Method for identifying and suppressing the hazard of closing inrush current on the power side of the MCR pre-excitation transformer

Abstract

The application discloses a kind of MCR pre-excitation transformer power side closing inrush current hazard identification and suppression method.It includes the following steps, step one: establishing electromagnetic transient simulation model;Step two: record the overcurrent amplitude Iy after closing and the amplitude Uy of overvoltage;Step three: set the critical threshold of current, voltage;When Iy and / or Uy exceed critical threshold, then enter step four;Otherwise, jump to step six;Step four: increase excitation inrush current suppression additional circuit;Step five: in electromagnetic transient simulation model, excitation inrush current suppression additional circuit is accessed;Step six: pre-excitation transformer power side equipment can safely run.The application has the advantages that it can effectively and accurately identify whether MCR closing inrush current hazard will spread to pre-excitation transformer power side, and suppress the overvoltage and / or overcurrent problem caused by corresponding closing inrush current hazard spreading to low-voltage side, to ensure the safety of pre-excitation transformer power side diesel generator and other electrical equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of power system transmission, and more specifically to a method for identifying and suppressing closing inrush current hazards on the power supply side of a high-voltage magnetically controlled shunt reactor (MCR) pre-excitation circuit. Background Art

[0002] Due to their long transmission distances, extra-high / ultra-high voltage (EHV) lines typically have large parallel capacitance values. In this case, when the line is unloaded or lightly loaded, the capacitor's charging effect causes the high-voltage line to transmit a large amount of capacitive reactive power. This can cause line overvoltages and, in the event of a single-phase ground fault, generate large secondary currents. The current conventional solution is to install reactors at both ends of the line to compensate for this reactive power.

[0003] However, when the operating mode of a transmission line changes, the capacity of the reactor to compensate also needs to be dynamically adjusted based on the operating mode. Therefore, a controllable shunt reactor can be used. The specific functions of a controllable shunt reactor include: compensating for line capacitive reactive power, stabilizing grid voltage; suppressing line-side backflow current, reducing recovery voltage, and improving reclosing success rate; limiting power frequency overvoltage; improving grid transmission capacity; suppressing system power oscillations; and reducing network losses. Controllable shunt reactors can minimize the transmission of reactive power in the grid, thereby reducing losses in grids with large load fluctuations and improving power supply quality, with significant economic and social benefits. Currently, controllable shunt reactors can be divided into transformer-type graded controllable shunt reactors and magnetic control-based continuous controllable shunt reactors (MCRs) based on their structural principles. The former achieves graded adjustment of the compensation capacity by controlling a composite fast-switching switch on the low-voltage side to change the impedance of the secondary winding. The latter achieves continuous adjustment of the compensation capacity by varying the DC current flowing through the control winding to change the core saturation level. Considering cost, control response speed, service life, and technological maturity, MCR has been widely adopted in practice.

[0004] However, when the MCR is currently closed and put into operation, the pre-excitation current is only 10% of the rated excitation current before closing. After closing, the pre-excitation is converted to main excitation, and the reactor body is suddenly energized, generating a large closing inrush current. Considering the delay caused by factors such as voltage detection time, control device output time, pre-excitation circuit switching time, and DC current avoidance delay time, this closing inrush current inevitably flows through the pre-excitation circuit. This may induce high current and overvoltage on the power supply side of the pre-excitation transformer, posing a significant electrical safety threat to electrical equipment on the power supply side of the pre-excitation transformer, such as diesel generators.

[0005] Therefore, it is necessary to develop a method for identifying and suppressing the surge current hazard on the power supply side of the pre-excitation transformer, which can solve the threat of the closing surge current of the high-voltage magnetically controlled shunt reactor to the electrical safety of the power supply side equipment of the pre-excitation transformer. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the background technology and provide a method for identifying and suppressing the hazard of closing inrush current on the power supply side of the pre-excitation transformer when the high-voltage magnetically controlled shunt reactor is closed. By establishing a refined electromagnetic transient simulation model of complete electrical equipment including a high-voltage magnetically controlled shunt reactor, a pre-excitation circuit, a main excitation circuit and a diesel generator, and the parameters of each device in the simulation model are taken from or referenced from actual parameters, the electrical quantity characteristics of the power supply side of the pre-excitation transformer caused by the closing inrush current of the high-voltage magnetically controlled shunt reactor can be accurately identified, and an appropriate additional electrical circuit is set according to the electrical quantity characteristics to suppress the closing inrush current, avoid damage to the electrical equipment, and ensure the safety of electrical equipment such as the diesel generator on the power supply side of the pre-excitation transformer; solve the problem that the closing inrush current of the high-voltage magnetically controlled shunt reactor threatens the electrical safety of the equipment on the power supply side of the pre-excitation transformer.

[0007] In order to achieve the above object, the technical solution of the present invention is: a method for identifying and suppressing the hazard of closing inrush current on the power supply side of an MCR pre-excitation transformer, characterized in that it includes the following steps:

[0008] Step 1: Establish electromagnetic transient simulation model of each device;

[0009] Step 2: Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor (MCR) and the line is closed, and record the overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed;

[0010] Step 3: Set the critical threshold of current and the critical threshold of voltage;

[0011] When Iy exceeds the critical current threshold, it indicates that the inrush current hazard occurs on the power supply side of the pre-excitation transformer, and the process goes to step 4; otherwise, the process jumps to step 6;

[0012] And / or, when Uy exceeds the critical voltage threshold, it indicates that the inrush current hazard occurs on the power supply side of the pre-excitation transformer, and the process goes to step 4; otherwise, the process jumps to step 6;

[0013] Step 4: Add an inrush current suppression circuit on the power supply side of the pre-excitation transformer to absorb overvoltage and suppress overcurrent;

[0014] Step 5: Connect the inrush current suppression additional circuit in step 4 to the electromagnetic transient simulation model in step 1, and jump to step 2;

[0015] Step 6: The closing inrush current of the high-voltage magnetically controlled shunt reactor will not harm the equipment on the power supply side of the pre-excitation transformer, and the equipment on the power supply side of the pre-excitation transformer can operate safely.

[0016] In the above technical solution, in step 1, the method for establishing the electromagnetic transient simulation model of each device is:

[0017] An electromagnetic transient simulation model is established in the electromagnetic transient simulation software, including a high-voltage magnetically controlled shunt reactor (MCR), a pre-excitation rectifier bridge, a pre-excitation transformer, a diesel generator, a main excitation rectifier bridge, a main excitation transformer, a fifth-order filter, a closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line, a pre-excitation transfer switch S2, and a pre-excitation AC power supply switch S3. The parameters of each device in the simulation model are set according to the actual parameters of each device.

[0018] In the above technical solution, in step 2, the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is set to be in the open state, and the pre-excitation switching switch S2 and the pre-excitation AC power supply switch S3 are set to be in the closed state;

[0019] At any time t0 after the pre-excitation process ends, close the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line. After a period of time Δt, open the pre-excitation AC power switch S3 to simulate the electromagnetic transient scenario on the power supply side of the pre-excitation transformer after the high-voltage magnetically controlled shunt reactor is connected in parallel.

[0020] The value of Δt is composed of the voltage detection time Δt1, the control device exit time Δt2, the action time Δt3 of the pre-excitation AC power switch S3, and the DC current avoidance delay time Δt4, satisfying Δt=Δt1+Δt2+Δt3+Δt4;

[0021] Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed, and record the overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed.

[0022] In the above technical solution, the diesel generator overcurrent safety factor Ki and overvoltage safety factor Ku are set;

[0023] The critical threshold of current is the product of the short-term overcurrent Iw (known) that the diesel generator on the AC side of the pre-excitation transformer can withstand and the diesel generator overcurrent safety factor Ki;

[0024] The critical threshold of voltage is the overvoltage allowed to be tolerated for a short time, which is the product of Uw (known) and the overvoltage safety factor Ku;

[0025] When Iy is greater than or equal to the product of Ki and Iw, and / or Uy is greater than or equal to the product of Ku and Uw, proceed to step 4; otherwise, jump to step 6.

[0026] In the above technical solution, in step 4, the method for setting the additional circuit for excitation inrush current suppression is as follows:

[0027] A zinc oxide arrester is connected between every two phases of the diesel generator power supply line on the power supply side of the pre-excitation transformer to absorb overvoltage and suppress overcurrent.

[0028] In the above technical solution, in step five, the reference voltage of the selected zinc oxide lightning arrester is not less than Uw, and the maximum absorbed energy is not less than 0.3×Uw×Iw×Δt, and the zinc oxide lightning arrester model is connected to the electromagnetic transient simulation model in step one;

[0029] The volt-ampere characteristic parameters of the arrester simulation model are taken from its real volt-ampere characteristic curve, which can more accurately evaluate whether the inrush current hazard has been avoided.

[0030] The present invention has the following advantages:

[0031] (1) The electromagnetic transient simulation model established by the present invention includes all electrical equipment involved in the electromagnetic transient process when the high-voltage magnetically controlled reactor is closed, and the electromagnetic transient modeling is refined; the electromagnetic transient simulation model parameters of each electrical equipment are taken from or referenced to their real parameters, and the electromagnetic transient model parameters are closer to reality, thereby ensuring the accuracy of the quantitative analysis of the high-voltage magnetically controlled reactor closing inrush current on the power supply side of the pre-excitation transformer, and achieving effective and accurate identification of whether the MCR closing inrush current hazard will propagate to the power supply side of the pre-excitation transformer, and suppressing the overvoltage and / or overcurrent problems caused by the corresponding closing inrush current hazard propagating to the low-voltage side, thereby ensuring the safety of electrical equipment such as the diesel generator on the power supply side of the pre-excitation transformer;

[0032] (2) The present invention considers in detail the action delay of the AC switch on the power supply side of the pre-excitation transformer, including factors such as voltage detection time, control device outlet time, AC switch action time and delay time for avoiding DC current. It can more accurately and realistically evaluate the duration of the transient process of the MCR closing inrush current acting on the power supply side of the pre-excitation transformer, and then confirm whether it will endanger the electrical safety of the diesel generator, thereby improving the accuracy of identifying and suppressing the closing inrush current hazard on the power supply side of the MCR pre-excitation circuit. It overcomes the problem that the prior art ignores the action delay of the AC switch on the power supply side of the pre-excitation transformer and believes that the hazard of the closing inrush current of the high-voltage magnetically controlled shunt reactor can be avoided by timely tripping the AC switch on the power supply side of the pre-excitation transformer. However, due to the delay in the actual process, the closing inrush current will briefly act on the power supply side of the pre-excitation transformer, which may damage the diesel generator, and the identification and suppression accuracy is not high.

[0033] (3) The present invention considers in detail the action delay of the AC switch on the power supply side of the pre-excitation transformer, combines the safety operation margin requirements of the diesel generator on the power supply side of the pre-excitation transformer (i.e., combines the tolerance capacity of the diesel generator), quantitatively analyzes the risk of equipment damage, and accordingly installs a lightning arrester protection scheme on the low-voltage side to improve the accuracy of identification and suppression. Under the premise of ensuring the safe operation of the equipment on the power supply side of the pre-excitation transformer, it can effectively avoid excessive installation of additional circuits to suppress closing inrush current, thereby avoiding cost waste;

[0034] (4) The present invention adopts a scheme of connecting a lightning arrester in parallel on the low-voltage side (380V). The cost of a low-voltage lightning arrester (below 3kV) is about several hundred yuan, which can protect expensive equipment such as diesel generators (the cost of diesel generators ranges from tens of thousands to hundreds of thousands of yuan) at a relatively low cost. It overcomes the defect that the existing technical scheme adopts a high-voltage lightning arrester in parallel on the high-voltage side to suppress the closing surge current. The cost of the high-voltage lightning arrester (110kV and above, below 220kV) is about several thousand yuan, which is relatively expensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic flow chart of the present invention;

[0036] Figure 2 is a schematic diagram of the electromagnetic transient simulation model established in step 1 of the present invention;

[0037] Figure 3 The waveforms of the AC current and AC voltage on the diesel generator side of the pre-excitation transformer power supply side before and after S1 is closed in step 2 of the present invention;

[0038] Figure 4 yes Figure 3 AC current and AC voltage waveforms on the diesel generator side of the pre-excitation transformer power supply side within 50ms after S1 is closed (enlarged view);

[0039] Figure 5 This is a schematic diagram of adding a zinc oxide arrester between phases of the diesel generator on the power supply side of the pre-excitation transformer in step 4 of the present invention (i.e., an additional circuit diagram for suppressing excitation inrush current of the present invention);

[0040] Figure 6 It is a schematic diagram of the effect of preventing the high-voltage magnetically controlled shunt reactor from causing a closing inrush current that endangers the safety of electrical equipment on the power supply side of the pre-excitation transformer, as proposed by the present invention. DETAILED DESCRIPTION

[0041] The following detailed description of the embodiments of the present invention is given in conjunction with the accompanying drawings, which do not limit the present invention but are merely examples. The description makes the advantages of the present invention clearer and easier to understand.

[0042] In response to the problem that the existing MCR is unable to accurately evaluate and effectively suppress the inrush current in the pre-excitation circuit during closing, the present invention utilizes electromagnetic transient simulation software and establishes an electromagnetic transient simulation model based on real equipment parameters that can over-simulate the MCR closing inrush current, thereby quantitatively analyzing the overvoltage and overcurrent conditions of the pre-excitation circuit. Based on the safety margin requirements of the diesel generator, a method is proposed in which zinc oxide lightning arresters are connected in parallel between the three phases of the transformer on the AC side of the pre-excitation circuit to suppress the overvoltage or overcurrent caused by the closing inrush current propagating to the power supply side of the pre-excitation transformer. The method can effectively and accurately identify and suppress the corresponding inrush current problem, thereby ensuring the safety of electrical equipment such as the diesel generator on the power supply side of the pre-excitation transformer.

[0043] See also Figure 2 Step 1 requires building an electromagnetic transient simulation model in electromagnetic transient simulation software based on the electrical connections of existing equipment. This equipment includes a high-voltage magnetically controlled shunt reactor (MCR), a pre-excitation rectifier bridge, a pre-excitation transformer, a diesel generator, a main excitation rectifier bridge, a main excitation transformer, a fifth-order filter, a closing switch S1 between the MCR and the line, a pre-excitation transfer switch S2, and a pre-excitation AC power switch S3. The parameters of each device in the electromagnetic transient simulation model must be set according to their actual parameters.

[0044] Step 2, set the closing switch S1 between the MCR and the line in the electromagnetic transient simulation model to be in the open state, and the pre-excitation switching switch S2 and the pre-excitation AC power switch S3 to be in the closed state, and pre-excitation the MCR. At any time after the pre-excitation process is completed, close the closing switch S1 between the MCR and the line, and open the pre-excitation AC power switch S3 after Δt time. This Δt time includes the voltage detection time Δt1, the control device exit time Δt2, the action time Δt3 of the switch S3 and the delay time Δt4 for avoiding the DC current, satisfying Δt=Δt1+Δt2+Δt3+Δt4. Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer before and after S1 is closed, as shown Figure 3 After S1 is closed, record the overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer, as shown in the figure. Figure 4 shown.

[0045] Step 3: The diesel generator's permitted short-term withstand current is Iw, and its permitted short-term withstand overvoltage is Uw. Set the diesel generator's overcurrent safety factor, Ki, and overvoltage safety factor, Ku. If Iy exceeds the product of Ki and Iw, or Uy exceeds the product of Ku and Uw, indicating an inrush current hazard on the power supply side of the pre-excitation transformer, proceed to Step 4; otherwise, jump to Step 6.

[0046] Step 4: Select a zinc oxide lightning arrester with a reference voltage not less than Uw and an absorbed energy not less than 0.3×Uw×Iw×Δt, and connect one zinc oxide lightning arrester between every two phases of the diesel generator on the power supply side of the pre-excitation transformer, such as Figure 5 As shown, it absorbs overvoltage and suppresses overcurrent;

[0047] Step 5: Connect the zinc oxide arrester model in step 4 to the electromagnetic transient simulation model in step 1. The volt-ampere characteristic parameters of the arrester simulation model are taken from its real volt-ampere characteristic curve, and jump to step 2.

[0048] Step 6, such as Figure 6 As shown in the figure, the MCR closing inrush current will not cause electrical damage to the power supply side of the pre-excitation transformer, and the equipment on the power supply side of the pre-excitation transformer can operate safely (such as Figure 1 shown).

[0049] Figure 2 、 Figure 3 、 Figure 4 and Figure 6 The shading in the figure is the shading that comes with the simulation software.

[0050] In order to more clearly illustrate the advantages of the method for identifying and suppressing the hazard of closing inrush current on the power supply side of a high-voltage magnetically controlled shunt reactor pre-excitation transformer described in the present invention compared with the prior art, the staff compared the two technical solutions. The comparison results are shown in Table 1 below:

[0051] Table 1 Comparison results

[0052]

[0053]

[0054] It can be seen from Table 1 above that, compared with the prior art, the method for identifying and suppressing the hazard of closing inrush current on the power supply side of the high-voltage magnetically controlled shunt reactor pre-excitation transformer described in the present invention can prevent the closing inrush current of the high-voltage magnetically controlled shunt reactor from propagating to the power supply side of the pre-excitation transformer. The present invention allows a certain amount of closing inrush current to pass through, and only starts the additional circuit with a lightning arrester when the closing inrush current exceeds the margin or threshold. This can not only protect the electrical safety of the low-voltage side equipment, but also reduce the loss of the power grid with large load changes and improve the power supply quality, while improving economic and social benefits. The identification and suppression accuracy is high, and the cost of the solution of connecting a lightning arrester in parallel on the low-voltage side is low. This overcomes the problem that the prior art directly suppresses the occurrence of closing inrush current by connecting a high-voltage lightning arrester in parallel on the high-voltage side, which is costly and cannot avoid the closing inrush current from briefly acting on the power supply side due to delay, which may damage the diesel generator, and the identification and suppression accuracy is not high.

[0055] Example

[0056] The present invention is now described in detail using an MCR project on a PSCAD / EMTDC platform as an example. PSCAD / EMTDC is a professional software for developing full-featured and technologically advanced simulation and analysis of electromagnetic transients in power systems, and is currently available.

[0057] See also Figure 2 First, an electromagnetic transient simulation model must be established in the electromagnetic transient simulation software based on the electrical connection method of the existing equipment. These equipment include the magnetically controlled shunt reactor (MCR), pre-excitation rectifier bridge, pre-excitation transformer, diesel generator, main excitation rectifier bridge, main excitation transformer, 5th order filter, closing switch S1 between the MCR and the line, pre-excitation transfer switch S2, and pre-excitation AC power switch S3. The parameters of each device in the electromagnetic transient simulation model must be set according to the actual parameters of each device. The parameters of each device are shown in the following table:

[0058] Device Name Device parameters MCR Voltage 400kV, capacity 40Mvar Pre-excited rectifier bridge 380V diode rectifier bridge, rated current 600A Pre-excitation transformer Capacity 30kVA, voltage ratio 0.4 / 0 / 03kV, connection group Yd11 diesel generators Rated voltage 380V, rated current 270A Main excitation rectifier bridge 380V diode rectifier bridge, rated current 2000A Main excitation transformer Capacity 1400kVA, voltage ratio 12 / 0.4kV, connection group Yd11 5th order filter Rated voltage 12kV, rated capacity 5.64Mvar, inductance 9.43mH Closing switch S1 Rated voltage 400kV, rated current 600A Closing switch S2 Rated voltage 24kV, rated current 3kA Closing switch S3 Rated voltage 400V. Rated current 350A

[0059] Secondly, set the closing switch S1 between the MCR and the line in the electromagnetic transient simulation model to be in the open state, and the pre-excitation switching switch S2 and the pre-excitation AC power switch S3 to be in the closed state to pre-excite the MCR. After the pre-excitation process is completed within 2s, at any time, taking the 5th second of the simulation time as an example, close the closing switch S1 between the MCR and the line, and open the pre-excitation AC power switch S3 after Δt = 100 milliseconds. These 100 milliseconds include the voltage detection time Δt1 = 30 milliseconds, the control device exit time Δt2 = 20 milliseconds, the action time of the switch S3 Δt3 = 20 milliseconds and the delay time for avoiding the DC current Δt4 = 30 milliseconds, satisfying Δt = Δt1 + Δt2 + Δt3 + Δt4. Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer before and after S1 is closed, as shown Figure 3 As shown in the figure, it can be seen that after S1 is closed, the AC side of the diesel generator generates an overcurrent and the AC voltage also rises. The overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer within 50m after S1 is closed are recorded, as shown in the figure. Figure 4 As shown, it can be obtained that after S1 is closed, an overcurrent occurs in the B phase of the diesel generator, and the B phase voltage also increases. After observation, Iy is recorded as the B phase current amplitude of 320A, and Uy is the B phase overvoltage of 390V.

[0060] Figure 3 and Figure 4 It is shown that by establishing an electromagnetic transient simulation model close to the actual situation in the present invention, the phenomenon of electrical safety hazards caused by the transient process of the high-voltage magnetically controlled shunt reactor closing surge current propagating to the power supply side of the pre-excitation transformer can be accurately identified (the figure shows the overcurrent situation).

[0061] Next, it is known that the diesel generator's allowable short-term withstand current Iw is 350A, and its allowable short-term withstand overvoltage Uw is 1500V. Set the diesel generator's overcurrent safety factor Ki to 0.9 and its overvoltage safety factor Ku to 0.85. It can be seen that the product of Ki and Iw is 315A, which is less than Iy's value of 320A, while the product of Ku and Uw is 1275V, which is greater than Uy's value of 390V. Therefore, after S1 is closed, the AC current on the power supply side of the pre-excitation transformer may pose an electrical safety threat to the diesel generator.

[0062] Then, we calculate Uw = 1500V, 0.3×Uw×Iw×Δt = 15.75kJ, so we select a zinc oxide lightning arrester with a reference voltage of 1500V (Uw value) and an absorbed energy of 30kJ (higher than 0.3×Uw×Iw×Δt), and connect a zinc oxide lightning arrester between every two phases of the diesel generator power supply panel on the power supply side of the pre-excitation transformer, as shown in the figure. Figure 5 As shown, it absorbs overvoltage and suppresses overcurrent;

[0063] Then, a zinc oxide lightning arrester model is connected to the electromagnetic transient simulation model, and the volt-ampere characteristic parameters of the lightning arrester simulation model are taken from its real volt-ampere characteristic curve;

[0064] Finally, the simulation model is re-run for the closing inrush current simulation. At this time, the AC current waveform of the diesel generator on the power supply side of the pre-excitation transformer is as follows: Figure 6 As shown ( Figure 6 This shows that the arrester parameter selection and installation scheme proposed in the present invention are effective in avoiding the electrical safety hazards of the low-voltage side equipment caused by the closing inrush current of the high-voltage magnetically controlled shunt reactor. It can be seen that the overcurrent amplitude is about 150A, which is less than the product of the overcurrent safety factor and the short-time withstand current of the diesel generator, 315A, and the voltage amplitude is also less than the product of the overvoltage safety factor and the short-time withstand voltage of the diesel generator. Therefore, the MCR closing inrush current will not cause overcurrent or overvoltage hazards to the equipment on the power supply side of the pre-excitation transformer, and the equipment on the power supply side of the pre-excitation transformer can operate safely.

[0065] Any content not described in detail in this specification is prior art known to those skilled in the art. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, to the extent such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to encompass such modifications and variations.

[0066] Other parts not described belong to the prior art.

Claims

1. A method for identifying and suppressing the hazard of closing inrush current on the power supply side of an MCR pre-excitation transformer, characterized by: The following steps are included: Step 1: Establish electromagnetic transient simulation model of each device; Step 2: Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor MCR and the line is closed, and record the overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed; Step 3: Set the critical threshold of current and the critical threshold of voltage; When Iy exceeds the critical current threshold, it indicates that the inrush current hazard occurs on the power supply side of the pre-excitation transformer, and the process goes to step 4; otherwise, the process jumps to step 6; And / or, when Uy exceeds the critical voltage threshold, it indicates that the inrush current pre-excitation transformer power supply side hazard occurs, and the process goes to step 4; otherwise, the process jumps to step 6; Step 4: Add an additional circuit for suppressing excitation inrush current on the power supply side of the pre-excitation transformer to absorb overvoltage and suppress overcurrent; Step 5: Connect the additional circuit for excitation inrush current suppression in step 4 to the electromagnetic transient simulation model in step 1, and jump to step 2; Step 6: The closing inrush current of the high-voltage magnetically controlled shunt reactor will not harm the equipment on the power supply side of the pre-excitation transformer, and the equipment on the power supply side of the pre-excitation transformer can operate safely; In step 1, the method for establishing the electromagnetic transient simulation model of each device is as follows: An electromagnetic transient simulation model is established in the electromagnetic transient simulation software, including the high-voltage magnetically controlled shunt reactor, pre-excitation rectifier bridge, pre-excitation transformer, diesel generator, main excitation rectifier bridge, main excitation transformer, 5th order filter, closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line, pre-excitation transfer switch S2, and pre-excitation AC power switch S3. The parameters of each device in the electromagnetic transient simulation model are set according to the actual parameters of each device; In step 2, the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is set to an open state, and the pre-excitation switching switch S2 and the pre-excitation AC power supply switch S3 are set to a closed state; At any time t0 after the pre-excitation process ends, close the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line. After a period of time Δt, open the pre-excitation AC power switch S3 to simulate the electromagnetic transient scenario on the power supply side of the pre-excitation transformer after the high-voltage magnetically controlled shunt reactor is connected in parallel. The value of Δt is composed of the voltage detection time Δt1, the control device exit time Δt2, the action time Δt3 of the pre-excitation AC power switch S3, and the DC current avoidance delay time Δt4, satisfying Δt=Δt1+Δt2+Δt3+Δt4; Observe the current waveform and voltage waveform on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed, and record the overcurrent amplitude Iy and overvoltage amplitude Uy on the power supply side of the pre-excitation transformer after the closing switch S1 between the high-voltage magnetically controlled shunt reactor and the line is closed.

2. The method for identifying and suppressing the hazard of closing inrush current on the power supply side of an MCR pre-excitation transformer according to claim 1 is characterized in that: Set the diesel generator overcurrent safety factor Ki and overvoltage safety factor Ku; The critical threshold of the current is the product of the short-term overcurrent Iw that the diesel generator on the AC side of the pre-excitation transformer is allowed to withstand and the diesel generator overcurrent safety factor Ki; The critical threshold of voltage is the product of the overvoltage allowed to be tolerated for a short time, Uw and the overvoltage safety factor Ku; When Iy is greater than or equal to the product of Ki and Iw, and / or Uy is greater than or equal to the product of Ku and Uw, proceed to step 4; otherwise, jump to step 6.

3. The method for identifying and suppressing the hazard of closing inrush current on the power supply side of an MCR pre-excitation transformer according to claim 2 is characterized in that: In step 4, the setting method of the additional circuit for excitation inrush current suppression is as follows: A zinc oxide arrester is connected between every two phases of the diesel generator power supply line on the power supply side of the pre-excitation transformer to absorb overvoltage and suppress overcurrent.

4. The method for identifying and suppressing the hazard of closing inrush current on the power supply side of an MCR pre-excitation transformer according to claim 3 is characterized in that: In step 5, the reference voltage of the selected zinc oxide lightning arrester is greater than or equal to Uw, and the maximum absorbed energy is greater than or equal to 0.3×Uw×Iw×Δt. The zinc oxide lightning arrester model is connected to the electromagnetic transient simulation model in step 1; The volt-ampere characteristic parameters of the arrester simulation model are taken from its real volt-ampere characteristic curve.

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