Beijing shelf factory Boeing and harm
Frequency converter is widely used in the field of industrial transmission. Due to the high power diode rectifier and high power transistor inverter in the input and output circuit to generate a higher harmonic current, thus the power supply system, load and other adjacent electrical equipment.
Beijing shelf factory with the transducer as the representation of the power electronic device is one of the main harmonic sources in the utility grid, the harmonic pollution has become hinder the major barrier to its development of power electronic technology.
Inhibition of inverter in power system harmonic pollution can reduce the additional loss of power generated by the harmonic current through the transmission lines and components, increase the efficiency of power grid equipment, avoid overheating damage to equipment; can also eliminate power system in series, parallel resonance, to avoid the misoperation of the power system automation device and relay protection device to ensure the normal work of the electric equipment. On the other hand, the suppression of the harmonic pollution can reduce the interference of the harmonics to the communication and the electronic equipment.
1 the cause of the harmonic generation is the root cause of the nonlinear in the load, when the current flows through the load, with the added voltage is not linear relationship, so as to form a non sinusoidal current and harmonic.
The main circuit of the inverter is usually made by hand. When the external input 380V/50Hz power frequency power, it is not controlled by the three-phase bridge rectifier into DC voltage, the capacitor filter and the high power transistor switching element for the variable frequency AC voltage. In the rectifier circuit, the input current waveform is irregular rectangular wave, and the wave is decomposed into the fundamental and second harmonic wave by Fu Liye series. Harmonic is the sine wave with different frequency and amplitude and phase angle, and is divided into even and odd times. In a balanced three-phase system, due to the symmetry relations, even harmonic is eliminated, only odd harmonics exist. Therefore, odd harmonics caused harm antithetic harmonics more. For a three-phase rectifier load, the harmonic current is 60 n*1 harmonics, for example 7, 11, 1 and 17, inferior 19, inverter mainly produce the 5th and 7th harmonics.
In the inverter output circuit, the output current signal is modulated by the PWM carrier signal. GTR high power contravariant components of PWM carrier frequency for 23 kHzIGBT high power contravariant components of PWM high frequency 15kH% similarly, the output signal of the current loop can also be decomposed into containing only the fundamental and the second harmonic.
2 the harm of the harmonic is the same as that of the ordinary radio electromagnetic interference. The frequency converter generates the harmonic pollution in the power supply and the adjacent power equipment in three ways: conduction, electromagnetic radiation and induction.
21 the harm to the transformer can make the transformer copper loss, iron loss and noise increase, especially the 3 harmonic and integer harmonics, greater harm. For delta connected transformer, harmonic in the winding to form circulation to make the winding heat; for the star connection of transformer, when winding neutral point grounding and the grid side distributed capacitance is large, or transformer with neutral point of shunt capacitor may form three times harmonic resonance and increase additional loss of transformer.
22 Beijing shelf factory of power cable damage due to the high frequency harmonics, the skin effect in wire will enable harmonic resistance increase than the wave resistance increased greatly, so that the additional line loss increases. In addition, the harmonic wave may cause the voltage waveform of the spike, so that the dielectric loss and temperature rise, causing the partial discharge of the immersed insulation, to accelerate the aging of the cable, shorten the service life of the cable.
The higher the rated voltage of the cable, the greater the harm to the cable. The distribution capacitance of the cable has an amplification effect on the harmonic current, which can cause the insulation breakdown.
23 the harm of electric motor on the motor of the motor is the main damage of the additional loss, resulting in reduced motor efficiency, mechanical vibration and noise increase. Due to the existence of skin effect, magnetic hysteresis and eddy current, the increase of the frequency increases with the increase of the additional loss of the core and winding of the motor. Because the power of the motor can not be adjusted according to the heat, the heating effect of the electric motor is considered by the harmonic voltage which can withstand the harmonic voltage. Test results show that the technology and application of building materials: h20*6 [emic motor under the rated power continued under 3% of the rated voltage of the negative sequence voltage, the motor insulation life to reduce 1/2> so, the general recommendations motor in continuous working conditions under the negative sequence voltage should not be more than the harm of 2% of the rated voltage. 24 of low voltage switch for distribution circuit breaker is concerned, the harmonic current can lead to full electromagnetic type circuit breaker iron consumption and fever, can also lead to the decrease of the electronic circuit breaker rated current.
25 the harm to the communication system will cause the communication system to appear the noise, reduce the call clarity, serious when will cause the signal loss. Under the joint action of the harmonic and its fundamental frequency, the interference may cause the telephone bell's abnormal opening, and threaten the safety of communication equipment and human body. Phase generated in the process of electromagnetic noise (3~10kHZ) HVDC converter station (HDDC) heat exchanger will interfere with the normal operation of the power line carrier communication, so that the carrier locking device and relay protection device fault of action and the grid interruption of normal operation.
6 of used electrical equipment of the harm of harmonics will make television, micro electronic computer graphic distortion, brightness fluctuations and heat generating components problem, resulting in computer data handling errors. With the start ballast or used to improve the power factor capacitor fluorescent lamps, mercury lamps, harmonic resonance can damage caused by overheating of the ballast or capacitor, also can cause the transmission device of thyristor control circuit malfunction, generate the false triggering.
3 harmonic suppression 1LC passive filter LC passive filter is a commonly used harmonic compensation device principle is to use the LC resonant circuit to suppress the harmonic current injected into the grid, when the resonant frequency of the resonant circuit and a harmonic current of the same frequency, you will be able to filter the harmonic current. By the resonance circuit composed of many different resonance frequency, the harmonic current can be filtered out.
32 the static var compensation method is to compensate reactive power and improve the power factor (SVC) in the power grid. Traditional fixed capacitors and crystal gate pipe controlled reactor of non reactive power compensation device has the behindhand, replaced for GTO a commutated inverter (commonly known as static free power generator or SVG) track the grid reactive power and harmonic wave dynamic compensation device, and its role is: 1 online real time automatic compensation control, keep the system voltage stability, reduce the voltage distortion; II absorption dynamic reactive power, reduce loss, improve power factor; third harmonic absorption, reduce the harmonic pollution, compensation for three-phase load imbalance, improve power system dynamic and static stability and power quality.
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