Effect of Series Resistance on Grounding Protection of Stator in Neutral Point of Arc Generator at Arc-suppressed Resonant Mode

The Effect of Series Resistance on the Grounding Protection of the Stator in the Neutral Mode of the Reciprocating Coil Resonance Ground of the Relay Generator Bi Daqiang, Wang Xiangheng, Wang Jue Department of Electrical Engineering, Tsinghua University. Beijing 100084 arc coil series small value resistor can play a role in limiting the transmission of overvoltage, it should be noted that the choice of resistance of the resistor should be checked from the compensation capacitor current and limiting the transmission overvoltage in the coupling capacitor caused by the transfer of When the voltage satisfies the stator winding requirements, care should be taken to verify its effect on the reliability of the fundamental zero-sequence voltage stator grounding protection operation. The example analysis shows that this over-voltage can cause misoperation of the fundamental zero-sequence voltage stator grounding protection.

1 Introduction It is generally believed that a large vomiting generator neutral point can reduce transient overvoltages by using a high transformer grounding method. With a large capacity, a single-phase earth fault may burn the core. When the neutral point is resonantly grounded by the arc-extinguishing coil, in theory, the grounding current can be reduced to a small extent, so that the grounding arc can be extinguished easily, and at the same time, the recovery voltage is reduced, so that the grounding arc is difficult to reignite and thus effectively reduces Transient overvoltages and small-to-small electrical pads in the arc suppression coil also play an important role in consuming transient process energy. Because the zero-sequence impedance is large when the resonant mode is grounded, if the ground fault occurs on the high-voltage side of the system, the over-voltage applied to the generator terminal will be very high. This can be limited by connecting the small value resistor in series with the arc suppression coil circuit. The voltage king is solved within the safety scope, it seems that it is difficult to meet the requirements at the same time because of comprehensive consideration of limiting the fault current within the safe grounding current range and the cost of the combined capacitance. Therefore, attention must be paid to the relevant protection setting process. 2 Large-scale generator neutrality The point should be adopted arc suppression coil grounding method 2.1 The difference between the ground current and the current flowing through the neutral point After the single-phase grounding fault of the stator winding of the generator, whether the neutral point is through the distribution transformer high-resistance grounding or the arc-extinguishing coil Grounding, grounding current and current flowing through the neutral point are different. Single-phase grounding, the current through the point of flow is the current through the grounding crowbar to eliminate the arc, and the grounding current is the vector sum of the current flowing through the earth's boundary and the current of the distribution transformer or the arc suppression coil. Because the square is proportional, 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 a criterion for determining the permissible value of the single-phase earth current of the generator. It flows through the neutral point. The current action is used to design the capacity of the distribution transformer or the arc suppression coil.

2.2 Large-scale generators should adopt a neutral point arc-suppressing coil to connect local generators that were developed by relevant departments in the early 1980s. Phase current allowed. Its rated 1 pressure 18 recognized above. Combining the parameters of the gorge generator set, the rated phase voltage is a capacity of 0.2 and the estimated value is 0.2. When the generator stator winding has a metallic single-phase earth fault at the machine end, the current flowing through the capacitor to ground is in accordance with international practice when generating electricity. When the neutral point of the machine is high impedance grounded by the distribution transformer, in order to limit the dynamic overvoltage 2.6 times the rated phase voltage, the secondary value of the neutral point grounding resistance should be taken as 13 generators, the fault current will exceed the N, = 31. Such a large grounding current set the grounding protection to be instantaneously actuated on the trip, but taking into account the actual de-excitation end requires a fixed time, during which the core may be damaged. When considering the over-voltage condition, the principle of selecting the center resistance should be to minimize grounding power under the condition of limiting dynamic overvoltage under the safe range. The main parameters of the neutral point grounding transformer provided in the grounding protection scheme are the rated change ratio = 200. 00. The rated area is the collapse of the Zhangzhou Iron and Steel Company. The original side current of the Mozhe space transformer is = 5 people. . Corresponding to this grounding resistance, the stator insulation of the generator according to the company's plan of 66, continues to withstand 6.5 times the AC rated line Tuen 1 or more. This settling price far exceeds the transient overvoltage that may occur, and transient overvoltage in this high insulation level will not damage the stator winding insulation. When the transient overvoltage has been fully considered in the generator insulation, the selection of the grounding resistance is mainly to limit the size of the neutral point current, and to prevent the occurrence of a ground fault on the high voltage side of the transformer, the generated overvoltage will not cause the fundamental wave. Zero-sequence voltage single-phase grounding protection malfunction. According to the earth fault grounding current is j52 +21.86222.42A, but also the big ten specified generator allowed grounding current fixed core also suffers from the burn.

According to the experimental results in the document 561, in the vicinity of the rated frequency, regardless of whether the series resistance on the arc suppression coil is taken into account, the transient overvoltage of the arc suppression coil resonant grounding method is not as high as the high voltage local resistance.

To maintain the rated frequency for a single-phase earth fault generator, it must be the generator's networked operation, and the ground current should be less than this. It is the neutral point that is grounded by the arc-extinguishing coil to compensate for the capacitive current, so that the ground current is very small when the single-phase ground is connected. In addition, a small series resistance on the arc suppression coil can play a very good role in limiting the transmission of overvoltage. In this way, on the basis of comprehensive consideration of the ground current and the transmission overvoltage, the neutral point of the canyon generator is more reasonable and safer via the arc suppression coil.

3 Arc suppression coil grounding current grounding and transmission on the basis of the above analysis, and then the case of the gypsy generator set as an example to discuss the arc suppression coil series resistance grounding ground current transmission conditions under the calculation conditions 1 ground current 1; Condition 2 Operational value of the single-phase grounding protection of the zero-phase voltage transmitted to the end-side wave through the coupling capacitance when the commercial pressure system is short-circuited to ground.

Equivalent circuit of fault current and transfer overvoltage in single-phase earth fault of motor. among them. Arc-extinguishing coil inductance, the capacitance of the machine winding each relative to the ground is 1.81叩, the generator terminal to the main transformer! 1 device is low. 1 each relative capacitance between windings 0. Million, 1 coupling capacitance between high and low voltage windings of the main transformer 0.00685; Uy generator rated deduction. 120 force; 7 pressure side of the maximum fundamental zero-phase voltage when the ground fault occurs, taken as 0.5X500j3 = 144.

34kY; U0 high-voltage system through the short-circuit current through the capacitor current; flow through the arc suppression coil, calculate the fault current equivalent circuit, calculate the equivalent circuit to pass the over-charging if you ignore the arc suppression coil resistance, arc suppression coil resonant grounding The impedance of the generator to ground is infinite. When the high-voltage system is short-circuited, it will generate a high transmission over-voltage, almost all of which will be added to the stator winding of the generator. The transmission of electricity will damage the stator insulation, and cause the fundamental zero-sequence voltage. Ground protection must be mistaken. Connecting a suitable resistor in series with the arc suppression coil reduces the overvoltage. After the arc suppression coil is connected in series, the parallel resonance condition is zero.

2. The inductive reactance of the arc suppression coil is calculated as = 526 and the series resistance value is 1 = 24, while the ratio team = 46.7. Although the transmission overvoltage is limited within the maximum allowable value of the generator earth voltage, it is the rated value of the generator. Line voltage, but zero-sequence voltage protection of the fundamental wave Secondly, the inductive reactance of the arc-extinguishing coil is calculated as the series resistance value along the =446.5 and =19 when the condition of the earth ground current =9.35 condition 1 is also satisfied. If the condition 2 is properly reduced, the sensitivity of the zero-sequence voltage protection of the fundamental wave is taken as 10, and then the conditions for the verification are 1. Calculate Az = 505.Ri 8., = 4.67. From the above calculations, it can be seen that it is difficult to achieve the two conditions at the same time after series resistance.

The basis for this is that the selection of small resistors guarantees that the transmission overvoltage is limited within a safe range, and the compensation effect of the arc suppression coil makes the fault current within the safe grounding current range, so the drinking water will not be damaged during the delay period. 5, Cases of misoperation caused by over-voltage transfer Example Example At 20:58 on May 29, 1998, 3 single-phase ground fault protection of the stator was analyzed. The rated capacity of the generator is 31 rated voltage is 20, the neutral point is arc-suppressed coil grounded, the capacitor current is 2.25 and the arc suppression coil compensation Tunliu is 2.47. It is not appropriate to overcompensate. Because the maintenance personnel are dealing with the high-voltage plant in the low-voltage side, there is an overvoltage in the generator voltage system, resulting in a very high displacement voltage at the neutral point of the generator. 9, so that the 3 partner grounding protection malfunction.

Example Zhangjia 1 Power Plant 1 Generator April 22, 2216 April 2001 Stator Ground Protection Malfunction caused the generator set to trip, the main steam valve was closed, and the boiler was extinguished. The rated capacity of the generator is 20, and the rated voltage is 18 teams. It is not appropriate for the neutral point to be grounded via an arc suppression coil in over-compensation mode. The ground zero-sequence voltage protection of the stator ground is set to 1 and delay 48. More than ten minutes after the generator tripped, the operator discovered that the condensate pump motor had a fire, indicating a grounding phenomenon. After checking the sub-equipment with no abnormality, it is basically determined that the zero-sequence voltage anomaly of the generator caused by the high-voltage transformer is grounded. After passing the test, two different grounding points are selected on the low-voltage side of the plant and the fundamental zero-sequence voltage is found. From the normal time of 4. respectively, to 13.1 and 13.7., so that the fundamental wave; catty electricity protection malfunction.

From the analysis of the above two examples of misoperation, it should be noted that from the perspective of preventing over-voltage, neutral arc suppression coil grounding method should adopt under-compensation mode and should not adopt over-compensation mode; not only main transformer high-voltage side Grounding due to the high zero-sequence voltage is easy to cause the fundamental zero-sequence voltage stator ground fault protection, high-voltage transformer side ground fault can also produce high transmission over-voltage zero-voltage protection of the fundamental wave voltage protection misoperation. Therefore, the simple fundamental zero sequence protection delay action cannot be ignored. It can only prevent the momentary ground fault in the main transformer high-voltage side or the high-voltage transformer side, and the stator grounding protection can malfunction. For example, a long, intermittent and permanent ground fault of this type cannot be prevented by misoperation due to a simple delay action. It is necessary to match the protective action time between the short circuit and the high voltage side ground fault, or to use the high voltage side of the main transformer. The zero-sequence voltage generated when the high-voltage generator is changed to the ground fault at the low-voltage side is used as the braking amount for the zero-sequence voltage ground protection of the generator fundamental wave. In this way, it is necessary to introduce the input of the other side of the transformer into the stator grounding protection of the generator, but the current microcomputer protection of the transformer group is mostly installed on the ±, protection screen, so the input of the corresponding transformer input in the ground protection is not Difficulties, 6 Conclusion To reduce the fault current in single-phase grounding, the neutral point of a large hydro-generator should be earthed through the arc-extinguishing coil, but at the same time it also brings about the over-voltage of the over-voltage caused by the short-circuit to the high-side ground. By passing a small value resistor in series in the arc suppression coil, the transmission overvoltage can be limited, but the influence of the transmission overvoltage caused by the coupling capacitance on the zero-sequence voltage grounding protection of the fundamental wave can not be ignored. When choosing the resistance value, the mutual inductance must be observed. During the process of setting up the system, the process of setting up the relay, Sen, this shop, the full range of pressure and ground pressure protection should consider the influence of the transmission overvoltage on the reliability of its operation, through the delay and the other side of the adjacent transformer zero sequence. Electric card for braking. To prevent protection from misoperation.

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Gas main equipment relay protection research; Wang Xiangqi 1940, male, professor, doctoral supervisor, mainly engaged in motor analysis and control of motor failure and protection; Wang Jue 1930, male, professor, has long been engaged in electrical main equipment relay protection teaching and research jobs.