Frequency Conversion Cable Structure Design

The energy saving effect of frequency conversion device is very obvious, the use of frequency conversion speed regulating motor in high power motor, the whole generator set can save 30% electricity. And after the use of 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 extended. Therefore, frequency control technology in petroleum, metallurgy, power generation, railway, mining and other industries have been widely used.


1. ACSR Cable 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 supply input cable, but the best use of symmetrical structure cable. Inverter and frequency conversion motor ask cable all needs to adopt symmetrical cable structure, symmetrical cable structure with three core and 3 + 3 core 2 kinds, 3 + 3 core cable structure is a small four to three core insulation wire core in the fourth core (neutral) is decomposed into three smaller insulation wire core section, the three big three symmetrical string cable core cable, special cable for 6/10 kv frequency conversion motor, the cable structure and 6/10 kv power cable, ordinary ordinary power cable is three insulation wire core adopts copper tape screened cable, special cable is made by copper wire and frequency conversion motor copper tape screened after extruded phase splitting the sheath, and symmetric cabling, The symmetrical cable structure has better electromagnetic compatibility because of the interchangeability of the wires, which plays a certain role in suppressing electromagnetic interference, can offset the odd frequency in the high order harmonic, improve the anti-interference of the special cable for frequency conversion motor, and reduce the electromagnetic radiation in the whole system.

2.Design of shielding structure

The shielding of special cables for frequency conversion motor 1.8/3kV and below generally adopts the total shielding, and the shielding for special cables for frequency conversion motor 6/10kV is composed of phase separation shielding and the total shielding. The phase separation shielding can generally adopt copper tape shielding or copper wire and copper tape combination shielding. The total shielding structure can adopt copper wire and copper tape combined shielding, copper wire braided shielding, copper wire braided shielding, copper wire braided copper tape shielding, etc. The section of shielding layer and the section of main line core are in a certain proportion. The shielded cable with this structure can resist the interference of electromagnetic induction, bad grounding and power line conduction, reduce the inductance and prevent the induction electromotive force from being too large. The shielding layer can not only restrain the emission of electromagnetic wave, but also act as the channel of short-circuit current, which can protect the neutral wire core.6/10kV frequency conversion motor special cable, considering that the cable is often affected by radial external force in the process of use, galvanized steel belt pin mounting layer is added outside the cable shielding layer (isolation sleeve is added between the shielding layer and the steel belt pin mounting layer).The steel belt pin is mainly used as the radial mechanical protective layer of the cable, and it also plays an additional role of total shielding. In particular, the steel belt armor and the copper wire and copper belt shield are two different shielding materials, which play a complementary role in electromagnetic shielding, and the shielding effect will be better.


3.Overhead ACSR Cable 336.4 MCM design

1.8/3KV and below frequency conversion motor special cable electrical performance according to GB/ TL2706, 2002 standard design. In addition to meeting the GBT/ L2706.2002 standard, the cable for 6/10kV frequency conversion motor has increased the electrical performance requirements such as capacitance and inductance. According to the actual use of the special cable for frequency conversion motor and the technical conditions of GB/T 12706.2002 and ABB Company for electric power transmission cable, the electrical performance parameters of the cable are determined.

  1. Main manufacturing technology of cables

In the production process of special cable for frequency conversion motor, the extrusion process of insulating wire core and cable forming process are the most critical processes.

Insulation core extrusion process Insulation core quality will directly affect the electrical performance of the cable. In order to improve the quality of cables, we choose insulating materials with high electrical performance for production. For example, 10kV cross-linked insulating materials are used for 1.8/3kV variable frequency motor special cables, and 35kV cross-linked insulating materials are used for 6/10kV variable frequency motor special cables. Imported materials are used for conductor shielding, insulating shielding and insulating materials. In the production process, we pay special attention to the purification of raw materials, shielding and insulation material extrusion close, control insulation eccentricity and insulation diameter uniformity, which can reduce the interface effect, improve the electrical performance of the cable.

Variable frequency cable requires symmetrical structure, and uniform tension of insulating wire core must be ensured during cable construction, so that the length of wire core after cable construction should be kept as consistent as possible, otherwise it will lead to structural changes, resulting in inhomogeneity of capacitance and inductance, and affect the electrical performance of the cable.