Power transformer DC magnetic bias monitoring device

Abstract

The utility model discloses a power transformer DC magnetic bias monitoring device comprising an isolation circuit and a signal acquisition device, and the isolation circuit is composed of a capacitor C, a resistor R, a field effect transistor Q1, a first switch K11, a second switch K12, a third switch K13 and three parallel switch tube groups. The signal acquisition device can monitor the direct current at the neutral point grounding outgoing line of the transformer in real time, meanwhile, the first switch K11, the second switch K12 and the third switch K13 are used for opening and closing the circuit according to a set threshold value, the rapid discharging function of active control can be achieved, and when large current exists and passes through for a long time, the rapid discharging function can be achieved. A large amount of accumulated charges of the capacitor can be released in time, and the problem that the safe operation of a power grid is seriously harmed due to the breakdown risk of the capacitor is avoided.

Description

Technical Field

[0001] This utility model belongs to the field of online monitoring of power equipment, and in particular relates to a DC bias monitoring device for power transformers. Background Technology

[0002] As the power system develops into an era of large power grids, large generating units, and ultra-high voltage transmission, the quality of power supply directly impacts the speed of economic development. Therefore, ensuring the reliability of power supply is currently a hot research topic in the power system. Equipment failure has the greatest impact on the stability and reliability of the power system. Equipment failure not only causes enormous economic losses but also seriously affects people's production and daily life safety.

[0003] The problem of DC bias in AC power grids is a series of issues induced by the rapid development of high-voltage / ultra-high-voltage DC transmission in recent years. The main manifestations of DC bias risk are core saturation caused by the intrusion of DC current into the ground in power transformers operating on the ground, as well as a series of abnormal operating conditions such as overexcitation, vibration, heating, and noise. Besides the large return current of DC transmission lines, other factors can also lead to DC bias risk in transformers. Prominent examples include geomagnetic induced currents generated by solar storms interfering with the Earth's magnetic field, stray currents from urban rail transit, photovoltaic, new energy systems, and other traction systems. On the one hand, AC power grids will face a high risk of DC bias due to the extensive application of DC projects; on the other hand, other popular and emerging industries may also pose a risk of DC bias to AC systems. Currently, the detection of DC bias risk in transformers mainly relies on manual data collection and analysis. Traditional isolation devices lack the ability for active control and rapid discharge. When a large current flows for a prolonged period, capacitors will accumulate a large amount of charge, potentially leading to capacitor breakdown and seriously endangering the safe operation of the power grid. Utility Model Content

[0004] The purpose of this invention is to provide a DC bias monitoring device for power transformers, so as to overcome the problem that existing isolation devices do not have the function of active control for rapid discharge. When a large current passes through for a long time, the capacitor will accumulate a large amount of charge, which poses a risk of capacitor breakdown and seriously endangers the safe operation of the power grid.

[0005] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0006] A DC bias monitoring device for a power transformer includes an isolation circuit and a signal acquisition device. The isolation circuit includes a capacitor C, a resistor R, a field-effect transistor Q1, a first switch K11, a second switch K12, a third switch K13, and three sets of parallel switch groups. The capacitor C, resistor R, and control switch Q1 are all connected in parallel with the switch groups. The two ends of the third switch K13 are respectively connected to the two ends of the resistor R. One end of the first switch K11 is connected to the neutral point of the transformer, and the other end of the first switch K11 is connected to the signal acquisition device and grounded. One end of the second switch K12 is connected to the neutral point of the transformer, and the other end is connected to one end of the resistor R connected to the neutral point of the transformer. The signal acquisition device is connected to a switch driver, which is connected to the control switch Q1, the first switch K11, the second switch K12, and the third switch K13 respectively.

[0007] Preferably, each group of switching transistors includes two switching transistors connected in series, wherein the collector of one switching transistor is connected to one end of capacitor C, the emitter of one switching transistor is connected to the collector of the other switching transistor, and the emitter of the other switching transistor is connected to the other end of capacitor C.

[0008] Preferably, the switching transistor is an NPN type transistor.

[0009] Preferably, the control switch Q1 is an N-MOS field-effect transistor.

[0010] Preferably, the drain of the control switch Q1 is connected to one end of the capacitor C, the source of the control switch Q1 is connected to the other end of the capacitor C, and the gate of the control switch Q1 is connected to the switch driver.

[0011] Preferably, a current sensor is installed between the signal acquisition device and the neutral point of the transformer.

[0012] Preferably, an impedance L is provided between the isolation device and the neutral point of the transformer.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects:

[0014] This utility model provides a DC bias monitoring device for power transformers, including an isolation circuit and a signal acquisition device. The isolation circuit, composed of a capacitor C, a resistor R, a field-effect transistor Q1, a first switch K11, a second switch K12, a third switch K13, and three sets of parallel-connected switching transistors, along with the signal acquisition device, enables real-time monitoring of the DC current at the transformer's neutral point grounding lead. Simultaneously, the first switch K11, the second switch K12, and the third switch K13 open and close the circuit according to a set threshold, enabling active control of rapid discharge. When a large current flows for an extended period, the capacitor accumulates a significant amount of charge, which can be released promptly, avoiding the risk of capacitor breakdown and the resulting serious jeopardy of the safe operation of the power grid. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the monitoring device for DC bias of the transformer in an embodiment of this utility model.

[0016] In the diagram, 1 is the isolation device; 2 is the signal acquisition device; and 3 is the switch driver. Detailed Implementation

[0017] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0018] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0019] like Figure 1As shown, this utility model provides a DC bias monitoring device for power transformers, including an isolation device 1 and a signal acquisition device 2. The isolation device employs an isolation circuit, which includes a capacitor C, a resistor R, a field-effect transistor Q1, a first switch K11, a second switch K12, a third switch K13, and three sets of parallel-connected switch transistor groups. The capacitor C, resistor R, and control switch Q1 are all connected in parallel with the switch transistor groups. The two ends of the third switch K13 are respectively connected to the two ends of the resistor R. One end of the first switch K11 is connected to the neutral point of the transformer, and the other end of the first switch K11 is connected to the signal acquisition device. The acquisition device is grounded. One end of the second switch K12 is connected to the neutral point of the transformer, and the other end is connected to one end of the resistor R connected to the neutral point of the transformer. The signal acquisition device is connected to a switch driver 3, which is connected to the control switch Q1, the first switch K11, the second switch K12, and the third switch K13 respectively. When the transformer is running normally, the signal acquisition device detects that there is no DC component at the neutral point of the transformer (or the DC current is less than the set threshold). The first switch K11 is normally closed, the second switch K12 is normally open, and the neutral point of the transformer is normally grounded. When a DC component (or a DC current greater than a set threshold) is detected flowing through the transformer neutral point, the second switch K12 automatically closes, grounding capacitor C, and then the first switch K11 opens. When the DC component at the transformer neutral point disappears (or within a set time but less than a set threshold), the first switch K11 closes, short-circuiting capacitor C and disabling the DC blocking function. If the charging time of capacitor C by the current flowing through the main transformer neutral point exceeds a set time, or the accumulated charge capacity exceeds 70% of the threshold, the active rapid discharge function is achieved by controlling switch Q1 and the discharge resistor R1, improving the safety and reliability of capacitor C. If the AC current flowing through the main transformer neutral point exceeds a limit, it is determined that an asymmetrical short-circuit fault has occurred in the power grid. The short-circuit impact current flows through capacitor C, causing the voltage on capacitor C to rise rapidly, triggering the discharge resistor R to conduct, limiting the voltage across capacitor C and consuming short-circuit energy, thus protecting capacitor C.

[0020] Each group of switching transistors includes two switching transistors connected in series. The collector of one switching transistor is connected to one end of capacitor C, the emitter of one switching transistor is connected to the collector of the other switching transistor, and the emitter of the other switching transistor is connected to the other end of capacitor C.

[0021] like Figure 1 As shown in the specific embodiment of this application, the switching transistor is an NPN transistor.

[0022] The control switch Q1 is an N-MOS field-effect transistor.

[0023] The drain of the control switch Q1 is connected to one end of the capacitor C, the source of the control switch Q1 is connected to the other end of the capacitor C, and the gate of the control switch Q1 is connected to the switch driver. The switch driver is used to adjust the opening and closing of the control switch Q1.

[0024] like Figure 1 As shown, an impedance L is provided between the isolation device 1 and the neutral point of the transformer. The transformer is grounded through a small reactor, which can effectively reduce the short-circuit current at the neutral point and flowing through the main transformer winding.

[0025] Specifically, in the specific embodiments of this application, a current sensor is installed between the signal acquisition device and the neutral point of the transformer to obtain the current and its magnitude flowing through the neutral point of the transformer.

[0026] The signal acquisition device specifically adopts a signal acquisition unit and uses a PLC controller as the control and adjustment unit. By setting the current threshold in the PLC controller, the magnitude of the DC component at the neutral point of the transformer is detected, thereby directly adjusting the disconnection and reconnection of the isolation device using a switch. The structure is simple and the control is convenient.

[0027] Specifically, in the specific embodiments of this application, the signal acquisition device can also be an integrated terminal, which can condition the acquired information through a signal conditioning module, then convert the conditioned signal through an A / D conversion module and transmit it through a wireless transmission module, thereby achieving the purpose of remote monitoring. The staff can decode and analyze the acquired signal, and display and store the data in real time.

[0028] Specifically, vibration sensors are installed on the transformer surface to acquire vibration signals, and noise sensors are also installed to collect noise signals. The vibration sensors are B&K 4534 accelerometers, and the noise sensors are B&K 4189 free-field microphones. A 12-channel B&K 3053 acquisition module is used for synchronous signal acquisition, with a sampling frequency of 32768 Hz. B&K Time Data Recorder software is used for continuous monitoring of vibration and noise signals. The vibration signals detected at the measuring points on the transformer tank surface should have high sensitivity to defects in the internal components being inspected, requiring low vibration signal attenuation, high signal-to-noise ratio, and minimal influence from the vibration propagation path. Vibration and noise sensors can be used to monitor the change in transformer vibration with bias current. There are no specific requirements regarding the intensity distribution of vibration on the transformer surface. Based on the actual structure of the transformer tank surface, three vibration measurement points are arranged on the high-voltage side of the transformer during testing. Accelerometers are fixed to a large flat area on the transformer tank surface using permanent magnet bases, away from the reinforcing ribs, to reduce the influence of nonlinearity in the tank structure. To improve the representativeness of the vibration test results, the average value of the vibration amplitude and spectrum at the three measurement points is used to characterize the transformer's vibration amplitude and spectrum, which is beneficial for effective analysis of deviations in the transformer's DC bias signal.

Claims

1. A DC bias monitoring device for power transformers, characterized in that, The device includes an isolation circuit and a signal acquisition device. The isolation circuit includes a capacitor C, a resistor R, a field-effect transistor Q1, a first switch K11, a second switch K12, a third switch K13, and three sets of parallel switch groups. The capacitor C, resistor R, and control switch Q1 are all connected in parallel with the switch groups. The two ends of the third switch K13 are respectively connected to the two ends of the resistor R. One end of the first switch K11 is connected to the neutral point of the transformer, and the other end of the first switch K11 is connected to the signal acquisition device and grounded. One end of the second switch K12 is connected to the neutral point of the transformer, and the other end is connected to one end of the resistor R connected to the neutral point of the transformer. The signal acquisition device is connected to a switch driver, which is connected to the control switch Q1, the first switch K11, the second switch K12, and the third switch K13 respectively.

2. The DC bias monitoring device for power transformers according to claim 1, characterized in that, Each group of switching transistors includes two switching transistors connected in series. The collector of one switching transistor is connected to one end of capacitor C, the emitter of one switching transistor is connected to the collector of the other switching transistor, and the emitter of the other switching transistor is connected to the other end of capacitor C.

3. The DC bias monitoring device for power transformers according to claim 2, characterized in that, The switching transistor is an NPN type transistor.

4. The DC bias monitoring device for power transformers according to claim 1, characterized in that, The control switch Q1 uses an N-MOS field-effect transistor.

5. The DC bias monitoring device for a power transformer according to claim 4, characterized in that, The drain of control switch Q1 is connected to one end of capacitor C, the source of control switch Q1 is connected to the other end of capacitor C, and the gate of control switch Q1 is connected to the switch driver.

6. The DC bias monitoring device for power transformers according to claim 1, characterized in that, A current sensor is installed between the signal acquisition device and the transformer neutral point.

7. The DC bias monitoring device for power transformers according to claim 1, characterized in that, An impedance L is provided between the isolation device and the transformer neutral point.

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