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Electrical installation engineering knowledge

Electrical installation engineering knowledge
First, the characteristic parameter term
1. Rated voltage - The highest voltage that can be continuously operated under specified conditions of use and performance, and used to determine the relevant test conditions for high voltage switchgear.
2. Rated current - The current value that the main circuit of the high voltage switchgear can continuously carry under the specified normal use and performance conditions.
3. Rated frequency - the value of the grid frequency that can be continuously operated under the specified normal use and performance conditions, and determine the relevant test conditions of the high-voltage switchgear with it and the rated voltage and rated current.
4. Rated current breaking current - Under the specified conditions, the circuit breaker can guarantee the maximum short-circuit current of normal breaking.
5. Rated short-circuit closing current - Under the rated voltage and the specified use and performance conditions, the switch can ensure the normal breaking of the large short-circuit peak current.
6. Rated short-time withstand current (rated thermal steady current) - The rms current of the specified current that the switch can carry in the closed position within a defined short period of time under specified conditions of use and performance.
7. Rated peak withstand current (rated thermal stabilizing current) - The peak current of the first large half-wave of the rated short-time withstand current that the switch can withstand in the closed position under specified conditions of use and performance.
8. Rated short-circuit duration (rated dynamic settling time) - the time interval during which the switch can carry the rated short-time withstand current in the combined position.
9. Temperature rise - the difference between the temperature of each part when the switching device passes current and the ambient air temperature.
10. Power factor (loop) - the equivalent circuit of the switching device opening and closing test circuit, the ratio of resistance to inductive reactance at the power frequency, excluding the impedance of the load.
11. Rated short-duration power frequency withstand voltage - the standard value (effective value) of the power frequency voltage that the equipment is tolerated when tested according to the specified conditions and time.
12. Rated operation (lightning) impulse withstand voltage - The standard value of the operational (thunder) impulse voltage that the equipment insulation can withstand during the withstand voltage test.
Second, the term
1. Operation - the action of moving the contact from one position to another.
2. Split (gate) operation - the operation of switching from the position of the switch to the position of the switch.
3. Combination (gate) operation - the operation of switching from sub-position to re-position.
4. "Score" operation - After the switch is closed, the operation is performed immediately without any intentional delay.
5. Operation cycle - continuous operation from one position to another and back to the initial position; if there are multiple positions, all other positions are required.
6. Sequence of operations - a series of operations with specified time intervals and sequences.
7. Automatic reclosing (gate) operation - the sequence of operations that are automatically recombined after a predetermined time.
8. Close (on) - Used to establish the combined operation of the loop energized state.
9. Breaking (breaking) - Used in the power-on state for the sub-operation of the loop.
10. Automatic reclosing - automatic reclosing (gate) operation in the charged state.
11. Opening and closing - the general term for breaking and closing.
12. Short-circuit breaking - breaking the short-circuit fault current.
13. Short circuit closing - the closing of the short circuit fault current.
14. Near-field fault breaking--breaking of short-circuit current in near-field fault.
15. Contact opening distance - the total gap between the poles of a pole of a switch or any conductive part of the connection when the position is divided.
16. Travel
Third, the types and varieties of power cables mainly have the following aspects:
35kV and below power cable models and product representation methods

1. The uppercase of the first letter of Chinese Pinyin indicates the type of insulation, conductor material, inner sheath material and structural features. For example, Z stands for paper (zhi); L stands for aluminum (lv); Q stands for lead (qian); F stands for phase separation (fen); ZR stands for flame retardant (zuran); NH stands for fire resistance (naihuo).

2. The number of outer sheaths is represented by numbers and has two digits. No number represents no armor layer, no outer layer. The first digit indicates the armor and the second digit indicates the outer quilt, as indicated by the thick steel armor fiber.

3. The cable type is generally arranged according to the arrangement of the cable structure: insulating material; conductor material; inner sheath; outer sheath.

4. Cable products are indicated by model, rated voltage and specifications. The method is to add an Arabic number indicating the rated voltage, the number of cores and the nominal cross-sectional area after the model number. For example, VV42-103×50 means copper core, PVC insulated, thick steel wire armor, PVC sheath, rated voltage 10kV, 3 core, nominal cross-sectional area 50mm2 power cable.

The code of each part of the power cable model and its meaning D

1. Insulation type: V stands for polyvinyl chloride; X stands for rubber; Y stands for polyethylene; YJ stands for cross-linked polyethylene; Z stands for paper.

2. Conductor material: L represents aluminum; T (omitted) represents copper.

3. Inner sheath: V stands for PVC sheath; Y polyethylene sheath; L aluminum sheath; Q lead sheath; H rubber sheath; F neoprene sheath.

4. Characteristics: D does not drip; F phase separation; CY oil filling; P lean oil dry insulation; P shielding; Z DC.

5. Control layer: 0 no; 2 double steel strip; 3 thin steel wire; 4 thick steel wire.

6. Outer layer: 0 no; 1 fiber outer; 2 polyvinyl chloride sheath; 3 polyethylene sheath.

7. Flame-retardant cable is added with ZR before the code number; fire-resistant cable is added with NH before the code.

Oil-filled cable model and product representation

The oil-filled cable model consists of the product serial code and the cable structure. Self-contained oil-filled cable product line code CY. The outer sheath structure is represented by a combination of the reinforcing layer, the armor layer and the outer layer from the inside to the outside. The insulation type, conductor material, inner sheath code and the order of each code and the product are expressed in the same way as 35kV and below power cables. Such as CYZQ102220/1×4 indicates copper core, paper insulation, lead sheath, copper belt radial reinforcement, unarmored, PVC sheath, rated voltage 220kV, single core, nominal cross-sectional area 400mm2 self-contained Oil-filled cable. 6]

The outer layer of the oil-filled cable is coded as

1. Strengthening layer: 1 represents the radial strengthening of the copper strip; 2 represents the radial strengthening of the stainless steel strip; 3 the radial reinforcement of the steel strip; 4 the radial and narrow stainless steel strip of the stainless steel strip is longitudinally reinforced.

2. Armor layer: 0 no armor; 2 steel belt armor; 4 thick steel wire armor.

3. Outer layer: 1 fiber layer; 2 PVC sheath; 3 polyethylene sheath

Fourth, laying method

Wear welded steel pipe to lay SC

Wire laying MT

Wear a hard plastic tube to lay the PC

Wear FPC with flame retardant semi-rigid PVC pipe

Cable tray laying CT

Metal wire slot laying MR

Plastic trunking PR

Steel cable laying M

Laying PVC plastic corrugated wire tube to KPC

Laying the metal hose to the CP

Directly bury DB

Cable trench laying TC

Concrete pipe laying CR

AB/edge or span beam (roof)

BC/dark in the beam

AC/edge or cross-column laying

CLC/dark in the column

WS/laying along the wall

WC/dark in the wall

CE / laying along the ceiling or roof

CC/dark on the roof or roof

SCE / ceiling laying

ACC/dark coating in the suspended ceiling

ACE/laying in a suspended ceiling that can enter

F/floor or under the ground

Five, wire and cable and accessories knowledge question and answer

1, commonly used wires, cables, according to the type of use.

A: According to the use can be divided into bare wire, insulated wire, household wire, heat-resistant wire, shielded wire, power cable, control cable, communication cable, RF cable, etc.

2. What kinds of insulated wires are there?

Answer: There are commonly used insulated wires: polyvinyl chloride insulated wire, PVC insulated cord, nitrile polyvinyl chloride mixture insulated cord, rubber insulated wire, agricultural underground direct buried aluminum core plastic insulated wire, rubber insulated cotton yarn Textile cord, PVC insulated nylon sheathed wire, PVC insulated cord for power and lighting, etc.

3. What kind of occasion is the cable tray suitable for?

Answer: The cable tray is suitable for general industrial and mining enterprises to lay power cables indoors and outdoors, control cables, and can also be used for telecommunications, radio and television departments to erect indoors and outdoors.

4, what are the cable accessories?

Answer: Commonly used electrical accessories are cable terminal junction box, cable intermediate junction box, connecting pipe and terminal block, steel plate wiring slot, cable tray and so on.

5, what is the cable intermediate connector

Answer: The device that connects the cable to the conductor of the cable, the insulating shield and the protective layer to connect the cable line is called the cable intermediate joint.

6, what is the electrical main wiring

Answer: The main electrical wiring is the connection mode of the main electrical equipment and busbar in the power plant and substation, including the connection method of the main busbar and the plant power system according to certain functional requirements.

7. What regulations should be followed when selecting the cross section of the power cable?

A: The choice of power cable should follow the following principles:

(1) The rated voltage of the cable is greater than or equal to the rated voltage of the power supply system at the installation point;

(2) The continuous allowable current of the cable shall be equal to or greater than the maximum continuous current of the power supply load;

(3) The core section must meet the stability requirements of the short circuit of the power supply system;

(4) Check whether the voltage drop meets the requirements according to the cable length;

(5) The minimum short-circuit current at the end of the line should enable the protection device to operate reliably.

8. What are the advantages of XLPE cable and oil-paper cable?

Answer: (1) Easy to install because it allows a small minimum bending radius and is light in weight;

(2) not subject to line drop restrictions;

(3) Good thermal performance, allowing high operating temperature and large transmission capacity;

(4) The cable accessories are simple and all are dry structures;

(5) Simple operation and maintenance, no oil leakage problem;

(6) the price is lower;

(7) High reliability and low failure rate;

(8) Less manufacturing process, simple process and significant economic benefits.

9, what is the requirement for the clamp of the fixed AC single-core cable?

Answer: The clamp should be free of iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic flux is generated around it. The magnetic flux is proportional to the current passing through the core. If a magnetic material such as iron is used, Electromagnetic induction knows that eddy currents will be generated in the iron parts to heat the cable and even burn the cable. Therefore, iron parts cannot be used as fixing fixtures for single-core AC cables.

10, what are the biggest features and advantages of the following accessories for heat shrinkable cable heads?

A: The biggest feature of the heat shrinkable accessory is that it replaces the traditional stress cone with a stress tube. It not only simplifies the construction process, but also reduces the size of the terminal of the joint. It is easy to install, saves time and labor, has superior performance, saves metal. The cable accessory set is a combination of a perfusion type and a dry package, which combines the advantages of these two types of accessories.

11. What inspection work should be carried out before cable laying?

Answer: (1) The bracket should be complete and the paint should be complete.

(2) Cable type, voltage, and specifications conform to the design.

(3) The cable insulation is good. When there is doubt about the sealing of the oil-paper cable, it should be judged by damp; the direct-buried cable and the small-bottom cable should pass the DC withstand voltage test; the oil sample of the oil-filled cable should pass the test.

(4) The oil pressure of the oil-filled cable should not be lower than 1.47MPa.

12. When there is any doubt about the sealing of the oil-paper insulated power cable, how to check whether the cable insulation paper is damp with a simple method?

Answer: Ignite the cable insulation paper or put it into the cable oil of about 150 °C for inspection. There is no "beep" sound or white foam, indicating that it is not damp.

13, cable signs should indicate what is required to write content

Answer: The cable circuit design number, cable type, specification and starting point should be indicated on the signboard. The cable used in parallel should have a sequence number. The required writing is clear and not easy to fall off.

14. Where should the orientation mark of the direct buried cable be set?

Answer: At both ends of the cable, at the 50~100m straight section of the cable, the cable joints change the direction of the cable.

15, making yellow wax ribbons for cable joints, black glass paint strips, alkali-free glass ribbons, etc. How to carry out moisture treatment before construction"

Answer: (1) Constant temperature drying method: roll the insulating tape into a small roll with a diameter of 25~30mm, put it in a constant temperature drying oven of 110~120 °C for 4~5h, cool it out and put it into the dry sealed cylinder.

(2) Oil immersion method: put a small coil of insulation tape into the cable oil at a constant temperature of 120~130 °C, keep a distance of 30mm from the bottom of the pot, after a certain period of time, the oil no longer produces foam and then take it out and put it into storage. In barrels with cable oil, the oil level should exceed all loaded objects and seal them.

16, what is the role of the cable sheath?

A: Protect the inner sheath from mechanical damage and chemical corrosion, and enhance mechanical strength.

17, what requirements should be met for outdoor cable trenches?

Answer: The upper part of the cable trench should be slightly higher than the ground. Cover the cover made of concrete. The cable should be laid flat on the bracket and have a good drain.

18, what is the role of the inner sheath of the cable?

Answer: The insulation layer will not come into contact with water, air or other objects to prevent the insulation from being damp and the insulation layer from mechanical damage.

19. What should I pay attention to when using wire cutters?

Answer: Before use, be sure to check whether the insulation of the insulating handle is intact. When using it, do not use wire cutters to cut the metal wire beyond the specification. It is forbidden to use the wire cutter instead of the hammer to knock the tool to avoid damage.

20, what is the dielectric strength

Answer: In the electric field, when the electric field strength increases to a certain limit, it will be broken down. The electric field strength that causes the insulation breakdown is called the insulation strength.

21, what are the advantages of cross-linked heat shrinkable cable accessories

A: This is a new type of material. Compared with other types of accessories, it has superior electrical performance, small size, small quality, easy installation, material matching, etc. It also has weather resistance, anti-staining properties, flame retardant self-extinguishing, etc. ability.

22, what are the requirements for the mechanical strength of the cable conductor connection point?

Answer: The mechanical strength of the connection point is generally lower than the resistance of the cable conductor itself.

Sixth, low-voltage cable head production and installation

(1 Overview

There are many models of low-voltage cables. The indoor PVC insulated PVC sheath of 1KV or less is taken as an example to illustrate the production of cable ends for power cables.

(2) Construction process

Shake the grounding resistance → peel off the cable head → wrap the cable, set the cable end head → press the cable core wire to connect the nose → connect with the equipment

(3) Main construction methods and technical measures

1) Shake cable insulation

a. Select 1KV shaker to shake the cable, the insulation resistance should be greater than 10MΩ.

b. After the cable is shaken, the core wires should be discharged to the ground separately.

2) Wrapped cable, cable end cap

a. Strip the outer insulation of the cable and insert the lower part of the cable cover into the cable.

According to the model size of the cable head, according to the length and inner diameter of the cable ferrule, the cable is wrapped with a plastic strip in a half stack. The plastic tape should be wrapped tightly and have a jujube shape.

c. Put the upper part of the cable head cover on the upper part, and connect it to the lower part and set it tightly.

3) Press the cable core wire to connect the nose

a. Take the length from the end of the core wire to the depth of the wire nose, add 5mm, strip the cable core insulation, and apply Vaseline on the core wire.

b. Insert the core into the wire nose and press the wire nose with the crimping pliers. The crimping pit should be more than two. Large-size terminals should be hydraulically crimped.

c. According to different phases, use yellow, green, red, and four-color plastic tapes to wrap each core of the cable


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