Several questions in the protection and setting of generators and transformers for power automation equipment Cai Guangde Tongling Power Plant, the setting value of the Tongdi 24412 Youdi unit in Anhui Province, caused many hidden dangers and at the same time, the understanding of the setting principle was impervious, resulting in incorrect value. Doubt about the feasibility of some tuning principles in the development of the group. For some deep-protection coordination and actual field 774 document identification code; article number 10066 to 72.16102 1 transformer differential protection large-scale generator transformer relay protection setting calculation guide, proposed for 220,5001 transformer longitudinal differential protection Technical requirements When the transformer is overexcited, the differential protection should not malfunction.
The modern large-scale transformer core adopts cold-rolled silicon steel sheet, and its magnetization characteristics are very hard. The manufacturer will save the material and obtain a higher rated magnetic density. This is the excitation current of the card changer caused by over-excitation. Will surge, and differential protection minimum operating current, usually selected according to 24 times rated current, when overvoltage 3040, the excitation current can reach the rated current of the transformer, the current flows into the differential circuit, and there is no braking effect, so differential protection Inevitably, in this case, 6 should consider how to avoid the malfunction of the differential protection.
2 屯 machine stator overload generator inverse time limit overcurrent protection inverse time trip characteristic upper limit turbulence according to the end of the phase of the gold flexion short circuit, set 0.8; and the generator secondary transient reactance unsaturated value Change ratio.
Usually, the calculation using this formula does not occur. However, it is connected to the generator set of the infinite fire system. The system oscillates because the secondary transient reactance of the large unit is not much different from the transient reactance, and the impedance of the transformer is small, causing the oscillation center to fall into the generator. The reactance value of the generator is proportional to the number of turns and oscillates. The current increases sharply with the oscillation center deep inside the generator. At this time, the oscillating current will be larger than the metal short-circuit current of the machine phase. As a result, the short delay of the upper limit quick-break may not be able to escape the oscillation and cause malfunction.
Therefore, the upper limit current of the inverse time tripping characteristic should also take into account the vibrating current when the unit and the system oscillate. 3 The generator diurnal protection The 125 unit of the Tongling Power Plant is protected by a high filtering ratio for the subharmonics. Type zero sequence voltage relay implementation.
In the second external fault shortly after the start of the No. 1 machine, the protection of the daytime misoperation caused the protection of the No. 2 machine No. 2 to be put into operation.
The newly-introduced 300, the unit uses the 801 type microcomputer protection, the daytime protection uses the longitudinal zero-sequence voltage to protect the daytime, and the sensitive section and the sub-sensitive section. The sensitive section has a small fixed value, which reflects the short-circuit åŒ short inter-turn short circuit. The setting principle is based on the maximum fundamental unbalance of the normal operation and the short-delay exit. Daytime protection zero-sequence voltage setting, there is information introduced by some authoritative people simply recommend to take 23 actual adjustment, must take into account the mining of a branch of the twin-branch stator winding phase of the mining, if not found in time is very likely Damage to the generator, so the inter-turn short circuit protection is required to have an appropriate sensitive section when the stator winding is open.
The welding of the stator windings of the generator stator branches causes the magnetic field distribution of the stator windings to be no longer symmetrical. Due to the mutual inductance between the bars, the zero-sequence voltage cannot be accurately calculated. According to the practical calculation method, the 13.300 unit is opened at full load. Welding time; sequence voltage 3,7, is 6, for zero sequence voltage turn-to-turn protection, the critical load current value of the device is required to be 0.390.55, and the zero sequence voltage is calculated to be 2.343.3. Actual timing, Take the action positioning as 3, ensure that there are 20 people 1=63, the sensitivity coefficient, 4 overexcitation protection protection action caused the generator to jump twice and explain that the 2201 bus voltage reaches 242, that is, it is installed on the bus side. The value of the overexcitation protection is set to 220. After the 220th policy, it is considered that the setting value is wrong, and it is adjusted to 1.1 which is determined by the 2201 bus voltage. In particular, how to set the value, can not guarantee the correctness of the action, because the power plant 22 cut bus bus card is not only with the delivery. And related to the system voltage line parameters. When the main transformer No. 7 is over-excited, it may cause the bus voltage to increase, but whether it can reach the value of over-excitation protection, the system voltage is also checked. The line parameters are, therefore, the over-magnetic protection should not be installed on the side of the busbar, but should be installed at the exit of the hairpin machine, and the generator will be cut and ripped, and the ignorance will be known. , 1 magnetic characteristics are set.
In addition, for the setting of the inverse time curve of overexcitation protection, when the data + foot, many data recommend the formula =, 2, like the result of this type of juice calculation, the value is questionable.
According to the same type 4 introduced the foreign technology wood production of the hair dryer also provided him also curve. The overexcitation multiple and the logarithm of the factory at the time of the 1st time strictly meet the linear decreasing relationship. That is, the magnetic multiple is incremented by the equal difference, and the action time is decreased by the equal ratio. In the setting range, it is more in line with the time-accumulated effect characteristics of overexcitation.
In the tuning guide, the generator overexcited 1.1 times the signal and 1.3 times the trip; the allowable overexcitation capability of the transformer is higher than that of the generator. The setting is considered by a hair dryer with a low overexcitation capability.
According to this, the Tongling Power Plant did not provide the generator overexcitation curve for the manufacturer, and inserted and fitted the other fixed points with the data of 1.1 times 558, 1.2 times 68 provided by the same capacity unit of other plants. The overexcitation multiple is incremented by 0.025 step, the time is calculated by 155614, which is 1.74, and when it is greater than 1.325 times, it is tripped by 0.358. For an overvoltage greater than 1.325 times, the action time of overexcitation is no longer set to 358. It is considered that the differential protection will act. Therefore, the differential protection is protected by the over-excitation protection. How to restore the excitation when the excitation switch is falsely jumped or the excitation can be restored. Most power plants are considered. It is usually handled as an accident. On May 29, 2000, the excitation switch of No. 1 generator of Tongling Power Plant tripped, and the generator was demagnetized. Then the operator 1 reversed the power consumption of the plant and solved the operation of the generator.
In fact, after the generator is demagnetized, it is in an asynchronous state with the system, and the larger the load, the larger the slip. Reducing the load of the generator, reducing the slip, and facilitating the rapid pull-in synchronization after resuming the excitation; on the other hand, reducing the load can reduce the reactive power absorbed from the system and is beneficial to maintaining the system bus voltage and the factory bus voltage. After the large generator is demagnetized, it is necessary to quickly reduce the load of the generator and reduce the load to 50. During the period of the allowed operation, the excitation regulator is switched from the automatic cabinet or the moving position to the manual cabinet or the manual position. . Reduce the secondary excitation output to a minimum. Close the excitation switch. Gradually, add excitation. The generator is quickly synchronized. Then, according to the normal load, it is paid to the No. 300 unit of Tongling Power Plant; the company's 840 excitation regulator has a minimum excitation voltage of 50 no-load rating. In this case, the load is reduced as much as possible and then the lowest excitation. Voltage combined with 1 excitation switch. Gradually increase the excitation and resume normal operation. During the trial operation of the 300 units, when the generator is under low excitation limit, the demagnetization protection action. The low-excitation loss-of-magnetism protection is initially set according to the static and stable impedance circle, and the calculation result just falls into the boundary of the impedance circle. After that, according to the output line of the hair dryer. With 3001 work, reactive power 4151 is the boundary point between the phase and the demagnetization, 501 is the demagnetization, and the impedance calculated by the brother for the phase is slightly smaller than the static circle. = The asynchronous impedance circle is not used here because it is unstable. There is a period of time to the asynchronous impedance circle, and the action is late.
It is recommended that the impedance rounding be set to a small point if the static and stable impedance circle is not satisfied, but it is not necessary to use an asynchronous impedance circle.
6 Low-impedance protection The principle of setting the low-impedance protection of the power plant installed on the high-voltage side of the generator-transformer should be clearly defined using an impedance relay with an offset direction.
The square points to the transformer in the opposite direction to the busbar. The large unit generator and transformer group protection is equipped with double fast main protection. The double fast main protection consisting of the generator differential protection main transformer differential protection and the generator transformer group, the protection zone extends only to the high voltage side bus current transformer, in order to eliminate the transformer between the high voltage side current transformer and the circuit breaker The dead zone and the backup as the busbar protection, the low-impedance protection is installed on the high-voltage side of the main transformer, so that the busbar protection is doubled.
Il Wei, Meng Qinghe, Song Jicheng and so on. The calculation guide for the relay protection of large generator transformers is elbow. Beijing China Electric Power Press, 2000.
2 Wang Jingjun. Book 201 Microcomputer generator group protection application summary China Electrical Engineering Society main equipment relay protection sub-committee first academic conference proceedings Haikou China Electrical Engineering Society main equipment relay protection sub-committee, 2000.1080.
Responsible editor Su Li Cai Guangde 19650, male, Hefei, Anhui, engineer, engaged in on-site relay protection setting calculation work.
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