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Frequency conversion cable structure design

Frequency conversion cable structure design

  • Time of issue:2021-11-30

Frequency conversion cable structure design

  • Time of issue:2021-11-30
Information

The energy-saving effect of the frequency conversion device is very obvious. In the high-power motor, the frequency conversion speed-regulating motor is used, and the entire generator set can save 30% of electricity. And after using the frequency conversion speed regulation, the soft start of the motor is realized, so that the motor works smoothly, the motor bearing wear is reduced, and the service life and maintenance cycle of the motor are prolonged. Therefore, frequency conversion speed regulation technology has been widely used in industries such as petroleum, metallurgy, power generation, railways, and mining.
  1. Cable symmetry design   
  For 1.8/3KW and below frequency conversion motor special cables, and symmetrical 3+1 core and 4-core cables can only be used for the input cable of the main power supply, but it is better to use a symmetrical structure cable. Both the frequency converter and the frequency conversion motor cables need to adopt a symmetrical cable structure. The symmetrical cable structure has three cores and 3+3 cores. The 3+3 core cable structure is the fourth core ( The neutral core) is broken down into three insulated cores with small cross-sections, and the three three small cores are symmetrically formed into a cable. For the 6/10kV variable frequency motor special cable, the cable structure is different from the 6/10kV ordinary power cable , Ordinary power cables use copper tape to shield the three insulated cores to form a cable, while the frequency conversion motor special cable is shielded by copper wire and copper tape, and then squeezed into a separate phase sheath, and then symmetrically formed into a cable. The symmetrical cable structure is due to the mutual interaction of the wires. It has better electromagnetic compatibility and has a certain effect on suppressing electromagnetic interference. It can offset the odd frequencies in high-order harmonics, improve the anti-interference performance of the special cables for variable frequency motors, and reduce the amount of energy in the entire system. Electromagnetic radiation.
  2. Design of shielding structure   
  1.8/3kV and below frequency conversion motor special cable shield generally adopts general shielding, 6/10kv frequency conversion motor special cable shielding is composed of split-phase shielding and general shielding, split-phase shielding can generally adopt copper tape shielding or copper wire copper tape combined shielding. The overall shielding structure can adopt copper wire and copper tape combined shield, copper wire braided shield, copper tape shield, copper wire braided copper tape shield, etc. The cross section of the shielding layer is proportional to the cross section of the main core. The shielded cable of this structure can resist electromagnetic induction, poor grounding and power line conduction interference, reduce inductance, and prevent excessive induced electromotive force. The shielding layer not only plays a role in suppressing the external emission of electromagnetic waves, but also serves as a channel for short-circuit currents and can protect the neutral core. Special cables for 6/10kV variable frequency motors, considering that the cables are often subjected to radial external forces during use, add a galvanized steel strip pinning layer outside the cable shielding layer (add an isolation sleeve between the shielding layer and the steel strip pinning layer ). Steel tape pinning is mainly used as the radial mechanical protection layer of the cable, and it also plays an additional overall shielding role, especially the steel tape armor and copper wire and copper tape shielding. It uses two different shielding materials. The electromagnetic wave shielding plays a certain complementary role, and the shielding effect will be better.
  3. Cable electrical performance design   
  1.8/3kV and below frequency conversion motor special cable electrical performance are designed according to GB/Tl2706, 2002 standards. In addition to meeting the GBT/l2706.2002 standard, the 6/10kV variable frequency motor special cable has increased the electrical performance requirements such as capacitance and inductance. According to the actual use of special cables for variable frequency motors and with reference to GB/T 12706.2002 and ABB Japan’s technical conditions for power transmission cables, the electrical performance parameters of the cables have been determined.
  4. The main manufacturing technology of the cable   
  In the production process of special cables for frequency conversion motors, the process of extruding the insulated core and forming the cable is the most critical process.  
  The quality of the insulated wire core in the extrusion process of the insulated wire core will directly affect the electrical performance of the cable. In order to improve the quality of the cable, we choose high electrical performance insulating materials, such as 1.8/3kv inverter motor special cable, using 10kV cross-linked insulating material, 6/10kv inverter motor special cable using 35kv cross-linked insulating material, conductor shielding, insulation shielding Imported materials are used for insulation and insulation materials. In the production process, we pay special attention to the purification of raw materials. The shielding and insulating materials are tightly packed to control the eccentricity of the insulation and the uniformity of the insulation outer diameter, which can reduce the interface effect and improve the electrical performance of the cable.
The cable forming process requires a symmetrical structure for variable frequency cables. When forming the cable, the tension of the insulated core must be even, so that the length of the core after the cable is as consistent as possible, otherwise it will cause structural changes, resulting in uneven capacitance and inductance, and affecting the cable's performance. Electrical performance.

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