The insulation breakdown accident often occurred in generator. It includes interphases short circuit, inter-turn short circuit and ground fault.
The interphase short circuit: the generator windings ends will be greatly impacted by electric power and may make the coil end deformed under two-phase or three-phase short circuit and differential protection tripping happening.
Inter-turn short circuit: Generator outlet blasting, if it continues a long time, the stator copper wire will be melted. When no-load run, the generator three-phase voltage will be imbalance.
Ground fault: Generator breakdown location is in the linear portion or notch position and stator ground protection act. The insulation resistance value between stator ground and ground is zero or minimum.
The fundamental reason of generator insulation breakdown is that the stator coil insulation is weak or there is a corona etching in notch in run time. The treatment method is to find the point of breakdown and reworked and reinforced insulation. At the same time, eliminating the corona etching in a maximum extent is important.
III. A large noise or vibration with generator
The reasons of a large noise or vibration with generator are:
1. Foundation bolts loose, or STG subsidence. Treatment: fastening bolts. Recalibration concentricity.
2. Generator rotor and Steam Turbine shaft are misalignment. Treatment: calibration concentricity.
3. Bearing wall worn or damaged under short oil. Treatment: repaired bearing or replace a new bearing with same model.
4. There is a friction between the stator and rotor. Treatment: find the friction location and reason, and then eliminate it.
5. Fan or other fasteners loose. Treatment: Tighten fan and fasteners.
6. Rotor coil partial short circuit, two points grounding or wiring errors. Treatment: please inspect the insulation of slip ring and the rotor coil to the ground. Or connect to the DC power source and check the voltage drop of each coil, winding direction and wiring method. So we can identify the cause of the malfunction and eliminate them.
7. Brush is too hard, or the pressure is too large. Treatment: adjust the pressure or replace the same type of brush.
8. Three-phase current are severe asymmetry. Treatment: please investigate that the three-phase current imbalance is in the allowable range or not. If it is not in the allowable range, please adjust three-phase load or reduce the load.
9. Stator winding short circuit or ground. Treatment: Find out the fault and repair it.
10. External fault or lightning strike. Treatment: if the vibration time is too long, please stop the STG and inspect.
Typical
cases:
This is a 15 MW generator from a Shandong customer. The vibration of generator is reached to 0.12mm in running. After inspection the generator, we found that rotor dynamic AC impedance upheaval 12% in 2400-2700 and the dynamic inter-turn short circuit is serious. It destroys the balance of the magnetic field and causes the electromagnetic force uneven of generator rotor. After removal of the rotor retaining ring and treatment the rotor inter-turns, we start the STG. The vibration is about 0.01mm.
IV. The temperature of a generator is too high.
Generally the temperature of a generator will be in the allowable value, if the generator running normally and the current, voltage, frequency, power, excitation current and power factor are all within the allowable fluctuation range. If a generator stator, core and other parts temperature are too high, please consider the following cases:
1. Generator overload operation and exceed the allowable time. Treatment: Please reduce the generator load to the rated load or under rated load as soon as possible.
2. Three-phase current are serious imbalance. Treatment: please find out the reason of imbalance. If it is the voltage causing, please check if it is the generator inter-turn short circuit. If it is load causing, please adjust the load and make it balance.
3. The ventilation cooling system of generator is poor. For example, the temperature is too high, the air duct or exhaust duct are blocked, the coil and its ends are serious fouling. Treatment: please reduce the load suitability, improve ventilation, and remove fouling.
4. The stator winding portion short circuit or ground. Treatment: Find out the short circuit or ground point and repair them, and then eliminate short circuit or ground risks.
5. Insulation of the stator core may be partially damaged and short circuit, so there is a vortex and overheat. Treatment: please reduce the load suitability. If the generator reduces its efficiency obviously, please repair the generator stator core.
6. The bearing is short of lubricating oil. The oil number is wrong. The oil quality is bad. The bearing is installed with a wrong way or the bearing is damaged. Treatment: please find out the reason and then replace the oil or clean, adjust or replace bearing.
V. Generator rotor ground
Symptom: Generator grounding one point or two points grounding light plate light.
Fault Analysis: Generator rotor winding insulation damage, coil deformity and severe dust and greasy attached in the ends seriously are all leading to the grounding of the generator rotor windings. When the generator rotor winding grounding in one point, there is electrical current pass as the ground does not constitute an electrical circuit.
However, after one point grounded, it is easy of leading another grounding point. If any part in excitation circuit ground, it can form ground fault of two or more points ground. It is very dangerous.
After the failure, the rotor windings are short-circuited. Because of the small winding DC resistance, the excitation current will increase. So the magnetic field of generator is out of balance, and main magnetic flux reduces largely. So the STG will vibrant strongly. Meanwhile the power factor of the generator will be increased significantly and get into leading phase running (absorption of reactive power from the grid).
The stator field becomes in the frond and the rotor field becomes in the back. It will make the stator current increases. If the watcher notice that there is no excitation varying but the excitation current and stator current suddenly increases, and the excitation voltage and AC voltage are all suddenly drop, and power factor meter indicates increasing or leading phase, it means the generator rotor grounded or inter-turn short circuited. You should shut down the STG and blow-out magnetic. Please inspect the excitation system and rotor windings, and find out the short circuit point and treat it.
VI. Excitation upgrading and generator test
Excitation system upgrading, brushless exciter changes into the SCR excitation and make the generator maintenance easily. And it removes the disadvantage of brushless excitation dynamic adjustment slowly. The generator test includes stator insulation resistance test, the absorption ratio test, the iron loss test, leak test, AC and DC voltage withstand test, the rotor high speed balancing and overspeed test, dynamic and static AC impedance test, the generator no-load test, short circuit test, temperature rise test, residual pressure measurement, axis voltage measurement.
Generator Care,Steam Turbine Generator Care,Msw Power Generation,Combined Cycle Generating Unit Shandong Qingneng Power Co., Ltd. , https://www.steamturbine.be
The natural gas heavy truck market has increased by 927%! The industry ushered in the outbreak
The recent heavy truck overall market and natural gas heavy truck market segment are all good and astounding.
According to the production and sales news of China National Automobile Association, in February this year, the domestic heavy truck market sold 86,000 vehicles, a substantial increase of 146% over the same period of last year. In January-February, the cumulative sales volume of the heavy-duty truck market was 169,400, a sharp increase of 136% year-on-year.
At the same time, according to the production statistics of the Ministry of Industry and Information Technology, the domestic natural gas heavy truck market reached 4,119 units in February, an increase of 927% year-on-year. In the January-February period of this year, natural gas heavy trucks produced 6,950 vehicles, a year-on-year increase of 4.8 times, with a net increase of 5,800 vehicles.
The natural gas truck market has experienced explosive growth for several consecutive months. Does it mean that the market has begun to re-enter the rapid development channel?
The natural gas truck market of 2014-2017
Heavy natural gas market grows rapidly for 8 consecutive months
In fact, the growth of the natural gas heavy truck industry did not start from the beginning of this year but showed signs of recovery from the second half of last year. The above chart shows that since July of last year, the natural gas truck market has entered a continuous growth channel. The monthly production increased by 31% year-on-year; in August, the market increased by 128%; in September, it increased by 55%, and in October increased by 117% year-on-year; by November The demand for the natural gas heavy truck market accelerated significantly, with the monthly production up by 314% year-on-year; the market in December rose by 466% year-on-year. For the whole of 2016, the output of natural gas heavy truck market was close to 20,000 units, with a net increase of 7,000 vehicles, a year-on-year increase of 54%. In January 2017, the natural gas truck market grew by 257% year-on-year; in January-February, the market segment was up The increase further increased to 4.82 times.
The analysis of the first commercial vehicle network believes that the natural gas heavy truck market has continued to heat up since the fourth quarter of last year and “high fever does not recedeâ€, which is directly related to two factors. The first is the recovery of the entire heavy truck market. Since October last year, the heavy-duty truck market has been promoted and stimulated by the ultra-superiority policy, which has been on the rise. In the fourth quarter of last year, sales volume increased by 100,000 units, and the year-on-year growth rate reached 33%. In the first quarter of this year, the market continued to grow rapidly. In January-February, the accumulated sales of the heavy truck market reached 169,400, an increase of 136% year-on-year.
As the saying goes, “Owning eggs under the coversâ€, then, conversely, the market as a whole is becoming more and more popular, and the natural gas truck market in which it is located has naturally acquired a historic opportunity for substantial growth.
Oil and gas price difference stimulates rapid market recovery
The second reason for the rapid recovery of the natural gas truck market is the further widening of oil and gas prices. The natural gas heavy truck market hit a bottom in 2015, and its production and sales volume reached the lowest point in history. One of the important reasons is that the price of oil has been declining, and the gas price for vehicles has been rising. The price difference between oil and gas is very small and even in some regions, LNG gas prices have exceeded. With oil prices, the economic advantage of using natural gas heavy trucks has been lost, and users are “voting with their feet†and natural gas models are no longer favored.
However, things are changing. From January 2016 to March 12, 2017, the price of diesel fuel has risen more often than ever, and the number of declines has been small. According to the statistics of the first commercial vehicle network, the price of gasoline and diesel rose 11 times, a drop of 6 times, and the price of 0# vehicle diesel increased by 1 yuan from about 5 yuan per liter at the beginning of last year to the nearest 6 yuan per liter. (The price of 0# vehicle diesel in the Beijing area rose to 6.17 yuan/liter). The overall increase in oil prices (and the future expectations of the society and the public is also rising), the vehicle LNG gas prices have dropped slightly, the oil and gas price difference has begun to widen, and the enthusiasm of users to use natural gas trucks is also recovering.
Under such a good situation, it is not difficult to understand why domestic heavy-duty trucks have recently been single-frequency.
All across the line Liberation, Shaanxi Auto and Dongfeng rank the top three
The natural gas heavy truck market has grown substantially in the first quarter of this year, and the production and sales volume of various mainstream companies has also seen a full-scale gain. In February this year, all companies rose sharply, and cumulative production in January-February was also high. FAW Liberation jumped from the third place in the natural gas truck industry last year to No. 1 in the industry. In February this year, it produced 1225 natural gas trucks, a 12-fold increase; in January-February, it produced 2,099 units, an increase of 797% year-on-year. Shaanxi Auto maintained the second-largest natural gas heavy-duty industry. In February, it produced 780 units, which represented a year-on-year increase of 16.7 times. In January-February, it produced a total of 1,384 units, a substantial increase of 7.65 times year-on-year. Liberation and Shaanxi Auto are also two companies that have produced a thousand output so far this year, with market share reaching 30.2% and 19.9% ​​respectively.
Dongfeng Motor Co., Ltd. has temporarily dropped to the third in the industry from last year's industry first. In February, it produced 611 natural gas trucks, an increase of 413 percent year-on-year. In January-February, it produced 996 natural gas trucks, an increase of 2.94 times year-on-year. The share is 14.3%. China National Heavy Duty Truck Group has maintained its fourth position in the industry so far this year. In January-February, it produced 705 natural gas trucks, an increase of 8.8 times year-on-year, with a share of 10.1%. Heavy trucks and Hualing heavy trucks performed equally well. In the first two months of this year, the cumulative production of natural gas trucks was 542 and 371, a substantial increase of 10 times and 36 times year-on-year, and the rankings also rose to fifth and sixth (2016 Universiade and China) LNG gas trucks rank seventh and eighth respectively in the industry. The eighth joint truck produced a total of 209 natural gas heavy trucks in the January-February period (6th last year for the industry), an increase of 143% year-on-year, and a market share of 3%.
Judging from the current development trend, the first commercial vehicle network believes that since the heavy truck market will maintain rapid growth in the first half of this year, the natural gas truck segment will maintain the current rapid recovery momentum, and the annual production and sales volume is expected to grow by at least 50 percent. %. One of the destabilizing factors is how long the high-speed growth of the heavy-duty truck market will last, and whether the price of oil will rise further.