A high voltage current transformer calibration device and method
By setting a double-layer grounding shield to the primary winding of the reference current transformer in the calibration device of the high-voltage current transformer, the problem of inaccurate calibration of the current transformer at high voltage is solved, and the consistency between the calibration state and the use state is achieved, and error and measurement uncertainty are reduced.
Patent Information
- Application Number
- CN202110263975.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-03-08
- Publication Date
- 2025-03-18
- Estimated Expiration
- 2041-03-08
AI Technical Summary
The prior art cannot accurately calibrate current transformers operating at high voltages, resulting in inconsistent calibration states and usage states, introducing unknown deviations and measurement uncertainties.
By applying the same high voltage to the primary winding of the measured current transformer and the reference current transformer, and providing a double-layer ground shield at the primary winding of the reference current transformer, the leakage current flowing through the two-layer shields in the opposite direction, forming a closed loop to achieve calibration of the high-voltage current transformer.
The accurate calibration of the high-voltage current transformer in the high-voltage state is achieved, avoiding the problem of inconsistent calibration state and use state, and reducing errors and measurement uncertainty.
Smart Images
Figure CN112858987B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of metering technology and devices, and in particular relates to a high-voltage current transformer calibration device and method, which are used for calibrating the high-voltage current transformer. Background Art
[0002] At present, the calibration of current transformers (CTs) in China is basically carried out with the primary and secondary windings grounded. However, when the current transformer is actually used, the primary and / or secondary windings may be in a high-voltage working state. Since the calibration state is different from the use state, unknown deviations and additional measurement uncertainty components will be introduced. The current calibration method cannot accurately characterize the error of the calibrated high-voltage current transformer under the actual working state.
[0003] Internationally, research institutions such as the Canadian National Institute of Metrology, the Netherlands National Institute of Metrology, and the University of the Republic of Uruguay have conducted research on the calibration of current transformers under high voltage, but the equipment used is complex, and there is no detailed explanation of the errors and evaluation of the standard current transformers themselves under high voltage. Summary of the invention
[0004] The purpose of the present invention is to solve the problem of how to calibrate the current transformer under high voltage in the above-mentioned prior art, and to provide a high-voltage current transformer calibration device and method, so that the standard transformer does not introduce additional errors due to the high voltage state, thereby calibrating the transformer to be tested under high voltage state, so as to achieve the effect that the calibration state of the calibrated object is consistent with the usage state.
[0005] The present invention is achieved through the following technical solutions:
[0006] A first aspect of the present invention provides a high voltage current transformer calibration method, the method comprising:
[0007] Apply the same high voltage to the primary winding of the current transformer under test and the primary winding of the reference current transformer;
[0008] A double-layer grounding shield is provided at the primary winding of the reference current transformer, and the leakage current flowing in the two layers of the double-layer grounding shield is in opposite directions;
[0009] The current source is connected to the primary winding of the current booster; the reference current transformer is connected to the current transformer to be measured, and forms a closed loop with the secondary winding of the current booster.
[0010] A further improvement of the present invention is that the operation of providing a double-layer grounding shield at the primary winding of the reference current transformer includes:
[0011] The reference current transformer adopts a through-type transformer;
[0012] The head end of the double-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the double-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the double-layer shielded coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the double-layer shielded coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer; and the shielding layer of the double-layer shielded coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer is removed; then the outermost shielding layer of the double-layer shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the two shielding layers of the double-layer shielded coaxial cable are connected at the outflow end of the primary winding of the reference current transformer to achieve electrical conduction.
[0013] A further improvement of the present invention is that the operation of providing a double-layer grounding shield at the primary winding of the reference current transformer includes:
[0014] The reference current transformer adopts a through-type transformer;
[0015] The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the single-layer shielded coaxial cable is used as the secondary winding of the current booster or the middle part of the coaxial cable is disconnected and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the single-layer shielded coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer, and the shielding layer of the single-layer shielded coaxial cable from the tail end to the primary winding outflow end close to the reference current transformer is removed; then the shielding layer of the single-layer shielded coaxial cable is peeled off from its tail end, and then the tail end of the shielding layer is folded back and passed through the hole in the iron core of the reference current transformer in reverse, the folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shielding layer is grounded at the inflow end of the primary winding of the reference current transformer.
[0016] A further improvement of the present invention is that the operation of providing a double-layer grounding shield at the primary winding of the reference current transformer includes:
[0017] The reference current transformer adopts a through-type transformer;
[0018] The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer; and the shielding layer on the section of the coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer is removed; then a layer of metal foil is wrapped around the section of the single-layer shielded coaxial cable that serves as the primary winding of the reference current transformer, the head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer and is grounded, and the tail end of the metal foil is passed through the hole in the iron core and connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction.
[0019] A further improvement of the present invention is that the operation of providing a double-layer grounding shield at the primary winding of the reference current transformer includes:
[0020] The reference current transformer adopts a wiring type current transformer;
[0021] Connect the head end of the coaxial cable to the outflow end of the primary winding of the current transformer to be tested, and use the coaxial cable as the secondary winding of the current booster, or disconnect the middle of the coaxial cable and connect the two breakpoints to the two ports of the secondary winding of the current booster respectively, and then connect the tail end of the coaxial cable to the inflow end of the primary winding of the reference current transformer;
[0022] An inner shielding layer is first arranged on the core of the reference current transformer, and then an outer shielding layer is arranged outside the inner shielding layer, and finally a primary winding is wound outside the outer shielding layer; the inner shielding layer is grounded at the inflow end of the primary winding, and the outer shielding layer is connected to the shielding layer of the coaxial cable at the inflow end of the primary winding to achieve electrical conduction, and at the same time, the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction, and finally the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured.
[0023] A second aspect of the present invention provides a high-voltage current transformer calibration device, the high-voltage current transformer calibration device comprising: a current source, a current booster, a reference current transformer, and a voltage source;
[0024] The current source is connected to the primary winding of the current booster;
[0025] The primary winding of the reference current transformer, the primary winding of the current transformer to be measured and the secondary winding of the current booster form a closed loop;
[0026] A double-layer grounding shield is provided at the primary winding of the reference current transformer, and the leakage current flowing in the two layers of the double-layer grounding shield is in opposite directions;
[0027] One end of the voltage source is connected to the outflow end of the primary winding of the current transformer to be measured, and the other end of the voltage source is grounded.
[0028] A further improvement of the present invention is that the reference current transformer is a through-type transformer;
[0029] The head end of the double-shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured;
[0030] The middle part of the double-shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two breakpoints are respectively connected to two ports of the secondary winding of the current booster;
[0031] The rear part of the double-shielded coaxial cable serves as the primary winding of the reference current transformer;
[0032] The tail end of the double-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained in the section from the tail end to the outflow end of the primary winding of the reference current transformer on the double-layer shielded coaxial cable;
[0033] The outermost shielding layer of the double-shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the tail ends of the two shielding layers are connected at the outflow end of the primary winding of the reference current transformer to achieve electrical conduction.
[0034] A further improvement of the present invention is that the reference current transformer is a through-type transformer;
[0035] The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured;
[0036] The middle part of the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster;
[0037] The rear part of the single-shielded coaxial cable serves as the primary winding of the reference current transformer;
[0038] The tail end of the single-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained on the section of the single-layer shielded coaxial cable from the tail end to the outflow end of the primary winding close to the reference current transformer;
[0039] The tail end of the shield layer of the single-layer shielded coaxial cable is folded back and reversely passes through the hole in the iron core of the reference current transformer. The folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shield layer is grounded at the inflow end of the primary winding of the reference current transformer.
[0040] A further improvement of the present invention is that the reference current transformer is a through-type transformer;
[0041] The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured;
[0042] The middle part of the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster;
[0043] The rear part of the single-shielded coaxial cable serves as the primary winding of the reference current transformer;
[0044] The tail end of the single-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained in the section from the tail end to the outflow end of the primary winding of the reference current transformer on the single-layer shielded coaxial cable;
[0045] A layer of metal foil is wound around the section of the single-layer shielded coaxial cable that serves as the primary winding of the reference current transformer. The head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer and this end is grounded. The tail end of the metal foil passes through the hole in the iron core of the reference current transformer and is connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction.
[0046] A further improvement of the present invention is that the reference current transformer is a wiring type current transformer;
[0047] The head end of the coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured;
[0048] The middle part of the coaxial cable serves as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster;
[0049] The tail end of the coaxial cable is connected to the inflow end of the primary winding of the reference current transformer, and the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured;
[0050] Two shielding layers are arranged between the primary winding of the reference current transformer and the iron core, namely an inner shielding layer directly in contact with the iron core and an outer shielding layer located outside the inner shielding layer, and the primary winding of the reference current transformer is located outside the outer shielding layer;
[0051] The inner shielding layer is grounded at the inflow end of the primary winding; the outer shielding layer is connected to the shielding layer of the coaxial cable at the inflow end of the primary winding to achieve electrical conduction; the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction.
[0052] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention solves the contradiction that the calibration state and the use state are inconsistent when the high-voltage current transformer under test is calibrated at low voltage according to the traditional calibration method; the present invention makes the primary winding of the reference current transformer used work in a high-voltage state without adding additional errors compared with the low-voltage state, so it can be used as a standard for high-voltage calibration. The technical solution of the present invention is simple, the idea is clear, and it is easy for technicians to master. BRIEF DESCRIPTION OF THE DRAWINGS
[0053] Figure 1 A schematic structural diagram of an embodiment of a high-voltage current transformer calibration device of the present invention;
[0054] Figure 2 Schematic diagram of the reference current transformer and the current transformer to be tested;
[0055] Figure 3 A schematic structural diagram of another embodiment of a high-voltage current transformer calibration device of the present invention. DETAILED DESCRIPTION
[0056] The present invention provides a high-voltage current transformer calibration method. The method applies the same high voltage to the primary winding of a current transformer under test (DutCT) and the primary winding of a reference current transformer (Ref CT), and simultaneously sets a double-layer grounding shield at the primary winding of the reference current transformer, and the directions of leakage currents flowing through the two layers of the double-layer grounding shield are opposite.
[0057] The current transformer to be tested and the reference current transformer can both be of through-hole type or wiring type. Figure 2 The schematic diagram of the reference current transformer and the current transformer to be tested is shown. For the connection type current transformer, the primary winding and the secondary winding are coils with multiple turns wound on the iron core; for the through-type current transformer, the primary winding is a through-core conductor passing through the hole in the iron core, and the secondary winding is a coil with multiple turns wound on the iron core of the current transformer. Figure 2 The Ip in the figure is the current flowing through the primary winding. The current booster can also be a through-type or a wiring type.
[0058] like Figure 1 and Figure 3 As shown, during calibration, the current source I acConnect the reference current transformer to the primary winding of the current transformer to be tested, and form a closed loop with the secondary winding of the current transformer. Connect the two ends of the secondary winding of the reference current transformer to the two ends of a resistor, which is connected to a voltmeter, and the two ends of the secondary winding of the current transformer to be tested to the two ends of another resistor, which is connected to a voltmeter. Connect one end of the voltage source to the outflow end of the primary winding of the current transformer to be tested, and ground the other end of the voltage source.
[0059] The double-layer grounding shielding is provided at the primary winding of the reference current transformer by using a coaxial cable, wherein the coaxial cable is a double-layer shielded coaxial cable or a single-layer shielded coaxial cable.
[0060] Specifically, if the reference current transformer is a through-type transformer (such as Figure 1 As shown), and a double-shielded coaxial cable is used, the head end of the double-shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the coaxial cable is used as the secondary winding of the current booster (the coaxial cable is directly passed through the hole in the iron core of the current booster as the secondary winding of the current booster) or the middle of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and the tail end of the coaxial cable is passed through the hole in the iron core of the reference current transformer and then connected to the inflow end of the primary winding of the current transformer to be measured (at this time, the coaxial cable passes through the hole in the iron core of the reference current transformer The part is the primary winding of the reference current transformer), and the shielding layer on the section from the tail end to the outflow end of the primary winding of the reference current transformer on the coaxial cable is removed, leaving only the core wire, that is, a section of the shielding layer is removed from the tail end to the head end of the coaxial cable, so that there is only the core wire and no shielding layer between the outflow end of the primary winding of the reference current transformer and the inflow end of the primary winding of the current transformer to be measured, and the shielding layer is retained in other parts of the coaxial cable, that is, the shielding layer on the coaxial cable is retained from the outflow end of the primary winding of the current transformer to be measured to the outflow end of the primary winding of the reference current transformer. Then, the outermost shielding layer of the double-layer shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the two shielding layers are connected at the outflow end of the primary winding of the reference current transformer to achieve electrical conduction (the electrical conduction can be achieved by using a variety of existing methods, such as welding, etc.), so that the double-layer grounded shielding is achieved, and the two shielding layers of the double-layer shielded coaxial cable form two layers of shielding of the double-layer grounded shielding.
[0061] If the reference current transformer is a through-type transformer and a single-shielded coaxial cable is used, one of the following two methods is used:
[0062] The first method is: connect the head end of the single-layer shielded coaxial cable to the outflow end of the primary winding of the current transformer to be tested, and use the coaxial cable as the secondary winding of the current booster (directly pass the coaxial cable through the hole in the iron core of the current booster as the secondary winding of the current booster) or disconnect the middle of the coaxial cable, and connect the two breakpoints to the two ports of the secondary winding of the current booster respectively, and then pass the tail end of the coaxial cable through the hole in the iron core of the reference current transformer and connect it to the inflow end of the primary winding of the current transformer to be tested (at this time, the part of the coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer) , and remove the shielding layer from the tail end to the outflow end of the primary winding of the reference current transformer on the coaxial cable, leaving only the core wire, that is, remove a section of the shielding layer from the tail end to the head end of the coaxial cable, so that from a certain distance (the distance can be designed according to actual needs) from the outflow end of the primary winding of the reference current transformer to the tail end of the coaxial cable, there is only the core wire, no shielding layer, and the shielding layer is retained in other parts of the coaxial cable, that is, the shielding layer on the coaxial cable is retained from the outflow end of the primary winding of the current transformer to be measured to a certain distance after the outflow end of the primary winding of the reference current transformer. Then, the shielding layer of the single-layer shielded coaxial cable is stripped from its tail end, and the tail end of the shielding layer is folded back and reversely passed through the core hole of the reference current transformer, the folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shielding layer is grounded at the inflow end of the primary winding of the reference current transformer. The shield of the single-shielded coaxial cable and the folded-back shield form two layers of the double-layer grounded shield.
[0063] The second method is: connect the head end of the single-layer shielded coaxial cable to the outflow end of the primary winding of the current transformer to be measured, and use the coaxial cable as the secondary winding of the current booster (directly pass the coaxial cable through the hole in the iron core of the current booster as the secondary winding of the current booster) or disconnect the middle of the coaxial cable, and connect the two breakpoints to the two ports of the secondary winding of the current booster respectively, and then pass the tail end of the coaxial cable through the hole in the iron core of the reference current transformer and connect it to the inflow end of the primary winding of the current transformer to be measured (the part of the coaxial cable that passes through the hole in the iron core of the reference current transformer is the The primary winding of the reference current transformer is used as the primary winding of the reference current transformer, and the shielding layer on the section of the coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer is removed, leaving only the core wire, that is, a section of the shielding layer is removed from the tail end to the head end of the coaxial cable, so that there is only the core wire and no shielding layer between the outflow end of the primary winding of the reference current transformer and the inflow end of the primary winding of the current transformer to be measured, and the shielding layer is retained in other parts of the coaxial cable, that is, the shielding layer on the coaxial cable is retained from the outflow end of the primary winding of the current transformer to be measured to the outflow end of the primary winding of the reference current transformer. Then, a layer of metal foil is wrapped around the section of the coaxial cable that serves as the primary winding of the reference current transformer as the outermost shielding, the head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer, and the head end is grounded, and the tail end of the metal foil passes through the hole in the iron core and is connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction. The metal foil only passes through the hole in the iron core of the reference current transformer once, and then connects to the shielding layer of the coaxial cable, which is equivalent to the folded-back shielding layer. The shielding layer of the single-layer shielded coaxial cable and the metal foil form two layers of the double-layer grounded shielding.
[0064] If the reference current transformer is a wiring current transformer (such as Figure 3As shown), the double-layer grounded shield between the primary winding and the iron core of the reference current transformer is the internal winding of the current transformer. Specifically, the head end of the coaxial cable is first connected to the outflow end of the primary winding of the current transformer to be measured, and the coaxial cable is used as the secondary winding of the current booster (the coaxial cable is directly passed through the middle hole of the iron core of the current booster as the secondary winding of the current booster) or the middle of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the coaxial cable is connected to the inflow end of the primary winding of the reference current transformer; two shielding layers are set between the primary winding and the iron core of the reference current transformer. The two shielding layers can be two layers of enameled wire windings, or two layers of copper foil insulated from each other. For example, a group of enameled wire windings are first wound on the iron core as the inner shielding layer, and then another group of enameled wire windings are wound on the outside of the inner shielding layer as the outer shielding layer, and finally the primary winding is wound on the outside of the outer shielding layer. Finally, the shielding layer (i.e., the inner shielding layer) of the two shielding layers that is farther away from the primary winding is grounded at the inlet end of the primary winding, and the other layer (i.e., the outer shielding layer) is connected to the shielding layer of the coaxial cable at the inlet end of the primary winding to achieve electrical conduction. At the same time, the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction (for example, the ends of the core wires of the two enameled wires can be directly connected.), and finally the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured.
[0065] Because the main current conductor has a higher potential than the surrounding, it will generate leakage current to the surrounding through parasitic capacitance, so a shielding layer is needed to prevent leakage current from flowing into the secondary winding or generating additional interference flux inside the core. After adopting the above method, the primary winding of the current transformer to be tested and the primary winding of the reference current transformer are applied with the same high voltage, but because the primary winding of the reference current transformer is provided with a double-layer grounding shield, the primary winding of the reference current transformer will not generate leakage current to the secondary winding through parasitic capacitance due to the potential difference with the secondary winding, thereby solving the contradiction between the calibration state and the use state when the high-voltage current transformer to be tested is calibrated at low voltage according to the traditional calibration method.
[0066] like Figure 1 and Figure 3 As shown, the present invention also provides a high-voltage current transformer calibration device, which includes: a current source I ac , current booster, reference current transformer, voltage source V ac , where the current source I acThe primary winding of the reference current transformer, the primary winding of the current transformer to be measured and the secondary winding of the current transformer form a closed loop. A double-layer grounding shield is provided at the primary winding of the reference current transformer, and the leakage current flowing in the two layers of the double-layer grounding shield is in opposite directions. ac One end of the current transformer is connected to the outflow end of the primary winding of the current transformer to be measured, and the voltage source V ac The other end is grounded, so that the primary winding of the reference current transformer and the primary winding of the current transformer to be measured have a high voltage potential difference relative to the ground potential, thereby realizing calibration under high voltage.
[0067] An embodiment of the high voltage current transformer calibration device is as follows: Figure 1 As shown, Figure 1 The current transformer to be tested and the reference current transformer in the illustrated embodiment are both through-type transformers, and the double-layer grounding shielding can be achieved by using a double-layer shielded coaxial cable, or by folding the outer shielding layer of a single-layer shielded coaxial cable, or by winding an additional shielding layer outside the single-layer shielded coaxial cable.
[0068] Figure 1 If a double-shielded coaxial cable is used, the first end of the coaxial cable should be connected to the outflow end of the primary winding of the current transformer to be measured (i.e. Figure 1 The middle part of the coaxial cable is used as the secondary winding of the current booster, and the rear part of the coaxial cable passes through the core hole of the reference current transformer as the primary winding of the reference current transformer. The tail end of the coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and the coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer (i.e. Figure 1 The shielding layer on this section (point b in the figure) is removed, leaving only the core wire; the outermost shielding layer of the double-shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the tail end of the two shielding layers is grounded at the outflow end of the primary winding of the reference current transformer (i.e. Figure 1 The connection at point b) in the figure is made electrical conductive, thus achieving double-layer grounding shielding. Figure 1 In the figure, the dotted line between point a and point b represents the shielding layer of the grounded coaxial cable. Point a is the starting point of the coaxial cable, which is connected to the position after the through-hole conductor passes through the core hole of the current transformer to be measured (i.e., the outflow end of the primary winding). Point b is the end point of the coaxial cable, which is the position after the coaxial cable passes through the core hole of the reference current transformer (i.e., the outflow end of the primary winding. Because the through-hole transformer does not have a built-in double-layer shielding, it needs to be achieved with the shielding layer outside the coaxial cable. Therefore, the coaxial cable needs to pass through the reference current transformer, which is equivalent to terminating at the outflow end of the primary winding).
[0069] Figure 1If a single-layer shielded coaxial cable is used, one of the following two structures can be used:
[0070] The first structure is: the head end of the coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured (i.e. Figure 1 The middle part of the coaxial cable serves as the secondary winding of the current booster, the rear part of the coaxial cable passes through the hole in the iron core of the reference current transformer as the primary winding of the reference current transformer, the tail end of the coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and the shielding layer of the coaxial cable from the tail end to the outflow end of the primary winding close to the reference current transformer is removed, leaving only the core wire; the tail end of the shielding layer is folded back and passed through the hole in the iron core of the reference current transformer in reverse, the folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shielding layer is grounded at the inflow end of the primary winding of the reference current transformer.
[0071] The second structure is: the first end of the coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured (i.e. Figure 1 The middle part of the coaxial cable is used as the secondary winding of the current booster, and the rear part of the coaxial cable passes through the core hole of the reference current transformer as the primary winding of the reference current transformer. The tail end of the coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and the coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer (i.e. Figure 1 The shielding layer on the section (point b) is removed, leaving only the core wire; a layer of metal foil is wound around the outside of the section of the coaxial cable that serves as the primary winding of the reference current transformer, the head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer, and this end is grounded, and the other end of the metal foil passes through the hole in the iron core and is connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction.
[0072] Another embodiment of the high voltage current transformer calibration device is as follows: Figure 3 As shown, the reference current transformer adopts a wiring current transformer, and a double-layer grounding shield is provided between the primary winding and the iron core of the reference current transformer. Figure 3 As shown, the head end of the coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured (i.e. Figure 3 The middle part of the coaxial cable is used as the secondary winding of the current booster, and the tail end of the coaxial cable is connected to the inflow end of the primary winding of the reference current transformer ( Figure 3 At point b in the figure, since the wiring reference current transformer has a built-in shielding layer, the coaxial cable is terminated at the inflow end of the primary winding) and the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured. Two shielding layers are set between the primary winding of the reference current transformer and the iron core, which are the inner shielding layer in direct contact with the iron core (such as the inner shielding layer in direct contact with the iron core). Figure 3 As shown in the first dotted line above the core of the reference current transformer in the figure, the two small circles on the dotted line represent the two ends of the inner shielding layer, where the left end is aligned with the inflow end b of the primary winding, and the right end is aligned with the outflow end of the primary winding). The outer shielding layer outside the inner shielding layer (such as Figure 3 As shown by the second dotted line above the core of the reference current transformer in the figure, the two small circles on the dotted line represent the two ends of the inner shielding layer, wherein the left end is aligned with point b of the inflow end of the primary winding, and the right end is aligned with the outflow end of the primary winding), the primary winding of the reference current transformer is located outside the outer shielding layer; the inner shielding layer is grounded at the inflow end of the primary winding, the outer shielding layer is connected to the shielding layer of the coaxial cable at the inflow end of the primary winding to achieve electrical conduction, and the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction.
[0073] In the above embodiment, the current booster adopts a through-core type, so the coaxial cable is directly passed through the iron core of the current booster as the secondary winding of the current booster. If the current booster adopts a wiring type, the middle part of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster. The processing method of other parts of the coaxial cable is the same as above.
[0074] In this way, the current directions passing through the two shielding layers are opposite (such as Figure 1 and Figure 3 The magnetic fields they generate will cancel each other out, so the leakage current I leak No corresponding induced current will be generated in the secondary winding, and no error due to leakage current will be introduced.
[0075] During calibration, the current source I ac After passing through the current booster, the output current I p , the current I p The total current vector sum of the primary winding and shielding layer of the reference current transformer is I p +I leak -I leak =I p , the current flowing through the primary winding of the current transformer to be tested is I p , so both are the same.
[0076] Through the voltage source V acA high voltage is applied to the primary winding of the current transformer to be tested and the primary winding of the reference current transformer. However, since a double-layer grounded shield is provided at the primary winding of the reference current transformer and the leakage currents flowing through the two shields are in opposite directions, after adopting this structure, the primary winding of the reference current transformer will not generate leakage current to the secondary winding through parasitic capacitance due to the potential difference with the secondary winding (that is, the generated leakage current will not flow to the secondary winding) or generate additional interference flux in the iron core.
[0077] In this way, the reference current transformer will not have additional error compared with the low voltage state because its primary winding works in the high voltage state. For the current transformer to be tested, the design of "double-layer grounding shielding, and making the current flowing in the two layers of shielding in opposite directions" is generally not adopted. However, even if a similar design is adopted in the design of the current transformer to be tested, it still does not affect the application of the device of the present invention.
[0078] The reference current transformer and the current transformer to be tested can both be through-hole type, or both can be wired type, or one can be through-hole type and the other can be wired type. The positions of the reference current transformer and the current transformer to be tested can also be set as required. Figure 1 and Figure 3 In this way, the reference current transformer is not affected by high voltage through double-layer grounding shielding, and can be used to calibrate the current transformer under test. Because the current transformer under test is the test object, its structure is fixed, so there is no requirement for its structure. In the above embodiment, no matter whether the current transformer under test is a through-type or a wiring type, the wiring position of the coaxial cable and its primary winding remains unchanged.
[0079] Generally speaking, when the primary winding works in a high voltage state, the secondary winding generally works in a low voltage state. Since the method of the present invention will not add errors due to the different ground potentials of the primary winding, the primary winding working in a grounded state or a high voltage state will not affect its own error when calibrating the test object.
[0080] Furthermore, the voltage source V can be realized by using the existing closed-loop control technology. ac With current source I ac Same frequency and phase locked, and locked phase difference Different values can be set as needed. The closed-loop control technology uses a phase-locked loop to achieve the same frequency and phase lock of two signals. One of the uses of the phase-locked loop is to compare the frequency and phase difference of the two signals. If the frequency is different, or the phase is different from the set value, it will adjust the internal parameters to change the output signal, so that the frequency and phase of the output signal are adjusted to achieve the function of locking the frequency and phase of the output signal. These are mature technologies and will not be repeated here.
[0081] The steps for calibrating the current transformer under test using the above device are the same as the steps for calibrating the current transformer under test using the reference current transformer under low voltage conditions, and the data recording and analysis operations performed are also the same, which are briefly described as follows:
[0082] After the device of the present invention is installed, the outputs of the reference current transformer and the current transformer to be tested are connected to the current transformer tester respectively. Alternatively, the outputs of the two current transformers are respectively passed through shunts (sampling resistors), and then the output voltages of the two shunts are obtained using a dual-channel synchronous vector voltage acquisition device, so as to further calculate the ratio difference and angle difference.
[0083] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0084] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.
[0085] Finally, it should be explained that the above technical solution is only one implementation method of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific implementation method of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.
Claims
1. A high voltage current transformer calibration method, characterized in that: The method comprises: Apply the same high voltage to the primary winding of the current transformer to be measured and the primary winding of the reference current transformer; A double-layer grounding shield is provided at the primary winding of the reference current transformer, and the leakage current flowing in the two layers of the double-layer grounding shield is in opposite directions; Connect the current source to the primary winding of the current booster; connect the reference current transformer to the current transformer to be tested, and form a closed loop with the secondary winding of the current booster; The double-layer grounding shielding is provided at the primary winding of the reference current transformer by using a coaxial cable, wherein the coaxial cable is a double-layer shielded coaxial cable or a single-layer shielded coaxial cable.
2. The high voltage current transformer calibration method according to claim 1, characterized in that: The operation of providing a double-layer ground shield at the primary winding of the reference current transformer includes: The reference current transformer adopts a through-type transformer; The head end of the double-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the double-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the double-layer shielded coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the double-layer shielded coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer; and the shielding layer of the double-layer shielded coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer is removed; then the outermost shielding layer of the double-layer shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the two shielding layers of the double-layer shielded coaxial cable are connected at the outflow end of the primary winding of the reference current transformer to achieve electrical conduction.
3. The high voltage current transformer calibration method according to claim 1, characterized in that: The operation of providing a double-layer ground shield at the primary winding of the reference current transformer includes: The reference current transformer adopts a through-type transformer; The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the single-layer shielded coaxial cable is used as the secondary winding of the current booster or the middle part of the coaxial cable is disconnected and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the single-layer shielded coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the single-layer shielded coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer, and the shielding layer of the single-layer shielded coaxial cable from the tail end to the primary winding outflow end close to the reference current transformer is removed; then the shielding layer of the single-layer shielded coaxial cable is peeled off from its tail end, and then the tail end of the shielding layer is folded back and passed through the hole in the iron core of the reference current transformer in reverse, the folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shielding layer is grounded at the inflow end of the primary winding of the reference current transformer.
4. The high voltage current transformer calibration method according to claim 1, characterized in that: The operation of providing a double-layer ground shield at the primary winding of the reference current transformer includes: The reference current transformer adopts a through-type transformer; The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured, and the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle of the coaxial cable is disconnected, and the two breakpoints are respectively connected to the two ports of the secondary winding of the current booster, and then the tail end of the single-layer shielded coaxial cable is passed through the hole in the iron core of the reference current transformer and connected to the inflow end of the primary winding of the current transformer to be measured. At this time, the part of the coaxial cable that passes through the hole in the iron core of the reference current transformer is the primary winding of the reference current transformer; and the shielding layer on the section of the coaxial cable from the tail end to the outflow end of the primary winding of the reference current transformer is removed; then a layer of metal foil is wrapped around the outside of the section of the single-layer shielded coaxial cable that serves as the primary winding of the reference current transformer, the head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer and is grounded, and the tail end of the metal foil is passed through the hole in the iron core and connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction.
5. The high voltage current transformer calibration method according to claim 1, characterized in that: The operation of providing a double-layer ground shield at the primary winding of the reference current transformer includes: The reference current transformer adopts a wiring type current transformer; Connect the head end of the coaxial cable to the outflow end of the primary winding of the current transformer to be tested, and use the coaxial cable as the secondary winding of the current booster, or disconnect the middle of the coaxial cable and connect the two breakpoints to the two ports of the secondary winding of the current booster respectively, and then connect the tail end of the coaxial cable to the inflow end of the primary winding of the reference current transformer; An inner shielding layer is first arranged on the core of the reference current transformer, and then an outer shielding layer is arranged outside the inner shielding layer, and finally a primary winding is wound outside the outer shielding layer; the inner shielding layer is grounded at the inflow end of the primary winding, and the outer shielding layer is connected to the shielding layer of the coaxial cable at the inflow end of the primary winding to achieve electrical conduction, and at the same time, the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction, and finally the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured.
6. A high voltage current transformer calibration device, characterized in that: The high-voltage current transformer calibration device comprises: a current source, a current booster, a reference current transformer, and a voltage source; The current source is connected to the primary winding of the current booster; The primary winding of the reference current transformer, the primary winding of the current transformer to be measured and the secondary winding of the current booster form a closed loop; A double-layer grounding shield is provided at the primary winding of the reference current transformer, and the leakage current flowing in the two layers of the double-layer grounding shield is in opposite directions; One end of the voltage source is connected to the outflow end of the primary winding of the current transformer to be measured, and the other end of the voltage source is grounded; The double-layer ground shielding is achieved by using a coaxial cable, and the coaxial cable is a double-layer shielded coaxial cable or a single-layer shielded coaxial cable.
7. The high voltage current transformer calibration device according to claim 6, characterized in that: The reference current transformer is a through-type transformer; The head end of the double-shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured; The middle part of the double-shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two breakpoints are respectively connected to two ports of the secondary winding of the current booster; The rear part of the double-shielded coaxial cable serves as the primary winding of the reference current transformer; The tail end of the double-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained in the section from the tail end to the outflow end of the primary winding of the reference current transformer on the double-layer shielded coaxial cable; The outermost shielding layer of the double-shielded coaxial cable is grounded at the inflow end of the primary winding of the reference current transformer, and the tail ends of the two shielding layers are connected at the outflow end of the primary winding of the reference current transformer to achieve electrical conduction.
8. The high voltage current transformer calibration device according to claim 6, characterized in that: The reference current transformer is a through-type transformer; The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured; The middle part of the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster; The rear part of the single-shielded coaxial cable serves as the primary winding of the reference current transformer; The tail end of the single-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained on the section of the single-layer shielded coaxial cable from the tail end to the outflow end of the primary winding close to the reference current transformer; The tail end of the shield layer of the single-layer shielded coaxial cable is folded back and reversely passes through the hole in the iron core of the reference current transformer. The folding point is located at the outflow end of the primary winding of the reference current transformer, and the tail end of the shield layer is grounded at the inflow end of the primary winding of the reference current transformer.
9. The high voltage current transformer calibration device according to claim 6, characterized in that: The reference current transformer is a through-type transformer; The head end of the single-layer shielded coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured; The middle part of the single-layer shielded coaxial cable is used as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster; The rear part of the single-shielded coaxial cable serves as the primary winding of the reference current transformer; The tail end of the single-layer shielded coaxial cable is connected to the inflow end of the primary winding of the current transformer to be measured, and only the core wire is retained in the section from the tail end to the outflow end of the primary winding of the reference current transformer on the single-layer shielded coaxial cable; A layer of metal foil is wound around the section of the single-layer shielded coaxial cable that serves as the primary winding of the reference current transformer. The head end of the metal foil is located at the inflow end of the primary winding of the reference current transformer and this end is grounded. The tail end of the metal foil passes through the hole in the iron core of the reference current transformer and is connected to the tail end of the shielding layer of the single-layer shielded coaxial cable to achieve electrical conduction.
10. The high voltage current transformer calibration device according to claim 6, characterized in that: The reference current transformer is a wiring type current transformer; The head end of the coaxial cable is connected to the outflow end of the primary winding of the current transformer to be measured; The middle part of the coaxial cable serves as the secondary winding of the current booster, or the middle part of the coaxial cable is disconnected and two break points are respectively connected to two ports of the secondary winding of the current booster; The tail end of the coaxial cable is connected to the inflow end of the primary winding of the reference current transformer, and the outflow end of the primary winding of the reference current transformer is connected to the inflow end of the primary winding of the current transformer to be measured; Two shielding layers are arranged between the primary winding of the reference current transformer and the iron core, namely an inner shielding layer directly in contact with the iron core and an outer shielding layer located outside the inner shielding layer, and the primary winding of the reference current transformer is located outside the outer shielding layer; The inner shielding layer is grounded at the inflow end of the primary winding; the outer shielding layer is connected to the shielding layer of the coaxial cable at the inflow end of the primary winding to achieve electrical conduction; the inner shielding layer and the outer shielding layer are connected at the outflow end of the primary winding to achieve electrical conduction.
Citation Information
Patent Citations
Calibrating device for high-voltage current transformer
CN214895764U