At present, most hydropower plants under Guangdong Yuedian Group adopt 4-6a 1 regular maintenance, which is centralized by professional hydropower maintenance teams. As an electrical practitioner, the author has participated in the major and minor repairs of several different types of units in recent years, and found that there are some differences in the technical details of slot wedge treatment between maintenance personnel, hydropower plants and power plants and maintenance companies during the maintenance of stator slot wedges, which will bring inconvenience to the maintenance work. Especially when the wedge is repaired and accepted, due to different understanding and implementation standards, sometimes the maintenance personnel are required to rework, which seriously affects the maintenance period. Because there are few technical details of slot wedge treatment in various maintenance quality standards and regulations, the author thinks it is necessary to form a certain understanding in this respect. As we all know, the stator is the core component of the generator, and the quality of stator maintenance will directly affect the safe operation and economic benefits of the unit, and slot wedge treatment is one of the key links in stator maintenance engineering. Because the slot wedge treatment is generally not carried out when the unit is small or in medium repair, the maintenance of slot wedge needs to be more strict and serious when it is overhauled. According to the maintenance status of several hydropower stations in Guangdong, this paper briefly analyzes and discusses some technical problems of slot wedge treatment.

1 the significance of slot wedge treatment

Corona and electrical corrosion are the main causes of insulation damage of generator stator bar, and electrical corrosion is caused by spark discharge caused by the loss of good contact between the surface of stator bar and the wall of generator slot. There are many technical measures to prevent electric corrosion, such as the close cooperation between the bar and the stator slot, the use of semiconductor materials in the slot, and the reduction of vibration of the unit. It is also an important technical measure to make the stator slot wedge press the bar. If the groove wedge is not pressed tightly, the wire rod and groove wedge will have poor contact or gaps with the groove wall, which will easily lead to electrical corrosion. In addition, the running bar vibrates due to alternating radial electromagnetic force, which will gradually wear the anti-corona layer of the bar and aggravate the electrical corrosion, so an effective bar fastening system is very necessary. Obviously, whether the slot wedge is tightened is directly related to the fastening of the bar. Therefore, in the maintenance of generator stator, the inspection and treatment of slot wedge has always been one of the focuses of work, which is of great significance. Add the safety engineer website to your favorites.

Several key points of slot wedge treatment

2. 1 Selection of slot wedge and slot pad

At present, almost all hydropower plants use traditional slot wedges. First, choose a straight wedge. The second is to choose a slot wedge composed of positive and negative wedge pairs with a certain inclination. Several factories have always used the manufacturer's choice when installing machines. Due to the difference of installation level and the long-term operation and operation level of each generator set at the initial installation, the width of stator core notch surface and the depth of bar will change to some extent, and the surface of bar is uneven. This brings some difficulties to the treatment of slot wedges, and it is prone to the phenomenon that some slot wedges are difficult to fasten and the stator core is damaged carelessly. From the application effect, this traditional way is to make the slot wedge and wire rod hard connected (rigid). Due to the phenomenon of thermal expansion and cold contraction after long-term operation and the shrinkage of insulating materials, the slot wedge will become loose, and it needs to be wedged again every time the unit is overhauled. In particular, several hydro-generator units under Guangdong Electric Power Group, including several larger 80,000 kW units, have been using the most traditional straight slot wedge, and the effect is not satisfactory. Every time the unit is overhauled, a large area of slot wedge will be found loose; However, these units are not hoisted out of the rotor during routine maintenance, so it is very difficult to treat the slot wedge, and the treatment effect is difficult to meet the requirements. Here, it is suggested that these units be reformed to improve their reliability and operation level, and also to meet the requirements of the transition from regular maintenance to condition-based maintenance in the future.

In 2006, a hydropower plant in northern Guangdong took the lead in adopting the corrugated spring pad slot wedge fastening system in the capacity-increasing transformation of units. Elastic slot wedge has been used abroad for a long time, and its technology is relatively reliable. In the long-term operation, the possible looseness of the slot wedge is automatically compensated by the expansion and contraction of the corrugated spring gasket, so that the wire is kept tight. This method is mostly used in large turbo-generators in China, and it is the first time to apply it to small and medium-sized hydro-generators in Guangdong. This is a new attempt, and the effect has yet to be verified.

The gasket in the box is composed of semiconductor gasket and epoxy resin gasket, which is made by the manufacturer during supply or maintenance. A serious problem in practical application is that the width of the pad is always difficult to meet the actual needs. In particular, due to the uneven level of manufacturers or inaccurate measurement units, the self-made shim is too wide or too narrow, which affects the fastening quality of the slot wedge and must be paid enough attention. In addition, when machining the groove wedge, the preparation of gasket strips must be of various specifications, and the commonly used thicknesses in practice are 0.2mm, 0.5mm,1.0 mm.

2.2 slot wedge tightness inspection

Judging from the current maintenance situation of Guangdong hydropower station, there is still no scientific method to check the tightness of slot wedge, which is basically judged by manual tapping with a small copper hammer. This inspection method is simple and effective for traditional straight wedge and positive and negative chute wedge, but it depends entirely on the personal experience of the operator. Generally speaking, there is no looseness, fracture and displacement of slot wedge, and the empty response length of each slot wedge should not exceed 1/3. Under the condition that several wedges at the upper and lower ends are fastened, how to deal with it when only the middle 1 section is loose, the inspectors and maintenance personnel of each factory hold different attitudes. This is a common problem in practical operation. The author thinks that if this situation is loose seriously, it must be dealt with when beating with a hammer will produce jumping phenomenon. In the elastic slot wedge system, the generator is in a cold state because of the compression margin of the corrugated spring pad, and its knocking sound is fictitious and true, and the tightness boundary is blurred. Even so, in actual operation, the method of hammering is often used to judge its tightness. There is no quantifiable standard in many aspects of slot wedge treatment, which depends on the specific situation. This requires practitioners to continuously accumulate experience and improve their professional level.

2.3 Fastening of slot wedge and its precautions

First of all, you must prepare suitable special tools. Simple and commonly used are square punch, square shovel and processed hardwood board. Usually, when exiting the slot wedge, tap the wedge seam at the ventilation ditch with a special tool to separate the wedges by a certain distance, and then punch the slot wedge with a long hard plate. When the wedge hits people, it should be numbered in sequence. If the wedge is too wide, you can polish it a little, then brush it with white wax or select it. At the beginning, the filler in the groove should not be too thick, when

When approaching the fixed position, add a gasket with appropriate thickness and tighten the slot wedge. Using segmented cushion belt will make the slot wedge easy to penetrate and not easy to break. Every 1 segment should be checked for eligibility. Therefore, the matters that should be paid attention to in the treatment of slot wedge are as follows:

1) The selected wedge should be dried in an oven to remove moisture before use.

2) When the slot wedge is pulled out and driven in, it is necessary to prevent the tools used from scratching the bar or damaging the iron core, especially the metal appliances.

3) The upper and lower ends of the wire rod shall be protected by cardboard to prevent the wire rod and its end rope from being damaged.

4) The notch of the slot wedge should be aligned with the ventilation slot of the iron core, and the ventilation hole should be in the right direction.

5) The part exposed from the groove under the groove pad should be aligned with the groove wedge to avoid being too long or too short.

6) The groove wedge belt at the lower end must be fastened. In order to prevent the local binding line from breaking and affecting the looseness of other channels, each groove must be knotted.

3 Acceptance of slot wedge after repair

It is difficult to accept the slot wedge after treatment. This is related to the lack of quantitative indicators and regulatory standards. The author thinks that it is most appropriate to complete the acceptance of slot wedge treatment in the process of slot wedge treatment. It is an effective method for the construction personnel to check each section and each trough in time after treatment. Of course, this requires the builder to have a certain professional level and a high sense of responsibility. Considering the different technical level and operating experience of construction personnel, they can cross-check each other; In order to avoid missing inspection and rework, maintenance technicians and acceptance personnel can also check together before treatment, mark the slot wedge to be treated, and then adopt the method of sectional acceptance. No matter how the acceptance, we must be strict and carefully check.