Mining cable section selection

1. Selection principle of downhole high voltage power cable cross section
(1) Determine the cable cross section according to the economic current density.
(2) Allow the current to verify the cable cross-section for a long time.
(3) Check the cable cross-section as the voltage loss permitted by the grid when the cable passes the normal load current.
(4) Check the thermal stability of the cable in case of a three-phase short-circuit fault in the maximum operating mode.
(5) When the cable passes the minimum two-phase short-circuit current, the minimum sensitivity of the over-current protection device must be met.
2. The selection principle of downhole low-voltage power branch cable cross-section
(1) Select the cable cross-section according to the mechanical strength. The section of the core wire shall not be less than the minimum cross-section specified by the mechanical strength requirements of various electrical equipment.
(2) Verify that the maximum operating current actually passed by the cable does not exceed the allowable current of the cable for a long time.
(3) When a fuse is used for short-circuit protection, the rated current of the fuse in the fuse shall match the selected cable cross-section.
3. Selection principles of downhole low-voltage power trunk cable cross-section
(1) Select the main core wire section of the cable according to the allowable voltage loss of the low voltage system.
(2) Verify the cable cross-section by the long-term allowable current of the cable.
(3) Verify the selected cable section according to the start conditions. The motor with the longest distance from the power source and the largest capacity is started. The voltage loss during the normal operation of the rest of the motor should be less than the allowable voltage loss of the power grid.
(4) When the electrical winding passes the minimum two-phase short-circuit current, the minimum sensitivity of the over-current protection device should be satisfied.
The section of the rubber sheathed cable used in electrical equipment that is often moved, and the minimum cross-sectional area that satisfies the mechanical strength requirements are shown in the table.
The minimum cross-sectional area to meet the mechanical strength requirements




Sintered NdFeB magnets are prepared by the raw materials being melted in a furnace, cast into a mold and cooled to form ingots. The ingots are pulverized and milled; the powder is then sintered into dense blocks. The blocks are then heat-treated, cut to shape, surface treated and magnetized.

As of 2012, 50,000 tons of neodymium magnets are produced officially each year in China, and 80,000 tons in a "company-by-company" build-up done in 2013. China produces more than 95% of rare earth elements, and produces about 76% of the world's total rare-earth magnets.

Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets and range from N35 up to N52. Letters following the grade indicate maximum operating temperatures (often the Curie temperature), which range from M (up to 100 °C) to EH (200 °C).

Sintered Nd2Fe14B tends to be vulnerable to corrosion, especially along grain boundaries of a sintered magnet. This type of corrosion can cause serious deterioration, including crumbling of a magnet into a powder of small magnetic particles, or spallingof a surface layer.
This vulnerability is addressed in many commercial products by adding a protective coating to prevent exposure to the atmosphere. Nickel plating or two-layered copper-nickel plating are the standard methods, although plating with other metals, or polymer and lacquer protective coatings are also in use.

Neodymium magnets have replaced alnico and ferrite magnets in many of the myriad applications in modern technology where strong permanent magnets are required, because their greater strength allows the use of smaller, lighter magnets for a given application. Some examples are:
ï‚·Head actuators for computer hard disks
ï‚·Magnetic resonance imaging (MRI)
ï‚·Mechanical e-cigarette firing switches
ï‚·Locks for doors
ï‚·Loudspeakers and headphones
ï‚·Magnetic bearings and couplings
ï‚·Electric motors:
ï‚·Cordless tools
ï‚·Servomotors
ï‚·Lifting and compressor motors
ï‚·Synchronous motors
ï‚·Spindle and stepper motors
ï‚·Electrical power steering
ï‚·Drive motors for hybrid and electric vehicles. The electric motors of each Toyota Prius require 1 kilogram (2.2 pounds) of neodymium.
ï‚·Actuators
ï‚·Electric generators for wind turbines (only those with permanent magnet excitation)
ï‚·Direct-drive wind turbines require c. 600 kg of PM material per megawatt
ï‚·Turbines using gears require less PM material per megawatt
ï‚·Toys




Sintered NdFeB Magnet

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Jinyu Magnet (Ningbo) Co., Ltd. , https://www.magnetbonwin.com

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