Hydro-generator rotor winding pole damping structure

Abstract

The utility model relates to water turbine generator technical field, and disclose a water turbine generator rotor winding magnetic pole damping structure, including magnetic pole fixed base, connecting piece, magnetic pole body and the damping ring of adopting big damping plate structure, and the magnetic pole body is along the circumferential distribution of magnetic pole fixed base, the damping ring radial extension and completely cover one side of magnetic pole body, set up magnetic pole pressure block between every adjacent two sides damping ring, the magnetic pole pressure block inserts and has magnetic pole pull rod, through the damping ring radial extension to the whole magnetic pole pole body, with the magnetic pole through the tensioning screw screwing into one whole, make the damping ring centrifugal force can pass through the magnetic pole tensioning screw and the damping ring T shape tail plate bear, and then will not because centrifugal force is too big and flings out, and the damping ring both sides are bent into angle steel shape, and are screwed on the magnetic pole pressure block, the centrifugal force of the damping ring of the magnetic pole part that stretches out is borne by the magnetic pole pressure block, further improves stability.

Description

Technical Field

[0001] This utility model relates to the field of hydro-generator technology, specifically to a magnetic pole damping structure for a hydro-generator rotor winding. Background Technology

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

[0003] Loss of excitation, either completely or partially, in large hydro-generators is a common and serious fault. Compared to steam turbine generators, hydro-generators with salient pole structures have lower asynchronous power and larger governor time lag. After loss of excitation, the rotor will overspeed more quickly, accompanied by phenomena such as unit vibration, which poses a great threat to the unit itself and the power grid. Currently, the causes of loss of excitation during the operation of hydro-generators can be roughly divided into three types: 1. Short circuit in the excitation circuit through the demagnetizing resistor; 2. Sudden open circuit in the excitation circuit; 3. De-energization of the excitation winding rectifier.

[0004] Therefore, the demand for highly reliable products is urgent, so we proposed a magnetic pole damping structure for the rotor winding of a hydro generator.

[0005] Practical content

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a magnetic pole damping structure for the rotor winding of a hydro-generator. This structure enhances the generator's ability to operate without excitation, enabling it to run asynchronously for short periods. This allows operators to identify the cause of the demagnetization, quickly eliminate the fault, restore excitation, achieve resynchronization, and restore the generator to normal operation. This solution addresses the aforementioned problems.

[0008] (II) Technical Solution

[0009] To achieve the goal of enhancing the demagnetization operation capability of a hydro-generator, enabling the generator to operate asynchronously for short periods, allowing operators to identify the cause of demagnetization, quickly eliminate the demagnetization fault, restore excitation to achieve resynchronization, and restore the generator to normal operation, this utility model provides the following technical solution: A method for enhancing the demagnetization operation capability of a hydro-generator, using a system simulation model 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 demagnetizing resistor, ROTOR is the rotor, TURBINE is the turbine, and VREG1 is the excitation regulator;

[0010] The two operating conditions were simulated using a system simulation model. The specific simulation conditions are as follows:

[0011] Operating condition 1 is asynchronous operation with open circuit and loss of excitation of the excitation winding: The generator is running stably under rated load. After 2 seconds, the excitation circuit suddenly opens, and CE1 and CE3 are disconnected.

[0012] Operating condition 2 is asynchronous operation with demagnetization due to short circuit of excitation winding via demagnetizing resistor: The generator operates stably under rated load. After 2 seconds, the excitation circuit is short-circuited with demagnetizing resistor. CE1 is open and CE3 is closed. The resistance value of R is given as 5 times the excitation resistance.

[0013] As an optimization, simulations were then performed on the above two operating conditions under rated load for damping structure one and damping structure two. The simulation results for the two operating conditions under rated load for damping structure two were obtained. The base values ​​for the calculation results were selected as follows: the voltage base value was the rated voltage, the current base value was the rated current, and the active and reactive base values ​​were the rated capacity.

[0014] As an optimization, relevant parameter data of the generator after loss of excitation and asynchronous operation of the two damping structures were obtained based on the simulation results of the two working conditions mentioned above, and the relevant parameter data were compared and analyzed.

[0015] As an optimization, the number of slots per pole and per phase of the hydro turbine generator is an integer. Based on the symmetry of the magnetic field distribution, a model of one pole is used as the solution region. To ensure calculation accuracy, the moving air gap is divided into 4 layers, of which 2 layers are stationary parts and 2 layers are moving parts. In addition, considering the drastic changes in the magnetic field at the damping slot opening and between the damping strips, the local mesh is finely divided.

[0016] As an optimization, the stator outer circle gh and the rotor inner circle ab in the solution region geometric model are homogeneous boundary conditions, while ac, bd, eg and fh are periodic boundary conditions.

[0017] When performing numerical analysis of time-varying electromagnetic fields, the following assumptions are made:

[0018] 1) Neglecting displacement current, the electromagnetic field is quasi-steady;

[0019] 2) Assuming the magnetic field distribution remains constant along the axial direction, the magnetic field of the motor is equivalent to a two-dimensional field, that is, the current density vector and magnetic potential vector only have 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.

[0020] 3) The material is isotropic, and the hysteresis effect of ferromagnetic materials is ignored, so the BH curve is single-valued;

[0021] 4) The outer surface circumference of the stator and the inner surface circumference of the rotor are homogeneous boundary conditions, i.e., the vector potential is zero.

[0022] The time-varying electromagnetic field equation is:

[0023]

[0024] As an optimization, for the damping strip, the main loss is eddy current loss. This can be calculated using finite element analysis to determine the eddy current density of each sub-unit in the conductor, thus yielding the eddy current loss, as shown in the following formula:

[0025]

[0026] As an optimization, simulation calculations were performed on the two working conditions mentioned above to obtain the simulation results of the second damping structure and to draw 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 of the excitation winding after short-circuiting and losing magnetization through the demagnetizing resistor, the damping bar numbering diagram in the simulation model, the damping bar loss diagram under the two working conditions, and the damping bar loss table under different working conditions for the two damping structures.

[0027] As an optimization, the temperature field of the damping bar under two asynchronous operation conditions of open circuit excitation winding and short circuit through demagnetizing resistor under rated operating conditions is calculated and analyzed, and the calculation model diagram of damping bar temperature rise is obtained.

[0028] The transient simulation of the three-dimensional temperature field of the damping strip considers boundary value problems. The three-dimensional transient heat conduction equation in the anisotropic medium in rectangular coordinates is as follows:

[0029]

[0030] As an optimization, the semi-axial region of the magnetic pole is taken as the computational domain, including the rotor excitation winding, damping bars, iron core, insulating support plate, and iron support plate, etc.

[0031] The following basic assumptions are made:

[0032] 1) The central surface of the magnetic pole core section along the axial direction is an insulating surface;

[0033] 2) Considering the influence of the heat dissipation structure of the excitation winding, each layer of winding was split;

[0034] 3) Considering that the air coming out of the rotor yoke ventilation groove will exchange heat with the excitation winding when it passes through it, it is assumed that the inter-pole air temperature increases linearly in the radial direction; at the same time, based on the air flow state in the air gap, it is assumed that the air temperature is the same on the pole shoe surface.

[0035] 4) Assuming the heat source is uniformly distributed on the excitation winding and the damping bar, since the damping bar loss is periodically distributed after stabilization, the average value of the loss in one cycle is taken for heat source loading during the calculation.

[0036] 5) The effect of thermal radiation is not considered.

[0037] In the calculation, the cold air temperature is considered to be 32℃ based on the cooler outlet air temperature.

[0038] As an optimization, by applying boundary conditions and heat source loading to the finite element model, temperature field diagrams of damping structure 1 under rated operating conditions and two asynchronous demagnetization operating conditions, temperature field diagrams of damping structure 2 under two asynchronous demagnetization operating conditions, and a table of damping strip temperature conditions under rated operating conditions and two demagnetization operating conditions for the two damping structures are obtained.

[0039] As an optimization, based on the temperature rise calculation results of the damping winding in the previous section, the temperature rise of the secondary damping winding meets the requirements. The stator winding current is relatively large under both demagnetization operation conditions; therefore, the stator winding temperature rise under demagnetization asynchronous operation is calculated.

[0040] When calculating the stator temperature field, considering the circumferential symmetry of the stator structure, the axial region of half-tooth and half-slot is taken as the computational domain. This includes the windings, core, insulation, and slot wedges, with the following basic assumptions:

[0041] 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;

[0042] 2) It is believed that the insulation of the slot wedge and the outside of the conductor is the same material;

[0043] 3) Only the winding portion is considered at the end;

[0044] 4) Considering that the air in the stator radial ventilation groove exchanges heat with the stator core and coils, it is assumed that the air temperature increases linearly along the radial direction;

[0045] 5) The effect of thermal radiation is not considered.

[0046] As an optimization, based on the temperature calculation results of the second stator bar of the damping structure, the impact of 20 minutes of demagnetization operation on the insulation life of the stator bar was further analyzed.

[0047] The temperature index of stator bars can be evaluated using the conventional method, the point-slope method, and the secant method. All of these methods are based on the thermal aging life equation.

[0048]

[0049] The thermogravimetric analysis (TGA) method is derived directly from the TG curve. Its advantages include simplicity and speed, and the results can characterize the chemical stability of the material and roughly analyze the heat resistance temperature index. The thermogravimetric curves of the stator bar main insulation were tested using a TGA analyzer at speeds of 3℃ / min and 5℃ / min, respectively.

[0050] As an optimization, the thermogravimetric method was used to calculate the temperature resistance of the main insulation of the stator winding of the Bala power station hydroelectric generator to be 161.6℃, and the heat resistance class to be F, based on the apparent decomposition temperature, weight loss temperature and functional coefficient of the stator bars.

[0051] The formula relating insulation life (L) to the continuous operating temperature (T) of the motor is as follows:

[0052]

[0053]

[0054] The operating temperature of a typical generator set is around 100℃, and its insulation life is approximately 39.9 years. Based on the stator bar temperature calculated in the previous section, the insulation life of the stator bars under two demagnetization conditions was evaluated and calculated.

[0055] A magnetic pole damping structure for a hydro-generator rotor winding includes a magnetic pole fixing base, a connecting piece, a magnetic pole body, and a damping ring employing a large damping plate structure. The magnetic pole body is distributed circumferentially along the magnetic pole fixing base, and the damping ring extends radially and completely covers one side of the magnetic pole body. A magnetic pole clamping block is provided between each adjacent pair of damping rings. A magnetic pole tie rod is inserted into the magnetic pole clamping block, and the magnetic pole clamping block is tightened and fixed to the magnetic pole fixing base by the magnetic pole tie rod. A T-shaped tail rod is provided at the bottom of the magnetic pole body and is embedded therein. Within the T-shaped groove of the magnetic pole fixing seat, several thickened damping rods are inserted into the outer side of the damping ring, extending radially through the damping ring to the entire magnetic pole body. These rods are integrated with the magnetic pole via a tensioning screw, allowing the centrifugal force of the damping ring to be borne by the magnetic pole tensioning screw and the T-shaped tail plate of the damping ring, thus preventing it from being thrown out due to excessive centrifugal force. Furthermore, the two sides of the damping ring are bent into angle steel shapes and secured to the magnetic pole clamping block with screws. The centrifugal force of the damping ring extending beyond the magnetic pole is borne by the magnetic pole clamping block, further improving stability.

[0056] (III) Beneficial Effects

[0057] Compared with existing technologies, this utility model provides a method for improving the demagnetization operation capability of hydro-generators, which has the following beneficial effects:

[0058] 1. The magnetic pole damping structure of the rotor winding of the hydro-generator is improved by increasing the diameter of the damping ring and damping bar, and by conducting simulation analysis and test bench verification on various demagnetization asynchronous operation conditions of the rotor after the reinforcement design. This can effectively improve the demagnetization asynchronous operation capability of the hydro-generator unit.

[0059] 2. The rotor winding magnetic pole damping structure of this hydro-generator, by combining the excitation conditions, analyzes and calculates the current and temperature rise of the damping bars, damping rings, and excitation leads, and takes effective measures to meet the 20-minute demagnetization operation requirement. This provides operators with time to handle demagnetization faults, facilitates the rapid elimination of demagnetization faults, restores excitation to achieve resynchronization, enables the generator to return to normal operation, reduces power outage losses for users, and ensures reliable power supply.

[0060] 3. The rotor winding magnetic pole damping structure of this hydro-generator features a damping ring that extends radially to the entire magnetic pole body and is integrated with the magnetic pole via a tensioning screw. This allows the centrifugal force of the damping ring to be borne by the magnetic pole tensioning screw and the T-shaped tailplate of the damping ring, preventing it from being thrown out due to excessive centrifugal force. Furthermore, the damping ring is bent into an angle steel shape on both sides and secured to the magnetic pole clamping block with screws. The centrifugal force of the portion of the damping ring extending beyond the magnetic pole is borne by the magnetic pole clamping block, further improving stability. This structure also enhances the current-carrying capacity of components such as the generator rotor damping ring and damping bars, extending their service life. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the simulation model of the practical system;

[0062] Figure 2 This is a schematic diagram of the simulation results of the asynchronous operation of the excitation winding with open circuit and loss of excitation under the rated load condition of the two practical damping structures.

[0063] Figure 3 This is a schematic diagram of the simulation results of the asynchronous operation of the two excitation windings under rated load conditions with short circuit and loss of excitation through the demagnetizing resistor in this practical damping structure.

[0064] Figure 4 This is a schematic diagram of the finite element calculation model for the practical hydro-generator;

[0065] Figure 5 This is a schematic diagram of the magnetic field lines and magnetic flux density distribution during steady-state operation under rated working conditions of this utility model;

[0066] Figure 6 This is a schematic diagram of the magnetic field lines and magnetic flux density distribution under the asynchronous operation condition of short-circuit demagnetization resistor in this practical application.

[0067] Figure 7 This is a schematic diagram showing the numbering of the damping bars in this practical application;

[0068] Figure 8 This is a schematic diagram of the damping bar loss under different rated load conditions in the asynchronous operation state of the damping structure of this practical damping structure.

[0069] Figure 9 This is a schematic diagram of the temperature rise calculation model for damping bars in this practical application.

[0070] Figure 10The temperature field contour maps of the damping strips under rated conditions and two asynchronous operation conditions of demagnetization of this practical damping structure are shown.

[0071] Figure 11 Temperature field contour maps of the damping strips under two rated conditions and two asynchronous operation conditions with demagnetization of this practical damping structure;

[0072] Figure 12 This is a schematic diagram of the finite element model of the stator in this practical application.

[0073] Figure 13 This is a stator temperature cloud diagram under rated operating conditions for this application.

[0074] Figure 14 This is a stator temperature cloud map for 20 minutes under open-circuit demagnetization operation conditions.

[0075] Figure 15 This is a stator temperature cloud map for 20 minutes under the short-circuit demagnetization condition of the demagnetizing resistor in this practical application.

[0076] Figure 16 This is a schematic diagram of the thermal weight loss curve of the main insulation of the stator bar in this practical application.

[0077] Figure 17 This is a top view of a partial structure of the rotor in this practical application.

[0078] In the diagram: 1. Connecting plate; 2. Magnetic pole body; 3. Damping ring; 4. Magnetic pole clamping block; 5. Magnetic pole tie rod; 6. T-shaped tail plate; 7. Damping rod. Detailed Implementation

[0079] In the description of this application, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0080] The technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0081] refer to Figure 17A magnetic pole damping structure for a hydro-generator rotor winding includes a magnetic pole fixing base, a connecting piece 1, a magnetic pole body 2, and a damping ring 3 employing a large damping plate structure. The magnetic pole body 2 is distributed circumferentially along the magnetic pole fixing base, and the damping ring 3 extends radially and completely covers one side of the magnetic pole body 2. A magnetic pole clamping block 4 is provided between each adjacent pair of damping rings 3. A magnetic pole tie 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 base by the magnetic pole tie rod 5. A T-shaped tail rod 6 is provided at the bottom of the magnetic pole body 2. The damping ring 3 is embedded in a T-shaped groove within the magnetic pole fixing seat. Several thickened damping rods 7 are inserted into the outer side of the damping ring 3, extending radially through the damping ring to the entire magnetic pole body. They are integrated with the magnetic pole by a tensioning screw, allowing the centrifugal force of the damping ring to be borne by the magnetic pole tensioning screw and the T-shaped tail plate of the damping ring, thus preventing it from being thrown out due to excessive centrifugal force. Furthermore, the two sides of the damping ring are bent into the shape of angle steel and secured to the magnetic pole clamping block with screws. The centrifugal force of the damping ring extending beyond the magnetic pole is borne by the magnetic pole clamping block, further improving stability.

[0082] refer to Figures 1-16 A method for improving the demagnetization operation capability of a hydro-generator is proposed. The method uses a system simulation model 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 demagnetizing resistor, ROTOR is the rotor, TURBINE is the hydro-turbine, and VREG1 is the excitation regulator.

[0083] The specific method is as follows:

[0084] S1. First, the two operating conditions are simulated using a system simulation model. The specific simulation conditions are as follows:

[0085] Operating condition 1 is asynchronous operation with open circuit and loss of excitation of the excitation winding: The generator is running stably under rated load. After 2 seconds, the excitation circuit suddenly opens, and CE1 and CE3 are disconnected.

[0086] Operating condition 2 is asynchronous operation with demagnetization due to short circuit of excitation winding via demagnetizing resistor: The generator operates stably under rated load. After 2 seconds, the excitation circuit is short-circuited with demagnetizing resistor. CE1 is open and CE3 is closed. The resistance value of R is given as 5 times the excitation resistance.

[0087] S2. Simulate the above two working conditions under rated load for damping structure one and damping structure two, and obtain the simulation results of the two working conditions under rated load for damping structure two. The base values ​​for the calculation results are selected as follows: the base value of voltage is the rated voltage, the base value of current is the rated current, and the base values ​​of active and reactive power are the rated capacity.

[0088] S3, such as Figures 2-3As shown in the table below, the relevant parameter data of the generator after loss of excitation and asynchronous operation of the two damping structures are obtained based on the simulation results of the two working conditions. The relevant parameter data are compared and analyzed.

[0089]

[0090] As can be seen from the table above:

[0091] 1) The average stator current under both loss-of-excitation operating conditions exceeds the rated value.

[0092] 2) Compared with damping structure one, the average value of stator current and the minimum value of terminal voltage do not change much under the two operating conditions; the maximum speed is slightly reduced.

[0093] When a hydro-generator loses its magnetization during rated operation, a high voltage will be generated in the excitation winding at the moment of the fault. The excitation winding voltage under different loss-of-magnetization conditions is shown in the table below.

[0094]

[0095] As can be seen from the table above, the excitation winding voltage (during fault moment and steady-state operation) in operating condition 1 is higher than that in operating condition 2, with a maximum value of about 3000V. The rated excitation voltage of the hydro-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.

[0096] S4. The number of slots per pole and per phase of the hydro-generator is an integer. Based on the symmetry of the magnetic field distribution, a model of one pole is used as the solution area. To ensure the accuracy of the calculation, the moving air gap is divided into 4 layers, of which 2 layers are stationary parts and 2 layers are moving parts. In addition, considering the drastic changes in the magnetic field at the damping slot opening and between the damping strips, the local mesh is finely divided.

[0097] like Figure 4 As shown, in the solution domain geometric model, the stator outer circle gh and the rotor inner circle ab are homogeneous boundary conditions, while ac, bd, eg and fh are periodic boundary conditions.

[0098] When performing numerical analysis of time-varying electromagnetic fields, the following assumptions are made:

[0099] 1) Neglecting displacement current, the electromagnetic field is quasi-steady;

[0100] 2) Assuming the magnetic field distribution remains constant along the axial direction, the magnetic field of the motor is equivalent to a two-dimensional field, that is, the current density vector and magnetic potential vector only have 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.

[0101] 3) The material is isotropic, and the hysteresis effect of ferromagnetic materials is ignored, so the BH curve is single-valued;

[0102] 4) The outer surface circumference of the stator and the inner surface circumference of the rotor are homogeneous boundary conditions, i.e., the vector potential is zero.

[0103] The time-varying electromagnetic field equation is:

[0104]

[0105] For damping bars, the main loss is eddy current loss. The eddy current density of each sub-unit in the conductor can be calculated using finite element analysis, and thus the eddy current loss can be obtained, as shown in the following formula:

[0106]

[0107] S5. By performing simulation calculations on the above two working conditions, the simulation results of the second damping structure are obtained, and the magnetic field lines and magnetic flux density distribution diagram at a certain moment under the rated working condition are drawn (e.g., Figure 5 As shown), the magnetic field lines and magnetic flux density distribution diagram at a certain moment under the asynchronous operation condition of the excitation winding being short-circuited and losing excitation through the demagnetizing resistor (as shown). Figure 6 As shown), the damping bar numbering diagram in the simulation model (e.g.) Figure 7 As shown), the damping strip loss diagrams under two operating conditions (as shown) Figure 8 As shown in the figure, the damping strip loss table for the two damping structures under different operating conditions is as follows:

[0108]

[0109] As can be seen from the table above:

[0110] 1) The damping strip loss is very small under rated operating conditions; under demagnetized asynchronous operation, the damping strip loss value is much larger under operating conditions one than under operating conditions two.

[0111] 2) Damping structure II has significantly reduced losses compared to damping structure I.

[0112] S6. Calculate and analyze the temperature field of the damping bar under two conditions of asynchronous operation with the excitation winding open-circuited and short-circuited via the demagnetizing resistor, such as... Figure 9 As shown, the calculation model diagram for the temperature rise of the damping strip is obtained;

[0113] The transient simulation of the three-dimensional temperature field of the damping strip considers boundary value problems. The three-dimensional transient heat conduction equation in the anisotropic medium in rectangular coordinates is as follows:

[0114]

[0115] The computational domain is the semi-axial region of the magnetic pole, which includes the rotor excitation winding, damping bars, iron core, insulating support plate, and iron support plate, etc.

[0116] The following basic assumptions are made:

[0117] 1) The central surface of the magnetic pole core section along the axial direction is an insulating surface;

[0118] 2) Considering the influence of the heat dissipation structure of the excitation winding, each layer of winding was split;

[0119] 3) Considering that the air coming out of the rotor yoke ventilation groove will exchange heat with the excitation winding when it passes through it, it is assumed that the inter-pole air temperature increases linearly in the radial direction; at the same time, based on the air flow state in the air gap, it is assumed that the air temperature is the same on the pole shoe surface.

[0120] 4) Assuming the heat source is uniformly distributed on the excitation winding and the damping bar, since the damping bar loss is periodically distributed after stabilization, the average value of the loss in one cycle is taken for heat source loading during the calculation.

[0121] 5) The effect of thermal radiation is not considered.

[0122] In the calculation, the cold air temperature is considered to be 32℃ based on the cooler outlet air temperature.

[0123] S7. By applying boundary conditions and heat source loading to the finite element model, temperature field diagrams are obtained under the rated operating condition of the damping structure and damping strip, and under two asynchronous operation conditions of demagnetization (e.g., Figure 10 (As shown), temperature field diagrams under two asynchronous operation conditions of demagnetization of the damping structure (as shown) Figure 11 As shown in the table, the temperature of the damping strip under the rated operating conditions and the two demagnetization conditions for the two damping structures is as follows:

[0124]

[0125] The standard JB / T8445-1996, "Test Method for Negative Sequence Current Withstand Capability of Three-Phase Synchronous Generators", specifies that the maximum allowable temperature of copper damping strips for long-term and short-term operation of the generator is 130℃ and 220℃, respectively.

[0126] 1) According to the standard, the damping bar structure reaches the temperature limit after 143 seconds of open-circuit demagnetization under rated load, and the excitation coil can be safely operated for 20 minutes after short-circuiting demagnetization through the demagnetizing resistor.

[0127] 2) The damping bar structure can operate safely for 20 minutes under rated load with both the excitation winding open-circuited and short-circuited via the demagnetizing resistor.

[0128] S8. Based on the temperature rise calculation results of the damping winding in the previous section, the temperature rise of the secondary damping winding meets the requirements. The stator winding current is relatively large under both demagnetization operation conditions; therefore, the stator winding temperature rise under demagnetization asynchronous operation conditions is calculated.

[0129] When calculating the stator temperature field, considering the circumferential symmetry of the stator structure, the axial region of half-tooth and half-slot is taken as the computational domain. This includes the windings, core, insulation, and slot wedges, with the following basic assumptions:

[0130] 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;

[0131] 2) It is believed that the insulation of the slot wedge and the outside of the conductor is the same material;

[0132] 3) Only the winding portion is considered at the end;

[0133] 4) Considering that the air in the stator radial ventilation groove exchanges heat with the stator core and coils, it is assumed that the air temperature increases linearly along the radial direction;

[0134] 5) The effect of thermal radiation is not considered.

[0135] Considering the motor's altitude of 2700 meters, the air properties change, and the cooling air's heat exchange performance decreases. Therefore, outlet air temperature compensation is performed during the air cooler calculation. The stator temperature rise calculation assumes a cooler outlet air temperature of 32℃.

[0136] The geometric solution model and mesh lines are as follows: Figure 12 As shown, the stator temperature distribution of damping structure II under rated operating conditions and 20-minute demagnetization conditions (open circuit and short circuit via demagnetizing resistor) is as follows: Figure 13 , Figure 14 , Figure 15 As shown.

[0137] The calculated stator temperature field results under rated operating conditions and 20-minute demagnetization conditions (open circuit and short circuit via demagnetizing resistor) are shown in the table below:

[0138]

[0139] The stator temperature field calculation considers the changes in air physical parameters at an altitude of 2700 meters, with cold air calculated at 32℃. The calculation results show that:

[0140] 1) Under rated operating conditions, the highest temperature of the stator bars is approximately 105.64℃, with a temperature rise of 73.64K;

[0141] 2) During 20 minutes of open-circuit demagnetization operation, the highest temperature of the stator bars was approximately 164.79℃, with a temperature rise of 132.79K;

[0142] 3) After 20 minutes of operation with short-circuit demagnetization via the demagnetizing resistor, the highest temperature of the stator bar is approximately 166.61℃, with a temperature rise of 134.61K.

[0143] S9. Based on the temperature calculation results of the second stator bar of the damping structure, further analyze the impact of 20 minutes of demagnetization operation on the insulation life of the stator bar.

[0144] The temperature index of stator bars can be evaluated using the conventional method, the point-slope method, and the secant method. All of these methods are based on the thermal aging life equation.

[0145]

[0146] The thermogravimetric analysis (TGA) method directly calculates the thermogravimetric curves from the TG curve. Its advantages include simplicity and speed, and the results can characterize the chemical stability of the material and roughly analyze the heat resistance temperature index. The thermogravimetric curves of the stator bar main insulation were tested using a TGA analyzer at speeds of 3℃ / min and 5℃ / min (e.g.,...). Figure 16 (as shown)

[0147] Using the thermogravimetric method, the temperature resistance of the main insulation of the stator winding of the Bala power station hydro-generator was calculated to be 161.6℃ based on the apparent decomposition temperature, weight loss temperature and functional coefficient of the stator bars, and the heat resistance class was F.

[0148] The formula relating S10, insulation life (L), and continuous operating temperature (T) of the motor is as follows:

[0149]

[0150]

[0151] The normal operating temperature of a typical generator set is around 100℃, and the insulation life is approximately 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 table below:

[0152]

[0153] As can be seen from the table above, the two demagnetization operation conditions have basically the same impact on the stator bar insulation, accounting for about 0.002% of the entire stator bar lifespan, and have a very small impact on the overall lifespan of the stator bar.

[0154] S10. Through simulation analysis of the asynchronous operation under rated load loss of magnetization of two damping structures of the hydro-generator, the losses and temperature rise of the damping winding and stator bars were calculated, and the following conclusions were obtained:

[0155] 1) According to the reference standard JB / T8445-1996 "Test Method for Negative Sequence Current Withstand Capability of Three-Phase Synchronous Generators", the maximum allowable temperature of the copper damping strip during long-term and short-term operation of the generator is 130℃ and 220℃, respectively. The temperature rise results of the damping strip under rated load conditions for the two damping structures are as follows:

[0156] Damping Structure 1: Under rated load, after 143 seconds of open-circuit demagnetization operation, the temperature limit is reached. The excitation coil can be safely operated for 20 minutes after short-circuiting demagnetization via the demagnetizing resistor.

[0157] Damping Structure Two: Under rated load, the temperature of the damping strip did not exceed the standard after 20 minutes of operation under both demagnetization conditions. Therefore, this damping structure is adopted in the generator design.

[0158] 2) The stator bar losses and temperature rise under two working conditions of open circuit and short circuit through demagnetizing resistor under the rated load of the damping structure were calculated. The highest temperature of interlayer RTD / stator bar under the open circuit and short circuit through demagnetizing resistor conditions was 143℃ / 167℃.

[0159] The temperature rise of the stator bars is basically the same under both demagnetization operating conditions. Running under this condition for 20 minutes accounts for approximately 0.002% of the total stator bar lifespan, having a negligible impact on the overall lifespan. In other words, running under both demagnetization operating conditions for 20 minutes under rated load has little impact on the stator winding insulation, a small impact on the withstand voltage level, and the insulation will not carbonize.

[0160] 3) The insulation performance of the excitation winding meets the requirements for demagnetization operation.

[0161] In principle, hydro-generators are not allowed to operate asynchronously after loss of excitation, and the protection system will activate accordingly after the generator loses excitation to disconnect the hydro-generator to prevent impact on the power grid, or to ensure the stability of the unit and system by reducing the load.

[0162] In the description of this utility model, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," "link," and "fix" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0163] All standard parts used in this utility model can be purchased from the market, and irregular parts can be customized according to the instructions and attached drawings.

[0164] The above are merely preferred embodiments of this utility model, but the scope of protection of this utility model is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this utility model, based on the technical solution and practical concept of this utility model, should be included within the scope of protection of this utility model.

Claims

1. A magnetic pole damping structure for a rotor winding of a hydro-generator, characterized in that: The device includes a magnetic pole fixing base, a connecting piece (1), a magnetic pole body (2), and a damping ring (3) with a large damping plate structure. The magnetic pole body (2) is distributed circumferentially along the magnetic pole fixing base. The damping ring (3) extends radially and completely covers one side of the magnetic pole body (2). A magnetic pole clamping block (4) is provided between each adjacent two sides of the damping ring (3). The two sides of the damping ring (3) are bent into the shape of angle steel and screwed onto the magnetic pole clamping block (4). A magnetic pole pull rod (5) is inserted into the magnetic pole clamping block (4). The magnetic pole clamping block (4) is tightened and fixed on the magnetic pole fixing base by the magnetic pole pull rod (5). A T-shaped tail rod (6) is provided at the bottom of the magnetic pole body (2) and is embedded in the T-shaped groove opened in the magnetic pole fixing base. Several thickened damping rods (7) are inserted into the outer side of the damping ring (3).

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