Online monitoring method and storage medium for GCB contact resistance of large generators

Abstract

The invention discloses an online monitoring method for GCB contact resistance of a large generator and a storage medium, wherein the method comprises: step S1, obtaining GCB real-time load current, SF6 gas cooler size parameters, SF6 gas cooler real-time temperature, SF6 gas temperature change and GCB real-time temperature; step S2, determining SF6 gas cooler heat dissipation according to SF6 gas cooler size parameters and SF6 gas cooler real-time temperature; calculating generator contact heat dissipation according to GCB real-time temperature; calculating gas heat absorption work according to SF6 gas temperature change; step S3, calculating contact resistance according to GCB real-time load current, SF6 gas cooler heat dissipation, generator contact heat dissipation and gas heat absorption work; the method helps to prevent insulation damage such as rapid expansion, leakage and explosion of SF6 gas caused by abnormal increase of contact resistance and overheating of GCB by real-time monitoring of GCB contact resistance, thereby avoiding safety incidents.

Description

Technical Field

[0001] The invention relates to the technical field of generator monitoring, and in particular to an online monitoring method and storage medium for GCB contact resistance of a large generator. Background Art

[0002] GCB is the node for the generator to be connected to the grid. Its safe operation determines whether the generator can be reliably connected to the grid for power generation. Large GCBs are expensive and have complex manufacturing processes. GCBs are generally insulated with SF6 gas, and the heat generated by the GCB is taken out of the GCB through the cooler through SF6 gas. In normal operation, the heat generated by the GCB and the heat dissipated by the SF6 gas cooler can maintain a dynamic balance. However, if the GCB operating mechanism or GCB contact fails to operate properly, the contact contact is poor, and the contact resistance increases, the GCB will heat up abnormally under the action of the load current, burn the contact, and accelerate the vicious cycle of increased contact resistance and increased heat. In the insulation technology supervision work, the GCB contact resistance test is a must-test item in the annual preventive test. However, during operation, if the GCB contact resistance increases due to improper operation, the harm is fatal. Therefore, it is necessary to strengthen the online monitoring of the GCB contact resistance.

[0003] At present, the GCB contact resistance test must be carried out when the unit is under maintenance. It is necessary to remove the soft links at both ends of the GCB, give a DC current of at least 100A between the input and output ends, and then connect the measuring equipment to the given hole. According to the ratio of 100μV to 1μΩ, the voltage measured between these two points can be used to calculate the resistance value.

[0004] As for the operation status monitoring of GCB, the SF6 gas density relay is used to monitor the SF6 gas pressure, and an alarm or lock operation is issued when the pressure drops. Its principle has a fatal weakness. It only monitors the pressure. When the volume remains unchanged, P / T=P0 / T0 is established. However, if there is a gas leak, the temperature rises, and the pressure may rise instead of falling. This makes it impossible to correctly judge whether there is a SF6 gas leak, and it is also impossible to correctly judge the abnormal change of the contact resistance of the GCB. At the same time, because it consumes a certain amount of SF6 gas during monitoring, it needs to be replenished regularly. In addition, its monitoring is not continuous, and the defect of poor contact of the GCB cannot be reflected and judged in time, and the real-time protection of the GCB cannot be achieved. Summary of the invention

[0005] In view of the above problems, the inventors provide a method for real-time online monitoring of the contact resistance of a large GCB, so as to judge the operating condition of the GCB and improve safety.

[0006] According to a first aspect, the present invention provides a method for online monitoring of GCB contact resistance of a large generator, comprising:

[0007] Step S1: obtaining the real-time load current of the GCB, the size parameters of the SF6 gas cooler, the real-time temperature of the SF6 gas cooler, the temperature change of the SF6 gas and the real-time temperature of the GCB;

[0008] Step S2: determining the heat dissipation of the SF6 gas cooler according to the size parameters of the SF6 gas cooler and the real-time temperature of the SF6 gas cooler;

[0009] Calculate the heat dissipation of the generator contact according to the real-time temperature of the GCB;

[0010] Calculate the work done by the gas by absorbing heat according to the temperature change of SF6 gas between the measuring points;

[0011] Step S3: Calculate the contact resistance according to the real-time load current of the GCB, the heat dissipation of the SF6 gas cooler, the heat dissipation of the generator contact and the work done by the gas absorbing heat.

[0012] Furthermore, the real-time temperature of the SF6 gas cooler includes: the ambient temperature of the SF6 gas cooler, the inlet temperature of the SF6 gas cooler and the outlet temperature of the SF6 gas cooler;

[0013] In step S2, the step of determining the heat dissipation of the SF6 gas cooler includes:

[0014] The heat dissipation area of ​​the SF6 gas cooler is calculated according to the size parameters of the SF6 gas cooler, and the geometric characteristic length of the heat transfer surface of the cooler is calculated according to the heat dissipation area of ​​the SF6 gas cooler;

[0015] Based on the dry air physical property table, determine the corresponding characteristic quantity according to the ambient temperature of the SF6 gas cooler;

[0016] Calculating the Grashof number according to the characteristic quantity and the geometric characteristic length of the heat transfer surface of the cooler;

[0017] According to the Grashof number, calculate the Nusselt number;

[0018] The air convection heat dissipation coefficient is calculated based on the Nusselt number and the thermal conductivity of the SF6 gas cooler at ambient temperature;

[0019] The heat dissipation of the SF6 gas cooler is calculated based on the air convection heat dissipation coefficient, the SF6 gas cooler inlet temperature and the SF6 gas cooler outlet temperature.

[0020] Furthermore, the air convection heat dissipation coefficient h is:

[0021]

[0022] Among them, Nu is the Nusselt number; L is the geometric characteristic length of the heat transfer surface of the cooler; λ is the thermal conductivity of air.

[0023] Further, the GCB real-time temperature includes: GCB main transformer side busbar temperature, GCB generator side busbar temperature, GCB main transformer side busbar temperature and GCB generator side busbar temperature;

[0024] In step S2, the step of calculating the heat dissipation of the generator contact according to the real-time temperature of the GCB includes:

[0025] Calculate the heat dissipation at the GCB moving contact end based on the busbar temperature on the GCB main transformer side and the busbar temperature on the GCB main transformer side;

[0026] The heat dissipation at the GCB static contact end is calculated based on the busbar temperature on the GCB generator side and the busbar temperature on the GCB generator side.

[0027] Furthermore, the step S3 comprises:

[0028] The total heat dissipation of GCB is calculated by summing the heat dissipation of SF6 gas cooler, the heat dissipation of generator contacts and the work done by gas heat absorption;

[0029] Based on the electric power principle, the contact resistance is calculated according to the real-time load current of the GCB and the total heat dissipation of the GCB.

[0030] Furthermore, in step S1, the step of obtaining the real-time load current of the GCB includes:

[0031] Acquire current data of multiple sampling periods before the current sampling period;

[0032] The current data of the multiple sampling periods are weighted averaged to obtain the GCB real-time load current.

[0033] Furthermore, the method further comprises:

[0034] It is determined whether the calculated contact resistance reaches a threshold value, and if the calculated contact resistance is greater than or equal to the threshold value, an alarm is issued.

[0035] According to a second aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program can be executed by a processor to implement the steps of the method described above.

[0036] The principle of the present invention is:

[0037] According to the structural characteristics of GCB, under normal circumstances (GCB contact resistance is within the qualified range), the heat generated by the load current and the heat dissipation through the cooler and other parts will maintain a dynamic balance relationship under a certain temperature rise. By calculating all the heat dissipation, according to the electric power generated by the equivalent load current I per unit time of GCB and the total heat dissipation of GCB per unit time Q / t=I 2 R, calculate the contact resistance R.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The method provided by the present invention calculates the GCB contact resistance in real time by comprehensively considering the GCB temperature and the SF6 gas cooler, thereby providing a guarantee for safe production and also contributing to the protection of the GCB.

[0040] (2) This method helps prevent insulation damage such as rapid expansion, leakage, and explosion of SF6 gas due to overheating caused by abnormal increase in contact resistance of GCB by real-time monitoring of GCB contact resistance, thereby avoiding safety incidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the structure of GCB;

[0042] Figure 2 This is a schematic diagram of GCB heat dissipation;

[0043] Figure 3 It is a three-dimensional diagram of the SF6 gas cooler;

[0044] Figure 4 is a schematic diagram of a SF6 gas cooler;

[0045] Figure 5 A flow chart of the on-line monitoring method for GCB contact resistance of a large generator provided by the present invention;

[0046] Figure 6 This is a line graph of the data of GCB online monitoring in Example 2. DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0048] Example 1

[0049] like Figure 1-2 As shown, the principle of achieving thermal balance of large generator GCB is:

[0050] The current flows from the generator to the GCB and the related accessories of the disconnector. Due to the contact resistance of the GCB and the disconnector, the heat generated is mainly dissipated to the air through the SF6 gas cooler (convection heat dissipation). Since the GCB contacts are all in the SF6 gas chamber, the SF6 gas chamber material is epoxy material, which is considered to be non-heat conductive in this application; the disconnector is connected to the GCB moving contact, static contact and fixed accessories, and most of its heat is absorbed by the SF6 gas and taken out of the GCB through the cooler. Some of it is exchanged through heat conduction through the copper soft connection at both ends to connect the seal mother, and a small part is radiated to the air inside the seal mother through the conductor surface. Under normal circumstances, the overall contact resistance of the GCB is very small (usually a few uΩ), and its heat generation and heat dissipation can reach a dynamic equilibrium relationship after the load current stabilizes.

[0051] In view of the characteristics of GCB, the present invention provides a method for online monitoring of GCB contact resistance of a large generator by calculating the overall heat generated by GCB and then calculating the contact resistance based on the electric power principle, which specifically includes the following steps:

[0052] Step S1: Obtain the real-time load current I of the GCB, the size parameters of the SF6 gas cooler, the real-time temperature of the SF6 gas cooler, and the temperature change of the SF6 gas Δt 气 and GCB real-time temperature.

[0053] Among them, because the acquired data are all measured values, and the current changes rapidly with the load, with a large amplitude, while the temperature change is continuous and slow, which is a heat accumulation response process, and the load current changes rapidly with the system demand, the temperature, current and other measurement values ​​imported by the monitoring system are all real-time values. Therefore, in order to better reflect the relationship between temperature rise and load current, it is necessary to process the current data to eliminate the impact of its large changes. The data processing methods generally include Fourier transform, integration per unit time, weighted average, etc. In this application, the steps of obtaining the real-time load current I of GCB include:

[0054] Obtain current data of multiple sampling cycles (preferably 10 to 15 sampling cycles) before the current sampling cycle. Perform weighted averaging on the current data of the multiple sampling cycles to obtain the GCB real-time load current I. The GCB real-time load current I at this time is the average value of multiple sampling cycles, which can effectively suppress the impact of large load changes. The GCB real-time load current I at this time can reflect the relationship between temperature rise and current in this time period, and reach an effective time delay to truly reflect the effect of heat accumulation.

[0055] like Figure 3-4As shown, the SF6 gas cooler is mainly composed of heat dissipation pipes, fins and horizontal and vertical large pipes with the same diameter. Taking a certain model of cooler as an example, its main parameters are: large pipe diameter d1=200mm, vertical large pipe height h1=260mm, horizontal large pipe width L2=960mm, heat dissipation pipe diameter d2=45mm, pipe thickness m=6mm, fin number n=420 pieces / meter, fin thickness d3=0.8mm, fin height h2=6.5mm, heat dissipation pipe length l1=880mm, fin tube length l2=840mm, heat dissipation pipe number N=8, original pipe length L1=l1-l2=40mm, fin base thickness d4=1.2mm.

[0056] The GCB real-time temperature includes: GCB main transformer side busbar temperature t1, GCB generator side busbar temperature t2, GCB main transformer side busbar temperature t3 and GCB generator side busbar temperature t4.

[0057] The real-time temperature of the SF6 gas cooler includes: the ambient temperature t5 of the SF6 gas cooler, the outlet temperature t6 of the SF6 gas cooler and the inlet temperature t7 of the SF6 gas cooler.

[0058] Step S2: Determine the heat dissipation Q1 of the SF6 gas cooler according to the size parameters of the SF6 gas cooler and the real-time temperature of the SF6 gas cooler. Specifically:

[0059] The heat dissipation area of ​​the SF6 gas cooler is calculated based on the above SF6 gas cooler size parameters, and all heat dissipation areas are projected to the vertical direction to perform equivalent area calculation.

[0060] The heat dissipation of SF6 gas cooler consists of three parts: large tube heat dissipation, fin heat dissipation and fin tube heat dissipation. Therefore, its heat dissipation area is the sum of the heat dissipation areas of the three parts, and the equivalent area S is:

[0061] S=S 1-1 +S 1-2 +S 1-3 +S2+S 3-1 +S 3-2 +S 3-3

[0062] Among them, S 1-1 is the vertical equivalent area of ​​the heat dissipation area of ​​the two vertical large tubes; S 1-2 is the vertical equivalent area of ​​the heat dissipation area of ​​the two horizontal large tubes; S 1-3 is the vertical equivalent area of ​​the heat dissipation area at the ends of the two horizontal large tubes; S2 is the vertical equivalent area of ​​the heat dissipation area of ​​the warping sheet; S 3-1 is the vertical equivalent area of ​​the heat dissipation area of ​​the heat pipes at both ends; S 3-2 is the vertical equivalent area of ​​the heat dissipation area of ​​the total warped tube; S 3-3It is the vertical equivalent area of ​​the heat dissipation area of ​​a circular tube with the diameter of the heat pipe plus the base thickness of the warp plate d4.

[0063] Taking the above parameters as an example, the equivalent area S = 7.795667565m 2 , then convert all the heat dissipation pipes of the cooler to the height under the equivalent vertical area corresponding to 1m width, which is the geometric characteristic length L of the heat transfer surface. L = 7.795667565m.

[0064] Based on the dry air physical property table (as shown in Table 1), the corresponding characteristic quantity is determined according to the SF6 gas cooler ambient temperature t5.

[0065] Table 1 Physical properties of dry air (101.33Pa)

[0066]

[0067] Grashof number Where: g is the acceleration of gravity; L is the geometric characteristic length of the heat transfer surface; ρ is the air density corresponding to the ambient temperature t5 of the SF6 gas cooler; Δt is the temperature rise; μ is the air viscosity corresponding to t5.

[0068] Then Nusselt number Nu=0.36+0.363Gr 1 / 6 +0.0614Gr 1 / 3

[0069] The air convection heat dissipation coefficient h is calculated according to the Nusselt number:

[0070]

[0071] λ is the thermal conductivity of air.

[0072] The heat dissipation of the SF6 gas cooler is calculated based on the air convection heat dissipation coefficient h, the geometric characteristic length L of the heat transfer surface, the SF6 gas cooler inlet temperature t7, and the SF6 gas cooler outlet temperature t6. The heat dissipation of the SF6 gas cooler Q1 = h × L × (t7-t6)

[0073] The heat dissipation of the generator contact is calculated based on the real-time temperature of the GCB. By measuring the cross-sectional area of ​​the GCB end seal, consulting the copper-aluminum heat transfer coefficient, calculating the temperature difference between the GCB busbar and the busbar, the heat dissipation from the end to the busbar conductor (i.e. the heat dissipation of the contact) is calculated. This includes the heat dissipation of the GCB moving contact end and the heat dissipation of the GCB static contact end.

[0074] GCB moving contact end heat dissipation Q2 = δ × λ × S 端部 ×(t2-t4)

[0075] GCB static contact end heat dissipation Q3 = δ × λ × S 端部×(t1-t3)

[0076] Where, δ is the conductivity of copper, δ = 0.935; λ is the thermal conductivity of copper, λ = 401 W / (m·K); S 端部 It is the cross-sectional area of ​​the GCB end female flexible connection.

[0077] The work done by the gas by absorbing heat is calculated based on the temperature change of SF6 gas. Specifically:

[0078] The temperature change of SF6 gas between the previous sampling period and the current sampling period is Δt 气 , then the gas absorbs heat and does work Q4 = mcΔt 气 .

[0079] The total heat dissipation of GCB is Q = Q1 + Q2 + Q3 + Q4

[0080] Step S3: Calculate the contact resistance R according to the real-time load current I of the GCB and the total heat dissipation Q of the GCB per unit time.

[0081] Furthermore, the method further comprises:

[0082] It is determined whether the calculated contact resistance R reaches a threshold value. If the calculated contact resistance R is greater than or equal to the threshold value, an alarm is issued.

[0083] Example 2

[0084] Table 2 shows the GCB loop resistance test results of the GCB preventive test.

[0085] Table 2

[0086]

[0087]

[0088] Table 3 shows the online monitoring data of the same GCB.

[0089] Table 3

[0090]

[0091]

[0092] The corresponding line chart is as follows Figure 6 shown.

[0093] Comparing the online monitoring data with the preventive test results, although the online monitoring data is slightly smaller, it is greater than the handover test value. Therefore, the results of the online monitoring are consistent with the preventive test, and are both within the manufacturer's technical specification requirements (≤8.8μΩ).

[0094] The above specific examples are used to illustrate the present invention, which are only used to help understand the present invention and are not used to limit the present invention. For those skilled in the art to which the present invention belongs, some simple deductions, modifications or substitutions can be made according to the idea of ​​the present invention.

Claims

1. A method for online monitoring of GCB contact resistance of a large generator, characterized in that: include: Step S1: obtaining the real-time load current of the GCB, the size parameters of the SF6 gas cooler, the real-time temperature of the SF6 gas cooler, the temperature change of the SF6 gas and the real-time temperature of the GCB; Step S2: determining the heat dissipation of the SF6 gas cooler according to the size parameters of the SF6 gas cooler and the real-time temperature of the SF6 gas cooler; Calculate the heat dissipation of the generator contact according to the real-time temperature of the GCB; Calculate the work done by the gas absorbing heat based on the temperature change of SF6 gas; Step S3: Calculate the contact resistance according to the real-time load current of the GCB, the heat dissipation of the SF6 gas cooler, the heat dissipation of the generator contact and the heat absorption work of the gas; The real-time temperature of the SF6 gas cooler includes: the ambient temperature of the SF6 gas cooler, the inlet temperature of the SF6 gas cooler and the outlet temperature of the SF6 gas cooler; In step S2, the step of determining the heat dissipation of the SF6 gas cooler includes: The heat dissipation area of ​​the SF6 gas cooler is calculated according to the size parameters of the SF6 gas cooler, and the geometric characteristic length of the heat transfer surface of the cooler is calculated according to the heat dissipation area of ​​the SF6 gas cooler; Based on the dry air physical property table, determine the corresponding characteristic quantity according to the ambient temperature of the SF6 gas cooler; Calculating the Grashof number according to the characteristic quantity and the geometric characteristic length of the heat transfer surface of the cooler; According to the Grashof number, calculate the Nusselt number; The air convection heat dissipation coefficient is calculated based on the Nusselt number and the thermal conductivity of the SF6 gas cooler at ambient temperature; The heat dissipation of the SF6 gas cooler is calculated based on the air convection heat dissipation coefficient, the SF6 gas cooler inlet temperature and the SF6 gas cooler outlet temperature.

2. The method according to claim 1, characterized in that The air convection heat dissipation coefficient h is: Among them, Nu is the Nusselt number; L is the geometric characteristic length of the heat transfer surface of the cooler; λ is the thermal conductivity of air.

3. The method according to claim 2, characterized in that The GCB real-time temperature includes: GCB main transformer side busbar temperature, GCB generator side busbar temperature, GCB main transformer side busbar temperature and GCB generator side busbar temperature.

4. The method according to claim 3, characterized in that In step S2, the step of calculating the heat dissipation of the generator contact according to the real-time temperature of the GCB includes: Calculate the heat dissipation at the GCB moving contact end based on the busbar temperature on the GCB main transformer side and the busbar temperature on the GCB main transformer side; The heat dissipation at the GCB static contact end is calculated based on the busbar temperature on the GCB generator side and the busbar temperature on the GCB generator side.

5. The method according to claim 4, characterized in that The step S3 comprises: The total heat dissipation of GCB is calculated by summing the heat dissipation of SF6 gas cooler, the heat dissipation of generator contacts and the work done by gas heat absorption; Based on the electric power principle, the contact resistance is calculated according to the real-time load current of the GCB and the total heat dissipation of the GCB.

6. The method according to claim 1, characterized in that In step S1, the step of obtaining the real-time load current of the GCB includes: Acquire current data of multiple sampling periods before the current sampling period; The current data of the multiple sampling periods are weighted averaged as the GCB real-time load current.

7. The method according to any one of claims 1 to 6, characterized in that: Also includes: It is determined whether the calculated contact resistance reaches a threshold value, and if the calculated contact resistance is greater than or equal to the threshold value, an alarm is issued.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: The computer program can be executed by a processor to implement the steps of the method according to any one of claims 1 to 7.

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