Large generator low excitation out-of-step and rotor over-voltage protection bookmark0 (China Power Information Center, Beijing rumor synchronous generator without excitation out-of-step operation and abnormal operation in stator short-circuit fault or non-synchronous parallel operation, the rotor circuit will induce higher The AC potential. As the rated voltage of the generator increases with the increase of its rated capacity, and the use of thyristor rectification excitation, the overvoltage problem of the synchronous generator rotor circuit is more prominent. Protection came into being, but due to poor design and component quality, it has caused many faults and accidents, such as 1C machine of Baishan Power Plant, 3 machines of Guangxi Dahua Hydropower Plant, 3C, 4C machine and plump of Fuchunjiang Power Plant The No. 9 machine of the power plant had an accident due to the protection used, resulting in an accident in the generator and the power grid.
Type 2 low excitation out-of-step protection is illustrated as an example. The output power detected from the stator end of the generator when the generator is in steady state operation! As the amount of action and the excitation voltage "1" as the amount of braking from the end of the field winding, "L! The component group plus the slip component and the detecting component and the low voltage component for detecting the voltage of the high voltage side of the main transformer together constitute a BSB-2 type low excitation out-of-step protection device, see.
Set the generator active power to! When the excitation voltage is reduced to the static stable boundary, the excitation voltage is called the limit excitation voltage "L, and the synchronous potential of the generator is called the limit potential. According to the power of the generator, the angular characteristic equation: Bellow (1) is simplified as !: or written as E: the generator is easy to lose step. The high slip component uses S, that is, the stator current period is 5s, when S>2%, the high slip component acts on the trip, and the unit and the system are de-listed. Dropped to 85%, tripped after 0.5s delay.
Generator rotor circuit overvoltage protection bookmark3 substitution! In the case of an abnormal situation such as a shing network, the rotor winding induces a high AC potential. In the past, gap discharge protection was used in China. The main problem is that the gap is difficult to adjust. Because there are too many factors affecting the operating voltage, it is often impossible to automatically extinguish the arc after discharge. After switching to the magnetic blower arrester, although it has an arc extinguishing function, the magnetic blow arrester is easy to explode. For example, the 75 arrester of Luohe Power Plant has exploded 10 in 3 years after commissioning.
The AC power of the 300 MW generator rotor of the CEM factory in France is rectified by the semiconductor and applied to the rotor circuit. The rectifier is not conducting in the reverse direction. When the AC negative half cycle, the semiconductor rectifier is turned off, which is equivalent to applying a high voltage to the rotor coil. Since the inductance of the rotor winding is large, the rotor excitation current changes greatly from the positive half cycle to the negative half cycle, and the rotor winding also generates a self-inductive overvoltage. For this purpose, the large generator rotor circuit is provided with overvoltage protection.
3.1HCK overvoltage protection works The 300MW generator rotor circuit of CEM factory in France adopts HCK overvoltage protection device of Swiss BBG company, for example.
HCK is an electromechanical overvoltage protection device. When the rotor circuit LQ generates an overvoltage, the discharger FD is broken down, the fuse RD is blown by the current, and the spring TH is pulled to close the switch K contact within 5 ms and the FD and RD bypass. It can be seen that the HCK system can prevent the rotor circuit from overvoltage. The main disadvantage is that it cannot be automatically recovered after a voltage action, and must be reset. When a rotor circuit overvoltage action occurs during operation, the rotor circuit LQ can only be determined by the voltage drop across the resistor R before the shutdown process. The arrester FD no longer functions and actually loses the effect of overvoltage protection.
3.2 The varistor crossover method can be automatically reset. 3.2.1 The 125MW generator rotor overvoltage protection device of Gezhouba Power Plant is the overvoltage protection device for the 125MW hydro-generator rotor circuit of Gezhouba Power Plant, which is the product of Sweden ASEA company. It can be seen from the figure that when the voltage of the flip-flop (medium-reverse =) causes KP and KP2 to be turned on, the overvoltage of the excitation circuit LQ is controlled by the SiC varistor.
When the leakage current of the varistor is very small, KP and KP2 are cut off, it seems that the automatic reset of the device can be realized, but in fact, the current of the SiC element is maintained, so the KP can not be automatically reset after the action. Moreover, the SiC varistor has high residual voltage and high power consumption, and can reach 900W during operation. It relies on fan cooling to increase the power consumption of the plant. This device must be improved.
3.2.2 The improved ASLG device is proposed by the Institute of Plasma Physics of Hefei Chinese Academy of Sciences (hereinafter referred to as the plasmonics), ie the SiC varistor in the process, and the zinc oxide (ZnO) developed by the method is used for pressure sensitive The resistor solves the automatic reset and the power consumption is also significantly reduced.
It can be seen that the volt-ampere characteristics of ZcO are significantly better than those of SiO. 0mA refers to the residual voltage corresponding to the current of 10mA; 200A is the residual pressure under high current 200A impact; 200A/! 0mAG", the residual pressure ratio. The high-energy ZnO varistor developed by the plasma is <1.6. It is the peak value of the varistor operating voltage, and Sl is called the charge rate, ie! /! The ratio of 0 mA, the size of Sl determines the life of the varistor. The ZnO varistor of the plasma is specified to have a lifetime greater than 80a when S1% 0.7 at 40K; and a sharp decrease in life if S1>0.7.
The operating voltage of the turbine generator rotor with AC/DC excitation is lower, which can satisfy S1<0.6. 6. The ZnO varistor can be used for bridging. In order to prevent the individual branch ZnO from being broken under abnormal conditions, each branch has a fuse TRD. This method is simple and reliable, Qinghe, nonlinear-characteristic, and the leakage c current is often large (in the thyristor cat) The shingl, è°ç’§ and other power plants have been in operation for many years and are in good condition. It is recommended that the unit with the SiC crossover protection circuit can be replaced by a high-energy ZnO varistor. The improved ASLG type protection will continue to be available. 3.3 Select ZnO pressure sensitive The problem that the resistor should pay attention to is the selection of the varistor voltage, that is, the nominal voltage of ZnO, which is generally marked with -ia, which is the varistor voltage when the current is 1 mA. The peak value of the operating voltage of the varistor -8 refers to the working state. The peak value of the rotor is set at 311V, and the AC voltage is ±5%, and the S/V ion body requires S1%0.6. According to the required calculation, then -/=770, the varistor voltage is selected.
The residual voltage level voltage under the gradation voltage and the surge voltage is also known as the limiting voltage, which indicates the limiting voltage characteristic of the varistor in the working range. Under the specified current, the lower the protection voltage of the positive and negative terminals of the varistor, the higher the protection level. The ratio of this value to the varistor voltage is called the residual voltage ratio and is represented by 0. Generally, there are "1" and several kinds. The Zn of the plasmon is 0<1. 6, which means that the ZnO varistor has better flow capacity than other protective devices, for 8/20! The standard current wave of s, the current density of the charge rate can reach 2000A/cm2 or more. Impulse current capability is an important indicator to measure the pros and cons of varistor. The standard requires 8/20! After the wave impact 2 times, the varistor voltage changes by no more than ±10%. The varistor voltage in both directions after the impact is reduced, and the charge rate increases and the life is shortened when used continuously, so the varistor voltage change rate should be selected to be small. .
3.3.4 High temperature load durability High temperature load durability is the life standard of the varistor under the condition of strong load acceleration. The maximum continuous voltage is applied at 85T for 1000h, and the varistor change rate is 1920.), male, 1945 Graduated from the Department of Electrical Engineering of Zhejiang University.
In 1981, he was awarded the first batch of senior engineers. In 1988, he was awarded the first professor-level senior engineer. In 1992, he was listed as a Chinese power person. He was a graduate master of the Electric Power Academy and the chief engineer of Dianchi Power Plant. He has retired.
Two products of Dongfang Electric won the first prize of Sichuan Excellent New Product and won a prize. On May 7, 2003, the good news came from the Sichuan Industrial Technology Innovation Center. The Lijiaxia 400MW evaporative cooling turbine generator developed by Dongfang Electric Machinery Co., Ltd. and the Iranian 325MW steam turbine generator were awarded the first prize of excellent new products in Sichuan Province. prize.
Evaporative cooling technology is a new technology with completely independent intellectual property rights in China. It has obvious superiority over traditional motor cooling technology. It not only breaks through the limit capacity of air-cooled generator design and manufacture, but also can be used in the capacity expansion of large and medium-sized generators. Pumped storage units have good application prospects. The successful development of Lijiaxia 400MW stator winding evaporative cooling hydro-generator symbolizes that Dongfang Electric Machinery Co., Ltd. is in the forefront of the world's peers in the innovation of new cooling technology for generators, and develops for the development of China's giant hydro-generators and large-scale generator motors. A broad road.
Dongfang Electric Machinery Co., Ltd. designed and manufactured four 325MW steam turbine generators for the Iranian Arak Power Station. It is the largest turbine generator with the largest single unit capacity and the largest installed capacity of the power station in China. It has successfully established China Power Generation. The good image of equipment in the Middle East market.
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