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DFIG (Double-Fed Induction Generator) is a kind of winding induction generator, which is the core part of variable speed constant frequency wind turbine and is one of the key components of wind turbine generator. The generator is mainly composed of two parts: motor body and cooling system. The motor body consists of a stator, a rotor and a bearing system.
The stator windings of the doubly-fed asynchronous generator are connected directly to the grid. The rotor windings are connected to the grid through the converter. The frequency, voltage, amplitude and phase of the rotor winding power are automatically adjusted by the inverter. The unit can be connected at different speeds Under the realization of constant frequency power generation, to meet the electricity load and grid requirements. As a result of the use of AC excitation, generators and power systems constitute a "flexible connection", which can be based on grid voltage, current and generator speed to adjust the excitation current, accurate adjustment of the generator output voltage, to meet the requirements.
Sichuan Province to vote in the East New Energy Development Co., Ltd. Lunan, Rama wind farm is located in Huidong County Lama Township, the dam area, the site is mainly located in the Lunan Mountains ridge area, elevation of 2700m ~ 3100m, 66 Dongfang Electric Wind Power Co., Ltd. production of 1.5MW FD93H plateau wind turbine, the total installed capacity of 99MW, two wind field highland wind turbine using a factory to introduce German technology to produce high-altitude generators, the various indicators Process technology is very high, this paper will start from the structure of the collector ring, analysis of the collector ring failure and maintenance methods, collecting ring chamber and ventilation pipeline maintenance.
1 collector ring composition
1.1 Overview
The generator collecting ring provides the excitation current for the generator to set the stator voltage, set the frequency, adjust the sub-reactive power, and adjust the rotor's active power, which is a very important power unit of the wind turbine. The collecting ring is mainly composed of slip ring body, carbon brush (phase, ground). Slip ring and carbon brush with the role of the rotor current and external power supply equipment connected to achieve static and dynamic conversion; brush holder plays a supporting role in the carbon brush, and effectively combined with carbon brush and slip ring as a whole. Brush, support bar is a key component of the megawatt double feed asynchronous wind turbine slip ring system. The brush holder and support bar are mainly composed of K, L, M grounding brush holder and one support rod, , Auxiliary carbon brush wear micro switch 14 and so on.
1.2 collector ring system structure
The collector ring system is composed of three (K, L, M) independent spiral groove, grounding step, encoder connection bracket, corona-resistant insulation material and so on (Figure 1).
The main structure of the collector ring (Figure 1)

2 collector ring common fault
2.1 The fault situation and the consequences of the collecting ring of the mountain wind farm
2.1.1 abnormal collection ring (Figure 2) slide slip, traces of serious uneven, there are traces of electric burns (feels like a protruding or concave) slip ring surface, it is unqualified, must be deal with.
2.1.2 phase chute - different phase arc short circuit, burn the collector ring; inverter excitation contactor arc burning or burning excitation circuit 500A insurance; inverter synchronization difficult, can not be connected; trigger generator vibration Or aggravate the shaft vibration, causing the unit to shut down due to vibration.
2.1.3 grounding carbon brush slide - inverter DC bus voltage is high, reported fault; trigger generator bearing damage due to electrical burns, serious need to replace the generator.

2.2 Relevant fault alarms that can cause the fault of the collector ring
Generator stator temperature is high;
Replace the generator phase carbon brush, grounding carbon brush is not standardized;
Replacement of the generator bearing is not in place;
Inverter DC bus voltage caused by high frequency converter failure;
Inverter inverter ground current caused by a large inverter failure;
Inverter failure caused by external fault of inverter.
3 collector ring fault handling
3.1 Determination of the surface of the collector ring
For high-altitude areas of the mountain wind farm running a normal generator collector ring surface, the slide has a uniform or deep or shallow brown layer of oxide film, not only to protect the surface of the slip ring, but also to ensure the conductivity (Figure 3). Perhaps the surface color of some chutes seems to have some light-colored traces, as long as uniform, is also normal (Figure 4). 

3.2 high altitude area of the mountain wind farm collector ring collector ring surface treatment steps (Figure 5)
1) press the emergency stop button (the highest braking level to ensure that the fan completely shut down);
2) remove the carbon brush;
3) will be more than 200 # gold sandpaper cut into a size slightly larger than the size of the carbon brush;
4) the sandpaper installed in the chute surface, with carbon brush to suppress (need to install the elastic clip); if it is a chute need to polish, must be carried out at the same time, all the slide must be polished;
5) start the fan, to maintain low-speed rotation (by modifying the rated speed to achieve), such as the speed of stability in the 500-600rpm, polished for 3 minutes or so; check the chute surface after the original oxide layer are all polished clean, smooth surface smooth.

Note: Normally running an abnormal slip ring must be accompanied by a carbon brush problem, so you must check all the carbon brushes next. Replace the carbon brush, you must use the generator slip ring supporting the carbon brush, that is, different slip ring must use the provisions of the manufacturers, the provisions of the material and size of the carbon brush! Otherwise, due to different carbon brush manufacturers caused by differences in material expansion coefficient Different, different hardness caused by slip ring and brush frame burned; different size due to differences in the conductive area can not meet the flow requirements, or because of the length of the compression force is different, the same can not meet the flow requirements.
3.3 Collector ring chamber and ventilation pipe regular maintenance
High-altitude area of the mountain wind farm generator collector ring chamber indoor carbon (powder) serious, will lead to the collection ring inter-phase insulation decreased, phase short circuit and other failures, serious burned when the collector ring slide or brush holder; cooling ventilation Pipeline ventilation is poor, it will lead to the generator stator circuit temperature is high, causing high temperature shutdown protection; collector ring chamber ventilation duct ventilation is poor, will lead to collecting ring chamber set of carbon (powder), collecting ring chute Or brush holder attached to the toner.
3.3.1 Cleaning of the collector ring chamber
1) Brush attached to the toner to remove the carbon brush, the use of dry brush on the brush holder and all the surface of the line for toner removal treatment;
2) the collector ring slide between the groove set of toner, the use of dry brush on the chute surface and the slide between the groove for toner removal, the need to clean the edge of the plate axis system to ensure that the entire collection ring Can all clean;
3) phase insulation groove set of toner, the use of dry brush on the interphase insulation groove for toner removal process, the requirements of the edge of the side of the plate to clear the shaft to ensure that the entire insulation groove can be all clean;
4) Use the dry brush to clean the inside of the chamber, require the entire chamber to be clean, and then use the vacuum cleaner for toner to ensure that all the toner is fully adsorbed and cleaned.
Note: You must use a clean, oil-free dry brush, which can cause toner sticking. Wear thin rubber gloves and protective glasses, masks, toner to stimulate the skin and toxic.
3.3.2 cooling ventilation pipe inspection (Figure 6)
1) Damage to ventilation ducts Replacement of new ventilation ducts, temporary handling methods - Sealing breakage.
2) Ventilation pipe is too long, resulting in bending, accumulation, increase the wind resistance, poor exhaust, affect the stator cooling effect of measuring the correct length, eliminating the pipe bending, accumulation phenomenon, so exhaust ventilation.
3) The filter (Figure 7) inspects the installation location of the filter for the air vent in the cabin.
4) filter layer too much, increase the wind resistance, poor exhaust, the impact of row of toner effect check the filter layer, it is recommended to stay only one layer.
5) filter long-term unclean, too much toner accumulation, the impact of ventilation using a vacuum cleaner for toner adsorption, to ensure that all the toner adsorption of all clean.