Transformer DC resistance test wiring conversion box and test method

Abstract

The invention relates to a transformer DC resistance test wiring conversion box and a test method, and the structure of the wiring conversion box is that relays S1 and S6 are connected in series with A-phase wiring terminals to form a first branch circuit, relays S2 and S8 are connected in series with B-phase wiring terminals to form a second branch circuit, and the first branch circuit and the second branch circuit are connected in parallel and then are connected with wiring terminals I + and V +; the relays S3 and S7 are connected in series with the a-phase wiring terminal to form a third branch, the relays S4 and S9 are connected in series with the c-phase wiring terminal to form a fourth branch, and the third branch and the fourth branch are connected in parallel and then connected with the wiring terminals I-and V +; the O-phase wiring terminal is connected in series with a relay S5 and then is connected with a wiring terminal V +; and the C-phase wiring terminal is connected with the wiring terminal V-. During the test, the second group of test utilizes the residual magnetic flux generated in the iron core by the first group of test, so that the test time is shortened; seven groups of direct-current resistance values are read only through two groups of tests, so that the through-current time of a transformer winding is shortened, and the working efficiency is improved.

Description

Technical Field

[0001] The invention relates to a transformer winding test method, in particular to a transformer DC resistance test wiring conversion box and a test method. Background Art

[0002] The DC resistance test of transformer windings is one of the main items in the acceptance, temperature rise, and post-repair tests of power transformers. It can effectively discover manufacturing defects such as material selection, welding, loose connections, missing strands, broken wires, and hidden dangers after operation of transformer windings. Therefore, measuring the DC resistance of transformer windings is of great significance.

[0003] The previous test method took a long time to test. The test time for each phase of the high-voltage winding was 10-15 minutes, and the test time for each phase of the low-voltage winding was 45-60 minutes. Under the premise that everything went well, the total test time for the high and low voltage windings was about 4 hours. Powering on the transformer for a long time would not only cause overheating of the device and windings and affect the accuracy, but also cause deep saturation of the transformer core. After the test, a large residual magnetism would be generated in the core, which would cause a large excitation surge current (up to 6-8 times the rated current) when the transformer was closed at no-load, which could easily cause false protection and cause the transformer to fail to be put into operation, thus affecting power transmission. At the same time, the transformer and circuit breaker would also be damaged to varying degrees due to the strong electric force. Generally, the magnetic assist method can be used to shorten the test time. The high-voltage winding is connected in series with the low-voltage winding. Since the number of turns of the high-voltage winding is much larger than that of the low-voltage winding, the magnetic flux generated is also much larger than that of the low-voltage winding, which can accelerate the saturation of the core and shorten the test time to a certain extent. However, the magnetic assist method needs to establish a magnetic flux with one phase the same as the previous test and two phases opposite to each other for each test, which is equivalent to using only 1 / 3 of the residual magnetic flux in the previous test. Moreover, the residual magnetism in the transformer core is not eliminated after each test, and there is still a problem of large excitation inrush current when the transformer is closed.

[0004] On the other hand, the test wiring was cumbersome and complicated in the past. The existing transformer DC resistance test equipment generally has only two current output lines and two voltage input lines, and can only test one set of winding DC resistance at a time. For the main transformer YNd11 connection transformer, a total of 6 sets of tests are required. After each set of tests, manual wire replacement is required. After the high-voltage side is completed, it is necessary to climb to the top of the transformer again and re-wire the transformer low-voltage side test wire clamp. This involves the safety risk of multiple high-altitude operations for personnel, and the contact position and strength of each test wire clamp will affect the test results, which may easily lead to misjudgment of the test results by the test personnel. In addition, each time the personnel change the wire, personal electric shock accidents may occur due to incomplete discharge of the winding, posing a safety hazard.

[0005] Therefore, it is urgent to propose a DC resistance test method that can shorten the test time and improve the test efficiency, reduce the residual magnetism of the transformer core after the test, thereby reducing the excitation inrush current at the closing moment, and facilitate wiring and reduce the probability of safety accidents during the operation of the test personnel. Summary of the invention

[0006] In order to overcome the problems of long DC test time of transformer winding, influence of residual magnetism after test on closing excitation inrush current, complicated test wiring and prone to accidents, the present invention proposes a transformer DC resistance test wiring conversion box.

[0007] Another object of the present invention is to provide a transformer DC resistance testing method.

[0008] The technical solution of the present invention is as follows:

[0009] A transformer DC resistance test wiring conversion box, a circuit wiring board is provided with high-voltage winding A phase, B phase, C phase, O phase wiring terminals and low-voltage winding a phase, c phase wiring terminals, relay S1, A phase wiring terminal, relay S6 are connected in series to form a first branch, relay S2, B phase wiring terminal, relay S8 are connected in series to form a second branch, one end of the first branch after being connected in parallel with the second branch is connected to a current wiring terminal I+, and the other end of the first branch after being connected in parallel with the second branch is connected to a voltage wiring terminal V+; relay S3, a phase wiring terminal, relay S7 are connected in series to form a third branch, relay S4, c phase wiring terminal, relay S9 are connected in series to form a fourth branch, one end of the third branch after being connected in parallel with the fourth branch is connected to a current wiring terminal I-, and the other end of the third branch after being connected in parallel with the fourth branch is connected to a voltage wiring terminal V+; the O phase wiring terminal is connected in series with relay S5 and connected to the voltage wiring terminal V+; the C phase wiring terminal is connected to the voltage wiring terminal V-; the relays S1-S9 are controlled by a single chip microcomputer.

[0010] A transformer DC resistance test method, the transformer is a double-winding transformer, the transformer wiring method is YNd11, and the specific test method includes the following steps:

[0011] Step 1, firstly, lead the high-voltage winding phase A, phase B, phase C, phase O, and the low-voltage winding phase a, phase c to the corresponding wiring terminals of the wiring conversion box with leads, and connect the current output positive and negative terminals I+, I-, and the voltage input positive and negative terminals V+, V- of the DC resistance test device to the corresponding wiring terminals of the wiring conversion box, respectively, and connect the high-voltage side phase C with the low-voltage side phase b through the test line to complete the wiring work before the test;

[0012] Step 2, when conducting the first test, close the relays S1, S4, and S5 of the wiring conversion box, start the DC resistance test device, and the voltage measurement end is at both ends of OC. After the core saturation measurement value stabilizes, the resistance reading of the DC resistance test device is R1; at this time, disconnect the relay S5, close the relay S6, the voltage measurement end is at both ends of AC, and the reading is R2; at this time, disconnect the relay S6, close the relay S9, the voltage measurement end is at both ends of cC, and the reading is R3; at this time, disconnect the relay S9, close the relay S7, the voltage measurement end is at both ends of aC, and the reading is R4. At this point, the first test is over, and disconnect the relays S1, S4, and S7 to discharge the device until the discharge alarm sounds;

[0013] Step 3, after the first test discharge is completed, prepare for the second test, close relays S2, S3, S8, start the DC resistance test device, the voltage measurement end is at both ends of BC, and measure the series resistance value of the two-phase BC; after the core saturation measurement value is stable, the resistance reading of the DC resistance test device is R5; at this time, disconnect relay S8, close relay S7, the voltage measurement end is at both ends of aC, and the reading is R6; at this time, disconnect relay S7, close relay S9, the voltage measurement end is at both ends of cC, and the reading is R7. At this point, the second test is over, and the device is discharged until the discharge alarm sounds;

[0014] Step 4: Calculate the DC resistance. Combining formulas 1, 2, and 5, you can get the high-voltage side DC resistance R. A , R B , R C , any three terms in formulas 3, 4, 6, and 7 can be solved to obtain the low-voltage side DC resistance R ab , R bc , R ac ,In order to make the result more accurate, the average of three times can be taken as the final result;

[0015] R1=R C (1)

[0016] R2=R A +R C (2)

[0017] R3=R bc (3)

[0018]

[0019] R5=R B +R C (5)

[0020] R6=R ab (6)

[0021]

[0022] In the step 2, when the first test is performed, the positive pole of the power supply enters from phase A of the wiring conversion box, and the current is introduced into the low-voltage side after phase A and phase C on the high-voltage side are connected in series. Phases ab on the low-voltage side are connected in series and then in parallel with phase c, and finally return to the negative pole of the power supply.

[0023] In the step 3, during the second group of tests, relays S2, S3, and S8 are closed, the DC resistance test device is started, and the positive pole of the power supply enters from the high-voltage side phase B. After the high-voltage side phase B is connected in series with the phase C, the current is introduced into the low-voltage side. The two phases AC on the low-voltage side are connected in series with the phase B and then in parallel, and finally return to the negative pole of the power supply.

[0024] Furthermore, the present invention also includes a method for demagnetizing an iron core after a DC resistance test, comprising the following steps:

[0025] After the test, keep relays S2 and S3 of the wiring conversion box closed, disconnect relay S9, close relay S7, and reverse the positive and negative poles of the current output terminals. Connect the wiring conversion box to the power supply to demagnetize the transformer core. During this process, the magnetic flux of each phase will first decrease to 0 and then increase in the opposite direction. The resistance value measured by the wiring conversion box will first increase to the maximum value and then decrease. Record the maximum value Rm of the resistance during the demagnetization process. When the resistance value starts to decrease from the maximum value and reaches (Rm-0.2*(Rm-R6)), immediately cut off the power supply of the wiring conversion box. At this time, the residual magnetism in the core is much smaller than the initial residual magnetism, achieving the purpose of weakening the residual magnetism.

[0026] The advantages and effects of the present invention are as follows:

[0027] The present invention designs a special wiring conversion box, which connects 7 test points including high and low voltage windings and a neutral point to the wiring conversion box with leads at one time. The wiring changes of the test are realized by controlling relays S1-S9 through a single-chip microcomputer. During the test, there is no need to manually disconnect the wiring again, which avoids electric shock accidents caused by incomplete discharge of the windings during manual wire replacement, thereby ensuring the safety of the test personnel.

[0028] For the processing of test data, since the test measures 7 groups of data in total and there are 6 groups of DC resistance to be measured, the method of taking the average value by multiple calculations can be used to reduce the test error.

[0029] The invention proposes a method for quickly testing the direct current resistance of a transformer and a method for demagnetizing the core of a transformer after a direct current resistance test. First, by optimizing and improving the wiring mode, a high-voltage winding is connected in series with a low-voltage winding, and the core saturation is accelerated by using the magnetic assist principle, thereby shortening the test time. The direct current resistance test of the high-voltage winding and the direct current resistance test of the low-voltage winding are organically integrated, and only two tests are required to complete the direct current resistance test of a total of 6 phases of the high and low voltage windings, and the second test effectively utilizes the magnetic flux established by the first test, that is, the magnetic flux of the B and C phases is in the same direction as the first test, and the magnetic flux utilization rate is 2 / 3. Compared with the magnetic assist method, the residual magnetism utilization rate is increased by 33%, further shortening the test time and improving work efficiency. After the direct current resistance test, without changing the wiring, the residual magnetism in the core of the transformer after the test is weakened by reversely connecting the positive and negative current output terminals of the device, thereby reducing the closing excitation surge current and improving the reliability of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the excitation surge when the boiler transformer is closed at no-load in the prior art.

[0031] Figure 2 It is a schematic diagram of the magnetizing inrush current when the boiler transformer is no-loaded and switched on after the demagnetization method of the present invention is adopted.

[0032] Figure 3a This is a wiring diagram of the DC resistance test 1 of the present invention.

[0033] Figure 3b This is a wiring diagram of the DC resistance test 2 of the present invention.

[0034] Figure 3c ) is a wiring diagram of the demagnetization test of the present invention.

[0035] Figure 4 It is a schematic diagram of the structure of the wiring conversion box of the present invention. DETAILED DESCRIPTION

[0036] Example

[0037] like Figure 4As shown, a transformer DC resistance test wiring conversion box is provided with high-voltage winding A phase, B phase, C phase, O phase wiring terminals and low-voltage winding a phase, c phase wiring terminals on the circuit wiring board; relay S1, A phase wiring terminal, relay S6 are connected in series in sequence to form a first branch; relay S2, B phase wiring terminal, relay S8 are connected in series in sequence to form a second branch; one end of the first branch after being connected in parallel with the second branch is connected to a current wiring terminal I+, and the other end of the first branch after being connected in parallel with the second branch is connected to a voltage wiring terminal V+; relay S3, a phase wiring terminal, relay S7 are connected in series in sequence to form a third branch; relay S4, c phase wiring terminal, relay S9 are connected in series in sequence to form a fourth branch; one end of the third branch after being connected in parallel with the fourth branch is connected to a current wiring terminal I-, and the other end of the third branch after being connected in parallel with the fourth branch is connected to a voltage wiring terminal V+; the O phase wiring terminal is connected in series with the relay S5 to be connected to the voltage wiring terminal V+; the C phase wiring terminal is connected to the voltage wiring terminal V-; the relays S1-S9 are controlled by a single-chip microcomputer.

[0038] A transformer DC resistance test method, the transformer is a double-winding transformer, the transformer wiring method is YNd11, and the specific test method includes the following steps:

[0039] Step 1. First, lead the high-voltage winding phases A, B, C, and O, and the low-voltage winding phases a and c to the corresponding terminals of the wiring conversion box with leads. The current output positive and negative terminals I+ and I-, and the voltage input positive and negative terminals V+ and V- of the DC resistance test device are respectively connected to the corresponding terminals of the wiring conversion box. Connect the high-voltage side phase C and the low-voltage side phase b through the test line to complete the wiring work before the test.

[0040] Step 2, when conducting the first test, close the relays S1, S4, and S5 of the wiring conversion box, start the DC resistance test device, and the positive pole of the power supply enters from the A phase of the wiring conversion box. After the A phase on the high-voltage side is connected in series with the C phase, the current is introduced into the low-voltage side. After the two phases ab on the low-voltage side are connected in series and in parallel with the c phase, it finally returns to the negative pole of the power supply. The voltage measurement end is at both ends of OC. After the core saturation measurement value stabilizes, the resistance value reading of the DC resistance test device is R1; at this time, disconnect the relay S5, close the relay S6, the voltage measurement end is at both ends of AC, and the reading is R2; at this time, disconnect the relay S6, close the relay S9, the voltage measurement end is at both ends of cC, and the reading is R3; at this time, disconnect the relay S9, close the relay S7, the voltage measurement end is at both ends of aC, and the reading is R4. At this point, the first test is over, and disconnect the relays S1, S4, and S7 to discharge the device until the discharge alarm sounds.

[0041] Step 3, after the first test discharge is completed, prepare for the second test, close relays S2, S3, S8, start the DC resistance test device, close relays S2, S3, S8, start the DC resistance test device, the positive pole of the power supply enters from the high-voltage side B phase, the high-voltage side B phase is connected in series with the C phase, and the current is introduced into the low-voltage side, the low-voltage side ac two-phase is connected in series and then connected in parallel with the b phase, and finally returns to the negative pole of the power supply. The voltage measurement end is at both ends of BC, and the series resistance value of the two phases BC is measured; after the core saturation measurement value is stable, the resistance value reading of the DC resistance test device is R5; at this time, disconnect relay S8, close relay S7, the voltage measurement end is at both ends of aC, and the reading is R6; at this time, disconnect relay S7, close relay S9, the voltage measurement end is at both ends of cC, and the reading is R7. At this point, the second test is over, and the device is discharged until the discharge alarm sounds.

[0042] Step 4: Calculate the DC resistance. Combining formulas 1, 2, and 5, you can get the high-voltage side DC resistance R. A , R B , R C , any three terms in formulas 3, 4, 6, and 7 can be solved to obtain the low-voltage side DC resistance R ab , R bc , R ac ,In order to make the result more accurate, the average of three times can be taken as the final result;

[0043] R1=R C (1)

[0044] R2=R A +R C (2)

[0045] R3=R bc (3)

[0046]

[0047] R5=R B +R C (5)

[0048] R6=R ab (6)

[0049]

[0050] The present invention also includes a method for demagnetizing an iron core after a DC resistance test, comprising the following steps:

[0051] After the test, keep relays S2 and S3 of the wiring conversion box closed, disconnect relay S9, close relay S7, and reverse the positive and negative poles of the current output terminals. Connect the wiring conversion box to the power supply to demagnetize the transformer core. During this process, the magnetic flux of each phase will first decrease to 0 and then increase in the opposite direction. The resistance value measured by the wiring conversion box will first increase to the maximum value and then decrease. Record the maximum value Rm of the resistance during the demagnetization process. When the resistance value starts to decrease from the maximum value and reaches (Rm-0.2*(Rm-R6)), immediately cut off the power supply of the wiring conversion box. At this time, the residual magnetism in the core is much smaller than the initial residual magnetism, achieving the purpose of weakening the residual magnetism. The excitation inrush current will be greatly reduced when the switch is closed.

[0052] Preferably, the current loop of the wiring conversion box and the related relays S1-S4 should use devices with a current carrying capacity of more than 40A.

[0053] The transformer DC resistance test method of the present invention is compared with the traditional method, and the test data and results are shown in Tables 1 and 2. The core demagnetization method of the present invention is compared with the traditional method, and the schematic diagram is shown in Figure 1 , Figure 2 As shown, Figure 1 When no measures are taken in the past, the boiler will experience no-load closing excitation surge, with the maximum phase current reaching 607A, which is 2.57 times the rated current. Figure 2 After the demagnetization method of the present invention is adopted, the boiler changes the no-load closing excitation surge current, and the maximum phase current is reduced to 42A, that is, 0.18 times the rated current.

[0054] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

[0055] Table 1 Comparison of test results (transformer model: SPF10-370000 / 220)

[0056]

[0057] Table 2 Summary of test data

[0058]

Claims

1. A transformer DC resistance test wiring conversion box, characterized in that The circuit wiring board is provided with high-voltage winding A phase, B phase, C phase, O phase wiring terminals and low-voltage winding a phase, c phase wiring terminals; relay S1, A phase wiring terminal, relay S6 are sequentially connected in series to form a first branch; relay S2, B phase wiring terminal, relay S8 are sequentially connected in series to form a second branch; one end of the first branch after being connected in parallel with the second branch is connected to a current wiring terminal I+, and the other end of the first branch after being connected in parallel with the second branch is connected to a voltage wiring terminal V+; relay S3, a phase wiring terminal, relay S7 are sequentially connected in series to form a third branch; relay S4, c phase wiring terminal, relay S9 are sequentially connected in series to form a fourth branch; one end of the third branch after being connected in parallel with the fourth branch is connected to a current wiring terminal I-, and the other end of the third branch after being connected in parallel with the fourth branch is connected to a voltage wiring terminal V+; the O phase wiring terminal is connected in series with the relay S5 and connected to the voltage wiring terminal V+; the C phase wiring terminal is connected to the voltage wiring terminal V-; the relays S1-S9 are controlled by a single-chip microcomputer.

2. A DC resistance test method for a transformer DC resistance test wiring conversion box according to claim 1, wherein the transformer is a double-winding transformer, and the transformer wiring method is YNd11, characterized in that The steps include: Step 1, firstly, lead the high-voltage winding phase A, phase B, phase C, phase O, and the low-voltage winding phase a, phase c to the corresponding wiring terminals of the wiring conversion box with leads, and connect the current output positive and negative terminals I+, I-, and the voltage input positive and negative terminals V+, V- of the DC resistance test device to the corresponding wiring terminals of the wiring conversion box, respectively, and connect the high-voltage side phase C with the low-voltage side phase b through the test line to complete the wiring work before the test; Step 2, when conducting the first test, close the relays S1, S4, and S5 of the wiring conversion box, start the DC resistance test device, and the voltage measurement end is at both ends of OC. After the core saturation measurement value stabilizes, the resistance reading of the DC resistance test device is R1; at this time, disconnect the relay S5, close the relay S6, the voltage measurement end is at both ends of AC, and the reading is R2; at this time, disconnect the relay S6, close the relay S9, the voltage measurement end is at both ends of cC, and the reading is R3; at this time, disconnect the relay S9, close the relay S7, the voltage measurement end is at both ends of aC, and the reading is R4. At this point, the first test is over, and disconnect the relays S1, S4, and S7 to discharge the device until the discharge alarm sounds; Step 3, after the first test discharge is completed, prepare for the second test, close relays S2, S3, S8, start the DC resistance test device, the voltage measurement end is at both ends of BC, and measure the series resistance value of the two-phase BC; after the core saturation measurement value is stable, the resistance reading of the DC resistance test device is R5; at this time, disconnect relay S8, close relay S7, the voltage measurement end is at both ends of aC, and the reading is R6; at this time, disconnect relay S7, close relay S9, the voltage measurement end is at both ends of cC, and the reading is R7. At this point, the second test is over, and the device is discharged until the discharge alarm sounds; Step 4: Calculate the DC resistance. Combining formulas 1, 2, and 5, you can get the high-voltage side DC resistance R. A , R B , R C , any three terms in formulas 3, 4, 6, and 7 can be solved to obtain the low-voltage side DC resistance R ab , R bc , R ac ,In order to make the result more accurate, the average of three times can be taken as the final result; R1=R C (1) R2=R A +R C (2) R3=R bc (3) R5=R B +R C (5) R6=R ab (6) 3. A transformer DC resistance test method according to claim 2, characterized in that In the step 2, when the first test is performed, the positive pole of the power supply enters from phase A of the wiring conversion box, and the current is introduced into the low-voltage side after phase A and phase C on the high-voltage side are connected in series. Phases ab on the low-voltage side are connected in series and then in parallel with phase c, and finally return to the negative pole of the power supply.

4. A transformer DC resistance test method according to claim 2, characterized in that In the step 3, during the second group of tests, relays S2, S3, and S8 are closed, the DC resistance test device is started, and the positive pole of the power supply enters from the high-voltage side phase B. After the high-voltage side phase B is connected in series with the phase C, the current is introduced into the low-voltage side. The two phases AC on the low-voltage side are connected in series with the phase B and then in parallel, and finally return to the negative pole of the power supply.

5. A transformer DC resistance test method according to claim 2, characterized in that Also included is a method for demagnetizing an iron core after a DC resistance test, comprising the following steps: After the test, keep relays S2 and S3 of the wiring conversion box closed, disconnect relay S9, close relay S7, and reverse the positive and negative poles of the current output terminals. Connect the wiring conversion box to the power supply to demagnetize the transformer core. During this process, the magnetic flux of each phase will first decrease to 0 and then increase in the opposite direction. The resistance value measured by the wiring conversion box will first increase to the maximum value and then decrease. Record the maximum value Rm of the resistance during the demagnetization process. When the resistance value starts to decrease from the maximum value and reaches (Rm-0.2*(Rm-R6)), immediately cut off the power supply of the wiring conversion box. At this time, the residual magnetism in the core is much smaller than the initial residual magnetism, achieving the purpose of weakening the residual magnetism.

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