Control cable is a PVC insulated and PVC sheathed control cable suitable for use in industrial and mining enterprises, energy transportation departments, and for control and protection lines with AC rated voltages below 450/750 volts. Common faults of control cable lines include mechanical damage, insulation damage, insulation moisture, insulation deterioration, overvoltage, and cable overheating failures.
2. Insulation electrical strength: 1min 1kv between conductors without breakdown 1kv between conductor and shield 3kv without breakdown
3. Insulation resistance: Each core wire is grounded to the other cores, the control cable is greater than 10000MΩ.km, and the HYAT cable is greater than 3000MΩ.km.
4. Working capacitance: average value 52 ± 2nF / km
5. Far-end crosstalk defense: The average power of the specified combination at 150kHZ is greater than 69dB / km.
Power cables are used in power system trunks to transmit and distribute large-function electrical energy, and control cables transmit electrical energy from power distribution points in power systems directly to the power connection lines of various electrical equipment. The rated voltage of power cables is generally 0.6 / 1kV and above, and the control cables are mainly 450 / 750V. In the production of power cables and control cables of the same specifications, the insulation and sheath thickness of the power cables is thicker than that of the control cables.
(1) Control cables belong to electrical equipment cables, and power cables are two of the five categories of cables.
(2) The standard for control cables is 9330 and the standard for power cables is GB12706.
(3) The color of the insulated core of the control cable is generally printed in black and white, and the low voltage of the power cable is generally separated.
(4) The cross section of the control cable generally does not exceed 10 square meters. The power cable is mainly used to transmit power, and generally has a large cross section.
Due to the reasons mentioned above, the specifications of power cables can generally be larger, up to 500 square meters (the range that conventional manufacturers can produce), and the larger the cross section, the fewer manufacturers can generally do, and the control cable section is generally Small, the maximum generally does not exceed 10 square.
In terms of the number of cable cores, power cables generally have a maximum of 5 cores according to the requirements of the power grid, and the control cable transmits control signals with more cores. According to the standard, there are 61 cores, but it can also be produced according to user requirements. .
The wire and cable industry is the second largest industry in China after the automotive industry, with both product satisfaction and domestic market share exceeding 90%. In the world, China's total output value of wire and cable has surpassed the United States, becoming the world's largest wire and cable producer. With the rapid development of China's wire and cable industry, the number of new enterprises has continued to rise, and the overall technical level of the industry has been greatly improved.
The continuous and rapid growth of China's economy has provided huge market space for cable products. The strong temptation of the Chinese market has made the world focus on the Chinese market. In the short decades of reform and opening up, China's cable manufacturing industry The huge production capacity formed has made the world look amazing. With the continuous expansion of China's electric power industry, data communication industry, urban rail transportation industry, automobile industry and shipbuilding industries, the demand for wire and cable will also grow rapidly, and the wire and cable industry has huge development potential in the future.
In November 2008, in response to the world financial crisis, the government decided to invest 4 trillion yuan to stimulate domestic demand, of which about 40% was used for urban and rural power grid construction and transformation. The national wire and cable industry has a good market opportunity again. Wire and cable companies around the world seize the opportunity to welcome a new round of urban and rural power grid construction and transformation.
The control cable price formula is as follows: copper weight X copper price calculation: wire warp ÷ 2 = 1.25X1.25X3.14 = square number X number of wires X0.89X copper price + 10% processing fee at that time.
Cost price calculation of control cables
Square X1.83 = weight of copper X copper price at that time + armor price (weight X 0.4 yuan / catty) = cost price + 10% processing fee
The price of the cable = cost of manufacturing materials + fixed costs + taxes + business fees + profit
Manufacturing material cost = material cost * (1 + material consumption) (material cost is the value calculated theoretically)
The fixed fee varies according to the situation of each company, and generally includes production wages, management wages, utilities, repairs, depreciation, rent, and transportation costs.
Common faults of control cable lines include mechanical damage, insulation damage, insulation moisture, insulation deterioration, overvoltage, and cable overheating failures. When the above-mentioned fault occurs in the line, the power of the faulty cable should be cut off, the fault point should be found, the fault should be inspected and analyzed, and then repaired and tested. The removal of this cut will not resume the power supply until the fault is eliminated.
In order to ensure that the control cable reduces the scope of the impact when insulation breakdown, mechanical damage or fire occurs, the national standard GB50217-91 "Code for Design of Electric Power Engineering Cables" stipulates: double protection of current, voltage, DC power supply and trip control circuit, etc. Two systems that require enhanced reliability should use separate control cables.
After the control cable is put into operation, there is a problem of electrical interference between different cores of the same cable and between cables laid in parallel. The main causes of electrical interference are:
(1) The electrostatic interference generated by the capacitive coupling between the cores due to the applied voltage;
(2) Electromagnetic induction interference due to energized current. In general, when there are high-voltage, high-current interference sources nearby, the electrical interference is more serious. Because the distance between the cores of the same cable is small, the degree of interference is also much greater than the adjacent cables laid in parallel. For example, the control circuit of a phase-break circuit breaker of an ultra-high-voltage substation, which uses one cable for three phases, has occurred in such an accident. The pulses of phase separation operation triggered the thyristors of other phases, which caused the three-phase linkage by mistake. With separate cables, no more accidents occur. Another example is the computer monitoring system of a power plant. Because the analog low-level signal line and the transmitter's power line are combined with a four-core cable, it has caused a 70V interference voltage on the signal line. This is measured in millivolts. The low-level signal loop will obviously affect normal operation.
There are three main measures to prevent or reduce electrical interference.
1. Ground a spare core of the control cable
Practice has proved that when a spare core in the control cable is grounded, the amplitude of the interference voltage can be reduced to 25% to 50%, and the implementation is simple, and the cost of the cable is only slightly increased.
2. Do not use a control cable for circuits that have serious consequences when electrical interference occurs.
These include: (1) weak current signal control loop and strong current signal control loop; (2) low level signal and high level signal loop; (3) each phase weak current control loop of the AC circuit breaker split-phase operation. Use the same control cable. However, if each pair of back-and-forth wires of the weak current circuit belong to a control cable that is not the same, it may form a ring arrangement when laying, and the electric potential will be induced under the cross link of the electromagnetic wires of the similar power supply, and its value may affect the weak current circuit. Low-level parameter interference has a greater impact, so it is advisable to use a control cable for the round-trip conductor.
3.Ground metal shield and shield
Metal shielding is an important measure to reduce and prevent electrical interference, including overall shielding of cores, sub-shielding, and double-layer overall shielding. The selection of the metal shielding type of the control cable should be based on the comprehensive interference suppression measures according to the strength of the possible electrical interference effects to meet the requirements of reducing interference and overvoltage. The higher the requirements for anti-interference effects, the greater the corresponding investment. When steel tape armor and steel wire braiding are used, the price of the cable increases by about 10% to 20%.
The control interference in the strong current loop is strong because of its strong signal. Therefore, it can be used without the metal shield except for the location in the extra-high voltage power distribution device or the long parallel and high voltage cables. When the control cable used in the weak electric signal control loop is located in an environment affected by interference and does not have effective anti-interference measures, a control cable with a metal shield should be selected to prevent electrical interference from causing a malfunction of the low-level signal loop. Or make insulation breakdown. If the control cable of the weak current circuit can be pulled enough distance from the power cable or when it is laid in a steel pipe, it may reduce the external electrical interference to the allowable limit.
For the control cable of the computer monitoring system signal loop, the principle of its shielding type selection is:
(1) Switching signal can be shielded;
(2) High-level analog signals, the overall shielding of the core should be used, and the partial shielding of the core can also be used if necessary;
(3) For low-level analog signals or pulsed signals, it is better to use a separate shield for the core, and if necessary, a composite overall shield with a separate shield for the core.
Regarding the grounding method of the shielding layer, the following points should be paid attention to:
(1) The shielding layer of the control cable of the analog signal loop of the computer control system should be grounded with a centralized point. The reason is based on the requirements to ensure the normal operation of the computer monitoring system, because even only an interference voltage of about 1V may cause the fallacy of logical judgments. Concentrated grounding can avoid ground circulation;
(2) Except for the case where the control cable shielding layer of the computer monitoring system only allows one point of grounding to be concentrated, for other control cable shielding layers, when the electromagnetic induction interference is large, two points should be used for grounding, and the electrostatic induction interference is large A point ground is used;
(3) The inner shield of double shield or composite general shield should be grounded at one point, and the outer shield can be grounded at two points;
(4) When selecting two points for grounding, it should also be considered that the shielding layer will not be burned under the action of transient current.
Precautions for control cable installation and wiring:
Under the eaves. Cables can be used only if the cables are not directly exposed to sunlight or ultra-high temperatures. Pipes are recommended. Ultraviolet (UV)-Do not use cables without UV protection in direct sunlight.
2. On the outer wall. Avoid direct sunlight on the wall and man-made damage. Heat-The temperature of cables in metal pipes or trunkings is very high, and many polymeric materials will reduce their service life at this temperature.
3. In the pipeline (plastic or metal). For example, in pipes, pay attention to the damage of plastic pipes and the heat conduction of metal pipes. Mechanical damage (repair cost)-Repair of fiber optic cables is very expensive, requiring at least two terminations at each discontinuity.
4. Hanging application / overhead cable. Consider sag and pressure on the cable. Is the cable directly exposed to sunlight?
5. Laying directly in the underground cable trench, this environment has the smallest control range. The installation of cable trenches should be checked regularly for dryness or humidity. Grounding-If the shield of the control cable needs to be grounded, the appropriate standards must be followed.
6. Underground pipes. In order to facilitate future upgrades, cable replacement and isolation from surface pressure and surrounding environment, auxiliary pipelines are isolated, and auxiliary pipelines are a better method. But do not expect that the pipes will stay dry forever, which will affect the choice of cable type. Water-The moisture of the twisted-pair cable in the local area network will increase the capacitance of the cable, thereby reducing the impedance and causing near-end crosstalk problems.