1. The impact of pulse voltage on the frequency of […]
1. The impact of pulse voltage on the frequency of variable frequency power supply frequency adjustment range is wide, regardless of the frequency level, with a main frequency waveform profile, which contains many high-order harmonics, as a traveling wave by multiple reflections, amplitude Stacking can reach the operating voltage several times, the longer the cable, the higher the amplitude, if the cable insulation safety factor is not high, may be breakdown. Oil mining with more than 3000 meters long submersible pump cable, the frequency can be long-term normal operation, but in the frequency conditions, the cable was put into operation for several hours that breakdown, indicating the pulse over-voltage hazards, so prevention is necessary The As the cross-linked insulation power cable voltage level is high, the cable length is generally within 300 meters, over the years did not occur the breakdown of the event, however, the insulation thickness and process should be taken seriously, solid insulation is reliable, Insulation is not suitable.
2. Cable body of the external launch of electromagnetic waves General frequency of household appliances for the single-phase power supply, the length is very short, the power is also small, the design has been variable frequency power supply, connecting cable and inverter motor set together in the metal shell, The However, in the industrial field, the motor power is large, connecting the variable frequency motor and variable frequency power cable between the length of the cable, in the work of the cable is high frequency electromagnetic wave outward carrier effective carrier, for the surrounding areas of communication tools (such as cordless phone ) Or AM receiver (such as the radio amplitude band) will produce interference, and sometimes the situation is also more serious, known as the electromagnetic pollution of the environment, foreign countries have long made such a request, the domestic also attaches great importance to the current cable factory developed a business Standards, the future will be unified development of industry standards.
3. Neutral current superposition The complete three-phase sinusoidal power supply system, when the three-phase current balance, the neutral current is zero, if the third harmonic, the third harmonic current component in the neutral line is not There is a phase difference, so the amount of the superimposed component is tripled. If the original power supply is three single-phase variable frequency motor, and in the three-phase power distribution balance, the neutral current is greater, the neutral cross-section should be less than the phase cross-section.