Double-fed Wind Turbine Slip Ring
DFIG is currently one of the mainstream models grid wind generators. Slip ring, brush is a process prone to problems running the generator. By analyzing the vibrations caused by the slip ring brushes and shock hazards, as well as affect the resonant frequency of the brush security implications, to develop preventive measures to reduce accidents due to the brushes, slip ring failure.
1. The double-fed wind turbine slip ring magnetic brush design
DFIG have A, B, C three-phase excitation and the corresponding slip ring brushes, and also set up a slip ring D and the corresponding grounding brushes. Three-phase current is relatively large, so each set a number of brushes, D phase is only a slip ring brushes.
2. The slip ring brushes impact and harm caused by vibration
Slip ring there is a big vibration, for example, the magnetic gap is uneven, unbalanced rotor vibration and slip ring roundness uneven, causing a short separation point of contact with slip rings. Its corresponding brush slip ring arc and damage will occur. Suppose brush design reasonable, and it is composed of a mechanical compression spring with its second-order system to produce natural resonance frequency of FS, than the slip ring rotational frequency FN is much higher, it is assumed slip ring imbalance, uneven roundness problems will cause sine, "slip ring vibration" amplitude A = 1mm, forcing brushes exist. According to the mechanical model diagram can be seen quite understand, brushes positive displacement cannot be smaller than the slip ring positive displacement, otherwise, would be forced to slip ring brushes motion; brushes may be larger than the forward displacement of the slip ring, and slip ring separation. Negative brush displacement must be greater than the absolute value of the slip ring negative displacement, or slip ring brushes will run hindered formed.
3. Brush’s resonant frequency and the security implications
The resonant frequency of second-order system constituted by the brush as their compression spring, the design should be the maximum vibration source Z FN and the shaft is multiplied times, namely FN × Z, so not only can effectively reduce the vibration of the brush, also impact ring can slide the brush decreases its vibration.
A set of classical vibration theory pointed out: When the forced vibration frequency than the resonant frequency of the system to be high, the amplitude of the system will be affected, the vibration amplitude will decline. We assume that there is such a resonance frequency FS = 10Hz, resonant gain second-order system is G = 10 times, if forced vibration 25Hz, this time the vibration amplitude response is -1439dB, that is to say it is reduced to forced vibration of 19%. This is not a theory in the second-designed brush compression spring constituted its application, because most likely the vibration response and forced vibration phase difference of 177 ° ignored reality, means that if the excitation vibration relative electrical slip ring brush movement, while the slip ring brushes are doing the appropriate motion, so that they appear bound to cause a strong impact.
We should note that: because the presence of slip ring Mitsubishi and roundness is poor, so the vibration frequency of the slip ring more than its maximum speed in frequency. After our study can be found: When the gear thrust is large, the rotation frequency of the motor shaft FN light loads, would have FJ = FN × Z × 2 vibration frequency, will produce FJ when overloaded = FN × Z vibration frequency. For example: the maximum rotation frequency of the drive generator flexible coupling FN= 24, Z = 6, the vibration frequency of the shaft can be achieved FJ = 288Hz. Personal recommendations 500Hz-1000Hz brush resonant frequency is preferably designed to FS> 2FJ. Increase the compression spring stiffness can increase the frequency of the FS, some people may think that doing so will increase the friction and positive pressure brush slip ring friction, but also accelerate the wear and tear, but this is a gentle continuous contact friction, damage caused by the relatively strong impact is much smaller.
Above all, slip ring double-fed wind turbine, when the brush for maintenance need to take note of several aspects: Strengthening tour inspection, to check ignition phenomena dust peep through the window; brush the surface with infrared thermometer conduct collector ring surface temperature, the presence of abnormal brush the need for timely treatment, replaced; regular maintenance brushes, slip ring; electrochemical reaction occurs under high humidity conditions, the generator shut down longer, it is better to take the brush walk, prevent the formation of electrolytic corrosion marks.