Transformer and overcurrent suppression device and method
By connecting the current limit reactor in series in each phase of the primary side of the transformer and in parallel with the switch, controlling the phase-separation and phase angle of the switch, the effective limit on the closing surge current and short-circuit current of the high-power transformer is achieved, and the problem that the existing technology cannot control the closing surge current and short-circuit current at the same time is solved, and the reliability and service life of the transformer are improved.
Patent Information
- Application Number
- CN202411637921.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-15
- Publication Date
- 2025-03-11
AI Technical Summary
The prior art cannot effectively limit the closing surge current and short circuit current of high-power transformers at the same time, affecting the reliability and service life of the transformer.
The current limit reactor is connected in series in each phase of the primary side of the transformer and in parallel with the switches of each phase. By controlling the phase-separation and phase angle of the switch, the phase voltage is near the peak during closing, thereby minimizing the closing surge current. At the same time, the current is detected before closing. If the short circuit threshold is exceeded, the closing is terminated and the current limit reactor is reconfigured to limit the short circuit current.
It effectively limits the closing surge current and short circuit current of the transformer, improves the reliability and service life of the transformer, and avoids damage caused by current impact.
Smart Images
Figure CN119602197A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of transformer current limiting, and in particular relates to a transformer, an overcurrent suppression device and a method. Background Art
[0002] With the increase of the load on the user side of the power grid system, the corresponding main transformer transmission capacity increases, and the problem of increased short-circuit current is prone to occur. On the other hand, the access of a large number of distributed new energy sources makes the power grid system weakly damped, which will also cause the short-circuit current to increase. Since the power grid system usually cuts off the line of the short-circuit fault through the circuit breaker, but as the load increases, the circuit breaker has insufficient breaking capacity, and the transformer has insufficient resistance to short-circuit current shock, which affects the reliability and service life of the transformer. In addition, when the high-power transformer is closed, the surge current is very large, especially when the closing is at the zero point of each phase voltage, the closing surge current is the largest, and the closing surge current can reach 8-10 times the rated current, which will also affect the reliability and service life of the transformer. Therefore, without increasing the capacity of the power grid transmission equipment, it is of great significance to study the control method of limiting the transformer closing surge current and short-circuit current for the safe and stable operation of the power system.
[0003] The existing method of limiting short-circuit current is to connect a current-limiting reactor in series on the secondary side of the transformer, but this method does not have the ability to limit the inrush current when the switch is closed. The existing method of limiting the inrush current when the switch is closed is to use a phase-controlled circuit breaker, but this method does not have the ability to limit the short-circuit current. Therefore, the control devices in the prior art cannot limit the inrush current when the high-power transformer is closed and can also quickly limit the short-circuit current when the switch is closed during a short circuit. Summary of the invention
[0004] The object of the present invention is to provide a transformer, an overcurrent suppression device and a method to solve the problem that the control device in the prior art cannot limit the closing inrush current of a high-power transformer while also being able to quickly limit the short-circuit current when closing the transformer in a short circuit.
[0005] In order to solve the above technical problems, the present invention provides an overcurrent suppression method, comprising: connecting a current limiting reactor in series in each phase of the primary side of a transformer, and connecting a switch in parallel to the current limiting reactor in each phase; when the transformer is closed, first controlling the first phase switch to close, after the first phase switch is closed, controlling the second phase switch to close when the phase angle of the line voltage between the first phase and the second phase is 30 degrees or 210 degrees; after the second phase switch is closed, detecting the primary and secondary currents of the transformer, if the primary and / or secondary currents exceed the corresponding short-circuit threshold, the third phase switch is no longer closed, and the other two phase switches are controlled to open, and the current limiting reactor is connected to the primary side of the transformer; if both the primary and secondary currents do not exceed the corresponding short-circuit threshold, controlling the third phase switch to close when the phase angle of the line voltage between the first phase and the third phase is 30 degrees or 210 degrees, and completing the closing of the transformer.
[0006] Furthermore, the method also includes: after the transformer is closed, if it is detected that the secondary current of the transformer exceeds the short-circuit threshold of the secondary current, controlling the switch in each phase to open and connecting the current limiting inductor in each phase to the primary side of the transformer.
[0007] Furthermore, the impedance value of the current limiting reactor is a ratio of the voltage on each phase current limiting reactor to the short-circuit threshold corresponding to the primary current.
[0008] Furthermore, after the second phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and / or secondary currents exceed the corresponding short-circuit threshold, the incoming circuit breaker is controlled to open.
[0009] Further, the first phase is phase A, the second phase is phase B, and the third phase is phase C.
[0010] The beneficial effects of the above technical solution are as follows: the present invention is an improved invention, by connecting a current limiting reactor in series in each phase of the three-phase incoming line side of the primary side of the transformer, and a switch in parallel to the current limiting reactor in each phase, when the transformer needs to be closed, the switches in each phase are closed in turn, and when the phase angle of the line voltage between the first phase and the second phase, and between the first phase and the third phase is 30 degrees or 210 degrees, the second phase and the third phase switches are controlled to be closed accordingly, so that when the closing is completed, the phase voltages of the two phases are both near the peak value, the two phases are energized at their respective voltage peaks, the closing inrush current of the two phases is minimized, and when the closing is not completed due to The current limiting reactor is connected in series in the three-phase incoming line of the transformer, which increases the loop impedance, naturally reduces the starting current of the transformer, and can also reduce the current impact. At the same time, before the transformer is closed, that is, before the last phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and secondary currents are short-circuited, the transformer closing is terminated, and the switches of the other two phases are disconnected. The current limiting reactor is reconnected to the three-phase incoming line, thereby limiting the transformer closing surge current and the short-circuit current at the same time, avoiding the transformer from being impacted by the closing surge current and the short-circuit current, and improving the reliability and service life of the transformer.
[0011] In order to solve the above technical problems, the present invention also provides an overcurrent suppression device, including a controller and a current limiting inductor connected in series in each phase of the primary side of the transformer, and a switch is connected in parallel to the current limiting inductor in each phase; when the controller is used to close the transformer, the first phase switch is first controlled to close, and after the first phase switch is closed, the second phase switch is controlled to close when the phase angle of the line voltage between the first phase and the second phase is 30 degrees or 210 degrees; after the second phase switch is closed, the primary and secondary currents of the transformer are detected. If the primary and / or secondary currents exceed the corresponding short-circuit threshold, the third phase switch is no longer closed, and the other two phase switches are controlled to open, and the current limiting inductor is connected to the primary side of the transformer; when the primary and secondary currents do not exceed the corresponding short-circuit threshold, the third phase switch is controlled to close when the phase angle of the line voltage between the first phase and the third phase is 30 degrees or 210 degrees.
[0012] Furthermore, after the transformer is closed, if it is detected that the secondary current of the transformer exceeds the short-circuit threshold of the secondary current, the switch in each phase is controlled to open, and the current limiting reactor in each phase is connected to the primary side of the transformer.
[0013] Furthermore, the impedance value of the current limiting reactor is a ratio of the voltage on each phase current limiting reactor to the short-circuit threshold corresponding to the primary current.
[0014] Furthermore, after the second phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and / or secondary currents exceed the corresponding short-circuit threshold, the incoming circuit breaker is controlled to open.
[0015] The beneficial effects of the above technical solution are as follows: the present invention is an improved invention, by connecting a current limiting reactor in series in each phase on the three-phase incoming line side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase. When the transformer needs to be closed, the switches in each phase are closed in turn in phases, and when the phase angle of the line voltage between the first phase and the second phase, and between the first phase and the third phase is 30 degrees or 210 degrees, the second phase and the third phase switches are controlled to be closed accordingly, so that when the closing is completed, the phase voltages of the two phases are both near the peak value, the two phases are energized at their respective voltage peaks, the closing inrush current of the two phases is minimized, and when the closing is not completed, due to the current limiting reactor in series, the It is connected to the three-phase incoming line of the transformer, which increases the loop impedance, naturally reduces the starting current of the transformer, and can also reduce the current impact. At the same time, before the transformer is closed, that is, before the last phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and secondary currents exceed the set threshold, that is, a short circuit occurs, the transformer closing is terminated, and the switches of the other two phases are disconnected, and the current limiting inductor is reconnected to the three-phase incoming line, thereby limiting the transformer closing surge current and the short-circuit current at the same time, avoiding the transformer from being impacted by the closing surge current and the short-circuit current, and improving the reliability and service life of the transformer.
[0016] In order to solve the above technical problems, the present invention further provides a transformer, including a transformer body and an overcurrent suppression device, wherein the overcurrent suppression device is an overcurrent suppression device introduced above.
[0017] The beneficial effects of the above technical solution are as follows: the present invention is an improved invention creation, in which an overcurrent suppression device is arranged in the transformer, the device comprises a current limiting reactor connected in series in each phase of the primary side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase. When the transformer needs to be closed, the switches in each phase are closed in turn in phases, and the second phase and the third phase switches are controlled to be closed when the phase angle of the line voltage between the first phase and the second phase and the first phase and the third phase is 30 degrees or 210 degrees, so that when the closing is completed, the phase voltages of the two phases are both near the peak value, the two phases are energized at their respective voltage peaks, the closing inrush currents of the two phases are minimized, and Moreover, when the circuit is not closed, since the current limiting reactor is connected in series in the three-phase incoming line of the transformer, the loop impedance is increased, the starting current of the transformer is naturally reduced, and the current impact can also be reduced. At the same time, before the transformer is closed, that is, before the last phase switch is closed, the original and secondary currents of the transformer are detected. When a short circuit occurs, the transformer closing is terminated, and the switches of the other two phases are disconnected, and the current limiting reactor is reconnected to the three-phase incoming line, thereby limiting the transformer closing surge current and the short-circuit current at the same time, avoiding the transformer from being impacted by the closing surge current and the short-circuit current, and improving the reliability and service life of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 Schematic diagram of transformer topology of a transformer embodiment of the present invention. DETAILED DESCRIPTION
[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific implementation methods of the present invention are further described below in conjunction with the accompanying drawings.
[0020] The present invention connects a current limiting reactor in series in each phase of the three-phase incoming line side (primary side) of the transformer, and each current limiting reactor is connected in parallel with a switch. When the transformer needs to be closed, the switches in each phase are closed in phase in turn, and the second phase and the third phase switches are controlled to be closed when the phase angle of the line voltage between the first phase and the second phase and the first phase and the third phase is 30 degrees or 210 degrees, so that when the closing is completed, the phase voltages of the two phases are both near the peak value, the two phases are energized at their respective voltage peak values, the closing inrush currents of the two phases are minimized, and when the closing is not completed, the current limiting reactor is connected in series in the transformer. In the three-phase incoming line of the transformer, the loop impedance is increased, the starting current of the transformer is naturally reduced, and the current impact can also be reduced. At the same time, before the transformer is closed, that is, before the last phase switch is closed, the primary and secondary currents of the transformer are detected. When a short circuit occurs, the transformer closing is terminated, and the switches of the other two phases are disconnected, and the current limiting inductor is reconnected to the three-phase incoming line, thereby limiting the transformer closing surge current and the short-circuit current at the same time, avoiding the transformer from being impacted by the closing surge current and the short-circuit current, and improving the reliability and service life of the transformer.
[0021] Transformer Embodiment
[0022] The present invention provides a transformer, the topology of which is as follows Figure 1 As shown, it includes a transformer body and an overcurrent suppression device, which includes a controller, a current limiting reactor and a switch. A current limiting reactor is connected in series in each phase of the three-phase incoming line side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase. The current limiting reactor is a reactor, or is composed of multiple reactors connected in series. The controller is Figure 1 In the overcurrent suppression control protection device, a current limiting reactor is connected in series in each phase of the three-phase incoming line side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase. Preferably, in order to improve the control efficiency, the switch adopts a fast mechanical switch, and the fast mechanical switch can quickly complete the opening and closing within 5ms. The transformer also includes a measuring device, which includes a voltage transformer PT for testing the three-phase incoming line voltage and a current transformer CT for testing the primary and secondary currents of the transformer. The voltage transformer PT is set between the two phases. The controller obtains the voltage and current information collected by the measuring device to implement an overcurrent suppression method. The implementation principle of the method is as follows:
[0023] 1. Transformer closing inrush current control:
[0024] 1) Before the transformer is energized, the fast mechanical switch connected in parallel with the current limiting reactor is in the open state. The current limiting reactor is connected in series in the three-phase incoming line of the transformer, which increases the loop impedance and naturally reduces the starting current of the transformer;
[0025] 2) After receiving the closing command, when the transformer is closed, the first phase (e.g., phase A) fast mechanical switch is controlled to close. The first phase fast mechanical switch can complete the closing within 5ms, short-circuiting the current limiting reactor connected in series with the first phase;
[0026] 3) After the first phase fast mechanical switch is closed, that is, after the first phase of the transformer is closed, the voltage transformer detects the line voltage between the first phase and the second phase (for example, the AB line voltage), and controls the second phase fast mechanical switch to close when the phase angle of the line voltage between the first phase and the second phase (such as the B phase) is 30 degrees or 210 degrees. The fast mechanical switch is closed at the peak of the second phase phase voltage to ensure that the surge current is minimal when the second phase is closed. If the grid voltage frequency is 50HZ, the fast mechanical switch is closed within 5ms, then the line voltage U AB When the phase angle is 30 degrees or 210 degrees, the phase voltage of phase B is at zero. At this time, phase B is controlled to start closing. Then, when the closing of phase B is completed, the phase voltage of phase B is just at the peak value. At this time, the closing inrush current of phase B is the smallest.
[0027] 4) After the fast mechanical switch of the first two phases (for example, phase A and phase B) is closed, the voltage transformer detects the line voltage (for example, AC line voltage) between the first phase and the third phase (for example, phase C), and the current transformer detects the primary and secondary currents of the transformer. When the primary and secondary currents do not exceed the corresponding short-circuit thresholds, the third phase fast mechanical switch is controlled to close when the phase angle of the line voltage between the first phase and the third phase is 30 degrees or 210 degrees. In this way, the third phase of the transformer is closed near its phase voltage peak, ensuring that the surge current is minimized when the third phase is closed, thereby effectively limiting the closing surge current during the entire transformer closing process.
[0028] 2. Short-circuit current control when the transformer is closed in the short-circuit state:
[0029] When the second-phase fast mechanical switch is closed, that is, after the first two phases (for example, phase A and phase B) of the fast mechanical switch are closed, if the primary and / or secondary currents of the transformer exceed the corresponding short-circuit threshold, it can be determined that the transformer is closed in a short-circuit state, and the controller terminates the closing control of the third-phase (for example, phase C) fast mechanical switch, and no longer closes the third-phase fast mechanical switch. At the same time, the fast mechanical switches of the other two phases are controlled to open immediately. After opening, the current-limiting reactor is immediately reconnected to the three-phase incoming line of the transformer power supply, thereby limiting the short-circuit current. At the same time, the controller also issues an opening command for the incoming circuit breaker to control the opening of the incoming circuit breaker, thereby completing the opening of the incoming circuit breaker and the removal of the fault.
[0030] 3. Transformer steady-state short-circuit current control:
[0031] After the transformer is closed, the fast mechanical switch connected in parallel with the current limiting reactor is in the closed state, bypassing the current limiting reactor. If it is detected that the secondary current of the transformer exceeds the second set threshold, that is, a short circuit fault occurs on the secondary side of the transformer, and the secondary current increases rapidly and exceeds the short circuit threshold corresponding to the secondary current, that is, the second set threshold, the controller immediately issues a fast mechanical switch opening command, controls the fast mechanical switch in each phase to complete the opening within 5ms, and connects the current limiting reactor in each phase to the three-phase incoming line terminal of the transformer to limit the short-circuit current and prevent the transformer from being impacted by the short-circuit current.
[0032] In the above control process, the closing order of the three-phase switch can be: closing phase A, phase B and phase C in sequence, or closing phase B, phase C and phase A in sequence, or closing phase C, phase A and phase B in sequence, etc.
[0033] 4. Calculation of reactance value of current limiting reactor:
[0034] The reactor is a key device for current limiting. On the one hand, it limits the surge current of the transformer, and on the other hand, it limits the short-circuit current. Because the closing is controlled by phase, even without a current limiting reactor, it can ensure the suppression of the transformer closing surge current. After the series reactor is connected, the surge current will be further limited. Therefore, the current limiting reactor here only considers the current suppression of the short circuit of the secondary rectifier of the transformer. The impedance value of the current limiting reactor is the ratio of the voltage on each phase current limiting reactor to the first set threshold. The first set threshold is the short-circuit threshold of the primary current. When the primary current is greater than the corresponding short-circuit threshold, that is, the first set threshold, it is judged that the primary side of the transformer sends a short-circuit fault. The calculation method is as follows:
[0035] The transformer parameters are as follows: incoming power supply voltage U1, primary rated current I1, secondary rated voltage U2, secondary rated current I2, transformer impedance Z, transformer primary and secondary voltage ratio n, first set threshold I X , the second set threshold I Y The first set threshold and the second set threshold are set according to the current limiting requirements of the primary side and the secondary side.
[0036] First, calculate the effective value of the AC voltage Uyx on the secondary side of the transformer:
[0037]
[0038] Then, the transformer input voltage Uy after current limiting is calculated according to the effective value of the secondary voltage of the transformer and the transformer primary-secondary voltage transformation ratio: Uy=Uyx*n;
[0039] The three-phase power supply is star-connected, and the voltage Δu on each phase current limiting reactor is calculated:
[0040] Impedance value of current limiting reactor:
[0041]
[0042] For example, the inlet power supply voltage U1 of the ice melting transformer is 66kV, the rated current I1 is 1250A, the secondary rated voltage U2 is 33kV, the secondary rated current I2 is 2500A, the transformer impedance Z is 10%, the transformer primary and secondary voltage ratio n is 2, and the inlet power supply voltage frequency f is 50HZ. In actual use, the short-circuit current needs to be suppressed to 4 times the secondary rated current, that is:
[0043] The second threshold value I Y =4×2500A=10000A;
[0044] The first threshold value I X =33 / 66×10000=5000A;
[0045] The effective value of the AC voltage on the secondary side of the transformer
[0046] The transformer input voltage after current limiting is Uy=13200×2=26400V;
[0047] Voltage on each phase current limiting reactor
[0048] Inductive impedance value of current limiting reactor
[0049] Device Embodiment
[0050] The present invention provides an overcurrent suppression device, the specific implementation process of which has been described in detail in the transformer embodiment and will not be repeated here.
[0051] Method Embodiment
[0052] The present invention provides an overcurrent suppression method. The specific implementation process of the method has been described in detail in the transformer embodiment and will not be repeated here.
Claims
1. An overcurrent suppression method, characterized in that: include: A current limiting reactor is connected in series in each phase of the primary side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase; When the transformer is closed, the first phase switch is controlled to close first. After the first phase switch is closed, the second phase switch is controlled to close when the phase angle of the line voltage between the first phase and the second phase is 30 degrees or 210 degrees. After the second-phase switch is closed, the primary and secondary currents of the transformer are detected. If the primary and / or secondary currents exceed the corresponding short-circuit threshold, the third-phase switch will no longer be closed, and the other two-phase switches will be controlled to open, and the current-limiting reactor will be connected to the primary side of the transformer. When the primary and secondary currents do not exceed the corresponding short-circuit threshold, the third-phase switch will be controlled to close when the phase angle of the line voltage between the first phase and the third phase is 30 degrees or 210 degrees, and the transformer will be closed.
2. The overcurrent suppression method according to claim 1, characterized in that: The method also includes: after the transformer is closed, if it is detected that the secondary current of the transformer exceeds the short-circuit threshold of the secondary current, controlling the switch in each phase to open and connecting the current limiting reactor in each phase to the primary side of the transformer.
3. The overcurrent suppression method according to claim 1, characterized in that: The impedance value of the current limiting reactor is the ratio of the voltage on each phase current limiting reactor to the short-circuit threshold value corresponding to the primary current.
4. The overcurrent suppression method according to claim 1, characterized in that: After the second phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and / or secondary currents exceed the corresponding short-circuit threshold, the incoming circuit breaker is controlled to open.
5. The overcurrent suppression method according to claim 1, characterized in that: The first phase is phase A, the second phase is phase B, and the third phase is phase C.
6. An overcurrent suppression device, comprising a controller, characterized in that: It also includes a current limiting reactor connected in series in each phase of the primary side of the transformer, and a switch is connected in parallel to the current limiting reactor in each phase; when the controller is used to close the transformer, the first phase switch is first controlled to close, and after the first phase switch is closed, the second phase switch is controlled to close when the phase angle of the line voltage between the first phase and the second phase is 30 degrees or 210 degrees; after the second phase switch is closed, the primary and secondary currents of the transformer are detected, if the primary and / or secondary currents exceed the corresponding short-circuit threshold, the third phase switch is no longer closed, and the other two phase switches are controlled to open, and the current limiting reactor is connected to the primary side of the transformer; if both the primary and secondary currents do not exceed the corresponding short-circuit threshold, the third phase switch is controlled to close when the phase angle of the line voltage between the first phase and the third phase is 30 degrees or 210 degrees.
7. The overcurrent suppression device according to claim 6, characterized in that: After the transformer is closed, if it is detected that the secondary current of the transformer exceeds the short-circuit threshold of the secondary current, the switch in each phase is controlled to open, and the current limiting reactor in each phase is connected to the primary side of the transformer.
8. The overcurrent suppression device according to claim 6, characterized in that: The impedance value of the current limiting reactor is the ratio of the voltage on each phase current limiting reactor to the short-circuit threshold value corresponding to the primary current.
9. The overcurrent suppression device according to claim 6, characterized in that: After the second phase switch is closed, the primary and secondary currents of the transformer are detected. When the primary and / or secondary currents exceed the corresponding short-circuit threshold, the incoming circuit breaker is controlled to open.
10. A transformer, comprising a transformer body, characterized in that: It also includes an overcurrent suppression device, and the overcurrent suppression device is the overcurrent suppression device according to any one of claims 6-9.