How To Select Cables Under The Influence Of Temperature?
When the cable passes through the load current, it is certain to heat up, and as the load current increases, the higher the temperature of the cable surface. If not dealt with in time, it can seriously cause a fire and explosion, the consequences of which can be imagined.
For example, in polyvinyl chloride (PVC) cable, the core temperature of 70 degrees is the upper limit of consideration, and the surface temperature will be 5 to 10 degrees lower.
Today we will learn how to choose the cable in the end, from which aspects to consider. What are the effects of temperature on the selection of cables?
Cable Selection
Selecting Cables By Temperature Rise
We all know that the conductor temperature rises when the conductor passes through the load current.
The conductor has an insulation layer, and the conductor temperature should not exceed the maximum long-term allowable temperature withstood by the conductor insulation, once exceeded the conductor will be damaged.
By Mechanical Strength
When the conductor is laid, there is a minimum allowable cross-section of the conductor, depending on the laying method and the distance of the support point.
Selection According To Economic Conditions
That is, the selection is made according to the most cost-efficient way.
Selection By Line Voltage Drop
We all know that the current through the conductor, due to the existence of line impedance, will produce a pressure drop in the line.
If the voltage drop is too large, the voltage at the end of the line, that is, the load side, is too low, which will cause the equipment not to work or have an impact on the life equipment.
Therefore, this requires that the voltage drop should not be too large and that the cable cross-section should be selected with reasonable rules.
Cable Selection Should Meet The Requirements Of Load Protection
No matter it is a distribution circuit or a motor circuit, when the line fails, the protection device should act according to the specified time. Can reliable action and cable cross-section have a great relationship, so we choose the cable to consider the requirements of reliable action of protection?
Select The Cable According To The Requirements Of Thermal Stability
Cable or electrical equipment in the event of a fault, the cable to meet the thermal stability requirements.
To meet this requirement, the size of the cable cross-section should be considered.
Combining the above conditions, the largest cross-section among them is taken as the final result.
And it is also important to maintain the cable line daily.
The basic line maintenance work is to meet the needs of the grid and users for uninterrupted power supply, to prevent all kinds of cable accidents, and to ensure the safe power supply of cable lines.
Daily maintenance work is to improve the reliability of the line power supply, reduce the cable accident rate, shorten the outage repair time and reduce maintenance costs.
The next step is to learn more about it together with the editor.
Load Monitoring
The monitoring of cable load can grasp the change of cable line load and control the cable line in principle not to overload.
As overload is very harmful to the cable, the load of the cable should be measured and monitored frequently.
The measurement of cable line load can be measured with a clamp-on ammeter to keep the cable line operating under the specified allowable continuous load capacity.
To prevent premature aging of the cable insulation, the line voltage should not be too high and generally should not exceed 15% of the rated voltage of the cable.
Temperature Monitoring
Cable line operation will be affected by environmental conditions and heat dissipation conditions, and the cable line fault pre-local will be accompanied by the phenomenon of temperature rise, so it is necessary to monitor the temperature of the cable line.
Various instruments are used to measure the temperature of the outer skin of the cable line, the cable joints, and other parts.
The purpose is to prevent the cable insulation from exceeding the maximum allowable temperature and shorten the life of the cable and prevent cable accidents in advance.
Measurement of cable temperature should be carried out in the summer or the maximum cable load should choose the densest cable arrangement or the worst heat dissipation conditions and the influence of external heat sources of the line section.
Measurement of direct burial cable temperature, the soil temperature, should be measured.
Measure the soil temperature thermocouple thermometer device point and the distance between the cable is not less than 3 m.
Newly put into operation cable cold head to use infrared temperature tester for tracking and inspection, and arrange for personnel to tighten its conductive connection parts during power outage maintenance.
As the connection of the cable cold head by double-headed screws and other mechanical force crimps the conductive contact surface, the working load current, and fault short-circuit current all rely on the crimping surface to carry out energy transfer.
Thermal expansion and contraction and electromagnetic vibration may cause poor contact.
Corrosion Monitoring
Cable corrosion generally refers to the corrosion of the cable metal lead package or aluminum cladding, which can be divided into chemical corrosion and electrolytic corrosion.
The cause of chemical corrosion is generally the solution of acid and alkali, chloride, organic matter humus, and iron making furnace ash in the soil near the cable line.
The main source of electrolytic corrosion is caused by stray currents in the DC car track or electric railway runners from people.
Methods To Prevent Chemical Corrosion.
1 Collect soil information, and chemical analysis to determine the degree of soil and groundwater erosion.
Take measures to change the path, partially replace bad soil, or wear the cable in corrosion-resistant pipes, etc.
2 When corrosion is found on the cable, or when chemicals are found to be leaking from the cable route, dig up the soil to inspect the cable. And make a chemical analysis of the nearby soil to determine the extent of its damage.
3 For outdoor overhead laying of cables, regularly painted anti-corrosion paint.
Methods To Prevent Electrolytic Corrosion.
1 Strengthen the insulation between the cable sheath and the nearby huge metal objects.
2 Install drainage or forced drainage, polar drainage equipment, set up cathode stations, etc.
3 Add masking tube.
4 Online monitoring.
This is an introduction to the considerations for selecting cables under the influence of temperature.
