A test method for protection characteristics of DC current transformer

Abstract

The present invention is a DC current transformer protection characteristic test method, which uses a test current generating circuit and a controller. The DC current transformer protection characteristic test method provided by the present invention generates a large current by resonance under the control of the test current generating circuit controller, forces the resonance to stop at the zero crossing point, and the current decay presents a single polarity. Appropriate resonance parameters are selected, and the current peak value and the decay time constant are adjusted to meet the requirements of the DC protection test current for the waveform. The DC current transformer tester receives the trigger instruction of the test current generating circuit controller, compares and verifies the secondary signals from the DC current transformer test piece and the low residual inductance shunt, and completes the test verification of the DC current transformer protection characteristics.

Description

Technical Field

[0001] The invention relates to a direct current current transformer protection characteristic test method, belonging to the technical field of direct current power transmission engineering. Background Art

[0002] At present, the on-site handover test project of DC current transformers for DC projects has not been carried out ideally, especially the protection characteristic test has not been implemented on site. The main reason is that there are no test methods and test capabilities suitable for the on-site environment, especially the large dynamic range test current required for the protection characteristic test on site has power supply capacity limitations and technical bottlenecks. For the DC current transformers of flexible DC distribution networks, there are some problems in the test and detection of the accuracy characteristics of the large dynamic range and the step response characteristics. The national standards GB / T26216-2010 and IEC61869-14:2018, two current transformer product standards, stipulate the accuracy characteristics, step response characteristics and tests of the large dynamic range of DC current transformers in DC transmission systems, but lack requirements for DC current transformers for flexible DC projects. In order to achieve ultra-high-speed protection of flexible DC grids, higher requirements are put forward for the response characteristics of DC current transformers in flexible DC grid systems compared with conventional DC projects. With the increasing scale of DC transmission construction, especially the vigorous development of flexible DC transmission technology, the control and protection system has put forward higher requirements for the wide dynamic range measurement accuracy and step signal dynamic response of DC current measurement devices. Due to the lack of corresponding test methods and equipment, the field test of DC current transformer protection characteristics has not been carried out normally. Summary of the invention

[0003] The invention provides a method for generating a direct current transformer protection characteristic test current which meets the requirements of the direct current protection test current on the waveform.

[0004] In order to solve the above technical problems, the technical solution proposed in the present invention is: a DC current transformer protection characteristic test method, using a test current generating circuit and a controller, the test current generating circuit includes: a resonant capacitor, a resonant inductor, a resistor for time constant adjustment, a thyristor for cutoff, a cutoff branch switch, a discharge switch, a low residual inductance shunt, a charging switch and a charging DC power supply; the positive electrode of the charging DC power supply is connected to one end of the charging switch, the other end of the charging switch is connected to one pole of the resonant capacitor, one pole of the resonant capacitor is also connected to one end of the discharge switch, and the other end of the discharge switch is connected to The first embodiment of the present invention relates to a first embodiment of the present invention which is connected to one pole of the resonant inductor; the other pole of the resonant inductor is connected to one pole of the time constant adjustment resistor; the other pole of the time constant adjustment resistor is connected to one end of the low residual inductance shunt; the negative pole of the cut-off thyristor is connected to one pole of the resonant inductor; the other end of the low residual inductance shunt and the positive pole of the cut-off thyristor are connected to one end of the cut-off branch switch, and the other end of the cut-off branch switch and the other pole of the resonant capacitor are both connected to the negative pole of the DC power supply; the controller performs timing control on the charging DC power supply, the charging switch, the discharging switch and the cut-off branch switch;

[0005] The DC current transformer test piece can be mounted on the line between the other end of the cut-off branch switch and the other end of the cut-off branch switch; the voltage end of the low residual inductance shunt and the secondary side of the DC current transformer test piece are both connected to the DC current transformer tester;

[0006] The low residual inductance shunt is used as a reference standard for the DC current transformer protection characteristic test; the resonant capacitor and the resonant inductor form an LC second-order circuit; the fully charged resonant capacitor discharges to the resonant inductor and the transformer test piece, and the resonant current reaches a maximum value near the first zero crossing point of the resonant voltage waveform. At this time, the cut-off thyristor is turned on, and the resonance is forced to stop at the zero crossing point of the resonant voltage, and the resonant current decays to present a single polarity.

[0007] A further improvement of the above scheme is that the reverse peak voltage value of the resonant capacitor is 100%, and the quality factor of the resonant inductor is greater than 40.

[0008] A further improvement of the above scheme is that the resonant capacitor, the resonant inductor and the time constant adjustment resistor constitute a large current resonant circuit.

[0009] A further improvement of the above scheme is that the resonant current decays with a certain time constant according to the ratio of the inductance value of the resonant inductor to the resistance value of the time constant adjustment resistor.

[0010] A further improvement of the above scheme is that: a discharge branch is connected in parallel to the branch formed by the cut-off thyristor and the cut-off branch switch; the discharge branch includes a discharge branch switch and a discharge resistor connected in series.

[0011] A further improvement of the above scheme is that the DC current transformer tester receives a trigger instruction from the controller, compares and verifies the secondary signals from the DC current transformer test piece and the low residual inductance shunt, and completes the test verification of the DC current transformer protection characteristics.

[0012] A further improvement of the above scheme is that the resonant capacitor is a capacitor group composed of a plurality of capacitors connected in parallel and in series.

[0013] The DC current transformer protection characteristic test method provided by the present invention generates a large current in a resonant manner, stops the resonance at the zero crossing point, and the current decay presents a unipolar state. Appropriate resonant parameters are selected, the current peak value is adjusted, and the decay time constant is extended to meet the requirements of the DC protection test current for the waveform. The present invention is composed of a resonant capacitor and a resonant inductor to form a typical second-order circuit. Because the DC resistance value of the test loop is at the mΩ level, it belongs to an underdamped second-order circuit. The fully charged resonant capacitor discharges to the test loop, and the resonant current reaches the maximum value near the zero crossing point of the voltage waveform. At this time, the thyristor used for cutting is turned on, and the resonance is forced to stop. The current decays exponentially with a certain time constant. Appropriate capacitor, inductor and resistor parameters are selected to extend the decay time constant to meet the requirements of the DC protection test current for the waveform. A low residual inductance shunt is used as a reference standard for the DC current transformer protection characteristic test; a DC current transformer tester is used to compare and verify the secondary signals from the DC current transformer test product and the low residual inductance shunt, and the test verification of the DC current transformer protection characteristic is completed.

[0014] The invention has low power capacity requirement for field tests, compact structure and light weight, and is suitable for field tests of protection characteristics of direct current transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] Figure 1 It is a schematic diagram of the test current generation in the present invention.

[0017] Figure 2 It is a schematic diagram of the structure of a preferred embodiment of the present invention.

[0018] Figure 3 It is a typical underdamped current resonance waveform.

[0019] Figure 4 It is a waveform diagram of the test current that conforms to the protection characteristics of the DC current transformer.

[0020] The numbers in the figure are as follows: 1-resonant capacitor, 2-discharge switch, 3-resonant inductor, 4-resistor for time constant adjustment, 5-thyristor for cutoff, 6-cutoff branch switch, 7-discharge resistor, 8-discharge branch switch, 9-charging DC power supply, 10-charging switch, 11-DC current transformer test piece, 12-low residual inductance shunt, 13-DC current transformer calibrator, 14-DC current transformer protection characteristic test device controller. DETAILED DESCRIPTION Example

[0021] The DC current transformer protection characteristic test method provided in this embodiment uses a Figure 2 The test device shown in the figure comprises a test current generating circuit and a controller 14. The test current generating circuit comprises: a resonant capacitor 1, a resonant inductor 3, a resistor 4 for adjusting a time constant, a thyristor 5 for cutting off, a cutting off branch switch 6, a discharge switch 2, a low residual inductance shunt 12, a charging switch 10 and a charging DC power supply 9; the positive electrode of the charging DC power supply 9 is connected to one end of the charging switch 10, the other end of the charging switch 10 is connected to one pole of the resonant capacitor 1, and one pole of the resonant capacitor 1 is also connected to the discharge switch 2. The other end of the discharge switch 2 is connected to one pole of the resonant inductor 3; the other pole of the resonant inductor 3 is connected to one pole of the time constant adjustment resistor 4; the other pole of the time constant adjustment resistor 4 is connected to one end of the low residual inductance shunt 12; the negative pole of the cut-off thyristor 5 is connected to one pole of the resonant inductor 3; the positive pole of the cut-off thyristor 5 is connected to one end of the cut-off branch switch 6, and the other end of the cut-off branch switch 6, the other end of the low residual inductance shunt 12, and the other pole of the resonant capacitor 1 are all connected to the negative pole of the charging DC power supply 9. The controller 14 performs timing control on the charging DC power supply 9, the charging switch 10, the discharge switch 2, and the cut-off branch switch 6 according to the control logic.

[0022] When conducting the test, the DC current transformer test piece 11 is installed on the line between the other end of the low residual inductance shunt 12 and the other end of the cut-off branch switch 6; the voltage end of the low residual inductance shunt 12 and the secondary side of the DC current transformer test piece 11 are connected to the DC current transformer tester 13; the DC current transformer tester 13 receives the trigger instruction of the controller, compares and verifies the secondary signals from the DC current transformer test piece and the low residual inductance shunt, and completes the test of the DC current transformer protection characteristics.

[0023] A discharge branch is connected in parallel to the branch formed by the cut-off thyristor 5 and the cut-off branch switch 6; the discharge branch includes a discharge branch switch 8 and a discharge resistor 7 connected in series. The discharge branch switch 8 is also controlled by the controller 14 in time sequence according to the control logic.

[0024] The resonant capacitor 1 and the resonant inductor form a second-order LC circuit; the fully charged resonant capacitor 1 discharges to the resonant inductor 3 and the transformer test piece. Near the first zero crossing point of the resonant voltage waveform, the resonant current reaches its maximum value. At this time, the cut-off thyristor 5 is turned on, and the resonance is forced to stop at the zero crossing point of the resonant voltage. The resonant current decays and presents a single polarity.

[0025] The reverse peak voltage value of the resonant capacitor 1 is 100%, and the quality factor of the resonant inductor 3 is greater than 40. The resonant capacitor 1 is a capacitor group composed of a plurality of capacitors connected in parallel and in series. The resonant capacitor 1, the resonant inductor 3 and the time constant adjustment resistor 4 constitute a large current resonant circuit. The resonant current decays with a certain time constant.

[0026] The resonant capacitor 1, the resonant inductor 3 and the time constant adjustment resistor 4 constitute a typical second-order circuit, such as Figure 1 The principle is shown in the figure. The DC resistance value of the test circuit is in the mΩ level, which is an underdamped second-order circuit. The fully charged resonant capacitor 1 discharges to the resonant inductor 3 and the time constant adjustment resistor 4 through the discharge switch 2, and the circuit undergoes underdamped resonance. Figure 3 As shown. Before resonance, the cut-off branch switch 6 is closed, and the resonant current reaches its maximum value near the first zero-crossing point of the resonant voltage waveform. At this time, the cut-off thyristor is turned on, the resonance is forced to stop, and the current decays exponentially with a certain time constant. Figure 4 As shown. The time constant τ = the ratio of the inductance value of the resonant inductor 3 to the resistance value of the time constant adjustment resistor 4. By selecting appropriate parameters of the resonant capacitor 1, the resonant inductor 3 and the time constant adjustment resistor 4, the attenuation time constant is extended to meet the requirements of the DC protection test current for the waveform. The formula related to the RLC second-order zero input response circuit in this embodiment is shown below: (1);

[0027] (2);

[0028] (3);

[0029] (4);

[0030] In the formula, ,

[0031] ,

[0032] ,

[0033] ;

[0034] The above formula determines important parameters such as the peak value, rise time (i.e., one quarter of the oscillation decay period of the RLC second-order underdamped circuit), and time constant of the protection test current waveform at the initial stage. Among them, the peak value of the resonant current rising edge is determined by formula (1), the decay current amplitude is determined by formula (3), and the decay current time constant is determined by formula (4).

[0035] The specific test process is as follows: the test current generating circuit controller 14 controls the charging switch 10 and the charging DC power supply 9 to charge the resonant capacitor 1. The test current generating circuit controller 14 controls the discharge switch 2 to discharge the resonant capacitor 1, the resonant inductor 3, the time constant adjustment resistor 4, the DC current transformer test piece 11 and the low residual inductance shunt 12. The resonant capacitor 1 resonates with the resonant inductor 3. At the first zero crossing of the resonant voltage, the cut-off thyristor 5 is turned on, the resonant condition is destroyed, and the resonance stops. At this time, the current is at a peak value and decays with a certain time constant. The time constant is equal to the ratio of the inductance value of the resonant inductor 3 to the resistance value of the time constant adjustment resistor 4. By selecting appropriate parameters of the resonant capacitor 1, the resonant inductor 3 and the time constant adjustment resistor 4, the current peak value and the decay time constant can be adjusted to meet the requirements of the DC current transformer protection characteristic test. The DC current transformer tester 13 receives the trigger instruction of the test current generating circuit controller 14, compares and verifies the secondary signals from the DC current transformer test product 11 and the low residual inductance shunt 12, and completes the test verification of the DC current transformer protection characteristics.

[0036] The present invention is not limited to the above embodiments, and any technical solutions formed by equivalent replacement shall fall within the protection scope required by the present invention.

Claims

1. A DC current transformer protection characteristic test method, It is characterized in that A test current generating circuit and a controller are used, wherein the test current generating circuit includes: a resonant capacitor, a resonant inductor, a resistor for adjusting a time constant, a cutoff thyristor, a cutoff branch switch, a discharge switch, a low residual inductance shunt, a charging switch and a charging DC power supply; the positive electrode of the charging DC power supply is connected to one end of the charging switch, the other end of the charging switch is connected to one pole of the resonant capacitor, one pole of the resonant capacitor is also connected to one end of the discharge switch, the other end of the discharge switch is connected to one pole of the resonant inductor; the positive electrode of the resonant inductor is connected to one end of the discharge switch, and the positive electrode of the resonant inductor is connected to one end of the discharge switch. The other pole is connected to one pole of the time constant adjustment resistor; the other pole of the time constant adjustment resistor is connected to one end of the low residual inductance shunt; the negative pole of the cut-off thyristor is connected to one pole of the resonant inductor; the other end of the low residual inductance shunt and the positive pole of the cut-off thyristor are connected to one end of the cut-off branch switch, and the other end of the cut-off branch switch and the other pole of the resonant capacitor are both connected to the negative pole of the DC power supply; the controller performs timing control on the charging DC power supply, the charging switch, the discharging switch and the cut-off branch switch; The DC current transformer test piece can be mounted on the line between the other end of the cut-off branch switch and the other end of the cut-off branch switch; the voltage end of the low residual inductance shunt and the secondary side of the DC current transformer test piece are both connected to the DC current transformer tester; The low residual inductance shunt is used as a reference standard for the DC current transformer protection characteristic test; the resonant capacitor and the resonant inductor form an LC second-order circuit; the fully charged resonant capacitor discharges to the resonant inductor and the transformer test piece, and the resonant current reaches a maximum value near the first zero crossing point of the resonant voltage waveform. At this time, the cut-off thyristor is turned on, and the resonance is forced to stop at the zero crossing point of the resonant voltage, and the resonant current decays to present a single polarity.

2. The DC current transformer protection characteristic test method according to claim 1, Features: The reverse peak voltage value of the resonant capacitor is 100%, and the quality factor of the resonant inductor is greater than 40.

3. The DC current transformer protection characteristic test method according to claim 1, Features: The resonant capacitor, the resonant inductor and the time constant adjustment resistor constitute a large current resonant circuit.

4. The DC current transformer protection characteristic test method according to claim 1, Features: The resonant current decays with a certain time constant according to the ratio of the inductance value of the resonant inductor to the resistance value of the time constant adjustment resistor.

5. The DC current transformer protection characteristic test method according to claim 1, Features: A discharge branch is also connected in parallel to the branch formed by the cut-off thyristor and the cut-off branch switch; the discharge branch includes a discharge branch switch and a discharge resistor connected in series.

6. The DC current transformer protection characteristic test method according to claim 1, Features: The DC current transformer tester receives the trigger instruction of the controller, compares and verifies the secondary signals from the DC current transformer test product and the low residual inductance shunt, and completes the test verification of the DC current transformer protection characteristics.

7. The DC current transformer protection characteristic test method according to claim 2, Features: The resonant capacitor is a capacitor group composed of several capacitors connected in parallel and in series.

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