Method for searching non-metallic grounding position point of damp-caused rotor of generator and eliminating defect

Abstract

The invention relates to a non-metallic grounding position point searching and defect eliminating method for a damp-caused rotor of a generator. The method comprises the following steps: step 1, judging whether the position of a grounding point is in a winding or not; 2, determining the internal grounding defect of the generator rotor winding; 3, measuring resistance values between positive and negative electrodes of the winding and to ground; step 4, judging whether the grounding is non-metallic grounding; 5, calculating the grounding resistance of the generator; and step 6, determining the accurate position of the short-circuit contact. According to the invention, expensive funds for additionally purchasing a grounding resistance testing instrument and a large amount of cost and time cost for returning the generator rotor to a factory to repair are saved, and the testing method has the characteristics of simplicity, accuracy, reliability, economy, convenience and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-voltage test, and relates to a method for finding the location of non-metallic grounding of a rotor and eliminating defects, in particular to a method for finding the location of non-metallic grounding of a rotor due to moisture absorption in a generator and eliminating defects. Background Art

[0002] A generator is an important part of the power system, and the electric energy in cities is almost reliably supplied by synchronous generators in power plants. In modern life, all aspects of people require continuous and stable power output to operate normally. Based on the laws of electromagnetic induction and electromagnetic force, it converts other forms of energy into electrical energy to meet the power requirements of various devices and their systems. The basic composition structure of a generator is divided into: rotor, stator, winding, brush and slip ring, bearing and other parts. Among them, the rotor is the core component of the generator. During each regular maintenance process, the insulation measurement test of the rotor is essential. A qualified rotor insulation measurement value is the basis for the normal operation of the generator. When the test structure is abnormal, there may be problems such as partial discharge, aging or short circuit of the generator. The above may lead to generator operation failures, unplanned outages affecting urban power supply. It may even cause damage to the generator, bringing economic losses to production. After a single-point grounding occurs in the generator rotor, although it can still operate, it is not safe. Because in this case, if another single-point grounding occurs. That is, a two-point grounding is formed. At this time, it may burn out the rotor winding, iron core or retaining ring; it may also cause strong vibration of the unit and acidification of the rotor shaft, etc. Therefore, when a single-point grounding occurs in the rotor winding, measures should be taken promptly to put its two-point grounding protection into operation, or stop the machine for treatment, eliminate the fault, and restore it to normal operation.

[0003] In summary, the rotor insulation test of the generator is essential.

[0004] When the measured insulation value of the generator rotor winding is zero, its structure may be short-circuited to ground. After metallic grounding, the insulation measurement value of the generator is zero, and the resistance value is also zero when measuring the grounding resistance. When the insulation value is too low or runs to zero due to moisture absorption inside the generator, non-metallic grounding will occur, and a grounding resistance will appear between the rotor winding and the rotor casing. There are problems such as the processing time being urgent when this defect occurs, the external contracting construction team being prone to delaying the timely completion of the maintenance period and the need to spend expensive maintenance funds, and the operation of the complete set of special equipment being complex.

[0005] To solve the above problems, we propose a method for finding the location of non-metallic grounding of a rotor due to moisture absorption in a generator and eliminating defects.

[0006] After retrieval, no public documents of prior art identical or similar to the present invention were found. Summary of the Invention

[0007] The object of the present invention is to overcome the deficiencies of the prior art and propose a method for finding the location of non-metallic grounding of the rotor of a generator due to moisture ingress and eliminating defects, which is reasonably designed, easy to use, accurate and reliable.

[0008] The present invention solves its practical problems by adopting the following technical solutions:

[0009] A method for finding the location of non-metallic grounding of the rotor of a generator due to moisture ingress and eliminating defects, comprising the following steps:

[0010] Step 1, determine whether the grounding point is inside the winding;

[0011] Step 2, determine the internal grounding defect of the generator rotor winding;

[0012] Step 3, measure the resistance value between the positive and negative poles of the winding and its resistance value to the ground;

[0013] Step 4, determine whether it is non-metallic grounding;

[0014] Step 5, calculate the grounding resistance of the generator;

[0015] Step 6, determine the precise position of the short-circuit contact point.

[0016] Moreover, the specific method of step 1 is as follows:

[0017] When a non-metallic grounding occurs at a single point in the generator rotor circuit, the position of the grounding point should be judged first by measuring the potential between the positive and negative poles; when the potentials of the two poles to the ground are of opposite polarity, the grounding point is inside the winding between the two poles. When the potentials of the two poles to the ground are of the same polarity, the grounding point is in the excitation circuit outside the rotor winding.

[0018] Moreover, the specific method of step 2 is as follows:

[0019] Before measurement, first roughly measure the resistance value with a multimeter, and then accurately measure it with a double-arm bridge; first use a 500V range insulation resistance meter to measure that the resistance values of the positive and negative poles of the rotor coil to the ground are both zero; reduce the range of the insulation resistance meter and use a 100V range insulation resistance meter to measure the resistance values of the positive and negative poles of the rotor coil to the ground, and the measurement results are zero again. The two sets of data indicate that the insulation of the generator rotor winding is unqualified and there is an internal grounding defect.

[0020] Moreover, the specific method of step 3 is as follows:

[0021] Measure the resistance value R1 between the positive and negative poles of the rotor coil, the resistance value R2 between the positive pole of the rotor coil and the ground, and the resistance value R3 between the negative pole of the rotor coil and the ground.

[0022] Moreover, the specific method of step 4 is as follows:

[0023] If the resistance value between the positive and negative poles of the rotor winding is equal to the sum of the resistance values of the positive pole to the ground and the negative pole to the ground, that is, R1 = R2 + R3, it can be determined as a contact metal ground. If the resistance value between the positive and negative poles of the rotor winding is not equal to the sum of the resistance values of the positive pole to the ground and the negative pole to the ground, that is, R1 ≠ R2 + R3, it can be determined as a non-contact metal ground.

[0024] Moreover, the specific method of step 5 is as follows:

[0025] According to the formula for the grounding resistance Rg = [(R2 + R3) - R1] / 2, the resistance value of the generator grounding resistance can be obtained.

[0026] Moreover, the specific method of step 6 is as follows:

[0027] The resistance value from the positive pole of the rotor coil to the grounding resistance is R4 = Rg - R2, and the resistance value from the negative pole of the rotor coil to the grounding resistance is R5 = Rg - R3. According to the fact that the resistance value is proportional to the coil length, L1 / L2 = R4 / R5, the precise position of the short-circuit contact point can be determined.

[0028] Moreover, before step 2, the following steps are also included:

[0029] Tighten the wiring: Before measuring the internal grounding resistance of the generator rotor winding, the wiring must be tightened.

[0030] Moreover, after step 6, the following steps are also included:

[0031] Analyze the cause of the defect based on environmental factors. If it is caused by the moisture inside the generator rotor, use no-load warming up and drying through the holes of the warm air blower.

[0032] Advantages and beneficial effects of the present invention:

[0033] The present invention provides a method for finding the location of non-metallic grounding of a generator rotor due to moisture and eliminating defects. Combining theory with practice, first determine that the non-metallic grounding point of the generator rotor is inside the winding between the two poles. Then, use the existing double-arm bridge to measure the accurate value of the grounding resistance. According to the data imported into the formulas in step 6 and step 7, analyze and determine the position of the non-contact contact point. Then, analyze the cause of the defect based on environmental factors, etc. If it is caused by the moisture inside the generator rotor, use no-load warming up and drying through the holes of the warm air blower to eliminate the defect and make the generator operate safely and stably. The present invention saves the expensive funds for purchasing additional grounding resistance testing instruments, a large amount of costs and time for sending the generator rotor back to the factory for repair, and has the characteristics of simple, accurate, reliable, economical and convenient testing methods. Brief Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the testing method of the present invention. Detailed implementation manners

[0035] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:

[0036] A method for finding the location point of non-metallic grounding of the rotor of a generator due to moisture and eliminating defects is as Figure 1 shown, and includes the following steps:

[0037] Step 1: Determine whether the grounding point is inside the winding.

[0038] The specific method of step 1 is as follows:

[0039] When a non-metallic grounding occurs at one point in the rotor circuit of the generator, the position of the grounding point should be determined first by measuring the potential between the positive and negative poles; when the potentials of the two poles to the ground are of opposite polarity, the grounding point is inside the winding between the two poles. When the potentials of the two poles to the ground are of the same polarity, the grounding point is in the excitation circuit outside the rotor winding.

[0040] When it is determined that the grounding point is inside the rotor winding, the following method can be used to determine the position of the non-metallic grounding point.

[0041] Step 2: Fasten the wiring.

[0042] Before measuring the grounding resistance inside the rotor winding of the generator, the wiring must be fastened to make the measurement accurate.

[0043] Step 3: Determine the grounding defect inside the rotor winding of the generator;

[0044] The specific method of step 3 is as follows:

[0045] Before measurement, first roughly measure the resistance value with a multimeter, and then accurately measure it with a double-arm bridge; first use a 500V-range insulation resistance meter to measure that the values of the positive and negative poles of the rotor coil to the ground are both zero; reduce the range of the insulation resistance meter and use a 100V-range insulation resistance meter to measure the values of the positive and negative poles of the rotor coil to the ground. The measurement results are zero again. The two sets of data indicate that the insulation of the rotor winding of the generator is unqualified and there is a grounding defect inside.

[0046] Step 4: Measure the resistance between the positive and negative poles of the winding and its resistance to the ground;

[0047] Use a DC resistance tester of model 3396 to measure that the resistance between the positive and negative poles of the rotor coil is R1, the resistance between the positive pole of the rotor coil and the ground is R2, and the resistance between the negative pole of the rotor coil and the ground is R3.

[0048] Step 5: Determine whether it is non-metallic grounding;

[0049] The specific method of step 5 is as follows:

[0050] If the resistance between the positive and negative poles of the rotor winding is equal to the sum of the resistance from the positive pole to the ground and the resistance from the negative pole to the ground, i.e., R1 = R2 + R3, it can be determined as a contact metal ground. If the resistance between the positive and negative poles of the rotor winding is not equal to the sum of the resistance from the positive pole to the ground and the resistance from the negative pole to the ground, i.e., R1 ≠ R2 + R3, it can be determined as a non-contact metal ground. The occurrence of this situation indicates that there is no actual grounding point inside, but a "virtual" grounding situation caused by internal moisture absorption, that is, non-contact metal grounding.

[0051] Step 6: Calculate the grounding resistance of the generator;

[0052] According to the formula for the grounding resistance Rg = [(R2 + R3) - R1] / 2, the value of the grounding resistance of the generator can be obtained.

[0053] Step 7: Determine the precise position of the short-circuit contact point;

[0054] The resistance from the positive pole of the rotor coil to the grounding resistance is R4 = Rg - R2, and the resistance from the negative pole of the rotor coil to the grounding resistance is R5 = Rg - R3. According to the fact that the resistance is proportional to the coil length, L1 / L2 = R4 / R5, the precise position of the short-circuit contact point can be determined.

[0055] Step 8: Analyze the cause of the defect based on environmental factors. If it is caused by moisture absorption inside the generator rotor, use no-load warming and drying with a hot air blower through the holes.

[0056] In this embodiment, the process of cause analysis and treatment measures is as follows:

[0057] There are many reasons for rotor short circuits. For example, grounding caused by factors such as speed, temperature, and humidity. After reasonable analysis based on the above steps combined with the actual environmental situation, when the operating environment is humid or the construction period coincides with the rainy season, it is very likely that the defect is caused by the factor of moisture absorption. After determining that the defect is a non-metallic grounding caused by the moisture absorption of the generator, with the generator operating under no load, heat is generated by the excitation current passed through the rotor, and the hot air generated is circulated by the rotation of the rotor to achieve the effect of ventilation and drying, so that the moisture-absorbed part is quickly dried. In addition, external equipment is also used. A ventilator is aimed at the holes of the generator rotor for long-term ventilation, and the externally added hot air will also dry it. After drying, the insulation resistance rises to a qualified value. Combining the actual situation, various data are measured when the generator is rotating and when it reaches the rated speed. After the insulation resistance of the rotor increases, the ventilation of the ventilator is stopped, and the measured value is still qualified, and finally the defect is solved.

[0058] After drying, the insulation resistance also rises to a qualified value.

[0059] R1 = 0.1897Ω R2 = 1.145Ω R3 = 1.275Ω

[0060] Rg = [(R2 + R3) - R1] / 2 = [(1.145 + 1.275) - 0.1897] / 2 = 1.1151 Ω

[0061] R4 = Rg - R2 = 1.275 - 1.1151 = 0.1599 Ω

[0062] R5 = Rg - R3 = 1.145 - 1.1151 = 0.0299 Ω

[0063]

[0064] Through the above steps, it is possible to locate the position point of the rotor short circuit caused by moisture in the generator and eliminate its defects.

[0065] The working principle of the present invention is as follows:

[0066] When the measured insulation value of the generator rotor winding is zero, its structure may be short-circuited to ground. After a metallic ground connection, the insulation measurement value of the generator is zero, and the resistance value is also zero when measuring the ground resistance. When the insulation value is too low or runs to zero due to moisture inside the generator, a non-metallic ground connection will occur, and a ground resistance will appear between the rotor winding and the rotor housing. The present invention uses the above method to determine whether the generator will have the defect of non-metallic ground connection due to the influence of moisture.

[0067] The present invention uses simple equipment to quickly measure the ground resistance of the generator.

[0068] After the above-mentioned defects occur, the generator is run without load to achieve the purpose of self-heating.

[0069] In addition, an external warm air blower is aimed at the rotor holes for warm air drying. Eventually, the inside of the generator is dried as a whole, the ground resistance disappears, and the insulation is qualified.

[0070] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific implementation manners. Any other implementation manners obtained by those skilled in the art based on the technical solutions of the present invention also belong to the scope of protection of the present invention.

Claims

1. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture, characterized in that: The following steps are involved: Step 1: Determine whether the grounding point is inside the winding; Step 2, determining the internal grounding defect of the generator rotor winding; Step 3, measure the resistance between the positive and negative poles of the winding and the resistance to ground; Step 4: Determine whether it is non-metallic grounding; Step 5, calculate the generator grounding resistance; Step 6: Determine the exact location of the short-circuit contact.

2. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: The specific method of step 1 is: When a non-metallic grounding occurs in the generator rotor circuit, the position of the grounding point should be determined by first measuring the point between the positive and negative poles; when the potential of the two poles to the ground is opposite, the grounding point is located inside the winding between the two poles; when the potential of the two poles to the ground is the same polarity, the grounding point is located in the excitation circuit outside the rotor winding.

3. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: The specific method of step 2 is: Before measurement, use a multimeter to initially measure the resistance value, and then use a double-arm bridge to accurately measure; first use a 500V insulation megger to measure the positive and negative poles of the rotor coil to ground, and the values ​​are both zero; lower the insulation megger range, use a 100V insulation megger to measure the positive and negative poles of the rotor coil to ground, and the measurement result is zero again. The two data indicate that the insulation of the generator rotor winding is unqualified and there is an internal grounding defect.

4. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: The specific method of step 3 is: The resistance between the positive and negative poles of the rotor coil is measured to be R1, the resistance between the positive pole of the rotor coil and the ground is R2, and the resistance between the negative pole of the rotor coil and the ground is R3.

5. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 2, 3 or 4, characterized in that: The specific method of step 4 is: If the resistance of the positive and negative poles of the rotor winding is equal to the sum of the resistance of the positive pole to the ground and the negative pole to the ground, that is, R1=R2+R3, it can be determined as contact metal grounding; if the resistance of the positive and negative poles of the rotor winding is not equal to the sum of the resistance of the positive pole to the ground and the negative pole to the ground, that is, R1≠R2+R3, it can be determined as non-contact metal grounding.

6. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: The specific method of step 5 is: According to the formula grounding resistance Rg = [(R2+R3)-R1] / 2, the resistance value of the generator grounding resistance can be obtained.

7. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: The specific method of step 6 is: The resistance value from the positive pole of the rotor coil to the grounding resistor is R4=Rg-R2, and the resistance value from the negative pole of the rotor coil to the grounding resistor is R5=Rg-R3; since the resistance value is proportional to the coil length, L1 / L2=R4 / R5, the precise position of the short-circuit contact can be determined.

8. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: Before step 2, the method further includes the following steps: Tighten the wiring: Before measuring the internal grounding resistance of the generator rotor winding, the wiring must be tightened.

9. A method for finding and eliminating the non-metallic grounding position of a generator rotor due to moisture according to claim 1, characterized in that: After step 6, the method further includes the following steps: Analyze the cause of the defect based on environmental factors. If it is caused by moisture inside the generator rotor, use idling to heat up and the holes of the heater to dry it.

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