Natural Science Research = Influence of Negative-sequence Current on Generators Jiang Wenlin, Department of Electrical Engineering, Panzhihua University. Factors related to the ability of Panzhihua 617000 and proceed from the characteristics of negative sequence current formation. The requirements for the implementation of generator negative sequence current protection are proposed. The development of China’s power industry has entered the stage of development of large power grids and large generating units. The nationwide 500 transmission backbone network is forming a large-scale generating unit with a capacity of 200,600 and over. It has become the main power unit of the power grid, and the safety of power grid operation has become increasingly prominent; The machine is responsible for the normal operation of the grid and the main adjustments under the accident conditions. It is the heart and soul of the power grid. Its operational reliability directly affects the operation of the grid and the safety of the power supply. However, there are many accidents during the operation of the generator. The nature of the accident is serious and the loss is huge. In the main accident of the generator, the condition of the negative sequence current burning rotor occurs frequently. With the continuous expansion of the capacity of the power grid unit, the negative sequence current has become an important restriction factor for the safe operation of the generator, especially the large generator. This paper analyzes the different characteristics of negative sequence currents and analyzes their influence on the timing of the occurrence. On this basis. The requirements for the current protection of the rotor layer of the generator generator are presented. 1 Analysis of damage characteristics of the generator rotor by negative-sequence current The negative-sequence current generates a reverse synchronous rotating magnetic field between the air gaps of the stator rotor of the generator, and the rotor rotates in the forward direction, so the rotor Compared with the negative-sequence rotating magnetic field, it has twice the synchronous rotation speed. This magnetic field induces double-frequency current in the winding windings of various parts of the rotor surface, including large-toothed small-toothed slot wedges and guard rings and other windings. Since the rotor of the turbo-generator is single forged and has a strong damping effect, the component of the double-frequency current induced in the excitation winding is very small; and because the frequency-doubled current has a strong skin effect, the rotor surface Infiltration only a few millimeters of the flow path is the same as the medium-valued active resistor, so when the generator is running asymmetrically, the rotor surface will have a larger additional loss and a significant thermal effect. The negative-sequence current flow path is concentrated near the transverse grooves of the large-toothed magnetic poles toward both ends thereof, and passes through the groove windings of the respective sections through the groove wedges, and the damper rings flow along the circumferential direction under the guard ring. Asymmetrical failure around the rotor occurs at home and abroad. The rotor-induced frequency multiplication current is at the contact surface between the rotor end retaining ring and the rotor body wedge surface. Groove wedge connection area Damping ring and damping strip etc. Localized high temperatures in the shunted areas will cause localized high temperatures and will burn the rotor. In more serious cases, there will be melting or fatigue cracks in the above areas, such as turbulence, the temperature difference between the body and the ring will be too large, and it will also lead to loose ring. 1 Causes the damage of the machine to be severely damaged, and the characteristics and countermeasures of the formation of 2 negative-sequence currents. The normal operation of the power system is commensurate with the symmetrical phase impedance of each phase of the power supply potential. When the system or generator is in symmetry, palladium is destroyed. There will be a non-payment of phase voltage or current, and the mountain and inch components method can be decomposed into a negative current of 12 and a zero-sequence current. Since the generator is often star-connected, and the neutral point is not grounded or grounded by the impedance, Zero-sequence current According to the characteristics of power system operation, the influence of negative sequence current is analyzed in the following two cases: 2.1 Long-time asymmetrical operation 2. Long-term causes, asymmetrical load, such as extensively used railway electrical machines Metallurgical single-phase arcs Large-capacity single-phase loads, such as furnaces, create large negative-sequence currents and affect generators that are close to these loads. 2 The impedance of the transmission network is asymmetrical, such as maintenance and repair of the high-voltage line without phase failure; low-voltage power grid is provided with two phases and the power supply mode. 2.1.2 The ability of generators to withstand negative sequence currents for long periods of time. The increase in the capacity of a single turbine generator depends on the size of the large motor, and on the other hand, the improved cooling method improves the material utilization rate. Therefore, the electrode size does not increase proportionally with the capacity. Therefore, the thermal load on the rotor surface of a large-sized unit is correspondingly increased. In addition to the thermal load generated by the excitation current, plus the addition of the air-gap magnetic denser harmonics, the thermal 6-reservoir generation in the production converting surface is increased, for example. Guoguang Power Co., Ltd., your turbine, magnetic dense generator, due to the stator line load is high, the negative heat generated by the negative sequence current should be reduced accordingly. The turbine generators manufactured by various plants in various countries bear long-term negative-sequence current limit values ​​based on the rated current, which is generally equal to 1 沱, 12 0.05, and 60,000 in China. The large flash generators differ greatly due to the differences in the internal motor manufacturing technology and power systems. Judging from the operational needs of the power system, there are large asymmetrical load power systems such as railway electric locomotives. Sentences of these electrical loads that are closer to the load. A negative-sequence current that may withstand generations of negative-sequence capability, causing rotor damage accidents; desirable = 1.070.105 in other cases 1. = 0.040.06. However, due to differences in generator stator rated line load, the rotor material and allowable The difference in temperature rise and the difference in the normal heat load of the rotor make it possible for generators of the same capacity class from different manufacturers to have different values. Therefore, the generator's actual ability to withstand negative-sequence currents for a long period of time needs to be verified by the negative-sequence current test. 2.1.3 Negative-kilometer current protection constitutes condition 1. The operating criterion is that the generator should withstand long-term negative-sequence current capability requirements. It should be in China. The Standardization Committee of the Rotary Electric Machinery recommends the long-term maximum allowable temperature of 130 as the negative sequence current test standard; the value obtained from the test is used as the basis for setting the negative sequence current protection. 2 Protection Operation Requirements When the negative sequence current exceeds 12, the protection device must operate reliably and emit an acousto-optic signal so that it can be processed in time; when its duration reaches the specified value and the negative sequence current has not been eliminated, it shall act on Cut off the generator. 2.2 Short-time asymmetrical operation 1 Formation reasons 1 Asymmetrical faults in the power system include + short-circuit and phase-to-phase faults; 2 Generator + faults including single-phase two-phase short-circuits, short-circuits in branches, and short-circuits in turns; 3 Single-phase overlap Explain the action process; 4 In the normal and fault conditions, the outlet circuit breaker cannot fully close or open the action process. 5 In the normal and fault conditions, the high voltage side of the main transformer is open, and all the actions cannot be completed or disconnected. 6 When the output breaker is accidentally tripped, the extinction switch fails to extinguish the arc for some reason. 2 The generator is subjected to a short, split-sequence capability analysis. When analyzing the short-time listening current capability of the generator, the action time is very short, the rotor is considered as an insulator, and the frequency-doubling current generated by the negative-sequence magnetic field flows only in the rotor body and the wedge surface, and all the losses are used in the analysis. Transferring temperature rose. Neither thermal radiation to the old medium nor heat transfer to the center of the shaft of the rotor to define the negative heat of the rotor when the generator rotates, the negative heat current constant of the rotor is negative at the negative current of the generator. The product of the square and duration, in seconds, is 3. When the resulting heat effect color of 12 duration is 9, the generator can operate safely. For domestic generators, provision is made for indirect-cooled turbo-generators, taking 30; indirect-cooled hydro-generators, taking = 40, direct-cooled generators with very small values, 30 and, = 8.6 million = 7 national standards; 7064 86 stipulates that the generator stator line load is higher than indirect cooling type. 3 protection features. 1 From the above analysis, it can be seen that in order to adapt the generator to bear the short-term negative sequence current capability, its negative, flow, and operating criteria are analyzed by the Lingchi force system's operation value requirements and the work scale limitation. The face of the shortest case of the shortest case for analysis Assuming two-phase short-circuit at the machine side, analysis of the main protection and backup protection, respectively, the negative sequence current thermal effect 1 main protection action quickly sweat. breaker. The fastest rapid demagnetization is given by 2 5 for irreversible products; it is 4.0; the magnetic field switch is at 14, and the current interruption is required, and the interleaver 1 is set to 3.51 for the residual magnetic effect of the demagnetization process. According to the positive-sequence equivalent rule, from it, the thermal effect of the printing ink is defined as Hou Zhengzheng 12 to take the generator temporary resistance average bit 1=0.2, and the negative cathodic reactance to take the big bit=1.22 then the turbine generator, such as 600,000 Jia, GB, 8706486 regulations, = 7, is bound to reduce the stator rated line load, which will inevitably lead to excessive increase in the size of the unit, can not meet the manufacturing cost requirements. The conclusion is that this should be managed from the operational side. The simplest and most effective method is to abandon the long-range backup performance of large-scale generators and meet the motor manufacturing requirements. 3 Conclusions 1 The only basis for setting the rotors of the rotors with negative sequence overload protection shall be independently determined for the long-term and short-term withstand of the negative sequence current limit, and shall not be matched with the generator backup protection; It should be used as a generator backup protection μ. Yin. Electric Machine M. South China in the 7 feet published f, w. 2 Wang Weiwei. Relay protection applies elbow. China Electric Power Press, 1998 3 Fan Xipu. Power plant electrical section elbow. Burial Worker 7 Press. 17. 4 Wang Weijian's Discussion on Relay Protection of Guida Bi Daqiang + Large Generator Transformer Unit 1 . China Power. 2001., 134 Condition 1.1 China Electric Power Press. Household morals. People 0;1 skills and should. lead. 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