Direct current resistance test circuit for mutual inductor

Abstract

The utility model discloses a mutual inductor direct current resistance test circuit, the test circuit comprises a direct current power supply, a switch switching unit and a detection terminal which are connected in sequence, the detection terminal comprises a positive detection terminal and a negative detection terminal; the switch switching unit is arranged among the direct-current power supply, the positive detection terminal and the negative detection terminal, the switch switching unit comprises two contact groups, each contact group comprises a static contact and two movable contacts, the positive detection terminal is connected with the static contact in one contact group, the negative detection terminal is connected with the static contact in the other contact group, and the two movable contacts are respectively connected with the two movable contacts. The two movable contacts in each contact group are respectively connected with the positive electrode and the negative electrode of the direct-current power supply; and the positive detection terminal and the negative detection terminal are connected with a winding of the mutual inductor to be detected. The switch switching unit is arranged among the direct current power supply, the positive detection terminal and the negative detection terminal, so that the positive and negative polarities of the direct current power supply can be adjusted, and the direct current resistance of the winding of the to-be-measured mutual inductor can be measured, and the to-be-measured mutual inductor can be demagnetized after the measurement is completed.

Description

Technical Field

[0001] The utility model belongs to the technical field of resistance testing, and in particular relates to a transformer direct current resistance testing circuit. Background Art

[0002] The instrument transformer is a key device in the power system, used to measure and protect the current and voltage in the power system. The DC resistance test is an important means to evaluate the performance and reliability of the instrument transformer. By measuring the DC resistance between the primary winding and the secondary winding of the instrument transformer, it can be checked whether the winding resistance value is within the specified range, and whether there are defects such as short circuit and open circuit.

[0003] At present, the device for testing DC resistance usually uses a DC constant current power supply to pass current through the winding. The power supply outputs a positive voltage to the DC constant current source. The current output by the DC constant current source passes through the positive detection terminal, and the positive detection terminal is connected to one end of the transformer winding to be tested. The other end of the transformer to be tested is connected to the negative detection terminal, and the negative detection terminal is returned to the negative pole of the power supply through a current sampling device. When the iron core of the transformer to be tested reaches magnetic flux saturation, the winding loses its inductance effect. At this time, the winding behaves as a pure resistor. The DC resistance value of the winding can be calculated using the winding voltage of the transformer to be tested and the current value of the transformer to be tested at this time.

[0004] After the transformer DC resistance test, there will still be residual magnetic flux in the transformer core, which will gradually disappear over time. However, for the transformer to be put into use, the residual magnetism in the core needs to be eliminated, otherwise it may cause closing failure or even upstream tripping accidents, so it is necessary to perform demagnetization operations using demagnetizers and other equipment.

[0005] It can be seen that how to reduce the impact of the residual magnetic flux generated by the DC resistance test on the use of the transformer and realize the DC resistance test without the need for an additional demagnetizer to demagnetize the transformer is a problem that needs to be solved at present. Utility Model Content

[0006] In view of the defects existing in the above-mentioned prior art, the utility model provides a transformer DC resistance test circuit, comprising: a DC power supply, a switch switching unit and a detection terminal connected in sequence, the detection terminal comprising a positive detection terminal and a negative detection terminal;

[0007] The switch switching unit is arranged between the DC power supply and the positive detection terminal and the negative detection terminal, and is used to control the positive and negative polarity of the DC power supply. The switch switching unit includes two groups of contact groups, each of which includes a static contact and two moving contacts. The positive detection terminal is connected to the static contact in one of the contact groups, and the negative detection terminal is connected to the static contact in the other contact group. The two moving contacts in each contact group are respectively connected to the positive and negative electrodes of the DC power supply.

[0008] The positive detection terminal and the negative detection terminal are connected to the winding of the transformer to be tested.

[0009] Furthermore, the switch switching unit is a double-pole double-throw switch, the static contacts include a first static contact and a second static contact, the moving contacts include two moving contacts corresponding to the first static contact and two moving contacts corresponding to the second static contact, the first static contact of the double-pole double-throw switch is connected to the positive detection terminal, the two moving contacts corresponding to the first static contact are respectively connected to the two ends of the DC power supply, the second static contact of the double-pole double-throw switch is connected to the negative detection terminal, and the two moving contacts corresponding to the second static contact are respectively connected to the two ends of the DC power supply.

[0010] Further, the switch switching unit includes a first double-pole single-throw switch and a second double-pole single-throw switch, the static contacts include a first static contact and a second static contact of the first double-pole single-throw switch and a first static contact and a second static contact of the second double-pole single-throw switch, and the moving contacts include a first moving contact and a second moving contact of the first double-pole single-throw switch and a first moving contact and a second moving contact of the second double-pole single-throw switch;

[0011] The first static contact of the first double-pole single-throw switch is connected to the positive detection terminal, the second static contact of the first double-pole single-throw switch is connected to the negative detection terminal, the first moving contact corresponding to the first static contact in the first double-pole single-throw switch is connected to the positive electrode of the DC power supply, and the second moving contact corresponding to the second static contact in the first double-pole single-throw switch is connected to the negative electrode of the DC power supply;

[0012] The first static contact of the second double-pole single-throw switch is connected to the positive detection terminal, the second static contact of the second double-pole single-throw switch is connected to the negative detection terminal, the first moving contact corresponding to the first static contact in the second double-pole single-throw switch is connected to the negative pole of the DC power supply, and the second moving contact corresponding to the second static contact in the second double-pole single-throw switch is connected to the positive pole of the DC power supply.

[0013] Further, the switch switching unit is a first single-pole double-throw switch and a second single-pole double-throw switch, the static contacts include a static contact of the first single-pole double-throw switch and a static contact of the second single-pole double-throw switch, and the moving contacts include two moving contacts of the first double-pole single-throw switch and two moving contacts of the second double-pole single-throw switch;

[0014] The static contact of the first single-pole double-throw switch is connected to the positive detection terminal, and the two moving contacts corresponding to the static contact of the first single-pole double-throw switch are respectively connected to two ends of the DC power supply;

[0015] The static contact of the second single-pole double-throw switch is connected to the negative detection terminal, and the two moving contacts corresponding to the static contact of the second single-pole double-throw switch are respectively connected to two ends of the DC power supply.

[0016] Further, the switch switching unit is a first single-pole single-throw switch, a second single-pole single-throw switch, a third single-pole single-throw switch and a fourth single-pole single-throw switch, the static contact includes an input terminal of the first single-pole single-throw switch, an input terminal of the second single-pole single-throw switch, an input terminal of the third single-pole single-throw switch and an input terminal of the fourth single-pole single-throw switch, and the moving contact includes an output terminal of the first single-pole single-throw switch, an output terminal of the second single-pole single-throw switch, an output terminal of the third single-pole single-throw switch and an output terminal of the fourth single-pole single-throw switch;

[0017] An input terminal of the first single-pole single-throw switch is connected to the positive detection terminal, and an output terminal of the first single-pole single-throw switch is connected to the positive electrode of the DC power supply;

[0018] An input terminal of the second single-pole single-throw switch is connected to the negative detection terminal, and an output terminal of the second single-pole single-throw switch is connected to the negative electrode of the DC power supply;

[0019] An input terminal of the third single-pole single-throw switch is connected to the positive detection terminal, and an output terminal of the third single-pole single-throw switch is connected to the negative electrode of the DC power supply;

[0020] An input terminal of the fourth single-pole single-throw switch is connected to the negative detection terminal, and an output terminal of the fourth single-pole single-throw switch is connected to the positive electrode of the DC power supply.

[0021] Furthermore, a discharge resistor is included, and two ends of the discharge resistor are respectively connected to the positive detection terminal and the negative detection terminal, and are connected in parallel with the winding of the transformer to be tested.

[0022] Furthermore, it also includes a current sampling unit, a current measurement channel and a control unit;

[0023] The current sampling unit is arranged between the discharge resistor and the negative detection terminal;

[0024] The current measurement channel is connected in parallel with the current sampling unit and is used to output the current parameters in the test circuit;

[0025] The control unit is connected to the current measuring channel.

[0026] Further, it also includes a voltage measurement channel;

[0027] The voltage measurement channel is connected in parallel with the winding of the transformer to be tested, and is used to output the voltage parameters in the test circuit;

[0028] The control unit is connected to the voltage measurement channel.

[0029] Furthermore, it also includes a driving module;

[0030] The driving module is connected to the control unit and the switch unit respectively, and is used to control the switch unit to be turned on and / or off.

[0031] Furthermore, the current sampling unit is a resistor-type shunt.

[0032] The transformer DC resistance test circuit provided by the utility model has at least the following beneficial effects:

[0033] (1) By setting a switch switching unit between the DC power supply and the positive detection terminal and the negative detection terminal, the positive and negative polarities of the DC power supply can be adjusted, thereby measuring the DC resistance value of the transformer winding to be measured and demagnetizing the transformer to be measured after the measurement is completed.

[0034] (2) By setting a discharge resistor, in the gap between switching of the switch switching unit, the discharge resistor and the winding of the transformer to be tested form a closed loop, providing a discharge loop for the winding, thereby avoiding reverse voltage damage to the circuit caused by sudden disconnection of the winding loop.

[0035] (3) By using a resistive shunt as a current sampling unit, the output current is limited. Even if the winding of the transformer to be tested causes the positive detection terminal and the negative detection terminal to be short-circuited, the presence of the resistive shunt can limit the maximum output current of the DC power supply and protect the DC power supply from overcurrent damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A circuit block diagram of a transformer DC resistance test circuit provided by an embodiment of the utility model;

[0037] Figure 2 A circuit structure diagram of a transformer DC resistance test circuit provided by an embodiment of the utility model;

[0038] Figure 3 A circuit diagram of a transformer DC resistance test circuit provided by an embodiment of the utility model;

[0039] Figure 4 A circuit diagram of a transformer DC resistance test circuit corresponding to a double-pole double-throw switch in which the switch switching unit provided in the embodiment of the utility model is a double-pole double-throw switch;

[0040] Figure 5 A circuit diagram of a transformer DC resistance test circuit corresponding to a double-pole single-throw switch in which the switch switching unit provided in the embodiment of the utility model is a double-pole single-throw switch;

[0041] Figure 6 A circuit diagram of a transformer DC resistance test circuit corresponding to a single-pole double-throw switch in which the switch switching unit provided in the embodiment of the utility model is a single-pole double-throw switch;

[0042] Figure 7 The switch switching unit provided in the embodiment of the utility model is a circuit diagram of a transformer DC resistance test circuit corresponding to a single-pole single-throw switch.

[0043] Among them, 10, DC power supply; 20, switch switching unit; 30, positive detection terminal; 40, negative detection terminal; 50, discharge resistor; 60, drive module; 61, control unit; 70, current sampling unit; 80, current measurement channel; 90, voltage measurement channel. DETAILED DESCRIPTION

[0044] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the drawings and specific implementation methods of the specification. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the utility model.

[0045] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0046] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0047] The power transformer needs to test the DC resistance of each winding regularly. The change of this resistance reflects the performance status of the winding. At present, the method of testing DC resistance is to use a DC constant current power supply to pass current through the winding (the transformer test current is 1A~5A). When the core reaches magnetic flux saturation, the winding loses its inductance effect. At this time, the winding behaves as a pure resistor. The voltage at both ends of the winding and the current passing through the winding are collected at this time to calculate the DC resistance value of the winding.

[0048] After calculating the DC resistance of the winding, the constant current source stops outputting. Since only one-way current is passed through the winding and the core magnetic flux is excited in one direction, the constant current source stops outputting, and there will still be residual magnetic flux in the core, which will last for a long time (several weeks). For the transformer to be put into use, the residual magnetism in the core needs to be eliminated, otherwise it may cause a closing failure or even an upstream tripping accident.

[0049] However, the residual magnetic flux will affect other characteristic tests of the transformer, including volt-ampere characteristic test, ratio test, etc. For the transformer that needs to be put into use as soon as possible, the residual magnetism in the core needs to be eliminated, otherwise it may cause closing failure or even upstream tripping accidents, so it is necessary to perform demagnetization operation through demagnetizer and other equipment.

[0050] It can be seen that how to reduce the impact of the residual magnetic flux generated by the DC resistance test on the use of the transformer and realize the DC resistance test without the need for an additional demagnetizer to demagnetize the transformer is a problem that needs to be solved at present.

[0051] like Figure 1 As shown, the embodiment of the utility model provides a transformer DC resistance test circuit, the test circuit includes a DC power supply 10, a switch unit 20 and a detection terminal connected in sequence, the detection terminal includes a positive detection terminal 30 and a negative detection terminal 40; the switch unit 20 is arranged between the DC power supply 10 and the positive detection terminal 30 and the negative detection terminal 40, and is used to control the positive and negative polarity of the DC power supply 10, the switch unit 20 includes two groups of contact groups, each group of contact groups includes a static contact and two moving contacts, the positive detection terminal 30 is connected to the static contact in one group of contact groups, the negative detection terminal 40 is connected to the static contact in the other group of contact groups, and the two moving contacts in each group of contact groups are respectively connected to the positive and negative poles of the DC power supply 10; the positive detection terminal 30 and the negative detection terminal 40 are connected to the winding of the transformer to be tested. By adjusting the switch in the switch unit 20, the positive and negative polarity of the DC power supply 10 can be changed, and the effect of demagnetizing the transformer can be achieved.

[0052] In a specific embodiment, referring to Figure 2 The test circuit also includes a discharge resistor 50, two ends of which are respectively connected to the positive detection terminal 30 and the negative detection terminal 40, and are connected in parallel with the winding of the transformer to be tested.

[0053] In the interval when the switch unit 20 is switching, the discharge resistor 50 and the winding of the transformer to be tested form a closed loop, providing a discharge loop for the inductive winding, thereby avoiding reverse voltage damage to the circuit caused by sudden disconnection of the winding loop.

[0054] Reference Figure 3 In a specific embodiment, the test circuit further includes a current sampling unit 70, a current measurement channel 80 and a control unit 61. The current sampling unit 70 is arranged between the discharge resistor 50 and the negative detection terminal 40. The current measurement channel 80 is connected in parallel with the current sampling unit 70 to output the current parameter in the test circuit. The control unit 61 is connected to the current measurement channel 80.

[0055] In a specific example, the current sampling unit 70 is a resistive shunt, and the selection of the resistive shunt is related to the output voltage of the DC power supply 10. In the test circuit, the resistive shunt is used as the current sampling unit 70, and also plays a role in limiting the output current. Even if the winding of the transformer to be tested short-circuits the positive detection terminal 30Vo+ and the negative detection terminal 40Vo-, due to the existence of the resistive shunt, the maximum output current of the DC power supply 10 can be limited, and the DC power supply 10 is protected from overcurrent damage.

[0056] In a specific implementation, the test circuit further includes a voltage measurement channel 90 , which is connected in parallel with the winding of the transformer to be tested and is used to output voltage parameters in the test circuit. The control unit 61 is connected to the voltage measurement channel 90 .

[0057] In a specific implementation, the test circuit further includes a driving module 60 , which is connected to the control unit 61 and the switch unit 20 , respectively, and is used to control the switch unit 20 to be turned on and / or off.

[0058] The control unit 61 is used to receive the voltage parameters in the test circuit output by the voltage measurement channel 90, receive the current parameters in the test circuit output by the current measurement channel 80, and output the DC resistance value of the winding of the transformer to be tested based on the voltage parameters and the current parameters. The control unit 61 is also used to output control instructions to control the driving module 60 to drive each switch in the switch switching unit 20 to be turned on and / or off.

[0059] Reference Figure 4 The switch unit 20 includes two contact groups, wherein P0, P1 and P2 are one contact group, and P0', P1' and P2' are another contact group. P0 and P0' are respectively static contacts in each contact group, and the two static contacts are respectively connected to the positive detection terminal 30 and the negative detection terminal 40. P1, P2 and P1', P2' are respectively moving contacts in each contact group, and the positive and negative electrodes of the DC power supply 10 are respectively connected to different moving contacts of each contact group, that is, the positive electrode of the DC power supply 10 is connected to P1 and P2', and the negative electrode of the DC power supply 10 is connected to P2 and P1'.

[0060] In the first specific example, a double-pole double-throw switch is used to control the positive and negative polarities of the DC power supply 10, and the specific control process is as follows:

[0061] When the first static contact P0 of the double-pole double-throw switch is closed with the moving contact P1 corresponding to the first static contact and the second static contact P0' of the double-pole double-throw switch is closed with the moving contact P1' corresponding to the second static contact, Vo+→Vo- outputs a positive voltage. When the first static contact P0 of the double-pole double-throw switch is closed with the moving contact P2 corresponding to the first static contact and the second static contact P0' of the double-pole double-throw switch is closed with the moving contact P2' corresponding to the second static contact, Vo+→Vo- outputs a negative voltage. By continuously switching the double-pole double-throw switch, a bidirectional current is realized on the winding of the transformer to be tested.

[0062] By adding a discharge resistor 50 at the output end of the moving contact of the double-pole double-throw switch (the discharge resistor 50 is also between Vo+ and Vo-, and is connected in parallel with the winding of the transformer to be tested), when the first static contact P0 switches between P1 and P2 and the second static contact P0' switches between P1' and P2', that is, P0 and P0' are not connected to P1, P2, P1', and P2', the discharge resistor 50 forms a loop with the winding of the transformer to be tested, providing a discharge loop for the winding of the transformer to be tested.

[0063] The use of the test circuit includes two parts: the measurement phase and the degaussing phase. The measurement phase refers to measuring the DC resistance value of the winding of the transformer to be tested, and the degaussing phase refers to eliminating the residual magnetic flux generated in the winding of the transformer to be tested during the measurement of the DC resistance value. The specific use process is as follows:

[0064] Measurement phase: close the first static contact P0 of the double-pole double-throw switch and the moving contact P1 corresponding to the first static contact, and close the second static contact P0' of the double-pole double-throw switch and the moving contact P1' corresponding to the second static contact. At this time, Vo+→Vo- outputs a positive voltage. After the output current stabilizes, the DC resistance value of the winding of the transformer to be measured can be calculated through the voltage collected by the voltage measurement channel 90 and the current collected by the current measurement channel 80.

[0065] Demagnetization stage: After the DC resistance value test is completed, the first static contact P0 of the double-pole double-throw switch is closed with the moving contact P2 corresponding to the first static contact, and the second static contact P0' of the double-pole double-throw switch is closed with the moving contact P2' corresponding to the second static contact, Vo+→Vo- outputs a negative voltage, and reverse power is sent to the winding of the transformer to be tested for reverse excitation (i.e., eliminating the positive residual magnetism). By controlling the sequential and alternating connection of P0, P0' with P1, P2, P1', and P2', the direction of the output voltage Vo+→Vo- can be achieved, thereby realizing the demagnetization of the winding of the transformer to be tested.

[0066] The output of the DC power supply 10 is controlled by a double-pole double-throw switch, so that the test circuit can achieve bidirectional output of positive voltage and negative voltage. The double-pole double-throw switch can also be replaced by a solid-state relay, which can be an electronic switch such as a thyristor, a metal oxide semiconductor field effect transistor (MOSFET), or an insulate gate bipolar transistor (IGBT).

[0067] Reference Figure 5 In a second specific example, the switch switching unit 20 includes a first double-pole single-throw switch S1 and a second double-pole single-throw switch S2. The first static contact P0 of the first double-pole single-throw switch is connected to the positive detection terminal 30, the second static contact P0' of the first double-pole single-throw switch is connected to the negative detection terminal 40, the first moving contact P1 corresponding to the first static contact in the first double-pole single-throw switch is connected to the positive pole of the DC power supply 10, and the second moving contact P1' corresponding to the second static contact in the first double-pole single-throw switch is connected to the negative pole of the DC power supply 10. The first static contact P0 of the second double-pole single-throw switch is connected to the positive detection terminal 30, the second static contact P0' of the second double-pole single-throw switch is connected to the negative detection terminal 40, the first moving contact P2 corresponding to the first static contact in the second double-pole single-throw switch is connected to the negative pole of the DC power supply 10, and the second moving contact P2' corresponding to the second static contact in the second double-pole single-throw switch is connected to the positive pole of the DC power supply 10.

[0068] The first stationary contact P0 of the first double-pole single-throw switch S1 is closed with the moving contact P1 corresponding to the first stationary contact, and the second stationary contact P0' of the first double-pole single-throw switch S1 is closed with the moving contact P1' corresponding to the second stationary contact. At this time, Vo+→Vo- outputs a positive voltage, that is, the test circuit is in the measurement stage. After the output current stabilizes, the DC resistance value of the winding of the transformer to be tested can be calculated through the voltage collected by the voltage measurement channel 90 and the current collected by the current measurement channel 80.

[0069] After the DC resistance value test is completed, the demagnetization stage is entered, the first static contact P0 of the first double-pole single-throw switch S1 is disconnected from the moving contact P1 corresponding to the first static contact, the second static contact P0' of the first double-pole single-throw switch S1 is disconnected from the moving contact P1' corresponding to the second static contact, the first static contact P0 of the second double-pole single-throw switch S2 is closed with the moving contact P2 corresponding to the first static contact, and the second static contact P0' of the second double-pole single-throw switch S2 is closed with the moving contact P2' corresponding to the second static contact, Vo+→Vo- outputs a negative voltage, reversely sends power to the winding of the transformer to be tested for reverse excitation (i.e., eliminates the positive residual magnetism), and by controlling the sequential and alternating connection of P0, P0' with P1, P2, P1', and P2', the direction of the output voltage Vo+→Vo- can be achieved, thereby achieving the demagnetization of the winding of the transformer to be tested.

[0070] Reference Figure 6 The switch unit 20 includes two contact groups, wherein one static contact and two moving contacts of S1 form one contact group, and one static contact and two moving contacts of S2 form another contact group. The static contact of S1 and the static contact of S2 are static contacts in each contact group, respectively, and the two static contacts are connected to the positive detection terminal 30 and the negative detection terminal 40, respectively. The two moving contacts of S1 and the two moving contacts of S2 are moving contacts in each contact group, respectively, and the positive and negative electrodes of the DC power supply 10 are connected to different moving contacts of each contact group, namely, the positive electrode of the DC power supply 10 is connected to one moving contact of S1 and one moving contact of S2, and the negative electrode of the DC power supply 10 is connected to another moving contact of S1 and another moving contact of S2.

[0071] In the third specific example, the switch switching unit 20 is a first single-pole double-throw switch S1 and a second single-pole double-throw switch S2. The static contact of the first single-pole double-throw switch is connected to the positive detection terminal 30, and the two moving contacts corresponding to the static contact of the first single-pole double-throw switch are respectively connected to the two ends of the DC power supply 10. The static contact of the second single-pole double-throw switch is connected to the negative detection terminal 40, and the two moving contacts corresponding to the static contact of the second single-pole double-throw switch are respectively connected to the two ends of the DC power supply 10.

[0072] The static contact of the first single-pole double-throw switch S1 is closed with the moving contact corresponding to the positive pole of the DC power supply 10, and the static contact of the second single-pole double-throw switch S2 is closed with the moving contact corresponding to the negative pole of the DC power supply 10. At this time, Vo+→Vo- outputs a positive voltage, that is, the test circuit is in the measurement stage. After the output current stabilizes, the DC resistance value of the winding of the transformer to be tested can be calculated through the voltage collected by the voltage measurement channel 90 and the current collected by the current measurement channel 80.

[0073] After the DC resistance value test is completed, the demagnetization stage is entered. The static contact of the first single-pole double-throw switch S1 is closed with the moving contact corresponding to the negative pole of the DC power supply 10, and the static contact of the second single-pole double-throw switch S2 is closed with the moving contact corresponding to the positive pole of the DC power supply 10. A negative voltage is output from Vo+ to Vo-, and reverse power is sent to the winding of the transformer to be tested for reverse excitation (i.e., eliminating the positive residual magnetism). By controlling the first single-pole double-throw switch S1 and the second single-pole double-throw switch S2 to be connected in sequence and rotation, the direction of the output voltage from Vo+ to Vo- can be achieved, thereby achieving the demagnetization of the winding of the transformer to be tested.

[0074] Reference Figure 7 The switch unit 20 includes two contact groups, wherein the contacts of S1 and S3 form one contact group, and the contacts of S2 and S4 form another contact group, the static contacts of S1 and S3 are connected to the positive detection terminal 30, and the static contacts of S2 and S4 are connected to the negative detection terminal 40. The positive and negative electrodes of the DC power supply 10 are respectively connected to different moving contacts of each contact group, that is, the positive electrode of the DC power supply 10 is connected to the moving contact of S1 and the moving contact of S4, and the negative electrode of the DC power supply 10 is connected to the moving contact of S2 and the moving contact of S3.

[0075] In the fourth specific example, the switch switching unit 20 is a first single-pole single-throw switch S1, a second single-pole single-throw switch S2, a third single-pole single-throw switch S3 and a fourth single-pole single-throw switch S4. The input terminal of the first single-pole single-throw switch S1 is connected to the positive detection terminal 30, and the output terminal of the first single-pole single-throw switch S1 is connected to the positive electrode of the DC power supply 10. The input terminal of the second single-pole single-throw switch S2 is connected to the negative detection terminal 40, and the output terminal of the second single-pole single-throw switch S2 is connected to the negative electrode of the DC power supply 10. The input terminal of the third single-pole single-throw switch S3 is connected to the positive detection terminal 30, and the output terminal of the third single-pole single-throw switch S3 is connected to the negative electrode of the DC power supply 10. The input terminal of the fourth single-pole single-throw switch S4 is connected to the negative detection terminal 40, and the output terminal of the fourth single-pole single-throw switch S4 is connected to the positive electrode of the DC power supply 10.

[0076] The first single-pole single-throw switch S1 and the second single-pole single-throw switch S2 are closed, and the third single-pole single-throw switch S3 and the fourth single-pole single-throw switch S4 are opened. At this time, Vo+→Vo- outputs a positive voltage, that is, the test circuit is in the measurement stage. After the output current stabilizes, the DC resistance value of the winding of the transformer to be tested can be calculated through the voltage collected by the voltage measurement channel 90 and the current collected by the current measurement channel 80.

[0077] After the DC resistance value test is completed, the demagnetization stage is entered. The first single-pole single-throw switch S1 and the second single-pole single-throw switch S2 are disconnected, and the third single-pole single-throw switch S3 and the fourth single-pole single-throw switch S4 are closed. At this time, Vo+→Vo- outputs a negative voltage, and reverse power is sent to the winding of the transformer to be tested for reverse excitation (i.e., eliminating the positive residual magnetism). By controlling the first single-pole single-throw switch S1, the second single-pole single-throw switch S2, the third single-pole single-throw switch S3 and the fourth single-pole single-throw switch S4 to be connected in sequence and rotation, the direction of the output voltage Vo+→Vo- can be achieved, thereby achieving the demagnetization of the winding of the transformer to be tested.

[0078] The test circuit achieves demagnetization by passing a bidirectional current through the winding of the transformer to be tested. The current direction is switched based on the current output current. When the current output current reaches 50% of the last switching current, switching is performed until the output current reaches less than 1% of the test phase current (i.e., the initial current of the bidirectional switching).

[0079] By applying the test circuit to the transformer comprehensive tester, it is possible to complete the DC resistance measurement and perform demagnetization, thus creating good conditions for the subsequent transformation ratio test of the transformer to be tested.

[0080] After the measurement phase is completed, the test circuit provided by the utility model greatly eliminates residual magnetism by applying positive and negative alternating voltages to both ends of the winding of the transformer to be tested. At the same time, the measurement phase and the demagnetization phase are integrated into the test circuit, and the DC resistance test and demagnetization can be completed without additional demagnetization equipment, which reduces the size of the transformer comprehensive tester and creates good conditions for subsequent testing of the transformer to be tested.

[0081] Since the composition of the switch unit 20 is different, the switching time of the switch unit 20 is also different, and the specific switching time needs to be determined according to the actual characteristics of each device in the switch unit 20. In order to avoid that multiple switches in the switch unit 20 are in a closed state at a certain moment, so that the output of the DC power supply 10 is short-circuited through the switch unit 20, the original output needs to be disconnected first, and then the new (reverse) output needs to be closed during switching.

[0082] In the second and fourth specific examples, the switching unit composed of single-throw switches may cause the output of the DC power supply 10 to be short-circuited. Therefore, the driving module 60 must output at least two sets of control signals to control the switching of the switches. Specifically, when the voltage is positive, the driving module 60 needs to first output the first control signal to control the closed switch in the switch switching unit 20 to be disconnected, and then wait for a period of time to ensure that the switch is completely disconnected, and then output the second control signal to close the switch part in the switch switching unit 20 to achieve the reverse output of the DC power supply 10.

[0083] In a specific example, the direct current method is used to demagnetize the transformer. The specific process is as follows:

[0084] A 5A current is used to test the DC resistance value of the transformer winding to be tested. At this time, Vo+→Vo- outputs a forward DC current. The switch switching unit 20 is used to make Vo+→Vo- output a reverse voltage to reversely charge the transformer to be tested (the reverse charging process is the demagnetization process of the original forward magnetic flux). As the original forward magnetic flux is eliminated and the reverse magnetic flux begins to be established, the reverse current in the transformer to be tested begins to increase slowly from 0; when the reverse current increases to 50% of the previous forward current, for example, the first forward current is 5A, then the second reverse current is 2.5A; if the previous forward current is 1.25A, then the current reverse current is 0.62A, and the reverse output of Vo+→Vo- is controlled by the switch switching unit 20.

[0085] The switch switching unit 20 is used to make Vo+→Vo- output a forward voltage, and the transformer to be tested is forwardly charged again. When the forward current is 50% of the previous reverse current, for example, the previous reverse current is 2.5A, the current forward current is 1.25A, and the forward output of Vo+→Vo- is controlled by the switch switching unit 20.

[0086] The control of the switch unit 20 is repeated to realize the switching of the forward output and the reverse output of Vo+→Vo-, until the current is less than 5 mA, and the demagnetization process is stopped.

[0087] In the above process, the forward and reverse currents are reduced by 50% each time. In other embodiments, the current reduction amplitude can be adjusted according to actual needs. For example, it can be 80% or 30%. Increasing the current reduction amplitude will have a better demagnetization effect, but it will cause the demagnetization process to take longer; reducing the current reduction amplitude will make the demagnetization process faster, but the demagnetization effect may become worse, and there is no limitation on this.

[0088] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A transformer DC resistance test circuit, characterized in that: include: A DC power supply, a switch unit and a detection terminal connected in sequence, wherein the detection terminal includes a positive detection terminal and a negative detection terminal; The switch switching unit is arranged between the DC power supply and the positive detection terminal and the negative detection terminal, and is used to control the positive and negative polarity of the DC power supply. The switch switching unit includes two groups of contact groups, each of which includes a static contact and two moving contacts. The positive detection terminal is connected to the static contact in one of the contact groups, and the negative detection terminal is connected to the static contact in the other contact group. The two moving contacts in each contact group are respectively connected to the positive and negative electrodes of the DC power supply. The positive detection terminal and the negative detection terminal are connected to the winding of the transformer to be tested.

2. The transformer DC resistance test circuit according to claim 1, characterized in that: The switch switching unit is a double-pole double-throw switch, the static contacts include a first static contact and a second static contact, the moving contacts include two moving contacts corresponding to the first static contact and two moving contacts corresponding to the second static contact, the first static contact of the double-pole double-throw switch is connected to the positive detection terminal, the two moving contacts corresponding to the first static contact are respectively connected to the two ends of the DC power supply, the second static contact of the double-pole double-throw switch is connected to the negative detection terminal, and the two moving contacts corresponding to the second static contact are respectively connected to the two ends of the DC power supply.

3. The transformer DC resistance test circuit according to claim 1, characterized in that: The switch switching unit includes a first double-pole single-throw switch and a second double-pole single-throw switch, the static contacts include a first static contact and a second static contact of the first double-pole single-throw switch and a first static contact and a second static contact of the second double-pole single-throw switch, and the moving contacts include a first moving contact and a second moving contact of the first double-pole single-throw switch and a first moving contact and a second moving contact of the second double-pole single-throw switch; The first static contact of the first double-pole single-throw switch is connected to the positive detection terminal, the second static contact of the first double-pole single-throw switch is connected to the negative detection terminal, the first moving contact corresponding to the first static contact in the first double-pole single-throw switch is connected to the positive electrode of the DC power supply, and the second moving contact corresponding to the second static contact in the first double-pole single-throw switch is connected to the negative electrode of the DC power supply; The first static contact of the second double-pole single-throw switch is connected to the positive detection terminal, the second static contact of the second double-pole single-throw switch is connected to the negative detection terminal, the first moving contact corresponding to the first static contact in the second double-pole single-throw switch is connected to the negative pole of the DC power supply, and the second moving contact corresponding to the second static contact in the second double-pole single-throw switch is connected to the positive pole of the DC power supply.

4. The transformer DC resistance test circuit according to claim 1, characterized in that: The switch switching unit is a first single-pole double-throw switch and a second single-pole double-throw switch, the static contacts include a static contact of the first single-pole double-throw switch and a static contact of the second single-pole double-throw switch, and the moving contacts include two moving contacts of the first double-pole single-throw switch and two moving contacts of the second double-pole single-throw switch; The static contact of the first single-pole double-throw switch is connected to the positive detection terminal, and the two moving contacts corresponding to the static contact of the first single-pole double-throw switch are respectively connected to two ends of the DC power supply; The static contact of the second single-pole double-throw switch is connected to the negative detection terminal, and the two moving contacts corresponding to the static contact of the second single-pole double-throw switch are respectively connected to two ends of the DC power supply.

5. The transformer DC resistance test circuit according to claim 1, characterized in that: The switch switching unit is a first single-pole single-throw switch, a second single-pole single-throw switch, a third single-pole single-throw switch and a fourth single-pole single-throw switch, the static contact includes an input terminal of the first single-pole single-throw switch, an input terminal of the second single-pole single-throw switch, an input terminal of the third single-pole single-throw switch and an input terminal of the fourth single-pole single-throw switch, and the moving contact includes an output terminal of the first single-pole single-throw switch, an output terminal of the second single-pole single-throw switch, an output terminal of the third single-pole single-throw switch and an output terminal of the fourth single-pole single-throw switch; An input terminal of the first single-pole single-throw switch is connected to the positive detection terminal, and an output terminal of the first single-pole single-throw switch is connected to the positive electrode of the DC power supply; An input terminal of the second single-pole single-throw switch is connected to the negative detection terminal, and an output terminal of the second single-pole single-throw switch is connected to the negative electrode of the DC power supply; An input terminal of the third single-pole single-throw switch is connected to the positive detection terminal, and an output terminal of the third single-pole single-throw switch is connected to the negative electrode of the DC power supply; An input terminal of the fourth single-pole single-throw switch is connected to the negative detection terminal, and an output terminal of the fourth single-pole single-throw switch is connected to the positive electrode of the DC power supply.

6. The transformer DC resistance test circuit according to claim 1, characterized in that: It also includes a discharge resistor, the two ends of which are respectively connected to the positive detection terminal and the negative detection terminal, and are connected in parallel with the winding of the transformer to be tested.

7. The transformer DC resistance test circuit according to claim 1, characterized in that: It also includes a current sampling unit, a current measurement channel and a control unit; The current sampling unit is arranged between the discharge resistor and the negative detection terminal; The current measurement channel is connected in parallel with the current sampling unit and is used to output current parameters in the test circuit; The control unit is connected to the current measuring channel.

8. The transformer DC resistance test circuit according to claim 7, characterized in that: Also includes voltage measurement channels; The voltage measurement channel is connected in parallel with the winding of the transformer to be tested, and is used to output the voltage parameters in the test circuit; The control unit is connected to the voltage measurement channel.

9. The transformer DC resistance test circuit according to claim 7 or 8, characterized in that: Also includes a driver module; The driving module is connected to the control unit and the switch unit respectively, and is used to control the switch unit to be turned on and / or off.

10. The transformer DC resistance test circuit according to claim 7, characterized in that: The current sampling unit is a resistive shunt.

Images