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Analysis of The Causes of Damage To The Main Insulation of Hydro-generators
Author: source: date: 2020-06-19 11:47:51
Analysis of the causes of damage to the main insulation of hydro-generators
The small hydropower generating units currently distributed all over the country have made great contributions to the local economic and social development. However, there are many problems that need to be further studied and solved in terms of safety production and technical management, among which the main insulation damage of the generator accounts for a large proportion.
Poor design and manufacturing cause damage to the insulation of the hydroelectric generator
In order to reduce the cost and reduce the volume, the design of the main ball is low, and at the same time, the number of main insulation bandages in some parts is not enough and there is a disconnection phenomenon.
The production process directly affects the quality of the generator.
The vibration of the iron core of the hydro-generator set occurs from time to time, and it is often difficult to judge correctly during operation. For example, a hydroelectric generating unit put into operation in 1990 in a power station Shortly after commissioning, the operating personnel found that after the unit was boosted and connected to the grid, an abnormal screaming sound was produced when the load was brought to a certain level. The technical personnel analyzed and judged that the core vibration. The main reason is that the chip stacking is not enough during manufacturing
Tight, causing the silicon steel sheet to vibrate during operation. If it is not handled in time, it may cause the silicon steel sheet to break due to long-term vibration fatigue, and finally cut the coil insulation to cause a ground short circuit or interphase short circuit failure, which is often impossible to repair on site.
It needs to be shipped back to the manufacturing plant for iron core compaction and re-embedding. After being compacted on site by using a new process, it passes the DC leakage test and DC withstand voltage test twice the rated voltage, and then conducts 1.5 times the rated power AC withstand voltage test. The operation is still relatively normal.
The impact of the operating environment on the main insulation damage of the generator
The operating environment temperature directly affects the life of the motor.
Most of the small hydroelectric generating units that have been put into operation are insulated with asphalt mica. This kind of insulation uses mica tape to continuously wrap the entire bar straight and the end, and then is treated with vacuum dipping to eliminate the shortcomings of the end overlap. However, the softening point of asphalt is low, and the main insulation heat resistance level is relatively low, generally 105K. Vacuum impregnation process is complicated, and it is not easy to penetrate if it is not strictly controlled. There may be air bubbles inside, which makes the quality of the coil very unstable. In addition, because some power plants are built very low in order to improve the operation of the water head plant, in order to prevent the tailwater from flooding the equipment through the windows during the flood season, most main floors are not equipped with ventilation and light-transmitting windows. Insulation aging. In particular, some coils are poorly manufactured. The insulating material contains an air gap, which increases the insulation temperature difference. The temperature of the hottest spot directly shortens the service life of the stator insulation.
Small hydropower stations are located in remote mountainous areas, often at the end of the line in electrical wiring, and the voltage deviation is large.
Especially during the flood season, the bus voltage of 400V units sometimes rises to 470V, and the 6kV bus sometimes reaches 7kV. The grid-connected transformer of a small power station has only three-speed tap changers. It is far from meeting the actual operation needs and has to raise the generator output voltage.
Damage to the main insulation of the generator caused by poor maintenance
When performing extensive maintenance on vertical hydroelectric generators, most of them need to hang out the rotor, and the runner of the hydroturbine also needs to be hung out in the stator bore for repair welding. In the hoisting, if it is a little careless or the crane technology is not skilled, it will hit the stator coil.
Measures to damage the main insulation of the unit coil
Prevent the iron core from loosening. Pay attention to observe the stator core during overhaul. If red powder is found in the core, it indicates that There is looseness. You can use an electrician's knife and other thin sheet tools to test the degree of looseness. Normally, the insertion depth of the iron core teeth is generally not more than 3mm. Attention should also be paid to the tightening of the coil during operation. The upper and lower coils are in phase and electrically When the flow direction is the same, the maximum force will be pressed against the bottom of the letter. If the coil is not fixed firmly in the slot, vibration will occur and the anti-halo layer on the coil surface will be worn and damaged. When the current direction of the coils in the same layer is opposite, the tangential alternating bending force will be generated.
The moment is the largest and will also destroy the insulation. For loose coils, the slot wedge should be tightened in time, and oblique key slot wedge can be used if necessary. Loose ends can be reinforced with non-woven glass ribbons, and then epoxy resin paint is used for curing after the binding.
Prevent electric corrosion. Hydrogenerator set using epoxy powder mica as main insulation
The problems exposed during operation are mainly electrical corrosion. Electro-corrosion is divided into internal corrosion and external corrosion. Internal corrosion is because there is an air gap between the main insulation and the anti-corona semiconductor branch, and the voltage to ground is distributed in two different media of main insulation and air gap Upper. Make the air gap free discharge; external corrosion is because of the air gap free discharge between the anti-corona layer and the iron core. Internal corrosion first destroys the bonding glue between the main insulation and the conductor, loosening the insulation and loosening the glue line. Generate electromagnetic vibration, fine glue line.
It breaks and damages the main insulation; external corrosion firstly wears off the anti-corona layer, exacerbates the corona discharge, and causes damage to the insulation of the coil surface.
In order to prevent electrical corrosion, the following measures can be taken:
The degree of electrical corrosion is related to the voltage of the coil. Most of the corrosion occurs in the coil of the generator with a voltage greater than 4kV. The inversion of the center point of the coil and the outlet end can be relieved after the motor runs for a period of time.
If the running motor is found to have an ozone smell, it is often a precursor to electrical corrosion and can be checked with a partial discharge instrument. Small hydropower systems generally do not have this condition, and can make a preliminary observation with the naked eye in a dark environment. If a blue glow appears at the connection between the coil slot and the coil end band, there is a corona phenomenon. Need to be repaired.