Effect of Series Resistance of Generator Neutral Point on Resonant Grounding in Arcing Coil Grounding

The neutrality of the relay engine accounts for the influence of the series resistance in the grounding mode of the arc suppression coil on the grounding protection of the stator. Bi Daqiang, Wang Xiangheng, Wang Juzhen, Department of Electrical Engineering, Tsinghua University. The series small value resistor in the Beijing 100084 arc coil can play the role of limiting the transmission of overvoltage. It should be noted that the selection of the resistance value should be checked from the compensation capacitor current and the limit transmission overvoltage. The voltage satisfies the stator winding. When required, attention should be paid to verifying the influence of the fundamental zero-sequence voltage stator grounding protection. The analysis shows that this transmission overvoltage can cause the grounding zero-sequence voltage stator grounding protection to malfunction.

1 Introduction It is believed that the neutral point of the vomiting generator can reduce the transient over-voltage by the high grounding mode of the distribution transformer. As the hair machine capacity is large, the core may be burnt when a single-phase ground fault occurs. When the neutral point is grounded by the arc suppression coil, it is theoretically possible to reduce the ground current to a small value, so that the grounding arc is easily extinguished, and at the same time, the recovery voltage is lowered, making the grounding arc difficult to reignite and effectively reducing the grounding arc. Transient overvoltage and small small electric horns in the arc suppression coil also play an important role in consuming transient process energy. Since the zero-sequence impedance is large when the resonant mode is grounded, if a ground short circuit occurs on the high-voltage side of the system, the transmission over-voltage applied to the generator end will be high, which can be transmitted through the series-connected small-value resistor in the arc-suppression coil circuit. The voltage king can be solved within the safe range. It seems that it is difficult to meet the requirements at the same time by comprehensively considering limiting the fault current in the safe ground current range and the cost of the capacitor. Therefore, attention should be paid to the relevant protection setting process. 2 Large generator neutrality The point should be grounded by the arc suppression coil. 2.1 The difference between the ground current and the current flowing through the neutral point. After the single-phase ground fault occurs in the stator winding of the generator, the neutral point is grounded by the high-impedance grounding of the distribution transformer or the arc-suppressed coil. Grounding, ground current is different from current flowing through the neutral point. Single-phase grounding, the current flowing through the point is the current through the grounding squeezing device, and the grounding current is the vector sum of the current flowing through the grounding conductor and the current of the distribution transformer or arc suppression coil. Because the square is proportional, but the current flowing through the fault point is the ground current, not the current flowing through the neutral point. The latter cannot be used as the criterion for determining the allowable value of the single-phase ground current of the generator, flowing through the neutral point. The current action is used to design the capacity of the distribution transformer or arc suppression coil.

2.2 Large-scale generators should adopt a neutral point through the arc-extinguishing coil to connect the place in the early 1980s. The ground current is allowed. Its rated 1 pressure 18 is recognized as above. In combination with the parameters of the gorge generator set, the rated phase voltage is the capacity, = 0.2 estimated value, when the generator stator winding has a metallic single-phase ground fault at the machine end, the current flowing through the capacitance to the ground is in accordance with international practice, when generating electricity When the neutral point of the machine is grounded by the distribution transformer with high resistance, to limit the dynamic overvoltage to 2.6 times the rated phase voltage, the secondary side value of the neutral point grounding resistance should be taken as the 13th generator, and the fault current will exceed when the phase is grounded. Yes, = 31. Such a large grounding current determines that the grounding protection should be instantaneously tripped, but it takes a fixed time to take into account the actual end of the degaussing, which may cause damage to the core. When considering the over-voltage condition, the selection of the central 忭 屯 , , , , , , , 原则 原则 原则 原则 原则 原则 原则 原则 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 限制 选 选 选 选 选 选 选 选The main parameter of the neutral point grounding transformer provided in the grounding protection scheme is that the rated transformation ratio is =200 or 00. The rated boundary is the iron smash when the collapse is broken, and the primary current of the transformer is 5 塍栳 摩 摩 摩 摩 摩. Corresponding to this grounding resistance, the stator insulation of the generator according to the 66 company's scheme continues to withstand 6.5 times the AC rated line 屯1 or more. This squeezing price far exceeds the transient overvoltage that may occur, and transient overvoltages at this high level of insulation do not damage the stator winding insulation. When transient over-voltage is fully considered in generator insulation, the choice of grounding resistance is mainly to limit the neutral point current, and to prevent the transmission over-voltage generated after the ground fault of the high-voltage side of the transformer does not cause the fundamental wave. Zero-sequence voltage single-phase grounding protection is malfunctioning. The grounding current of the ground fault is j52+21.86222.42A, and the generator specified by the tenth is allowed to ground the current and the iron core is also threatened by burns.

According to the experimental results in the literature 561, in the vicinity of the rated frequency, regardless of whether or not the series resistance on the arc suppression coil is taken into account, the transient overvoltage of the arc suppression coil resonant grounding method is inversely smaller than the high pitch local curse.

To maintain the rated frequency for a single-phase ground fault generator, the generator must be networked, and the ground current should be less than the acknowledged. It is the neutral point that is grounded by the arc suppression coil to compensate the capacitor current, so that the ground current is small when the single phase is grounded. In addition, the small resistance in series on the arc suppression coil can play a very good role in limiting the transmission of overvoltage. In this way, based on the above consideration of the grounding current and the transmission of the overvoltage, the neutral point of the gorge generator is more reasonable and safer to be grounded via the arc suppression coil.

3 The grounding current of the arc suppression coil resonant grounding method is transmitted on the basis of the above analysis, and then the gorge generator set is taken as an example to discuss the grounding current transmission overcurrent calculation condition 1 grounding current 1 of the arc suppression coil series resistance resonant grounding; Condition 2 When the commercial system is short-circuited to ground, the value of the single-phase grounding protection transmitted to the machine-side zero-sequence voltage through the coupling capacitor is 5.

The equivalent circuit of fault current and overvoltage transmission when the motor is single-phase ground fault. among them. Arc-suppression coil inductance, the relative winding capacitance of the winding machine is 1.81叩, the generator end to the main transformer! 1 device is low. 1 The relative capacitance between the windings is 0. 10,000, the coupling capacitance between the high and low voltage windings of the main transformer is 0.00685; the Uy generator is rated for deduction. 120 force; the maximum fundamental zero-sequence voltage when a ground fault occurs on the 7-voltage side, which is taken as 0.5X500j3=144.

34kY; U0 high voltage system short-circuit current through the current through the capacitor; flow through the arc suppression coil, calculate the fault current equivalent circuit, calculate the equivalent circuit of the transfer over-electricity, if the arc-suppression coil resistance is ignored, the arc-suppression coil is grounded in a resonant manner The impedance of the generator to the ground is infinite. When the high voltage system is short-circuited, it will generate a high transmission over-voltage, which is almost all added to the generator winding. This transmission of the electric jade will damage the stator insulation and cause the fundamental zero-sequence voltage. Ground protection must be misplaced. Connecting an appropriate resistor in series in the arc suppression coil branch reduces the transfer overvoltage. After the arc suppression coil is connected in series with the resistance core, the condition of the parallel resonance is zero.

2. Calculate the inductive reactance of the arc suppression coil is = 526, the series resistance value is 1 = 24, and the ratio of the current team = 46.7. Although the transmission overvoltage limit is within the maximum allowable value of the generator to ground voltage, the generator is rated. Line voltage, but the fundamental zero-sequence voltage protection is calculated according to the conditional check condition, and the inductive reactance of the arc-suppressing coil is calculated as the value of the series resistance = 446.5 and the phase 19 turbulence = 9.35 condition 1 can not be satisfied. If condition 2 is properly reduced, the sensitivity of the fundamental zero-sequence voltage protection is recognized as = 10, and then the condition is calculated. 1. Calculate Az = 505.Ri 8., = 4.67. It can be seen from the above calculations that it is difficult to achieve both conditions simultaneously after the series resistance.

The basis for this is that the selection of the small resistance ensures that the limit transmission overvoltage is within a safe range, and the compensation effect of the arc suppression coil causes the fault current to be within the range of the safe ground current, so the drinking heart is not damaged during the delay period. 5, the example of misoperation caused by over-voltage transmission is analyzed. At 30:58 on May 29, 1998, the stator single-phase grounding protection malfunction was analyzed. The rated capacity of the generator is 31 rated voltage is 20, the neutral point is grounded by the arc suppression coil, and the capacitance current is 2.25. The arc suppression coil compensates the turbulence to 2.47. The overcompensation method is not appropriate. As the maintenance personnel are dealing with the low-voltage side of the high-rise plant, the over-voltage is transmitted in the generator voltage system, resulting in a high displacement voltage at the neutral point of the generator, and the secondary side value. 9, the 3 sets of stator grounding protection is mis-operated.

Example Zhangjia 1 Power Plant 1 Generator April 22,216, 58 min. Stator grounding protection misoperation caused the generator set to trip, the main steam valve of the steam turbine was closed, and the boiler was extinguished. The rated capacity of the generator is 20, and the rated voltage is 18 teams. The neutral point is grounded by the arc suppression coil in overcompensation mode. Stator grounding fundamental zero-sequence voltage protection setting value is 1 sink, delay 48 action. After the generator was turned off for more than ten minutes, the operator found that there was a fire at the motor of the condensate pump, indicating that there was a grounding phenomenon. After checking the secondary equipment without abnormal conditions, it is basically determined that the low-voltage side of the high-voltage plant is grounded and the zero-sequence voltage of the generator is abnormally high. By testing two different grounding points on the low-voltage side of the factory, the fundamental zero-sequence voltage is found. From the normal time of 4. respectively, to 13.1 and 13.7., make the fundamental wave;

From the above two examples of misoperation, it should be noted that from the perspective of preventing overvoltage, the grounding method of the neutral point via the arc suppression coil should adopt the under-compensation method, and should not adopt the over-compensation method; Grounding Due to the high zero-sequence voltage, it is easy to cause the fundamental zero-sequence voltage stator grounding protection to malfunction. The high-voltage-to-low-voltage grounding fault can also generate a high transmission overvoltage to cause the fundamental zero-voltage protection to malfunction. Therefore, the simple fundamental zero-sequence rolling protection delay action can not be ignored to prevent the instantaneous grounding of the main transformer high-voltage side or the high-voltage low-voltage side of the main transformer, and the stator grounding protection is malfunctioned. Such as long, intermittent and permanent such ground faults can not prevent misoperation by simple delay action, should match the protection action time between the extension and the high-voltage side ground short circuit, or use the main transformer high-voltage side and The zero sequence voltage generated when the high factory changes to the low-voltage side ground fault is used as the braking amount of the generator fundamental zero-sequence voltage grounding protection. In this way, it is necessary to introduce the input of the other side of the transformer in the grounding protection of the generator stator. However, since the microcomputer protection of the current generator set is mostly installed on the ± screen, the corresponding transformer input is not introduced in the grounding protection. Difficult, 6 conclusions To reduce the fault current during single-phase grounding, the neutral point of the large hydro-generator should be grounded via the arc-suppression coil, but it also brings about the excessive transmission over-voltage caused by the short-circuit on the high-voltage side. By connecting a small value resistor in the arc suppression coil, the overvoltage can be limited, but the influence of the transmission overvoltage caused by the coupling capacitor on the fundamental zero-sequence voltage grounding protection can not be ignored. When selecting the resistance value, mutual sense must be obtained. In the process of 揠 作 , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , The electric card is used for braking. Achieve protection against misoperation.

Nl wants to rejuvenate. Discussion on the neutral point grounding method of hydroelectric generators. China Electric, Wang Weiwei. Principle and application of relay protection for main equipment. Beijing China Electric Power Press. 1998.

Wang Weiwei. Liu Junhong. Tang Lianxiang. Wait. From the point of view of the safety of the gorge generator set, the neutral point grounding method of the unit is analyzed. Power automation equipment. 1995.

4 Li Yijun. Selection and calculation of neutral point grounding method for generators in Xia'an left bank power station. Hydropower. 199944850.

6 Li Yuliang, Li Yixiang, Wang Xiangyu. Neutral grounding transient study of large generator stator. Power Automation Equipment, 1999, 19415.

7 Li Guomin, Meng Chonglin. Cause Analysis of Grounding Protection of No. 2 Generator 3 Stator of Shanxi Sunshine Power Generation Co., Ltd. Shanxi Electric Power Technology, 20023435.

Wang Zhongyu, 1940, male, professor, doctoral tutor, mainly engaged in motor analysis and control of motor faults and protection; Wang Juyi 1930, male, professor, has long been engaged in the teaching and research of relay protection of electrical main equipment jobs.

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