As we all know, a variable frequency motor (VFM) is a motor that, under standard environmental conditions, operates continuously at 100% rated load within a speed range of 10% to 100% of its rated speed without exceeding the motor's rated allowable temperature rise. So, what are the differences in maintenance methods between VFM and ordinary motors? Due to the special nature of variable frequency power supplies, the winding insulation requirements for VFM motors are more stringent than those for ordinary motors. Let's take a closer look!
1. Select electromagnetic wire with good corona resistance to meet the requirements of motor resistance to high-frequency pulses and partial discharge. Generally, polyesterimide/polyamide-imide composite enameled wire is used, which is corona-resistant and anti-corona electromagnetic wire.
II. Construction process for winding and embedding wires.
The processing of variable frequency motors, including winding, winding, and binding, must be strictly managed. In particular, damage to the conductors must be prevented during winding and winding. During winding, slot insulation, phase insulation, and interlayer insulation must be properly placed. Phase insulation should use materials that are easily penetrated by insulating varnish, and the coil ends should be reinforced and fixed to ensure that the ends form a single unit.
Strengthening insulation at the bottom of the motor slot, between phases, between layers, and at the first and last turns of the coil can improve the motor's electrical withstand strength.
3. The main insulation must be gapless insulation.
Air gaps in the insulation structure of variable frequency motors are a major factor contributing to corona discharge. To ensure that the overall insulation structure of the motor is free of air gaps, according to the national standard GB/TZ1707-2008 "Insulation Specification for Three-Phase Asynchronous Motors for Variable Frequency Speed Control," the impregnating varnish used in these motors must be solvent-free varnish of at least Class F, with a volatile content of less than 10%, and must employ the VPI (Vacuum Insulation Process). This process also improves the overall mechanical strength of the insulation structure.
Fourth, ensure proper matching between the frequency converter, cables, and motor, and limit the length of the cable between the motor and the power supply.
Due to impedance mismatch in the power lines, the overvoltage amplitude at the motor terminals increases with the length of the cable between the inverter and the motor, which can easily lead to partial discharge. Therefore, the length of the connecting cable should be shortened as much as possible, based on the specific characteristics of the inverter power supply and actual needs, to reduce the overvoltage amplitude and partial discharge at the motor terminals and extend the motor's lifespan.
Variable frequency motor power cords generally use professional cables, also called symmetrical conductor variable frequency cables, which are 3P+3N/E series, meaning that the original 3+1 is split into 3 strands.
