A Double-Layer Insulation Online Condition Assessment Method for Generator Bearings

Abstract

An embodiment of the present invention discloses a method for on-line condition assessment of the double-layer insulation of a generator bearing, which determines whether the double-layer insulation meets the insulation requirements. When the double-layer insulation meets the insulation requirements, by monitoring the voltage to ground and shaft voltage of the intermediate body of the double-layer insulation of the bearing, the single-layer insulation status of the inner and outer layers can be accurately judged by using the ratio of the voltage to ground of the intermediate body of the double-layer insulation to the shaft voltage; when the double-layer insulation does not meet the insulation requirements, by judging the shaft voltage, shaft current, and the parallel resistance R of the outer insulation and the inner insulation t and the parallel resistance R of the outer insulation and the inner insulation in the start-up test 初 The ratio of the double-layer insulation intermediate body to the ground voltage and the ratio of the shaft voltage are used to further distinguish whether the double-layer insulation of the bearing needs to be replaced immediately or is effective in a short period of time. The present invention can reduce the maintenance frequency and reduce unnecessary shutdowns.

Description

Technical Field

[0001] The present invention relates to the field of generator bearing condition monitoring and fault diagnosis, and particularly to a method for on-line condition assessment of double-layer insulation of a generator bearing. Background Art

[0002] The bearing is a key component of the generator support system and is used to support the high-speed rotation of the rotor. During the operation of the generator, due to reasons such as fluid erosion, friction, asymmetry of the magnetic circuit, and magnetic leakage, voltages of several volts or even dozens of volts will be generated on the large shaft of the rotor. This voltage is called the shaft voltage. Due to the existence of the shaft voltage, a grounding brush or copper braid is usually installed outside the steam end cover to ground the steam end rotating shaft and make it close to zero potential. For the exciter end bearing, because it bears the shaft voltage, GB / T 7064 stipulates that components such as the bearing bush and the seal bush are provided with double-layer insulation to the ground. When the insulation fails, the shaft voltage forms a short-circuit large current through the exciter end bearing bush, causing burns and heating of the large shaft and the bearing bush, making the large shaft lose lubrication, and even causing the phenomenon of shaft seizure, resulting in the damage of the entire generator. Therefore, the insulation detection at the exciter end bearing bush is very important.

[0003] Statistical data shows that the frequency of bearing insulation deterioration or even non-conformance is relatively high, and huge economic losses will be caused if an accident occurs. However, the on-line monitoring of shaft current and shaft voltage cannot directly reflect the bearing insulation level. For the bearing insulation resistance in the megohm range, there is no essential difference between a shaft voltage of several volts or dozens of volts. As long as the insulation is effective, even if the shaft voltage of the generator is dozens of volts, it will not endanger the safe operation of the generator at all. At present, the method of using a megohmmeter to measure or the method of installing a bearing insulation resistance monitoring device is often used to monitor the bearing insulation resistance. Under normal circumstances, the inner and outer double-layer insulation performances are similar, and the measured insulation resistance can reach 1 - 1000 MΩ. The national standard stipulates that when measuring the insulation resistance with a 1000V megohmmeter for thermal power generation, the insulation resistance is greater than 1 MΩ (for hydroelectric power generation, the insulation resistance is not less than 2 MΩ), that is, the insulation is qualified, otherwise it is unqualified. However, the actually measured bearing insulation resistance is the parallel resistance of the inner and outer layer insulations, which has disadvantages such as false alarms (for example, the situation where the inner and outer layer insulation resistances of thermal power generation are both less than 2 MΩ while the series resistance meets the design requirements) and the inability to accurately judge the inner and outer layer insulation states. Summary of the Invention

[0004] The main purpose of the present invention is to propose a method for on-line condition assessment of double-layer insulation of a generator bearing, aiming to solve the above problems existing in the prior art.

[0005] To achieve the above purpose, the present invention provides a method for on-line condition assessment of double-layer insulation of a generator bearing, wherein the double-layer insulation includes an inner layer insulation and an outer layer insulation, and the method includes:

[0006] Obtain the shaft voltage U1(t) at time t and the voltage U0(t) of the intermediate body of the double-layer insulation to the ground;

[0007] When the double-layer insulation meets the insulation requirements, the evaluation result is determined according to p(t) and the first preset threshold u1, where p(t) is the ratio of U0(t) to U1(t);

[0008] When p(t) < u1, a warning message of deterioration of the outer-layer insulation is issued;

[0009] When u1 ≤ p(t) ≤ 1 - u1, a comparison message is issued according to the magnitude of p(t), and the comparison message is used to indicate the comparison result of the insulation states of the outer-layer insulation and the inner-layer insulation;

[0010] When p(t) > 1 - u1, a warning message of deterioration of the inner-layer insulation is issued.

[0011] In some embodiments, when u1 ≤ p(t) ≤ 1 - u1, the step of issuing a comparison message according to the magnitude of p(t) includes:

[0012] When u1 ≤ p(t) ≤ u′1, the comparison message is used to indicate that the insulation state of the outer-layer insulation is worse than that of the inner-layer insulation;

[0013] When u′1 < p(t) ≤ 1 - u1, the comparison message is used to indicate that the insulation state of the outer-layer insulation is better than that of the inner-layer insulation;

[0014] where u′1 is the ratio of the resistance design value of the outer-layer insulation to the series resistance design value of the inner-layer insulation and the outer-layer insulation.

[0015] In some embodiments, the first preset threshold u1 is obtained by the following method:

[0016] Resistors R 内 and R 外 are connected in series and a voltage U1 is applied across the two ends. Among them, the resistance value of R 内 is R1, the resistance value of R 内 is R 测 - R1, R1 is the national / industry standard alarm threshold, and R 测 is the maximum series resistance of the inner-layer insulation and the outer-layer insulation to ensure the effectiveness of the method. The voltage U1 is the shaft voltage alarm value;

[0017] Measure the voltage U0 of R 外 The first preset threshold u1 = U0 / U1.

[0018] In some embodiments, the method further includes:

[0019] Obtain the parallel resistance R t, and obtaining the parallel resistance R of the outer insulation and the inner insulation in the start-up test 初 ;

[0020] Determine whether the double-layer insulation meets the insulation requirements;

[0021] When f t > R1 / R 初 The double-layer insulation meets the insulation requirements, where f t is the percentage value of R t occupying R 初 , and R1 is the national / industry standard alarm threshold.

[0022] In some embodiments, the method further includes:

[0023] Obtain the shaft current at time t;

[0024] When f t ≤R1 / R 初 An alarm message that the double-layer insulation fails to meet the insulation requirements is issued;

[0025] Determine whether the shaft voltage reaches the shaft voltage alarm value U1 and whether the shaft current reaches the shaft voltage alarm value I1;

[0026] When the shaft voltage reaches the shaft voltage alarm value U1 or the shaft current reaches the shaft voltage alarm value I1, an alarm message that the double-layer insulation fails and needs to be shut down immediately for replacement is issued.

[0027] In some embodiments, the method further includes:

[0028] When the shaft voltage does not reach the shaft voltage alarm value U1 and the shaft current does not reach the shaft voltage alarm value I1, determine the magnitude of f t and R min / R 初 , where R min = 0.25R2, and R2 is the series resistance threshold of the outer insulation and the inner insulation when the insulation is effective;

[0029] When f t ≤R min / R 初 An alarm message that the double-layer insulation fails and needs to be shut down immediately for replacement is issued.

[0030] In some embodiments, the method further includes:

[0031] When f t >R min / R 初 Determine whether p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, where u2 is the second preset threshold;

[0032] If p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, an alarm message indicating that the double-layer insulation has failed and needs to be immediately shut down and replaced is issued.

[0033] In some embodiments, the second preset threshold u2 is obtained by the following method:

[0034] Connect resistors R 内 ′ and R 外 ′ in series and apply voltage U1 across the two ends. Among them, the resistance value of R 外 ′ is R min , and the resistance value of R 内 ′ is R 测 - R min , and R 测 is the maximum series resistance value of the inner-layer insulation and the outer-layer insulation when ensuring the effectiveness of the method.

[0035] Measure the voltage U0′ of R 外 ′, and the second preset threshold u2 = U0′ / U1.

[0036] In some embodiments, the method further includes:

[0037] If p(t) does not satisfy u2 ≤ p(t) ≤ 1 - u2, an information indicating that the double-layer insulation is short-term effective is issued.

[0038] The present invention accurately judges the single-layer insulation states of the inner and outer layers by monitoring the voltage to ground and the shaft voltage of the double-layer insulation intermediate body of the bearing, and it is convenient for the staff to carry out operation and maintenance work accordingly.

[0039] In addition, when an alarm indicating that the double-layer insulation does not meet the insulation requirements has occurred, the present invention further distinguishes whether the double-layer insulation of the bearing needs to be immediately replaced or is short-term effective by judging the ratio of the shaft voltage, shaft current, the parallel resistance R t of the outer layer insulation and the inner layer insulation to the parallel resistance R 初 of the outer layer insulation and the inner layer insulation in the start-up test, and the ratio of the voltage to ground of the double-layer insulation intermediate body to the shaft voltage. When it is identified that the double-layer insulation of the bearing is short-term effective, the reaction time of the staff can be increased and unnecessary shutdowns can be reduced. Description of the Drawings

[0040] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0041] These exemplary embodiments will be described in detail with reference to the drawings. These exemplary embodiments are non-limiting exemplary embodiments, where reference numerals represent similar mechanisms in various views of the drawings.

[0042] Figure 1 It is a schematic flowchart of a method for online status evaluation of the double-layer insulation of a generator bearing according to some embodiments of the present invention;

[0043] Figure 2 It is a schematic circuit diagram of the online status evaluation of the double-layer insulation of a generator bearing according to some embodiments of the present invention;

[0044] Figure 3 It is a schematic circuit diagram of a double-layer insulation state simulation test according to some embodiments of the present invention;

[0045] Figure 4 It is another schematic flowchart of a method for online status evaluation of the double-layer insulation of a generator bearing according to some embodiments of the present invention. Detailed implementation manners

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] Figure 1 It is a flowchart of a method for online status evaluation of the double-layer insulation of a generator bearing shown according to some embodiments of the present application, specifically including the following steps S100, S310 - S340. It should be noted that these embodiments should be understood as examples and should not be understood as essential technical features for implementing this solution.

[0048] Step S100, obtain the shaft voltage U1(t) at time t and the voltage U0(t) of the double-layer insulation intermediate to the ground.

[0049] As Figure 2As shown, the double-layer insulation of this embodiment includes an inner-layer insulation and an outer-layer insulation. The double-layer insulation monitoring device for the generator bearing intervenes and monitors at the intermediate body between the outer-layer insulation and the inner-layer insulation in the double-layer insulation, and can collect the ground voltage U0(t) of the double-layer insulation intermediate body at time t and / or the double-layer insulation resistance (i.e., the parallel resistance of the outer-layer insulation and the inner-layer insulation). The shaft voltage U1(t) at time t can be obtained from the shaft voltage and shaft current data in the power plant data system or the on-line monitoring device for shaft voltage and shaft current.

[0050] Step S310, when the double-layer insulation meets the insulation requirements, determine the evaluation result according to p(t) and the first preset threshold u1, where p(t) is the ratio of U0(t) to U1(t).

[0051] In this embodiment, it is possible to judge whether the double-layer insulation meets the insulation requirements according to relevant national or industry standards, or to judge whether the double-layer insulation meets the insulation requirements through self-set standards, such as by judging whether the resistance value of the double-layer insulation is higher than a certain threshold. When the double-layer insulation meets the insulation requirements, in this embodiment, according to the obtained ratio of U0(t) to U1(t) and in combination with the pre-obtained threshold u1, the insulation states of the outer-layer insulation and the inner-layer insulation can be further evaluated.

[0052] Step S320, when p(t) < u1, issue a warning message for the deterioration of the outer-layer insulation.

[0053] Step S330, when u1 ≤ p(t) ≤ 1 - u1, issue a comparison message according to the magnitude of p(t), and the comparison message is used to indicate the comparison result of the insulation states of the outer-layer insulation and the inner-layer insulation in the double-layer insulation.

[0054] Step S340, when p(t) > 1 - u1, issue a warning message for the deterioration of the inner-layer insulation.

[0055] In this embodiment, p(t) can reflect the voltage division situation at both ends of the inner insulation and the outer insulation. When p(t) is too small and lower than the first preset threshold u1, it indicates that the voltage at both ends of the outer insulation is too small, the resistance of the outer insulation is much smaller than that of the inner insulation, and the insulation state of the outer insulation deteriorates severely. When u1 ≤ p(t) ≤ 1 - u1, it indicates that both the inner insulation and the outer insulation are in a relatively healthy insulation state: the smaller the p(t) value, the smaller the voltage and resistance at both ends of the outer insulation, and the worse the insulation state of the outer insulation relative to that of the inner insulation; the larger the p(t) value, the larger the voltage and resistance at both ends of the outer insulation, and the better the insulation state of the outer insulation relative to that of the inner insulation. When p(t) > 1 - u1, it indicates that the voltage at both ends of the inner insulation is too small, the resistance of the inner insulation is much smaller than that of the outer insulation, and the insulation state of the inner insulation deteriorates severely. Insulation failure may occur subsequently, and early warning attention is required.

[0056] In this embodiment, by monitoring the ground voltage U0(t) and the shaft voltage U1(t) of the bearing double-layer insulation intermediate body, the ratio of the ground voltage U0(t) of the double-layer insulation intermediate body to the shaft voltage U1(t) can be used to accurately judge the single-layer insulation state of the inner and outer layers. Using the above information, the staff can understand the inner and outer layer insulation states in time before the bearing double-layer insulation fails, which is convenient for formulating and carrying out subsequent operation and maintenance work.

[0057] In some embodiments, step S330 specifically includes:

[0058] Step S331, when u1 ≤ p(t) ≤ u′1, the comparison information is used to indicate that the insulation state of the outer insulation is worse than that of the inner insulation.

[0059] Step S332, when u′1 < p(t) ≤ 1 - u1, the comparison information is used to indicate that the insulation state of the outer insulation is better than that of the inner insulation.

[0060] Generally, when designing double-layer insulation for a generator, the resistance design values of the inner insulation and the outer insulation will be determined in advance according to the insulation requirements. In this embodiment, u′1 is the ratio of the resistance design value of the outer insulation to the series resistance design value of the inner insulation and the outer insulation. Taking u′1 as the relative state dividing line between the inner insulation and the outer insulation, when p(t) ≤ u′1, the insulation state of the outer insulation is worse than that of the inner insulation, and the smaller the p(t), the worse the outer insulation relative to the inner insulation; conversely, when p(t) > u′1, it indicates that the insulation state of the outer insulation is better than that of the inner insulation, and the larger the p(t), the better the outer insulation relative to the inner insulation. As a feasible way, when the same insulation requirements are imposed on the inner insulation and the outer insulation, the value of u′1 is 0.5.

[0061] In some embodiments, the first preset threshold u1 is obtained in the following manner:

[0062] Connect resistor R 内 and resistor R 外 in series and apply voltage U1 across the two ends. Here, the resistance value of R 内 is R1, and the resistance value of R 内 is R 测 - R1. R1 is the national / industry standard alarm threshold, and R 测 is the maximum series resistance of the inner insulation and the outer insulation under the condition of ensuring the effectiveness of the method. The voltage U1 is the shaft voltage alarm value;

[0063] Measure the voltage U0 of R 外 . The first preset threshold u1 = U0 / U1.

[0064] In this embodiment, due to the existence of the internal circuit of the monitoring device, when the series resistance of the double-layer insulation (i.e., the series resistance of the inner insulation and the outer insulation) is too large, it will cause the measured voltage value of the monitoring device to be distorted. For example, the measured voltage value will instantaneously drop to nearly zero, seriously deviating from the actual voltage value of the double-layer insulation intermediate body to the ground. To make the voltage U0(t) of the double-layer insulation intermediate body to the ground monitored in this embodiment effective, the series resistance of the inner insulation and the outer insulation shall not be greater than R 测 .

[0065] It can be obtained through the double-layer insulation state simulation test circuit as shown in Figure 3 : By using two variable resistors (R 测 , R 内 ) to simulate the inner and outer insulations. After the two variable resistors are connected in series, apply the simulated voltage U1 of the shaft voltage alarm value across the two ends; adjust R 外 and R 外 and ensure that R 内 = R 外 = r. Use the monitoring device in Figure 1 to measure the voltage U0 of R 内 approximately equal to half of U1 and slightly increase R 外 (R 外 ≈ R 外 ), when the voltage U0 of the monitoring device measuring R 内 is approximately equal to zero, at this time, R 外 = 2r. 测 = 2r.

[0066] This embodiment can use the double-layer insulation state simulation test circuit shown in Figure 3 to obtain the first preset threshold u1: By using two resistors (R 内 , R 外)Simulate the inner and outer insulation. After two resistors are connected in series, apply a simulated voltage U1, which is the alarm value of the shaft voltage, across both ends. The simulated resistor for the outer insulation is R 外 Take R1, the simulated resistor for the inner insulation is R 内 Take R 测 -R1, measure the voltage U0 of R 外 . At this time, the ratio of U0 to U1 is u1.

[0067] In some embodiments, the method further includes:

[0068] Step S110, obtain the parallel resistance R of the outer insulation and the inner insulation at the moment t t , and obtain the parallel resistance R of the outer insulation and the inner insulation during the startup test 初 .

[0069] Step S200, determine whether the double insulation meets the insulation requirements.

[0070] Step S400, when f t > R1 / R 初 , the double insulation meets the insulation requirements, where f t is the percentage value of R t occupying R 初 , and R1 is the national / industry standard alarm threshold.

[0071] In this embodiment, in order to determine whether the double insulation meets the insulation requirements, it is necessary to first obtain the parallel resistance R of the outer insulation and the inner insulation t (which can also be called the bearing insulation resistance R t ), and the parallel resistance R of the outer insulation and the inner insulation measured during the power plant startup test 初 (which can also be called the initial value of the bearing insulation resistance R 初 ). By calculating the percentage of the bearing insulation resistance R t at the current moment t occupying the initial value of the bearing insulation resistance R 初 (i.e., the remaining insulation resistance amount) f t to evaluate the bearing insulation status. When f t > R1 / R 初 , it can be considered that the current bearing insulation resistance R t is above the national / industry standard alarm threshold and meets the insulation requirements.

[0072] In some embodiments, the method further includes:

[0073] Step S120, obtain the shaft current at the moment t.

[0074] Step S400, when f t ≤ R1 / R初 When it does, an alarm message indicating that the double-layer insulation fails to meet the insulation requirements is issued.

[0075] Step S500: Determine whether the shaft voltage reaches the shaft voltage alarm value U1 and whether the shaft current reaches the shaft current alarm value I1.

[0076] Step S510: When the shaft voltage reaches the shaft voltage alarm value U1 or the shaft current reaches the shaft current alarm value I1, an alarm message indicating that the double-layer insulation fails and needs to be immediately shut down for replacement is issued.

[0077] When the double-layer insulation fails to meet the insulation requirements, there may not be insulation failure. There may be a problem of short-circuit large current formed by the shaft voltage grounding through the excitation end bearing. If an alarm is directly issued to require immediate replacement of the bearing at this time, it may not leave a buffer time for the staff and increase the losses caused by shutdown for maintenance; but if no alarm is issued, it may further develop into a problem of insulation failure, resulting in serious consequences.

[0078] In this embodiment, when the double-layer insulation fails to meet the insulation requirements, an alarm message indicating that the double-layer insulation fails to meet the insulation requirements is issued, and the insulation state is further judged. When it is further monitored that the shaft voltage reaches the shaft voltage alarm value U1 or the shaft current reaches the shaft current alarm value I1, it indicates that the double-layer insulation has failed at this time, and there is already a short circuit in the excitation end bearing, and the double-layer insulation needs to be immediately shut down and replaced.

[0079] In some embodiments, the method further includes:

[0080] Step S600: When the shaft voltage does not reach the shaft voltage alarm value U1 and the shaft current does not reach the shaft current alarm value I1, judge f t and R min / R 初 for their magnitudes.

[0081] Step S610: When f t ≤R min / R 初 an alarm message indicating that the double-layer insulation fails and needs to be immediately shut down for replacement is issued.

[0082] When the shaft voltage does not reach the shaft voltage alarm value U1 and the shaft current does not reach the shaft current alarm value I1, it cannot be guaranteed that the double-layer insulation has not failed. At this time, further monitoring and judgment are required to ensure power generation safety.

[0083] In the actual process of preventing the generation of harmful shaft current, the inner insulation and the outer insulation act in series. As long as the overall series resistance of the inner insulation and the outer insulation reaches the megohm level, the double-layer insulation of the bearing can be guaranteed to be effective. In this embodiment, R min= 0.25R2, where R2 is the series resistance threshold of the double insulation when it is effective. That is, when the sum of the resistance value of the inner insulation and the resistance value of the outer insulation is greater than or equal to R2, the double insulation of the bearing can be ensured to be effective. Since R t is the parallel resistance of the inner insulation and the outer insulation. When R 内 + R 外 = R2, in the case of ignoring the shaft resistance, the maximum value of R t is 0.25R2. Therefore, when f t ≤ R min / R 初 , it can be determined that R 内 + R 外 <R2, that is, the overall series resistance of the inner insulation and the outer insulation can no longer prevent the generation of harmful shaft current. Therefore, an alarm message indicating that the double insulation has failed and needs to be immediately shut down and replaced is issued.

[0084] In some embodiments, the method further includes:

[0085] Step S700, when f t > R min / R 初 , determine whether p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, where u2 is the second preset threshold.

[0086] Step S710, if p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, issue the alarm message indicating that the double insulation has failed and needs to be immediately shut down and replaced.

[0087] Step S720, if p(t) does not satisfy u2 ≤ p(t) ≤ 1 - u2, issue the information indicating that the double insulation is temporarily effective.

[0088] Figure 4 is a flowchart of an embodiment including steps S700 - S720. When f t > R min / R 初 , it cannot be guaranteed that R 内 + R 外 ≥ R2, that is, it cannot be ensured that the double insulation has not failed. Therefore, in this embodiment, by calculating and comparing the ratio p(t) of U0(t) to U1(t) with the previously obtained second preset threshold u2, when u2 ≤ p(t) ≤ 1 - u2, it can be ensured that R 内 + R 外 <R2, that is, the double insulation has failed and the double insulation needs to be immediately shut down and replaced; when p(t) does not satisfy u2 ≤ p(t) ≤ 1 - u2, it can be ensured that R 内 + R 外≥R2. At this time, although the double-layer insulation does not meet the insulation requirements, the double-layer insulation has not failed yet. Therefore, information indicating that the double-layer insulation is temporarily effective is sent, which is convenient for subsequent staff to flexibly formulate maintenance and repair plans.

[0089] Further, in some embodiments, the second preset threshold u2 can be obtained by means of a preliminary test: Connect resistors R 内 ′ and resistor R 外 ′ in series and apply voltage U1 across the two ends. Among them, the resistance value of R 外 ′ is R min , the resistance value of R 内 ′ is R 测 - R min , and R 测 is the maximum series resistance value of the inner-layer insulation and the outer-layer insulation to ensure the effectiveness of the method; measure the voltage U0′ of R 外 ′, then the second preset threshold u2 = U0′ / U1.

[0090] This embodiment can use the double-layer insulation state simulation test circuit shown in Figure 3 to obtain the second preset threshold u2: By using two variable resistors (R 内 ′, R 外 ′) to simulate the inner and outer layer insulations, apply the simulated voltage U1 of the shaft voltage alarm value across the two ends after the two variable resistors are connected in series. The simulated resistance R 外 ′ of the outer layer insulation takes R min , the simulated resistance R 内 ′ of the inner layer insulation takes R 测 - R min , measure the voltage U0′ of R 外 ′, and the ratio of U0′ to U1 at this time is u2.

[0091] Further, in some embodiments, after completing the evaluation of the double-layer insulation state at time t and sending relevant comparison information, early warning information, and alarm information, step S800 is started: Evaluate the double-layer insulation state at the next moment. For example, after completing any one of steps S320, step S331, step S332, step S340, step S510, step S610, step S710, and step S720, the evaluation of the double-layer insulation state at the next moment can be started.

[0092] It should be noted that in this document, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or system comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or system. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or system comprising such element.

[0093] The serial numbers of the embodiments of the present invention above are for description only and do not represent the superiority or inferiority of the embodiments.

[0094] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for on-line status assessment of the double-layer insulation of a generator bearing, wherein the double-layer insulation includes an inner layer insulation and an outer layer insulation, and the method includes: Obtain the shaft voltage U1(t) at time t and the voltage U0(t) of the double-layer insulation intermediate with respect to ground; When the double-layer insulation meets the insulation requirements, determine the evaluation result according to p(t) and the first preset threshold u1, where p(t) is the ratio of U0(t) to U1(t); When p(t) < u1, issue a warning message for the deterioration of the outer insulation; When u1 ≤ p(t) ≤ 1 - u1, issue a comparison message according to the magnitude of p(t), and the comparison message is used to indicate the comparison result of the insulation states of the outer insulation and the inner insulation; When p(t) > 1 - u1, issue a warning message for the deterioration of the inner insulation; Among them, the first preset threshold u1 is obtained by the following method: Connect resistor R 内 and resistor R 外 in series and apply voltage U1 across the two ends. Among them, the resistance value of R 内 is R1, and the resistance value of R 内 is R 测 - R1. R1 is the national / industry standard alarm threshold, and R 测 is the maximum series resistance of the inner insulation and the outer insulation under the condition of ensuring the effectiveness of the method. The voltage U1 is the shaft voltage alarm value; Measure R 外 The voltage U0 of, the first preset threshold u1 = U0 / U1.

2. The method according to claim 1, wherein When u1 ≤ p(t) ≤ 1 - u1, the step of issuing a comparison message according to the magnitude of p(t) includes: When u1 ≤ p(t) ≤ u′1, the comparison message is used to indicate that the insulation state of the outer insulation is worse than that of the inner insulation; When u′1 < p(t) ≤ 1 - u1, the comparison message is used to indicate that the insulation state of the outer insulation is better than that of the inner insulation; Among them, u′1 is the ratio of the resistance design value of the outer insulation to the series resistance design value of the inner insulation and the outer insulation.

3. The method according to claim 1, wherein The method further includes: Obtain the parallel resistance R of the outer insulation and the inner insulation at the t-th moment t , and obtain the parallel resistance R of the outer insulation and the inner insulation in the start-up test 初 ; Judge whether the double-layer insulation meets the insulation requirements; When f t > R1 / R 初 the double insulation meets the insulation requirements, where f t is the percentage value of R t occupied by R 初 and R1 is the national / industry standard alarm threshold.

4. The method according to claim 3, wherein The method further includes: Obtain the shaft current at time t; When f t ≤R1 / R 初 an alarm message indicating that the double insulation cannot meet the insulation requirements is issued; Judge whether the shaft voltage reaches the shaft voltage alarm value U1 and whether the shaft current reaches the shaft voltage alarm value I1; When the shaft voltage reaches the shaft voltage alarm value U1 or the shaft current reaches the shaft voltage alarm value I1, issue an alarm message that the double-layer insulation fails and needs to be immediately shut down and replaced; 5. The method according to claim 4, wherein The method further includes: When the shaft voltage does not reach the shaft voltage alarm value U1 and the shaft current does not reach the shaft current alarm value I1, judge f t and R min / R 初 of the magnitude, where R min = 0.25R2, and R2 is the series resistance threshold of the outer insulation and the inner insulation when the insulation is effective; When f t ≤ R min / R 初 an alarm message indicating that the double insulation has failed and immediate shutdown for replacement is required shall be issued.

6. The method according to claim 5, wherein The method further includes: When f t >R min / R 初 , it is determined whether p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, where u2 is a second preset threshold value; If p(t) satisfies u2 ≤ p(t) ≤ 1 - u2, issue an alarm message that the double-layer insulation fails and needs to be immediately shut down and replaced; 7. The method according to claim 6, wherein The second preset threshold u2 is obtained by the following method: Connect the resistor R 内 ′ in series with the resistor R 外 ′ and apply a voltage U1 across the two ends. Among them, the resistance value of R 外 ′ is R min , and the resistance value of R 内 ′ is R 测 -R min , where R 测 is the maximum series resistance of the inner insulation and the outer insulation when ensuring the effectiveness of the method; Measure R 外 ′ of the voltage U0 ′ , where the second preset threshold u2 = U0 ′ / U1.

8. The method according to claim 6, wherein The method further includes: If p(t) does not satisfy u2 ≤ p(t) ≤ 1 - u2, issue a message that the double-layer insulation is temporarily effective.

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