Variable frequency cable structure design
Release time： 2021-11-30 15:58
The energy-saving effect of frequency conversion device is very obvious. The frequency conversion speed regulating motor is adopted in the high power motor, and the whole generating set can save 30% of electricity. And after the use of frequency control, 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 extended. Therefore, frequency control technology has been widely used in petroleum, metallurgy, power generation, railway, mining and other industries.
1. Cable symmetry design
For 1.8/3KW and below frequency conversion motor special cable, and symmetrical 3+1 core and 4 core cable can only be used for the main power input cable, but it is better to use symmetrical structure cable. The symmetrical cable structure is divided into 3 core and 3+3 core. The 3+3 core cable structure is to decompose the fourth core (neutral core) of the three and one small four-core insulated wire cores into three insulated wire cores with smaller sections. The three and three small wire cores into symmetrical cables. The cable structure is different from the 6/10kV ordinary power cable. The ordinary power cable is made of three insulated wire cores shielded by copper tape, while the special cable for variable frequency motor is made of copper wire shielded by extrusion and phase sheathing, and then formed symmetrically. The symmetrical cable structure has better electromagnetic compatibility due to the interchangeability of the wire, which plays a certain role in suppressing electromagnetic interference. It can offset the odd frequency in the high order harmonic, improve the anti-interference of the special cable of the inverter motor, and reduce the electromagnetic radiation in the whole system.
2. Design of shielding structure
The shielding of special cable of 1.8/3kV and below frequency conversion motor generally adopts total shielding. The shielding of special cable of 6/10kv frequency conversion motor is composed of phase separation shielding and total shielding. The phase separation shielding can generally adopt copper strip shielding or copper wire copper strip combination shielding. The total shielding structure can be copper wire copper belt combination shield, copper wire braided shield, copper wire braided copper belt shield, etc., the shielding layer section and the main line core section according to a certain proportion. The shield cable of this structure can resist electromagnetic induction, poor grounding and power line conduction interference, reduce inductance, prevent induction electromotive force is too large. The shielding layer can not only inhibit electromagnetic wave emission, but also act as the channel of short circuit current, which can play the role of neutral core protection. Special cable for 6/10kV frequency conversion motor, considering that the cable is often subjected to radial external force in the process of use, add galvanized steel strip pin mounting layer outside the cable shield layer (add isolation sleeve between the shield layer and steel strip pin mounting layer). Steel belt pin installation is mainly used as the radial mechanical protection layer of cable, but it also plays the role of additional shielding, especially steel belt armor and copper wire, copper belt shielding, is the use of two different shielding materials, electromagnetic wave shielding plays a certain complementary role, shielding effect will be better.
3. Cable electrical performance design
The electrical performance of special cables for frequency conversion motor of 1.8/3kV and below is designed according to GB/Tl2706, 2002 standard. 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 inverter motor special cable and referring to GB/T 12706.2002 and ABB company's technical conditions on power transmission cable, the electrical performance parameters of the cable are determined.
4. The main manufacturing technology of cable
In the production process of special cable for frequency conversion motor, the extruding process of insulated wire core and cable forming process are the most critical processes.
The quality of insulated core will directly affect the electrical performance of the cable. In order to improve the quality of cables, we choose high electrical performance insulation materials for production, such as 1.8/3kv frequency conversion motor special cable, 10kV cross-linked insulation materials, 6/10kv frequency conversion motor special cable, 35kv cross-linked insulation materials, conductor shielding, insulation shielding and insulation materials are imported materials. In the production process, we pay special attention to the purification of raw materials, shielding and insulation materials squeezed tightly, control the eccentricity of insulation and insulation diameter uniform, so as to reduce the interface effect, improve the electrical performance of the cable.
Variable frequency cables must be symmetrical in structure. During cable formation, the tension of the insulated wire core must be even, and the length of the wire core should be as consistent as possible after cable formation. Otherwise, the structure will change, resulting in uneven capacitance and inductance, and affecting the electrical performance of the cable.