the development of modern industrial technology, the application of power electronic devices in the power system of the manufacturing industry is increasingly widespread, and the large-scale application of various non-linear electronic device devices such as inverters, rectifiers, and various switching power supplies has improved the modern industrial automatic control. the technology also generates a large amount of harmonic interference to the grid. among them, frequency converters are widely used in various production industries.
compared with the traditional dc speed regulation, the frequency converter can realize the stepless speed regulation of the ac motor, meet the requirements of the motor speed control of the production process, to improve the output and quality of the product, and can greatly save energy and reduce production. cost. however, whether it is dc speed regulation or ac speed regulation technology, the rectifier circuit is adopted in the electrical design, which brings serious harmonic pollution to the system.
typical load
a large number of automated pipelines are used in the manufacturing industry, which contain a large number of non-linear loads, which generate a large amount of harmonics and are injected into the grid. the quality of the power is greatly reduced, which affects the normal operation of the equipment.
the harm of harmonics to the power supply system of the manufacturing industry
(1) for transformers, harmonic currents can cause copper loss and stray loss to increase, and harmonic voltages increase iron loss.
(2) the heating effect of the harmonic current is greater than the power frequency current with the same effective value. the current with higher harmonic content can reduce the breaking capacity of the circuit breaker and increase the configuration of the circuit breaker capacity. harmonics also cause the voltage protection of the low-voltage switchgear of the low-voltage distribution system to be mis-operated or rejected due to phase changes.
(3) in the power system, the high harmonic frequency increases the harmonic resistance of the wire because of the skin effect. therefore, harmonic currents increase line losses and reduce the transmission capacity of the line. in addition, harmonics may cause partial discharge of immersion insulation, accelerate cable insulation aging, and shorten cable life.
(4) if the waveform of the voltage and current applied to the meter is non-sinusoidal, the waveform of the working flux becomes non-sinusoidal, and any non-sinusoidal wave can be decomposed into a series of higher harmonics, the same frequency is high. the interaction between the subharmonic fluxes creates additional torque, which causes additional errors and even confusion.
(5) the existence of harmonics will greatly increase the probability of damage or malfunction of the control equipment. power electronics are sensitive to harmonic distortion of the supply voltage, such as programmable controllers (plcs), where higher distortions can cause control equipment to malfunction, resulting in production or operation interruptions, resulting in greater economic losses.
(6) for the harmonic pollution load, once the product is in the process of production, the computer may lose data, which may cause certain economic loss. brought very bad effects.
manufacturing industry power quality management solutions
1, using apf to control harmonics
the manufacturing industry load contains inverters, rectifiers and switching power lamps, which are typical harmonic sources and will seriously affect the stability of the power system. for the harmonic status of the power grid in the manufacturing industry, the best solution for harmonic control is to use active filtering technology. in general, the active filter (controlled current source) is connected in parallel with a load generating harmonics. the current source produces a compensating current of the same magnitude as the harmonic current of the load, thereby eliminating the effects of harmonics generated by the load on the distribution network.
apf selection:
active filter design capacity = operating current * current distortion rate
note: in order to make the compensation effect better, there is generally a margin, so the calculated capacity is generally multiplied by 1.2 as the final configured capacity.
2, project configuration plan
| device name | installation location | way of governance | solve the problem |
| static var generator svg | load line breaker bottom | centralized governance | improve power factor, stabilize system voltage, and reduce line loss. |
| active filter | load line breaker bottom | centralized governance | filter harmonic currents and improve the reliability of the power supply system. |
summary: after the device is put into use, not only can the harmonic current drop in the manufacturing industry be very obvious, but also the power factor in the field can be improved. when the capacity is sufficient, the current current distortion rate will drop from 23% to 5%. .