selection of transformer capacity
Selection of transformer capacity, taking into account the transformer operating power loss calculation transformer apparent power Sjs' :
Sjs' = ( Pjs + ΔPb)2 + ( Qjs + ΔQb) 2 (kV-A)
Considering the construction of transformers usually take Considering that construction transformers are usually installed in the open air on poles or platforms, the impact of high ambient temperatures on the reduction of capacity, the apparent power of the selected transformer Sjs″:
Sjs″ ≥ K × Sjs' (K 1.05 ~ 1.1)
Transformer rated capacity selection: according to the principle of the rated capacity of transformer Se ≥ the apparent power of the transformer Sjs″ is selected, and then calibrated power Transformer load rate β = Sjs″/ Se , β generally take 0.8 ~ 0.95 can be.
ΔPb for power transformer active power loss, generally take 0.01SjskW;
ΔQb for power transformer reactive power loss, generally take 0.05Sjskw .
Five ﹑ cable and electrical switch selection
① distribution line cable according to its laying mode selection
overhead lines must be insulated copper (aluminum) core wire or cable; buried shall be selected cable, and add conduit protection. Cables are generally laid according to the conditions and environmental conditions of choice, the general site selection of plastic cables, mobile boxes and switch boxes in and out of the line shall be used in medium-sized or heavy rubber-insulated cables, conditions are also suitable for the selection of oil corrosion-resistant type.
Distribution line cable cross-section selection in accordance with the allowable current, and at the same time, according to the mechanical strength of the line laying requirements can be reviewed.
② Distribution lines and loads for short-circuit, overload and single-phase grounding (earth leakage) and other protective devices to choose
Construction sites generally use the molded case earth leakage circuit breaker (MCC); for the construction of lighting circuits can be used for miniature circuit breaker (MCB).
In order to ensure that the three-stage power distribution system between the upper and lower two levels of circuit breakers selective action, usually on the first level of circuit breakers suitable for use with a short delay overcurrent detector, and its action current should be greater than the next level of overcurrent detector action current of more than one level (at least 1.2 times).
③ Electrical switches and accessories
Switch box electrical assembly according to the "one machine, one gate, one leakage" and the specification requirements for the configuration of disconnecting switches and leakage circuit breakers, sub-distribution box according to the system diagram selection of power supply circuit breakers and sub-circuit breakers and their accessories, the total distribution box with the total disconnecting switches, the total circuit breaker and sub-distributing disconnecting switches, sub-leakage circuit breakers, and sub-circuit leakage circuit breakers and the total distribution box. The main distribution box is equipped with main disconnecting switch, main circuit breaker and branch disconnecting switch, branch leakage circuit breaker and power voltage and current indicating device. All electrical boxes are set up N, PE terminal row.
Sixth, safe use of electricity organizational measures
① Establishment of technical briefing system. To professional electricians, all kinds of electricity personnel to introduce temporary electricity construction organization design and safety of electricity technical measures of the overall intention, technical content and attention, and should be performed in the technical submission of text data and acceptance of the person who signed the formalities, indicating the date of submission.
②Establishment of a safety inspection system. Starting from the temporary electricity works, regular testing of electricity works.
③ Establishment of electrical maintenance system. Strengthen the daily and regular maintenance work, timely detection and elimination of hidden dangers, and the establishment of maintenance work records.
④ Establishment of the project removal system. After the completion of the construction project, the demolition of temporary electricity works should be unified organization and command, and must provide for the demolition of time, personnel, procedures, methods, precautions and protective measures.
⑤ Establishment of safety inspection and assessment system. Construction management departments and enterprises should regularly check and assess the safety of electricity on site in accordance with JGJ59-99 "Building Construction Installation Inspection and Scoring Standards".
⑥ Establishment of safety education and training system. Regular professional electricians and various types of electricity personnel for electricity safety education and training, where personnel must hold a labor department issued induction certificate, is strictly prohibited without a license.
VII ﹑ lightning protection and grounding
① construction site low-voltage power distribution system should be used TNOS grounding system. Three-phase five-wire power supply into the line, PE line in the line to repeat the grounding.
② The electrical system in a variety of types of grounding resistance value of the grounding device is generally taken ≤ 4Ω, PE line repeated grounding should be set in the power supply terminal and intermediate lines every 50m or so in the sub-distribution box.
③ All normal non-electrified electrical equipment in the power system of the metal casing, should be through the PE wire and grounding device reliably connected to the same time on the mixer, tower crane, gantry and other equipment safety regulations require, PE wire to be repeated grounding, repeated grounding device resistance ≤ 4Ω.
④ Protection wire, repeated grounding wire connection using welding, crimping or bolting.
⑤ Leakage protector leakage action current selection value should be greater than the total leakage current value of the power supply line and power equipment more than 2 times, and in the power distribution line power supply end and the end of the installation of leakage protector, the formation of hierarchical segmentation protection, to ensure that each piece of power equipment have two levels of leakage protection.
Eight ﹑ safety technology briefing
Including construction site tower cranes, elevator cars, ramming machinery and welding machinery, hand-held power tools, such as inspection and maintenance, as well as the use of measures such as briefing.
Chapter 5: Common Diseases and Prevention of Temporary Power Distribution
The location of the power distribution room is wrongly selected, the building does not meet the specifications, and the safety distance of the indoor arrangement is not enough.
Control measures: power distribution room location as close as possible to the load center, in the dirty air upwind side and not easy to accumulate water and vibration of the orientation of the arrangement; power distribution room buildings and structures fire-resistant grade not less than 3, can prevent rain and snow door, open to the outside, the indoor natural ventilation; indoor equipment layout is strictly in accordance with the norms of the arrangement.
▼ Distribution line cable material is inferior, overhead arrangement is not standardized, pulling the line does not meet the requirements, indoor wiring error.
Control measures: cable conductors should have a certificate of conformity, cross-section and insulation in line with the standard; overhead conductor tied to the insulator, itself and the arrangement of accessories and the arrangement of the surrounding buildings in accordance with the norms to minimize the joints; pulling the line should be galvanized wire, and the ground angle and buried depth in line with the norms;
The outdoor end of the house line should be fixed by insulators and add protective casing, the indoor wiring height from the ground of at least 2.5 feet. Wiring height from the ground at least 2.5M.
▼The production and installation of power distribution boxes and switch boxes do not meet the requirements, the installation of electrical appliances in the box and wiring errors, power distribution box management and use is not in place.
Countermeasures: box material selection 1.2~2.0mm thick tin or high-quality insulating materials, installation should be in a dry, ventilated, vibration-free places and in line with the installation specifications, the box can be protected from rain and dust; the box electrical installation to follow the left and right small (i.e., large-capacity switches on the left, small capacity in the right)
The box and the box of electrically non-existing metal parts are for the protection of zero or protection grounding, wire access for the left and right, and the wiring is not in place. Protective grounding, wire in and out of the lower into the lower out and card solid, strengthen the insulation; distribution boxes and switch boxes have a person responsible for the management, operation and guardianship, the box marked with a full range of effective signs, to grasp the correct sequence of opening and closing the gate to ensure that "a machine, a
gate, a leakage, a box".
▼The construction of the grounding device does not meet the requirements, and the wiring of the protective zero system is wrong.
Protective measures: grounding body should be used angle steel, steel pipe or round steel, grounding body length, depth and spacing should be in line with the specification, grounding wire should be used multi-stranded copper wire; protective zero line shall not be equipped with any switches, and shall not be connected to the work of the grounding wire, in addition to the protective zero line in the main distribution room or the main distribution box for repeated grounding, but also in the middle, the end of the repeat grounding, and grounding resistance of not more than 10 ohms; in the leakage of electricity leakage system is not required for construction, the protection of zero system wiring errors. Ohm; in the leakage protector after the work of the zero line is strictly prohibited repeated grounding.
▼ Lightning grounding design errors, lightning protection devices do not meet the requirements.
Protective measures: the design and calculation of lightning grounding should take into account the actual situation of the site to integrate all aspects of the factors, follow the design specifications design; lightning rods are generally selected
round steel cross-section and size according to the norms to determine the use of lightning straps, lightning straps should be formed to close the diameter of not less than 8mm round steel and galvanized flat steel with a width of 40mm production.
▼Inappropriate use of site lighting safety voltage, line material and erection does not meet the requirements, lighting switch lamps and lanterns do not meet the requirements.
Countermeasures: the use of safe voltage to be reasonable, the lighting transformer must use a double-winding transformer, is strictly prohibited autotransformer, safe voltage transformer should be placed indoors, and the shell to take protection to zero; site lighting should be two-core or three-core insulated cable for the wire, the line should be set up with a short circuit breaker or fuse and to make the total line load balancing; lighting fixtures and fittings installed in accordance with the requirements of the sockets must be connected with the plug, and is strictly prohibited to directly insert the wire. The lighting fixtures are installed in accordance with the requirements, the socket must be connected with a plug, it is strictly prohibited to directly insert wires, switches, sockets placed on the wall, the wires should be extended wall laying.
Chapter 6: Management Measures for Temporary Power Distribution
◎The basic requirements and duties of power users are strictly in line with the norms and regulations
◎Temporary power rules and regulations should be sound:
Safety management of the distribution room should be strict: the distribution room must be "four preventive and one pass", that is, fire, rain, snow, moisture, small, and the power distribution room should be "four preventive and one pass", that is, fire, rain, snow, moisture, and small, and the power distribution room should be "four preventive and one pass". rain and snow, moisture, small animals and maintain good ventilation.
Operation and maintenance management should be rigorous: to ensure the normal operation of the line, must be responsible for the strict implementation of the provisions; maintenance must ensure that two people are present, one overhaul, one guardian.
Temporary electricity inspection and management should be strict: temporary electricity by time period and order of detailed inspection, there are emergencies and harsh environments should be more frequent and subtle inspection.
The knowledge of safe use of electricity and the dormitory safe use of electricity system should be popularized.
A, the construction of electricity files should be complete:
Temporary electricity safety files include:
Temporary electricity construction organization design of all the information; modification of the temporary electricity construction organization design of the information; technical delivery of information; temporary electricity project inspection and acceptance form; electrical equipment
testing, checking vouchers and debugging records; earth resistance, insulation resistance and leakage protector test jumps. Earth resistance, insulation resistance and leakage protector test jump determination record sheet; regular inspection (review) checklist; electrician installation inspection maintenance and removal work records.
B. Improve the quality of employees, equipped with the necessary safety protection equipment.
2011-4-9 in Dongguan Nancheng Royal Garden