According to the type of wind turbine, slip rings can be divided into 1.5/1.65MW slip rings and 2MW slip rings, which are installed on the hub side and the nacelle side respectively. The working conditions of the hub slip ring are worse than that of the nacelle slip ring, and the hub vibrates more frequently than the nacelle. This is an important factor for the higher failure rate of the 1.5/1.65MW slip ring. From the feedback of wind farms, the main fault phenomena are communication faults and loop faults. The following is the inspection statistics of 476 repaired slip rings . The fault locations of slip rings are mainly distributed in the following categories.
Analysis of Typical Failures of Slip Rings
According to the fault phenomena reported by the wind farm, the typical faults of slip rings are mainly divided into the following categories: communication faults, encoder faults, ring burning, etc. The main reasons for the problems are analyzed from the aspects of slip ring structure, technology and maintenance.
1. Communication failure
Communication failure is a common failure. The root cause of the problem is poor contact between the brush pin and the loop, which affects signal transmission. From the analysis of the nature of the problem, it can be divided into two categories: One is the defect of the slip ring itself, which leads to poor contact. The second category is poor contact caused by failure to maintain timely.
(1) Slip ring structure and process defects lead to poor contact between the brush needle and the coil
After disassembling the faulty slip ring, it was found that the brand slip ring has the following defects in structure and workmanship:
a) The anti-corrosion ability of the support rod of the early slip ring products of this brand is not enough, the support rod rusts and falls off, contaminates the loop, and causes poor contact (even short circuit burnout) (see Figure 2, a certain brand of slip ring support rod is rusty).
b) The materials of the brush and conductive ring are not wear-resistant (Figure 3 shows the state of the brand slip ring running for about 1.5 years), the brush needle is worn and broken, which leads to poor contact, friction loss causes dust pollution in the circuit, and ash deposits increase contact resistance At the same time, the surface finish of the slideway is damaged, causing the gold needle to bend and jump, causing instantaneous disconnection or even short-circuit, and at the same time reducing the insulation performance of the slip ring, causing communication failure or burning of the wind turbine circuit.
c) The brush is elastically fatigued, and the brush pressure cannot be guaranteed to cause poor contact, causing the surface of the copper ring to burn out due to ignition. In severe cases, the brush wire will burn out.
d) Due to the misalignment of the coils, the brush needles have poor contact or abnormal wear. According to the disassembly of the faulty parts, it is found that the slip ring spindle of this brand is made of plastic, which is insufficient in rigidity and easy to break. It cannot guarantee the concentricity of the loop, which may easily lead to hidden dangers such as poor contact and cause communication failure (see Figure 4 for the slip ring spindle) .
e) The protection level of the slip ring is not enough. Dust, water vapor and oil mist from the outside enter the slip ring, polluting the circuit and causing poor contact. At the same time, the insulation performance of the slip ring is reduced, and the breakdown is burned.
(2) Improper maintenance leads to poor contact between the brush needle and the coil
According to the failure statistics, the slip ring fed back by the wind farm is a communication failure, and about 15.5% of the slip rings have been tested by the supplier without failure. After the slip ring is cleaned and lubricated, it functions normally, mainly because it is not maintained in time. From the analysis of slip ring technology in the industry, no matter which technical solution is adopted, it belongs to the category of sliding contact, which will inevitably produce friction and powder, but the degree of wear of slip rings of different brands is different. In order to improve the reliability and service life of the slip ring, regular cleaning and lubrication are required. If it is not cleaned up in time, dust generated by wear will accumulate on the surface of the slide. During the rotation, the gold needle will jump away when it encounters dust spots, resulting in unreliable contact, flickering, unstable information transmission, and even communication failure.
2. The loop was burned down
Through the disassembly and analysis of the faulty parts, the following factors are the main reasons for the burning of the loop:
(1) Electrical process defects: the welding process is not good, the core is exposed, and the solder joints are sharp, resulting in too small electrical gaps, breakdown and burnout (as shown in Figure 5, slip ring PCB welding);
(2) The slip ring has the structural and technological defects described in 1.1, which leads to combustion;
(3) Burned by lightning.
3. Encoder failure
(1) The slip ring encoder of this brand is fixed at the end of the plastic main shaft. Due to the rigidity of the plastic main shaft, it is not easy to deform, and the encoder runs in a shaking state. At the same time, the structure of the encoder coupling is unreasonable and the connection flexibility is not enough, resulting in the encoder being damaged in different centers.
(2) The quality of the encoder itself.