On-load tap changer switching buffer device and its control method

Abstract

This invention relates to an on-load tap changer switching buffer device and its control method. The on-load tap changer switching buffer device includes a first bidirectional switching device controlled by a first control signal, a second bidirectional switching device controlled by a second control signal, a capacitor, a reactor, a current measurement module, a voltage measurement module, and a controller. The current measurement module is connected in series on the transformer's incoming line, and the voltage measurement module is connected in parallel on the transformer's incoming line. The capacitor and the first bidirectional switching device are connected in series, and the reactor and the second bidirectional switching device are connected in series and then bridged between the two incoming lines of the transformer. The control method involves detecting the incoming line current and incoming line voltage, determining whether the incoming line current amplitude exceeds an incoming line current amplitude threshold, whether the incoming line current change rate exceeds an incoming line current change rate threshold, and the phase relationship between the incoming line current and voltage, and outputting a first control signal or a second control signal. This invention can effectively suppress overcurrent problems during on-load tap changer switching.

Description

Technical Field

[0001] This invention belongs to the technical field of electrical testing equipment, specifically relating to an on-load tap changer switching buffer device for a power transformer and the control method thereof. Background Technology

[0002] A transformer on-load tap changer is a voltage regulating device operated during transformer operation to change the tap connection position of the transformer windings. It can switch between taps in the transformer windings without interrupting the load current, thereby changing the effective number of turns of the windings, i.e., changing the voltage ratio of the transformer, and achieving the purpose of voltage regulation.

[0003] The on-load tap changer switching of a transformer includes two test scenarios: rated voltage under no-load and rated current under load. It generally requires dozens or even thousands of tap changes. Especially during the no-load test, the current change can be tens of times, which can easily cause overcurrent during the switching test, triggering the overcurrent protection and leading to the failure of the test.

[0004] Because on-load tap changers on transformers must maintain current continuity and prevent short circuits between taps during adjustment, a resistor must be connected in series between the two bridged taps to circulate the current and prevent short circuits. This resistor is called a transition resistor. However, overcurrent problems can occur during tap switching. Existing on-load tap changers on transformers lack switching buffer devices. During tap changer switching tests, due to system transient parameters, sudden current changes can occur, especially during no-load tests, where the current change can reach tens of times. This can easily trigger overcurrent protection, leading to transformer test failure. Currently, there is no effective solution to the overcurrent problem during on-load tap changer switching. Summary of the Invention

[0005] The purpose of this invention is to provide an on-load tap changer switching buffer device and its control method that can effectively suppress overcurrent problems and avoid current surges during tap changer switching tests.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An on-load tap changer switching buffer device is installed between the on-load tap changer and the transformer controlled by the on-load tap changer. The on-load tap changer switching buffer device, the on-load tap changer, and the transformer constitute a test system. The on-load tap changer switching buffer device includes a first bidirectional switching device controlled to be turned on or off by a first control signal, a second bidirectional switching device controlled to be turned on or off by a second control signal, a capacitor, a reactor, a current measurement module, a voltage measurement module, and a controller. The current measurement module is connected in series on one of the transformer's input lines and is used to detect the input line current data in real time. The voltage measurement module is connected in parallel on the transformer's input lines and is used to detect the voltage data in real time. The input voltage data is obtained by connecting the capacitor and the first bidirectional switching device in series to form a capacitor branch and bridging the two input lines of the transformer. The reactor and the second bidirectional switching device in series to form a reactor branch and bridging the two input lines of the transformer. The controller is connected to the current measurement module, the voltage measurement module, the first bidirectional switching device, and the second bidirectional switching device respectively. The controller is used to generate the first control signal to control the first bidirectional switching device or generate the second control signal to control the second bidirectional switching device based on the input current data detected by the current measurement module and the input voltage data detected by the voltage measurement module.

[0007] Both the first bidirectional switching device and the second bidirectional switching device are anti-parallel thyristor modules, and the anti-parallel thyristor module includes two thyristors connected in anti-parallel.

[0008] The test system also includes a VF converter. The two sides of the on-load tap changer are connected to the AC power grid and the input side of the VF converter, respectively. The output side of the VF converter is connected to the two incoming lines of the transformer.

[0009] The test system is a system for conducting no-load tests on the transformer.

[0010] A control method for the aforementioned on-load tap changer switching buffer device is as follows: the controller has preset input current amplitude threshold and input current change rate threshold; the current measurement module detects the input current data in real time and transmits it to the controller; the voltage measurement module detects the input voltage data in real time and transmits it to the controller; the controller calculates the input current amplitude and input current change rate based on the input current data; the controller determines whether the input current amplitude exceeds the input current amplitude threshold and whether the input current change rate exceeds the input current change rate threshold; if the input current amplitude exceeds the input current amplitude threshold or the input current change rate exceeds the input current change rate threshold, the controller further determines the phase relationship between the input current data and the input voltage data and outputs either a first control signal to control the first bidirectional switching device to turn on or a second control signal to control the second bidirectional switching device to turn on.

[0011] If the controller determines that the phase of the input current data lags behind the phase of the input voltage data, the controller outputs the first control signal to control the first bidirectional switching device to turn on. If the controller determines that the phase of the input current data leads the phase of the input voltage data, the controller outputs the second control signal to control the second bidirectional switching device to turn on.

[0012] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art: the present invention can effectively suppress the overcurrent problem when the on-load tap changer is switched, and avoid the current surge problem generated during the on-load tap changer switching test. Attached Figure Description

[0013] Appendix Figure 1 This is a circuit diagram of a test system including the on-load tap changer switching buffer device of the present invention.

[0014] Appendix Figure 2 This is a flowchart of the control method used in the on-load tap changer switching buffer device of the present invention. Detailed Implementation

[0015] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0016] Example 1: As shown in the attached document Figure 1 As shown, the test system for no-load testing of a transformer includes an on-load tap changer K1, a transformer T, and an on-load tap changer switching buffer device. The on-load tap changer switching buffer device is installed between the on-load tap changer K1 and the transformer T controlled by the on-load tap changer K1, that is, its two ends are connected to the on-load tap changer K1 and the transformer T respectively.

[0017] The on-load tap changer switching buffer device includes a first bidirectional switching device V1, a second bidirectional switching device V2, a capacitor C1, a reactor L1, a current measurement module CT, a voltage measurement module VT, and a controller D. The current measurement module CT is connected in series on one of the incoming lines of transformer T to detect the incoming line current data in real time. The voltage measurement module VT is connected in parallel on the incoming line of transformer T to detect the incoming line voltage data in real time. The first bidirectional switching device V1 is controlled to be turned on or off by a first control signal. The first bidirectional switching device V1 and the capacitor C1 are connected in series to form a capacitor branch, which is bridged between the two incoming lines of transformer T. The second bidirectional switching device V2 is controlled to be turned on or off by a second control signal. The second bidirectional switching device V2 and the reactor L1 are connected in series to form a reactor branch, which is bridged between the two incoming lines of transformer T. Controller D is connected to the current measurement module CT, the voltage measurement module VT, the first bidirectional switching device V1, and the second bidirectional switching device V2. The incoming current data detected in real time by the current measurement module CT is transmitted to controller D, and the incoming voltage data detected in real time by the voltage measurement module VT is transmitted to controller D. After receiving the incoming current data detected in real time by the current measurement module CT and the incoming voltage data detected in real time by the voltage measurement module VT, controller D generates a first control signal to control the first bidirectional switching device V1 or generates a second control signal to control the second bidirectional switching device V2 based on the incoming current data detected by the current measurement module CT and the incoming voltage data detected by the voltage measurement module VT. In this scheme, the first bidirectional switching device V1 and the second bidirectional switching device V2 are both anti-parallel thyristor modules. Each anti-parallel thyristor module includes two thyristors connected in anti-parallel, and controller D can control the two thyristors respectively.

[0018] The test system also includes a VF converter. The two sides of the on-load tap changer K1 are connected to the AC power grid and the input side of the VF converter, respectively. The output side of the VF converter is connected to the two incoming lines of the transformer T.

[0019] The control method adopted by the above-mentioned on-load tap changer switching buffer device is as follows: The controller D is preset with an input current amplitude threshold i' and an input current change rate threshold δ. The current measurement module CT detects the input current data in real time and transmits it to the controller D. The voltage measurement module VT detects the input voltage data in real time and transmits it to the controller D. The controller D calculates the input current amplitude i and the input current change rate di / dt based on the input current data. The controller D determines whether the input current amplitude i exceeds the input current amplitude threshold i' and whether the input current change rate di / dt exceeds the input current change rate threshold δ. If the input current amplitude i exceeds the input current amplitude threshold i' or the input current change rate di / dt exceeds the input current change rate threshold δ, the controller D further determines the phase relationship between the input current data and the input voltage data and outputs a first control signal to control the first bidirectional switching device V1 to turn on or outputs a second control signal to control the second bidirectional switching device V2 to turn on. That is, the controller D determines whether to connect capacitor C1 or reactor L1 based on the phase relationship between the input current data and the input voltage data. If controller D determines that the phase of the incoming current data lags behind the phase of the incoming voltage data, controller D outputs a first control signal to turn on the first bidirectional switching device V1 and connects it to the capacitor branch. If controller D determines that the phase of the incoming current data leads the phase of the incoming voltage data, controller D outputs a second control signal to turn on the second bidirectional switching device V2 and connects it to the reactor branch.

[0020] The specific steps of this control method are attached. Figure 2 As shown: After the on-load tap changer switching buffer device is started, the current measurement module CT detects the incoming current data in real time, and the voltage measurement module VT detects the incoming voltage data in real time. The controller D calculates the incoming current amplitude i and the incoming current change rate di / dt, and makes the following judgments: ① Whether the incoming current amplitude i exceeds the incoming current amplitude threshold i'; ② Whether the incoming current change rate di / dt exceeds the incoming current change rate threshold δ. If neither is satisfied, there is no need to switch the capacitor branch and the reactor branch, and the incoming current detection continues. If either is satisfied, the capacitor branch or the reactor branch needs to be switched. At this time, the controller D continues to determine whether to switch the capacitor branch or the reactor branch based on the phase relationship between the incoming current data and the incoming voltage data. If the controller D determines that the phase of the incoming current data lags behind the phase of the incoming voltage data, it issues a first control signal to control the first bidirectional switching device V1 to conduct. If the controller D determines that the phase of the incoming current data leads the phase of the incoming voltage data, it issues a second control signal to control the second bidirectional switching device V2 to conduct. Once the amplitude of the incoming current i and the rate of change of the incoming current di / dt have both recovered, the first bidirectional switching device V1 or the second bidirectional switching device V2 is turned off to continue detecting the incoming current and voltage.

[0021] The aforementioned on-load tap changer switching buffer device can effectively suppress overcurrent problems during on-load tap changer switching and avoid current surges during on-load tap changer switching tests. The controller D determines the control signal for turning on or off the first bidirectional switching device V1 or the second bidirectional switching device V2 based on the magnitude of the incoming current amplitude i, the rate of change of the incoming current di / dt, and the phase relationship between the incoming current and the incoming voltage. When the first bidirectional switching device V1 is turned on, i.e., both anti-parallel thyristors included in the first bidirectional switching device V1 are turned on, capacitor C1 is connected in parallel to the main circuit of the test system, and the first bidirectional switching device V1 can achieve bidirectional flow of current in the capacitor branch. When the second bidirectional switching device V2 is turned on, i.e., both anti-parallel thyristors included in the second bidirectional switching device V2 are turned on, reactor L1 is connected in parallel to the main circuit of the test system, and the second bidirectional switching device V2 can achieve bidirectional flow of current in the reactor branch. Therefore, by switching on the capacitor branch or reactor branch according to the overcurrent condition of the test system, the sudden change in the main circuit current of the test system can be suppressed, ensuring the smooth progress and effectiveness of the on-load tap changer switching test.

[0022] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A load tap changer switching buffer device arranged between a load tap changer and a transformer controlled by switching of the load tap changer, the load tap changer switching buffer device, the load tap changer and the transformer forming a test system, characterized in that: The on-load tap changer switching buffer device includes a first bidirectional switching device controlled to be turned on or off by a first control signal, a second bidirectional switching device controlled to be turned on or off by a second control signal, a capacitor, a reactor, a current measurement module, a voltage measurement module, and a controller. The current measurement module is connected in series on one of the transformer's input lines and is used to detect the input current data in real time. The voltage measurement module is connected in parallel on the transformer's input line and is used to detect the input voltage data in real time. The capacitor and the first bidirectional switching device are connected in series to form a capacitor branch and are bridged between the two input lines of the transformer. The reactor and the second bidirectional switching device are connected in series to form a reactor branch and are bridged between the two input lines of the transformer. The controller is connected to the current measurement module, the voltage measurement module, the first bidirectional switching device, and the second bidirectional switching device respectively. The controller is used to generate the first control signal to control the first bidirectional switching device or generate the second control signal to control the second bidirectional switching device based on the input current data detected by the current measurement module and the input voltage data detected by the voltage measurement module.

2. The on-load tap changer switching buffer device of claim 1, wherein: Both the first bidirectional switching device and the second bidirectional switching device are anti-parallel thyristor modules, and the anti-parallel thyristor module includes two thyristors connected in anti-parallel.

3. The on-load tap changer switching buffer device according to claim 1, characterized in that: The test system also includes a VF converter. The two sides of the on-load tap changer are connected to the AC power grid and the input side of the VF converter, respectively. The output side of the VF converter is connected to the two incoming lines of the transformer.

4. The on-load tap changer switching buffer device according to claim 1, characterized in that: The test system is a system for conducting no-load tests on the transformer.

5. A control method for an on-load tap changer switching buffer device as described in any one of claims 1 to 4, characterized in that: The control method is as follows: the controller has preset input current amplitude threshold and input current change rate threshold; the current measurement module detects the input current data in real time and transmits it to the controller; the voltage measurement module detects the input voltage data in real time and transmits it to the controller; the controller calculates the input current amplitude and input current change rate based on the input current data; the controller determines whether the input current amplitude exceeds the input current amplitude threshold and whether the input current change rate exceeds the input current change rate threshold; if the input current amplitude exceeds the input current amplitude threshold or the input current change rate exceeds the input current change rate threshold, the controller further determines the phase relationship between the input current data and the input voltage data and outputs either the first control signal to control the first bidirectional switching device to turn on or the second control signal to control the second bidirectional switching device to turn on.

6. The control method according to claim 5, characterized in that: If the controller determines that the phase of the input current data lags behind the phase of the input voltage data, the controller outputs the first control signal to control the first bidirectional switching device to turn on. If the controller determines that the phase of the input current data leads the phase of the input voltage data, the controller outputs the second control signal to control the second bidirectional switching device to turn on.

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