Method for improving excitation loss operation capability of hydraulic generator

Abstract

The invention relates to the technical field of hydro-generators, and discloses a method for improving the field loss operation capability of a hydro-generator, a system simulation model is adopted for simulation analysis, in the system simulation model, VS1 is an infinite power grid, LN1 is line impedance, T1 is a main transformer, SM1 is a generator, CE1 and CE3 are single-phase switches, VS2 is an excitation voltage source, R is a field suppression resistor, and ROTOR is a rotor. TURBINE is a water turbine, VREG1 is an excitation regulator, two working conditions are subjected to analogue simulation through a system simulation model, and simulation results of the two working conditions under the rated load of the damping structure I and the damping structure II are obtained by simulating the two working conditions under the rated load of the damping structure II; by improving the damping structure of the hydro-generator rotor, increasing the diameters of a damping ring and a damping strip and carrying out analogue simulation analysis and test bed verification on various field loss asynchronous operation conditions of the rotor subjected to reinforced design, the field loss asynchronous operation capability of the hydro-generator set can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of hydro-generators, and in particular to a method for improving the demagnetization operation capability of a hydro-generator. Background Art

[0002] The asynchronous operation of a synchronous motor due to demagnetization refers to the abnormal operating mode in which the generator continues to operate with a certain active power and low slip in the power grid after losing excitation due to reasons such as the automatic demagnetization switch tripping, accidental contact or misoperation of the demagnetization switch, the tripping of the two-point grounding demagnetization switch in the DC circuit, malfunction of the demagnetization protection and excitation regulation failure.

[0003] Complete or partial demagnetization of large hydro-turbine generators is a common and serious fault. Compared with steam turbine generators, hydro-turbine generators with salient pole structures have smaller asynchronous power and larger governor lag. After demagnetization, the rotor will overspeed faster and be accompanied by unit vibration and other phenomena, which poses a huge threat to the unit itself and the power grid. At present, there are roughly three reasons for demagnetization during the operation of hydro-turbine generators: 1. The excitation circuit is short-circuited through the demagnetization resistor; 2. The excitation circuit is suddenly open; 3. The excitation winding rectifier is powered off.

[0004] Therefore, the demand for high-reliability products is imminent. Therefore, we proposed a method to improve the demagnetization operation capability of hydro-turbine generators. It can simulate and analyze the demagnetization operation conditions of the excitation winding open circuit and the demagnetization resistor short circuit under the rated load of the two damping structures of the hydro-turbine generator and verify the test bench. It is proved that the structural design can effectively improve the demagnetization asynchronous operation capability of the hydro-turbine generator set. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a method for improving the demagnetization operation capability of a hydraulic turbine generator, which has the advantages of improving the demagnetization operation capability of a hydraulic turbine generator, so that the generator can operate asynchronously for a short time, and the operating personnel can take this opportunity to find the cause of the demagnetization, quickly eliminate the demagnetization fault, restore the excitation to achieve resynchronization, and restore the generator to normal operation, thereby solving the above-mentioned problems.

[0007] (II) Technical solution

[0008] In order to achieve the above-mentioned purpose of improving the demagnetization operation capability of the hydro-generator, so that the generator can be asynchronously operated for a short time, the operating personnel can take this opportunity to find the cause of the demagnetization, quickly eliminate the demagnetization fault, restore the excitation to achieve resynchronization, and restore the normal operation of the generator, the present invention provides the following technical solutions: a method for improving the demagnetization operation capability of the hydro-generator, using a system simulation model for simulation analysis, in which VS1 is an infinite power grid, LN1 is a line impedance, T1 is a main transformer, SM1 is a generator, CE1 and CE3 are single-phase switches, VS2 is an excitation voltage source, R is a demagnetization resistor, ROTOR is a rotor, TURBINE is a turbine, and VREG1 is an excitation regulator;

[0009] Two working conditions are simulated through the system simulation model. The specific simulation conditions are as follows:

[0010] Working condition 1 is asynchronous operation with open circuit and demagnetization of the excitation winding: the generator operates stably with rated load, and at 2s, the excitation circuit is suddenly opened, and CE1 and CE3 are disconnected;

[0011] Working condition 2 is asynchronous operation with the excitation winding demagnetized by a short-circuit demagnetization resistor: the generator runs stably with rated load, the excitation circuit with the demagnetization resistor short-circuited at 2s, CE1 is disconnected, CE3 is closed, and the resistance value of R is set to 5 times the excitation resistance.

[0012] As an optimization, the above two working conditions under the rated load of damping structure one and damping structure two are simulated to obtain the simulation results of the two working conditions under the rated load of damping structure two, wherein the base values ​​of the calculation results are selected as follows: the voltage base value is the rated voltage, the current base value is the rated current, and the active and reactive base values ​​are the rated capacity.

[0013] As an optimization, the relevant parameter data of the two damping structures of the generator after demagnetization asynchronous operation are obtained according to the simulation results of the above two working conditions, and the relevant parameter data are compared and analyzed.

[0014] As an optimization, the number of slots per phase per pole of the hydro-turbine generator is an integer. According to the symmetry of the magnetic field distribution, the model of one pole is used as the solution area. To ensure the calculation accuracy, the moving air gap is divided into 4 layers, 2 of which are static parts and 2 are moving parts. In addition, considering the drastic changes in the magnetic field between the damping slot notch and the damping strips, the local grid is finely divided.

[0015] As an optimization, the stator outer circle gh and the rotor inner circle ab in the solution area geometric model are homogeneous boundary conditions, and ac, bd, eg and fh are periodic boundary conditions;

[0016] When performing numerical analysis of time-varying electromagnetic fields, the following assumptions are made:

[0017] 1) Ignore the displacement current, that is, the electromagnetic field is a quasi-steady field;

[0018] 2) Assuming that the magnetic field distribution along the axial direction remains unchanged, the magnetic field of the motor is equivalent to a two-dimensional field, that is, the current density vector and the magnetic potential vector have only axial components, which are not distinguished in the electromagnetic field equation; the end effect is taken into account by the constant end leakage inductance in the winding circuit equation;

[0019] 3) The material is isotropic, the hysteresis effect of ferromagnetic materials is ignored, and the BH curve is single-valued;

[0020] 4) The outer circumference of the stator surface and the inner circumference of the rotor surface are homogeneous boundary conditions, that is, the vector potential is zero.

[0021] The time-varying electromagnetic field equation is:

[0022]

[0023] Where: J-source current density, - eddy current density, μ - magnetic permeability, σ - electrical conductivity.

[0024] As an optimization, for the damping strip, the loss is mainly eddy current loss. The eddy current density of each subdivided unit in the conductor can be calculated through the finite element calculation results, thereby obtaining the eddy current loss, as shown in the following formula:

[0025]

[0026] Where: is the eddy current density of unit i, and ρ is the resistivity of the unit.

[0027] As an optimization, by simulating and calculating the above two working conditions, the simulation results of the damping structure 2 are obtained and the magnetic field lines and magnetic flux density distribution diagram at a certain moment under the rated working condition, the magnetic field lines and magnetic flux density distribution diagram at a certain moment under the asynchronous operation condition where the excitation winding is short-circuited and demagnetized by the demagnetizing resistor, the damping bar numbering diagram in the simulation model, the damping bar loss diagram under two working conditions, and the damping bar loss table under different working conditions of the two damping structures are drawn.

[0028] As an optimization, the temperature field of the damping strip in two demagnetization asynchronous operation modes, open circuit of the excitation winding and short circuit of the demagnetization resistor, is calculated and analyzed, and the calculation model diagram of the damping strip temperature rise is obtained.

[0029] The transient working condition simulation of the three-dimensional temperature field of the damping strip takes the boundary value problem into consideration during the calculation. In rectangular coordinates, the three-dimensional transient heat conduction equation in the anisotropic medium is:

[0030]

[0031] Where: x , y , zare the thermal conductivity in the x, y and z directions, and Ω1 and Ω3 are the boundary conditions.

[0032] As an optimization, the semi-axial region of the magnetic pole is taken as the calculation domain, including the rotor excitation winding, damping strips, core, insulation support plate and iron support plate.

[0033] The following basic assumptions are made:

[0034] 1) The central plane of the magnetic pole core segment along the axial direction is an insulating surface;

[0035] 2) Considering the influence of the heat dissipation turn structure of the excitation winding, each layer of winding is split;

[0036] 3) Considering that the wind coming out of the ventilation groove of the rotor yoke exchanges heat with the excitation winding when passing through it, it is assumed that the inter-pole wind temperature increases linearly along the radial direction; at the same time, according to the flow state of the air in the air gap, it is assumed that the wind temperature on the surface of the pole shoe is the same;

[0037] 4) Assuming that the heat source is evenly distributed on the excitation winding and the damping strip, since the damping strip loss is periodically distributed after stabilization, the average value of a period loss is taken for heat source loading during calculation;

[0038] 5) Ignore the effect of thermal radiation.

[0039] When calculating, the cold air temperature is considered as the cooler outlet air temperature of 32℃.

[0040] As an optimization, by subjecting the finite element model to boundary conditions and heat source loading, the temperature field diagram of the damping strip of damping structure one under rated conditions and two demagnetization asynchronous operation conditions, the temperature field diagram of damping structure two under two demagnetization asynchronous operation conditions, and the temperature condition table of the damping strips under the rated conditions and two demagnetization conditions of the two damping structures are obtained.

[0041] As an optimization, according to the calculation results of the damping winding temperature rise in the previous section, the temperature rise of the damping winding of structure 2 meets the requirements. The stator winding current is large under the two demagnetization operating conditions, so the stator winding temperature rise calculation under the demagnetization asynchronous operating condition is carried out.

[0042] When calculating the stator temperature field, the circumferential symmetry of the stator structure is taken into account, and the half-tooth and half-slot axial area is taken as the calculation domain. Including windings, cores, insulation and slot wedges, the following basic assumptions are made:

[0043] 1) When considering the copper loss of the stator winding, it is assumed that the eddy current effect has the same effect on each strand, that is, the average value is taken;

[0044] 2) It is believed that the insulation of the slot wedge and the conductor is made of the same material;

[0045] 3) Only the winding part is considered at the end;

[0046] 4) Considering that the wind in the radial ventilation groove of the stator generates heat exchange with the stator core and coil, it is assumed that the wind temperature increases linearly along the radial direction;

[0047] 5) Ignore the effect of thermal radiation.

[0048] As an optimization, based on the calculation results of the temperature of the second stator bar of the damping structure, the influence of demagnetization operation for 20 minutes on the insulation life of the stator bar is further analyzed.

[0049] The stator bar temperature index can be evaluated by conventional method, point slope method and secant method, all of which are based on the thermal aging life equation:

[0050] lnτ=a+b / T (4)

[0051] In the formula: a, b are constants, T is the ambient temperature, and τ is the time (h) required for the material performance to reach the failure index or critical value at temperature T.

[0052] The thermal gravity secant method is directly calculated from the TG curve. The advantages are that it is very simple and fast. The results can characterize the chemical stability of the material and roughly analyze the heat resistance temperature index.

[0053] / min, using TGA analysis instrument to test the thermal weight loss curve of stator bar main insulation;

[0054] As an optimization, the thermal gravity secant method was used to calculate the temperature resistance of the main insulation of the stator winding of the Bala Power Station hydro-generator according to the apparent decomposition temperature, weight loss temperature and functional coefficient of the stator bar, and the heat resistance grade was F.

[0055] The relationship between insulation life (L) and motor continuous operating temperature (T) is as follows:

[0056] L=A0e (-ln2 / m)T

[0057] Where: A0 is the insulation life at 0℃, T is the insulation continuous temperature, m is a constant. For Class F insulation, the value of m is 12, that is, the life is shortened by half for every 12℃ increase in temperature.

[0058] The temperature of the unit is about 100℃ during normal operation, and the insulation life is about 39.9 years. Based on the stator bar temperature calculated in the previous section, the insulation life of the stator bar under two demagnetization conditions was evaluated and calculated.

[0059] A structure for improving the demagnetization operation capability of a hydro-turbine generator, comprising a magnetic pole fixing seat, a connecting piece, a magnetic pole body and a damping ring with a large damping plate structure, wherein the magnetic pole body is distributed along the circumference of the magnetic pole fixing seat, the damping ring extends radially and completely covers one side of the magnetic pole body, a magnetic pole clamping block is arranged between each of the two adjacent damping rings, a magnetic pole pull rod is inserted in the magnetic pole clamping block, and the magnetic pole clamping block is tightened and fixed on the magnetic pole fixing seat by the magnetic pole pull rod, a T-shaped tail rod is arranged at the bottom of the magnetic pole body, and Embedded in the T-slot provided in the magnetic pole fixing seat, a plurality of thickened damping rods are inserted into the outer side of the damping ring, radially extending to the entire magnetic pole body through the damping ring, and integrated with the magnetic pole through the tightening screw, so that the centrifugal force of the damping ring can be borne by the magnetic pole tightening screw and the T-shaped tail plate of the damping ring, and thus will not be thrown out due to excessive centrifugal force; and the two sides of the damping ring are bent into the shape of angle steel, and screwed to the magnetic pole pressure plate, and the centrifugal force of the damping ring extending out of the magnetic pole part is borne by the magnetic pole pressure plate, further improving the stability.

[0060] (III) Beneficial effects

[0061] Compared with the prior art, the present invention provides a method for improving the demagnetization operation capability of a hydro-generator, which has the following beneficial effects:

[0062] 1. The method for improving the demagnetization operation capability of a hydro-turbine generator can effectively improve the demagnetization asynchronous operation capability of a hydro-turbine generator set by improving the rotor damping structure of the hydro-turbine generator, increasing the diameters of the damping ring and the damping bar, and conducting simulation analysis and test bench verification on various demagnetization asynchronous operation conditions of the rotor after the enhanced design.

[0063] 2. The method for improving the demagnetization operation capability of the hydro-turbine generator is to analyze and calculate the current and temperature rise of the damping strip, damping ring and excitation lead in combination with the excitation working conditions, and take effective measures to meet the 20-minute demagnetization operation, thereby providing the operating personnel with time to deal with the demagnetization fault, facilitating the rapid elimination of the demagnetization fault, restoring the excitation to achieve resynchronization, and restoring the generator to normal operation, thereby reducing the power outage losses of users and ensuring reliable power supply.

[0064] 3. The method for improving the demagnetized operation capability of the hydro-generator is that the damping ring is radially extended to the entire pole body and is integrated with the pole through a tightening screw, so that the centrifugal force of the damping ring can be borne by the pole tightening screw and the T-shaped tail plate of the damping ring, and thus the damping ring will not be thrown out due to excessive centrifugal force. The two sides of the damping ring are bent into an angle steel shape and screwed to the pole pressure plate. The centrifugal force of the damping ring extending out of the pole is borne by the pole pressure plate, which further improves the stability, and can also improve the current capacity of the generator rotor damping ring, damping strip and other components, and improve the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic diagram of the simulation model of the system of the present invention;

[0066] Figure 2 It is a schematic diagram of simulation results of asynchronous operation of the excitation winding under open circuit demagnetization under the working condition 1 of the damping structure of the present invention under rated load;

[0067] Figure 3 It is a schematic diagram of simulation results of asynchronous operation of the second excitation winding of the damping structure of the present invention under the second rated load condition after the demagnetization resistor is short-circuited and demagnetized;

[0068] Figure 4 It is a schematic diagram of the finite element calculation model of the hydro-generator of the present invention;

[0069] Figure 5 It is a schematic diagram of magnetic lines of force and magnetic flux density distribution when the present invention is in steady-state operation under rated working conditions;

[0070] Figure 6 It is a schematic diagram of the magnetic lines of force and magnetic flux density distribution under the asynchronous operation condition of the present invention after the demagnetization resistor is short-circuited and demagnetized;

[0071] Figure 7 This is a schematic diagram of the numbering of the damping strips of the present invention;

[0072] Figure 8 It is a schematic diagram of the loss of the damping strips in the demagnetized asynchronous operation state under different rated load conditions of the damping structure of the present invention;

[0073] Fig. 9 It is a schematic diagram of the temperature rise calculation model of the damping strip of the present invention;

[0074] Fig.10 It is a temperature field cloud diagram of the damping strip under the rated and two demagnetized asynchronous operation conditions of the damping structure of the present invention;

[0075] Fig.11 The cloud diagram of the temperature field of the damping strip under two rated and two demagnetized asynchronous operation conditions of the damping structure of the present invention;

[0076] Fig.12 It is a schematic diagram of the stator finite element model of the present invention;

[0077] Fig.13 The stator temperature cloud diagram of the rated working condition of the present invention;

[0078] Fig.14 The stator temperature cloud diagram of the present invention under the open circuit demagnetization operation condition for 20 minutes;

[0079] Fig.15 The stator temperature cloud diagram of the present invention after the demagnetization resistor is short-circuited and demagnetized for 20 minutes;

[0080] Fig.16 It is a schematic diagram of the thermal weight loss curve of the stator wire bar main insulation of the present invention;

[0081] Fig.17 It is a top view schematic diagram of the local structure of the rotor of the present invention.

[0082] In the figure: 1, connecting piece; 2, magnetic pole body; 3, damping ring; 4, magnetic pole clamping block; 5, magnetic pole pull rod; 6, T-type tail plate; 7, damping rod. DETAILED DESCRIPTION

[0083] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0084] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0085] A method for improving the demagnetization operation capability of a hydro-generator, using a system simulation model for simulation analysis, in which VS1 is an infinite power grid, LN1 is a line impedance, T1 is a main transformer, SM1 is a generator, CE1 and CE3 are single-phase switches, VS2 is an excitation voltage source, R is a demagnetization resistor, ROTOR is a rotor, TURBINE is a turbine, and VREG1 is an excitation regulator;

[0086] The specific method is as follows:

[0087] S1. First, two working conditions are simulated through the system simulation model. The specific simulation conditions are as follows:

[0088] Working condition 1 is asynchronous operation with open circuit and demagnetization of the excitation winding: the generator operates stably with rated load, and at 2s, the excitation circuit is suddenly opened, and CE1 and CE3 are disconnected;

[0089] Working condition 2 is asynchronous operation with the excitation winding demagnetized by a short-circuit demagnetization resistor: the generator runs stably with rated load, the excitation circuit with the demagnetization resistor short-circuited at 2s, CE1 is disconnected, CE3 is closed, and the resistance value of R is set to 5 times the excitation resistance.

[0090] S2. Simulate the above two working conditions under rated load of damping structure 1 and damping structure 2, and obtain the simulation results of the two working conditions under rated load of damping structure 2, wherein the base value of the calculation result is selected as follows: the voltage base value is the rated voltage, the current base value is the rated current, and the active and reactive base values ​​are the rated capacity.

[0091] S3, such as Figure 2-Figure 3 As shown, according to the simulation results of the above two working conditions, the relevant parameter data of the two damping structures of the generator after demagnetization asynchronous operation are obtained as shown in the following table, and the relevant parameter data are compared and analyzed.

[0092] Table 3-1 Comparison of relevant parameters of damping structure under different demagnetization asynchronous operation under rated load (unit: pu)

[0093] Different demagnetization conditions Average stator current Minimum terminal voltage Maximum speed Working condition 1 (open circuit) 1.78 0.91 1.0151 Working condition 2 (short circuit through demagnetization resistor) 1.86 0.904 1.0115

[0094] Note: The stator current is the effective value after stabilization

[0095] Table 3-2 Comparison of relevant parameters of asynchronous operation with different demagnetization under rated load of damping structure II (unit: pu)

[0096] Different demagnetization conditions Average stator current Minimum terminal voltage Maximum speed Working condition 1 (open circuit) 1.87 0.90 1.01 Working condition 2 (short circuit through demagnetization resistor) 1.88 0.898 1.0055

[0097] Note: The stator current is the effective value after stabilization

[0098] From the table above, we can see that:

[0099] 1) The average value of stator current in two demagnetization operating conditions exceeds the rated value.

[0100] 2) Compared with damping structure 1, the average value of stator current and the minimum value of terminal voltage under damping structure 2 do not change much under the two working conditions; the maximum speed is slightly reduced.

[0101] When the turbine generator is operating at rated conditions, demagnetization occurs and a high voltage will be generated in the excitation winding at the moment of failure. The excitation winding voltages under different demagnetization conditions of damping structure 2 are shown in the following table.

[0102] Table 3-3 Excitation winding voltage under different demagnetization conditions of damping structure 2 (unit: V)

[0103] Excitation voltage (fault moment) Excitation voltage (steady state operation) Working condition 1 (open circuit) 2980 2400 Working condition 2 (short circuit through demagnetization resistor) 1630 635

[0104] Note: Excitation voltage is the maximum value

[0105] It can be seen from the above table that the excitation winding voltage in working condition 1 is higher than that in working condition 2 (fault instant and steady-state operation), with a maximum value of about 3000V. The rated excitation voltage of the hydro-turbine generator is 339.3V. During the factory withstand voltage test, the excitation winding is subjected to 10 times the rated excitation voltage, and the insulation performance of the excitation winding meets the requirements for demagnetization operation.

[0106] S4. The number of slots per phase per pole of the hydro-turbine generator is an integer. According to the symmetry of the magnetic field distribution, a model of one pole is used as the solution area. In order to ensure the calculation accuracy, the moving air gap is divided into 4 layers, 2 of which are static parts and 2 are moving parts. In addition, considering the drastic changes in the magnetic field between the damping slot and the damping strips, the local grid is finely divided;

[0107] like Figure 4 As shown, in the geometric model of the solution area, the stator outer circle gh and the rotor inner circle ab are homogeneous boundary conditions, and ac, bd, eg and fh are periodic boundary conditions;

[0108] When performing numerical analysis of time-varying electromagnetic fields, the following assumptions are made:

[0109] 1) Ignore the displacement current, that is, the electromagnetic field is a quasi-steady field;

[0110] 2) Assuming that the magnetic field distribution along the axial direction remains unchanged, the magnetic field of the motor is equivalent to a two-dimensional field, that is, the current density vector and the magnetic potential vector have only axial components, which are not distinguished in the electromagnetic field equation; the end effect is taken into account by the constant end leakage inductance in the winding circuit equation;

[0111] 3) The material is isotropic, the hysteresis effect of ferromagnetic materials is ignored, and the BH curve is single-valued;

[0112] 4) The outer circumference of the stator surface and the inner circumference of the rotor surface are homogeneous boundary conditions, that is, the vector potential is zero.

[0113] The time-varying electromagnetic field equation is:

[0114]

[0115] Where: J-source current density, Eddy current density, μ-magnetic permeability, σ-electrical conductivity.

[0116] For the damping strip, the loss is mainly eddy current loss. The eddy current density of each subdivided unit in the conductor can be calculated through the finite element calculation results, thereby obtaining the eddy current loss, as shown in the following formula:

[0117]

[0118] Where: is the eddy current density of unit i, and ρ is the resistivity of the unit.

[0119] S5. By simulating the above two working conditions, the simulation results of the damping structure 2 are obtained and the magnetic field lines and magnetic flux density distribution diagram at a certain moment under the rated working condition are drawn (such as Figure 5 As shown), the magnetic field lines and magnetic flux distribution diagram at a certain moment under the asynchronous operation condition when the excitation winding is short-circuited and demagnetized by the demagnetization resistor (as shown Figure 6 As shown in the figure), the damping strip number diagram in the simulation model (as shown in the figure Figure 7 As shown), the damping strip loss diagram under two working conditions (as shown Figure 8 The damping strip loss table under different working conditions of the two damping structures is as follows:

[0120] Table 3-4 Calculation results of the damping strip loss on one pole of the damping structure (unit: kW)

[0121] Damping No. 1 2 3 4 5 6 7 8 9 Rated operating conditions 0.026 0.026 0.031 0.04 0.086 0.11 0.198 0.115 0.115 Working condition 1 (open circuit) 66.89 19 4.24 2.17 8.57 13.51 14.96 13.44 12.38 Working condition 2 (short circuit through demagnetization resistor) 9.41 3.21 1.33 1.94 2.72 2.84 2.13 3.74 5.3

[0122] Note: The loss result is the maximum value after stabilization

[0123] Table 3-5 Calculation results of the damping strip loss on the first pole of the damping structure 2 (unit: kW)

[0124] Damping No. 1 2 3 4 5 6 7 8 9 Working condition 1 (open circuit) 44.39 17.79 5.23 1.5 3.26 7.47 10.8 12.08 12.05 Working condition 2 (short circuit through demagnetization resistor) 6.0 2.6 1.14 0.73 0.77 1.13 1.27 2.0 4.17

[0125] Note: The loss result is the maximum value after stabilization

[0126] From the table above, we can see that:

[0127] 1) The damping strip loss is very small under rated conditions; during demagnetized asynchronous operation, the damping strip loss value under condition 1 is much larger than that under condition 2.

[0128] 2) The loss of damping structure 2 is significantly reduced compared with damping structure 1.

[0129] S6. Calculate and analyze the temperature field of the damping strip under two demagnetization asynchronous operation conditions: open circuit of the excitation winding and short circuit of the demagnetization resistor. Fig. 9 As shown, the calculation model diagram of the temperature rise of the damping strip is obtained;

[0130] The transient working condition simulation of the three-dimensional temperature field of the damping strip takes the boundary value problem into consideration during the calculation. In rectangular coordinates, the three-dimensional transient heat conduction equation in the anisotropic medium is:

[0131]

[0132] Where: x , y , z are the thermal conductivity in the x, y and z directions, and Ω1 and Ω3 are the boundary conditions.

[0133] The semi-axial region of the magnetic pole is taken as the calculation domain, including the rotor excitation winding, damping strips, iron core, insulating support plate and iron support plate.

[0134] The following basic assumptions are made:

[0135] 1) The central plane of the magnetic pole core segment along the axial direction is an insulating surface;

[0136] 2) Considering the influence of the heat dissipation turn structure of the excitation winding, each layer of winding is split;

[0137] 3) Considering that the wind coming out of the ventilation groove of the rotor yoke exchanges heat with the excitation winding when passing through it, it is assumed that the inter-pole wind temperature increases linearly along the radial direction; at the same time, according to the flow state of the air in the air gap, it is assumed that the wind temperature on the surface of the pole shoe is the same;

[0138] 4) Assuming that the heat source is evenly distributed on the excitation winding and the damping strip, since the damping strip loss is periodically distributed after stabilization, the average value of a period loss is taken for heat source loading during calculation;

[0139] 5) Ignore the effect of thermal radiation.

[0140] When calculating, the cold air temperature is considered as the cooler outlet air temperature of 32℃.

[0141] S7. By applying boundary conditions and heat source loading to the finite element model, the temperature field diagrams of the damping structure under rated working conditions and two demagnetized asynchronous operating conditions are obtained (e.g. Fig.10 As shown), the temperature field diagram of the damping structure under two demagnetization asynchronous operation conditions (as shown Fig.11 The temperature of the damping strips under the rated working conditions of the two damping structures and the two demagnetization working conditions are shown in the following table:

[0142] Table 3-6 Damping structure - Temperature values ​​of damping strips under different working conditions (unit: °C)

[0143]

[0144] Table 3-7 Damping strip temperature under different working conditions of damping structure 2 (unit: °C)

[0145]

[0146] The standard JB / T8445-1996 "Test method for negative sequence current tolerance of three-phase synchronous generators" stipulates that the maximum allowable temperature of the copper damping strip when the motor is running for a long time and short time is 130℃ and 220℃ respectively.

[0147] 1) According to the standard, the damping strip structure reaches the temperature limit after 143 seconds of open-circuit demagnetization under rated load, and the excitation coil can operate safely for 20 minutes after short-circuit demagnetization by demagnetization resistance.

[0148] 2) Damping strip structure 2 can operate safely for 20 minutes under rated load with the excitation winding open circuit or short circuited through the demagnetization resistor.

[0149] S8. According to the calculation results of the damping winding temperature rise in the previous section, the temperature rise of the damping winding of structure 2 meets the requirements. The stator winding current is large under the two demagnetization operating conditions, so the stator winding temperature rise calculation under the demagnetization asynchronous operating condition is carried out.

[0150] When calculating the stator temperature field, the circumferential symmetry of the stator structure is taken into account, and the half-tooth and half-slot axial area is taken as the calculation domain. Including windings, cores, insulation and slot wedges, the following basic assumptions are made:

[0151] 1) When considering the copper loss of the stator winding, it is assumed that the eddy current effect has the same effect on each strand, that is, the average value is taken;

[0152] 2) It is believed that the insulation of the slot wedge and the conductor is made of the same material;

[0153] 3) Only the winding part is considered at the end;

[0154] 4) Considering that the wind in the radial ventilation groove of the stator generates heat exchange with the stator core and coil, it is assumed that the wind temperature increases linearly along the radial direction;

[0155] 5) Ignore the effect of thermal radiation.

[0156] Considering that the motor is located at an altitude of 2700 meters, the air physical parameters change and the cooling air heat exchange performance decreases. Therefore, the outlet air temperature compensation is performed when calculating the air cooler. When calculating the stator temperature rise, the cold air temperature is considered to be 32℃ based on the cooler outlet air temperature.

[0157] The geometric solution model and mesh division lines are as follows Fig.12 As shown, the stator temperature distribution of damping structure 2 under rated working condition and demagnetization 20min working condition (open circuit and short circuit through demagnetization resistor) is as follows Fig.13 , Fig.14 , Fig.15 shown.

[0158] The calculation results of the stator temperature field under rated working conditions and demagnetization 20min working conditions (open circuit and short circuit through demagnetization resistor) are as follows:

[0159] Table 3-8 Calculation results of temperature field of the second stator of the damping structure

[0160]

[0161] The stator temperature field calculation takes into account the changes in air physical parameters at an altitude of 2700 meters, and the cold wind is calculated at 32°C. According to the calculation results, we know that:

[0162] 1) Under rated working conditions, the maximum temperature of the stator bar is about 105.64℃, and the temperature rise is 73.64K;

[0163] 2) When the open circuit demagnetization operation lasts for 20 minutes, the maximum temperature of the stator bar is about 164.79℃, and the temperature rise is 132.79K;

[0164] 3) After 20 minutes of demagnetization operation with a short-circuit demagnetization resistor, the maximum temperature of the stator bar is about 166.61℃, with a temperature rise of 134.61K.

[0165] S9. Based on the calculation results of the stator wire bar temperature of the damping structure II, further analyze the impact of demagnetization operation for 20 minutes on the insulation life of the stator wire bar.

[0166] The stator bar temperature index can be evaluated by conventional method, point slope method and secant method, all of which are based on the thermal aging life equation:

[0167] lnτ=a+b / T (4)

[0168] In the formula: a, b are constants, T is the ambient temperature, and τ is the time (h) required for the material performance to reach the failure index or critical value at temperature T.

[0169] The thermal gravity secant method is directly calculated from the TG curve. The advantages are that it is very simple and fast. The results can characterize the chemical stability of the material and roughly analyze the heat resistance temperature index.

[0170] / min, and use TGA analysis instrument to test the thermal weight loss curve of stator bar main insulation (such as Fig.16 shown);

[0171] Then, using the thermogravimetric secant method, according to the apparent decomposition temperature, weight loss temperature and functional coefficient of the stator bar, it was calculated that the temperature resistance of the main insulation of the stator winding of the Bala Power Station hydro-generator is 161.6℃ and the heat resistance grade is F.

[0172] The relationship between S10, insulation life (L) and motor continuous operating temperature (T) is as follows:

[0173] L=A0e (-ln2 / m)T

[0174] Where: A0 is the insulation life at 0℃, T is the insulation continuous temperature, m is a constant. For Class F insulation, the value of m is 12, that is, the life is shortened by half for every 12℃ increase in temperature.

[0175] Generally, the unit is in normal operation with a temperature of about 100°C and an insulation life of about 39.9 years. Based on the stator bar temperature calculated in the previous section, the stator bar insulation life under two demagnetization conditions was evaluated and calculated, and the results are shown in the following table:

[0176] Table 3-9 Damping structure two stator wire rod insulation life assessment

[0177]

[0178] It can be seen from the above table that the two demagnetization operating conditions have basically the same impact on the insulation of the stator bar, accounting for about 0.002% of the entire stator bar life, and have little impact on the overall life of the stator bar.

[0179] S10. Through simulation analysis of the rated load demagnetization asynchronous operation conditions of two damping structures of the hydro-turbine generator, the damping winding and stator bar losses and temperature rise were calculated, and the following conclusions were obtained:

[0180] 1) According to the reference standard JB / T8445-1996 "Test Method for Negative Sequence Current Withstanding Capacity of Three-Phase Synchronous Generators", the maximum temperature allowed for the copper damping strip during long-term and short-term operation of the motor is 130°C and 220°C respectively. The temperature rise results of the damping strip under rated load conditions of the two damping structures are as follows:

[0181] Damping structure 1: Under rated load, the temperature limit is reached after 143s of operation with open circuit excitation and demagnetization. The excitation coil can operate safely for 20 minutes after short circuit demagnetization by demagnetization resistor.

[0182] Damping structure 2: The temperature of the damping strip does not exceed the standard in both demagnetization operation conditions under rated load for 20 minutes. Therefore, this structure is adopted in the damping of the generator solution.

[0183] 2) The stator bar loss and temperature rise of the damping structure under two rated load conditions, open circuit and short circuit through demagnetization resistor, were calculated, and the maximum temperature of interlayer RTD / stator bar under open circuit and short circuit through demagnetization resistor was 143℃ / 167℃.

[0184] The temperature rise of the stator bar under the two demagnetization operating conditions is basically the same. This condition lasts for 20 minutes, accounting for about 0.002% of the entire stator bar life, and has little effect on the overall life of the stator bar. That is, the two demagnetization operating conditions under rated load for 20 minutes have little effect on the insulation of the stator winding, and have little effect on the withstand voltage level, and the insulation will not be carbonized.

[0185] 3) The insulation performance of the excitation winding meets the requirements of demagnetization operation.

[0186] In principle, hydro-turbine generators are not allowed to run asynchronously due to demagnetization, and the protection will act accordingly after the generator loses magnetism, cutting off the hydro-turbine generator to prevent impact on the power grid, or ensuring the stability of the unit and the system by reducing the load.

[0187] A structure for improving the demagnetization operation capability of a hydro-turbine generator, comprising a magnetic pole fixing seat, a connecting piece 1, a magnetic pole body 2 and a damping ring 3 with a large damping plate structure, wherein the magnetic pole body 2 is distributed along the circumference of the magnetic pole fixing seat, the damping ring 3 extends radially and completely covers one side of the magnetic pole body 2, a magnetic pole clamping block 4 is arranged between each of the two adjacent damping rings 3, a magnetic pole pull rod 5 is inserted in the magnetic pole clamping block 4, and the magnetic pole clamping block 4 is tightened and fixed on the magnetic pole fixing seat by the magnetic pole pull rod 5, and a T-shaped tail rod 6 is arranged at the bottom of the magnetic pole body 2 , and embedded in the T-shaped groove opened in the magnetic pole fixing seat. A number of thickened damping rods 7 are inserted in the outer side of the damping ring 3, which radially extend to the entire magnetic pole body through the damping ring, and are combined with the magnetic pole through the tightening screw to form a whole, so that the centrifugal force of the damping ring can be borne by the magnetic pole tightening screw and the T-shaped tail plate of the damping ring, and will not be thrown out due to excessive centrifugal force; and the two sides of the damping ring are bent into the shape of angle steel and screwed to the magnetic pole pressure plate. The centrifugal force of the damping ring extending out of the magnetic pole is borne by the magnetic pole pressure plate, which further improves stability.

[0188] In the description of the present invention, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect", and "fix" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0189] The standard parts used in the present invention can all be purchased from the market, and the special-shaped parts can all be customized according to the description and the drawings.

[0190] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for improving the demagnetization operation capability of a hydro-generator, characterized in that: The system simulation model is used for simulation analysis. In the system simulation model, VS1 is an infinite power grid, LN1 is the line impedance, T1 is the main transformer, SM1 is the generator, CE1 and CE3 are single-phase switches, VS2 is the excitation voltage source, R is the demagnetization resistor, ROTOR is the rotor, TURBINE is the turbine, and VREG1 is the excitation regulator. The simulation conditions are as follows: Working condition 1 is asynchronous operation with open circuit and demagnetization of the excitation winding: the generator operates stably with rated load, and at 2s, the excitation circuit is suddenly opened, and CE1 and CE3 are disconnected; Working condition 2 is asynchronous operation with the excitation winding demagnetized by a short-circuit demagnetization resistor: the generator runs stably with rated load, the excitation circuit with the demagnetization resistor short-circuited at 2s, CE1 is disconnected, CE3 is closed, and the resistance value of R is set to 5 times the excitation resistance.

2. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 1, characterized in that: Then the above two working conditions under the rated load of damping structure one and damping structure two are simulated, and the simulation results of the two working conditions under the rated load of damping structure two are obtained, wherein the base value of the calculation results is selected as follows: the voltage base value is the rated voltage, the current base value is the rated current, and the active and reactive base values ​​are the rated capacity; according to the simulation results of the above two working conditions, the relevant parameter data of the two damping structures of the Bala hydroelectric generator after demagnetization and asynchronous operation are obtained, and the relevant parameter data are compared and analyzed.

3. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 1, characterized in that: The number of slots per phase per pole of the hydro-turbine generator is an integer. According to the symmetry of the magnetic field distribution, a model of one pole is used as the solution area. To ensure the calculation accuracy, the moving air gap is divided into 4 layers, 2 of which are static parts and 2 are moving parts. In addition, considering the drastic changes in the magnetic field between the damping slot notch and the damping strips, the local grid is finely divided.

4. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 3, characterized in that: In the geometric model of the solution area, the stator outer circle gh and the rotor inner circle ab are a type of homogeneous boundary conditions, and ac, bd, eg and fh are periodic boundary conditions.

5. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 1, characterized in that: When performing numerical analysis of time-varying electromagnetic fields, the following assumptions are made: 1) Ignore the displacement current, that is, the electromagnetic field is a quasi-steady field; 2) Assuming that the magnetic field distribution along the axial direction remains unchanged, the magnetic field of the motor is equivalent to a two-dimensional field, that is, the current density vector and the magnetic potential vector have only axial components, which are not distinguished in the electromagnetic field equation; the end effect is taken into account by the constant end leakage inductance in the winding circuit equation; 3) The material is isotropic, the hysteresis effect of ferromagnetic materials is ignored, and the BH curve is single-valued; 4) The outer circumference of the stator surface and the inner circumference of the rotor surface are homogeneous boundary conditions, that is, the vector potential is zero. The time-varying electromagnetic field equation is: Where: J-source current density, - eddy current density, μ - magnetic permeability, σ - electrical conductivity.

6. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 5, characterized in that: For the damping strip, the loss is mainly eddy current loss. The eddy current density of each subdivided unit in the conductor can be calculated through the finite element calculation results, thereby obtaining the eddy current loss, as shown in the following formula: Where: is the eddy current density of the unit, and ρ is the resistivity of the unit.

7. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 6, characterized in that: By simulating and calculating the above two working conditions, the simulation results of the damping structure 2 are obtained and the following charts are drawn: the magnetic field lines and magnetic flux distribution diagram at a certain moment under the rated working condition, the magnetic field lines and magnetic flux distribution diagram at a certain moment under the asynchronous operation condition where the excitation winding is short-circuited and demagnetized by the demagnetizing resistor, the damping bar numbering diagram in the simulation model, the damping bar loss diagram under two working conditions, and the damping bar loss table under different working conditions of the two damping structures.

8. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 1, characterized in that: The temperature field of the damping strip in two demagnetization asynchronous operation conditions, open circuit of the excitation winding and short circuit of the demagnetization resistor, is calculated and analyzed, and the calculation model diagram of the damping strip temperature rise is obtained; The transient working condition simulation of the three-dimensional temperature field of the damping strip takes the boundary value problem into consideration during the calculation. In rectangular coordinates, the three-dimensional transient heat conduction equation in the anisotropic medium is: Where: x , y , z are the thermal conductivity in the x, y and z directions, and Ω1 and Ω3 are the boundary conditions. The semi-axial region of the magnetic pole is taken as the calculation domain, including the rotor excitation winding, damping strips, iron core, insulating support plate and iron support plate. The following basic assumptions are made: 1) The central plane of the magnetic pole core segment along the axial direction is an insulating surface; 2) Considering the influence of the heat dissipation turn structure of the excitation winding, each layer of winding is split; 3) Considering that the wind coming out of the ventilation groove of the rotor yoke exchanges heat with the excitation winding when passing through it, it is assumed that the inter-pole wind temperature increases linearly along the radial direction; at the same time, according to the flow state of the air in the air gap, it is assumed that the wind temperature on the surface of the pole shoe is the same; 4) Assuming that the heat source is evenly distributed on the excitation winding and the damping strip, since the damping strip loss is periodically distributed after stabilization, the average value of a period loss is taken for heat source loading during calculation; 5) Ignore the effect of thermal radiation; When calculating, the cold air temperature is considered as the cooler outlet air temperature of 32℃.

9. The method for improving the demagnetization operation capability of a hydraulic generator according to claim 1, characterized in that: By applying boundary conditions and heat source loading to the finite element model, the temperature field diagram of the damping strip of the damping structure 1 under rated working conditions and two demagnetization asynchronous operation conditions, the temperature field diagram of the damping structure 2 under two demagnetization asynchronous operation conditions, and the temperature table of the damping strip under the rated working conditions and two demagnetization conditions of the two damping structures are obtained; According to the calculation results of the damping winding temperature rise in the previous section, it can be seen that the temperature rise of the damping winding of structure 2 meets the requirements; the stator winding current is large under the two demagnetization operating conditions, so the stator winding temperature rise calculation under the demagnetization asynchronous operating condition is carried out. When calculating the stator temperature field, the circumferential symmetry of the stator structure is taken into account, and the half-tooth and half-slot axial area is taken as the calculation domain; including the winding, core, insulation and slot wedge, etc., and the following basic assumptions are made: 1) When considering the copper loss of the stator winding, it is assumed that the eddy current effect has the same effect on each strand, that is, the average value is taken; 2) It is believed that the insulation of the slot wedge and the conductor is made of the same material; 3) Only the winding part is considered at the end; 4) Considering that the wind in the radial ventilation groove of the stator generates heat exchange with the stator core and coil, it is assumed that the wind temperature increases linearly along the radial direction; 5) Ignore the effect of thermal radiation; Considering that the motor is located at an altitude of 2700 meters, the physical properties of the air change and the heat exchange performance of the cooling air decreases; therefore, outlet air temperature compensation is performed when calculating the air cooler; when calculating the stator temperature rise, the cold air temperature is considered to be 32°C based on the cooler outlet air temperature. According to the calculation results of the stator bar temperature of the damping structure II, the influence of demagnetization operation for 20 minutes on the insulation life of the stator bar is further analyzed; the evaluation of the stator bar temperature index includes conventional method, point slope method and secant method, and their principles are all based on the thermal aging life equation: lnτ=a+b / T(4) Where: a, b are constants, T is the ambient temperature, and τ is the time (h) required for the material performance to reach the failure index or critical value at temperature T. The thermogravimetric secant method is directly calculated from the TG curve. It is very simple and fast. The result can characterize the chemical stability of the material and roughly analyze the heat resistance temperature index. The thermogravimetric curve of the main insulation of the stator bar was tested by TGA analysis instrument at 3℃ / min and 5℃ / min respectively. The thermogravimetric secant method was used to calculate the temperature resistance of the main insulation of the stator winding of the Bala Power Station hydro-turbine generator according to the apparent decomposition temperature, weight loss temperature and functional coefficient of the stator bar. The heat resistance temperature is 161.6℃, and the heat resistance grade is F. The relationship between insulation life (L) and motor continuous operating temperature (T) is as follows: L=A 0e (-ln2 / m)T Where: A0 is the insulation life at 0℃, T is the insulation continuous temperature, m is a constant. For Class F insulation, the m value is 12, that is, the life is shortened by half for every 12℃ increase in temperature.

10. The hydro-generator rotor winding magnetic pole damping structure according to claim 1, characterized in that: The invention comprises a magnetic pole fixing seat, a connecting plate (1), a magnetic pole body (2) and a damping ring (3) with a large damping plate structure, wherein the magnetic pole body (2) is distributed along the circumference of the magnetic pole fixing seat, the damping ring (3) extends radially and completely covers one side of the magnetic pole body (2), a magnetic pole clamping block (4) is arranged between each two adjacent damping rings (3), a magnetic pole pull rod (5) is inserted into the magnetic pole clamping block (4), and the magnetic pole clamping block (4) is tightened and fixed to the magnetic pole fixing seat by the magnetic pole pull rod (5), a T-shaped tail rod (6) is arranged at the bottom of the magnetic pole body (2) and is embedded in a T-shaped groove provided in the magnetic pole fixing seat, and a plurality of thickened damping rods (7) are inserted into the outer side of the damping ring (3).

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