Current protection circuit based on differential protection and control method thereof

Abstract

The invention relates to the technical field of circuit protection, and discloses a current protection circuit based on differential protection and a control method thereof. The circuit comprises a power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load, the first end of the first circuit breaker is electrically connected with the power supply module; the second end of the first circuit breaker is electrically connected with the first end of the first transformer; the second end of the first transformer is electrically connected with the first end of the second circuit breaker; the second end of the second circuit breaker is electrically connected with the load; the first end of the first relay protection module is electrically connected with the first end of the first transformer; the second end of the first relay protection module is electrically connected with the second end of the first transformer. According to the circuit, whether a first transformer breaks down or not is judged in real time through a first relay protection module, and when the first transformer breaks down, connection between the first transformer and the circuit is disconnected. The circuit can be effectively protected when a fault occurs, the response rate of the circuit is increased, and the safety of the circuit is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit protection, and in particular to a current protection circuit based on differential protection and a control method thereof. Background Art

[0002] Power transformers (PTRF) are important equipment in the power transmission network, which manages the transfer of large amounts of power from one line to another while maintaining the frequency. Power transformers work on the principle of electromagnetic induction and are generally used to step up and down the voltage in power stations and distribution substations. The working principle of PTRF is Faraday's law of electromagnetic induction. PTRF electrical faults are considered the most serious disturbances in the power system, so the protection of transformers is very important.

[0003] There are different types of protection schemes for power transformers, such as overcurrent, distance, Buchholz relay and differential protection. However, the current protection schemes have low sensitivity and cannot protect the transformer and circuit in time when a PTRF electrical fault occurs. Summary of the invention

[0004] The present invention provides a current protection circuit based on differential protection and a control method thereof, which effectively protects the circuit in case of a fault, speeds up the response rate of the circuit and improves the safety of the circuit.

[0005] In order to solve the above technical problems, the present invention provides a current protection circuit based on differential protection, comprising: a power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load;

[0006] The first end of the first circuit breaker is electrically connected to the power supply module;

[0007] The second end of the first circuit breaker is electrically connected to the first end of the first transformer;

[0008] The second end of the first transformer is electrically connected to the first end of the second circuit breaker;

[0009] The second end of the second circuit breaker is electrically connected to the load;

[0010] The first end of the first relay protection module is electrically connected to the first end of the first transformer;

[0011] The second end of the first relay protection module is electrically connected to the second end of the first transformer.

[0012] Further, the first relay protection module includes: a first differential relay, a first current transformer and a second current transformer;

[0013] The first end of the first current transformer is electrically connected to the first circuit breaker;

[0014] The second end of the first current transformer is electrically connected to the first end of the first differential relay;

[0015] The second end of the first differential relay is electrically connected to the first end of the second current transformer;

[0016] The second end of the second current transformer is electrically connected to the second circuit breaker.

[0017] Furthermore, the current protection circuit based on differential protection further includes:

[0018] The current ratings of the first current transformer and the second current transformer are determined by the full rated current of the first transformer and the transformer turns ratio, specifically:

[0019]

[0020] In the formula, I Max_Load(Pri / Sec) I is the current rating of the first current transformer and the second current transformer; FL-(Pri / Sec) is the full rated current of the first transformer; N (Pri / Sec) is the transformer turns ratio of the first transformer.

[0021] Furthermore, the current protection circuit based on differential protection further includes:

[0022] The full rated current of the first transformer is determined by the rated capacity and rated voltage of the first transformer, specifically:

[0023]

[0024] In the formula, I FL-(Pri / Sec) is the full rated current of the first transformer; S (VA) is the rated capacity of the first transformer; V P / S is the rated voltage of the first transformer.

[0025] Furthermore, the current protection circuit based on differential protection further includes: a second transformer, a second relay protection module, a third circuit breaker and a fourth circuit breaker;

[0026] The first end of the third circuit breaker is electrically connected to the power supply module;

[0027] The second end of the third circuit breaker is electrically connected to the first end of the second transformer;

[0028] The second end of the second transformer is electrically connected to the first end of the fourth circuit breaker;

[0029] The second end of the fourth circuit breaker is electrically connected to the load;

[0030] The first end of the second relay protection module is electrically connected to the first end of the second transformer;

[0031] The second end of the second relay protection module is electrically connected to the second end of the second transformer.

[0032] Furthermore, the second relay protection module comprises: a second differential relay, a third current transformer and a fourth current transformer;

[0033] The first end of the third current transformer is electrically connected to the third circuit breaker;

[0034] The second end of the third current transformer is electrically connected to the first end of the second differential relay;

[0035] The second end of the second differential relay is electrically connected to the first end of the fourth current transformer;

[0036] The second end of the fourth current transformer is electrically connected to the fourth circuit breaker.

[0037] Accordingly, the present invention provides a control method for a current protection circuit based on differential protection, which is used to control the current protection circuit based on differential protection described above, comprising:

[0038] Calculating a first differential current and a first braking current of a first transformer in real time by using a first relay protection module, and judging whether the first transformer is faulty according to a comparison relationship between the first differential current and the first braking current;

[0039] When it is determined that the first transformer fails, the first circuit breaker and the second circuit breaker are switched to an open state.

[0040] Further, the first relay protection module is used to calculate the first differential current and the first braking current of the first transformer in real time, and according to the comparison relationship between the first differential current and the first braking current, it is determined whether the first transformer is faulty, specifically:

[0041] obtaining a starting current of the first transformer;

[0042] Using a first current transformer to collect the primary winding current of the first transformer in real time;

[0043] Using the second current transformer to collect the secondary winding current of the first transformer in real time;

[0044] Calculating the differential current and the braking current of the first transformer respectively according to the primary winding current and the secondary winding current of the first transformer;

[0045] When the differential current of the first transformer is greater than the starting current of the first transformer and greater than a preset multiple value of the braking current of the first transformer, it is determined that the first transformer is faulty.

[0046] Further, the differential current and the braking current of the first transformer are calculated respectively according to the primary winding current and the secondary winding current of the first transformer, specifically:

[0047] Calculating the differential current of the first transformer using a preset differential current calculation formula according to the primary winding current and the secondary winding current of the first transformer;

[0048] The preset differential current calculation formula is specifically:

[0049] I OP =(|I W1 |+|I W2 |)

[0050] In the formula, I OP is the differential current; I W1 is the primary winding current; I W2 is the secondary winding current;

[0051] Calculating the braking current of the first transformer using a preset braking current calculation formula according to the primary winding current and the secondary winding current of the first transformer;

[0052] The preset braking current calculation formula is specifically:

[0053]

[0054] In the formula, I RT is the braking current; I W1 is the primary winding current; I W2 is the secondary winding current; θ is the angle between the primary winding current and the secondary winding current.

[0055] Furthermore, the control method of the current protection circuit based on differential protection also includes:

[0056] Calculate the second differential current and the second braking current of the second transformer in real time by using the second relay protection module, and determine whether the second transformer is faulty according to the comparison relationship between the second differential current and the second braking current;

[0057] When it is determined that the second transformer fails, the third circuit breaker and the fourth circuit breaker are switched to an open state.

[0058] The present invention provides a current protection circuit based on differential protection and a control method thereof, the circuit comprising: a power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load; the first end of the first circuit breaker is electrically connected to the power supply module; the second end of the first circuit breaker is electrically connected to the first end of the first transformer; the second end of the first transformer is electrically connected to the first end of the second circuit breaker; the second end of the second circuit breaker is electrically connected to the load; the first end of the first relay protection module is electrically connected to the first end of the first transformer; the second end of the first relay protection module is electrically connected to the second end of the first transformer. The circuit uses the first relay protection module to determine in real time whether the first transformer is faulty, and disconnects the first transformer from the circuit when the first transformer is faulty. The present invention can effectively protect the circuit in the event of a fault, speed up the response rate of the circuit, and improve the safety of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A first structural schematic diagram of a current protection circuit based on differential protection provided by the present invention;

[0060] Figure 2 A second structural schematic diagram of a current protection circuit based on differential protection provided by the present invention;

[0061] Figure 3 A structural schematic diagram of a dual-winding differential module provided by the present invention;

[0062] Figure 4 A third structural schematic diagram of the current protection circuit based on differential protection provided by the present invention;

[0063] Figure 5 A fourth structural schematic diagram of the current protection circuit based on differential protection provided by the present invention;

[0064] Figure 6 A flow chart of an embodiment of a control method for a current protection circuit based on differential protection provided by the present invention;

[0065] Figure 7 A flow chart of another embodiment of a control method for a current protection circuit based on differential protection provided by the present invention;

[0066] Figure 8 A schematic structural diagram of an embodiment of an operating network model of a current protection circuit based on differential protection provided by the present invention.

[0067] The reference numerals in the accompanying drawings of the specification are as follows:

[0068] B: busbar; G: generator; PTRF: power transformer; CB: circuit breaker; CT: current transformer; SCB: busbar circuit breaker; L: load; SEL487E: transformer protection relay; MICOMP645: relay protection device. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0070] The flowcharts shown in the accompanying drawings are only examples and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may also be decomposed, combined or partially merged, so the actual execution order may change according to actual conditions.

[0071] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0072] See also Figure 1 , is a first structural schematic diagram of a current protection circuit based on differential protection provided by the present invention, the circuit comprising a power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load;

[0073] The first end of the first circuit breaker is electrically connected to the power supply module;

[0074] The second end of the first circuit breaker is electrically connected to the first end of the first transformer;

[0075] The second end of the first transformer is electrically connected to the first end of the second circuit breaker;

[0076] The second end of the second circuit breaker is electrically connected to the load;

[0077] The first end of the first relay protection module is electrically connected to the first end of the first transformer;

[0078] The second end of the first relay protection module is electrically connected to the second end of the first transformer.

[0079] In an embodiment of the present invention, a relay protection module is configured in parallel with the transformer in the circuit, and a circuit breaker is configured at both ends of the transformer. When an electrical fault occurs in the transformer, a trip signal is generated by the relay protection module to control the circuit breakers at both ends of the transformer to disconnect, thereby protecting the safety of the transformer and the circuit.

[0080] Further, in the embodiments of the present invention, see Figure 2 , is a second structural schematic diagram of a current protection circuit based on differential protection provided by the present invention, wherein the first relay protection module comprises: a first differential relay, a first current transformer and a second current transformer;

[0081] The first end of the first current transformer is electrically connected to the first circuit breaker;

[0082] The second end of the first current transformer is electrically connected to the first end of the first differential relay;

[0083] The second end of the first differential relay is electrically connected to the first end of the second current transformer;

[0084] The second end of the second current transformer is electrically connected to the second circuit breaker.

[0085] In an embodiment of the present invention, the relay protection module includes a differential relay and two current transformers, the two current transformers are connected in series at both ends of the differential relay and in parallel with the transformer. The two current transformers are used to collect the primary winding current and the secondary winding current of the transformer respectively, and the primary winding current and the secondary winding current of the transformer are analyzed by the differential relay. When it is judged that there is an imbalance in the current, the differential relay will be activated and the circuit breaker corresponding to the transformer in the circuit will be turned on and off. As the main protection of the transformer, the differential relay can provide reliable and fast protection for the transformer.

[0086] In the embodiment of the present invention, the differential relay has the communication function of the IEC 61850 standard. The IEC 61850 standard provides a universal communication platform, which enables the current protection circuit to exchange data quickly and accurately. Therefore, using the IEC 61850 standard communication in the current protection circuit can improve the speed, reliability and accuracy of information transmission of the current protection circuit.

[0087] As an example of an embodiment of the present invention, see Figure 3 , is a structural schematic diagram of a dual-winding differential module provided by the present invention, Figure 3 I W1 is the primary winding current, I W2is the secondary winding current, CT1 and CT2 are current transformers. The dual-winding differential module is two current transformers connected in series with a differential relay. The dual-winding differential module is connected in parallel with the power transformer. The differential relay can respond to faults occurring in the transformer differential protection zone. When the current of the power transformer is unbalanced, the power transformer is differentially protected.

[0088] Optionally, currently transformer failures account for 10% of all power system failures, of which transformer winding short circuits account for 70%. Therefore, connecting a relay protection module in parallel to the transformer in the circuit to protect the transformer winding short circuit failure can greatly improve the reliability of the circuit.

[0089] Furthermore, in an embodiment of the present invention, the current protection circuit based on differential protection further includes:

[0090] The current ratings of the first current transformer and the second current transformer are determined by the full rated current of the first transformer and the transformer turns ratio, specifically:

[0091]

[0092] In the formula, I Max_Load(Pri / Sec) I is the current rating of the first current transformer and the second current transformer; FL-(Pri / Sec) is the full rated current of the first transformer; N (Pri / Sec) is the transformer turns ratio of the first transformer.

[0093] In the embodiment of the present invention, in order to ensure that the secondary current of the current transformer is consistent, when selecting the current transformer in the relay protection module, it is necessary to ensure that the current rating of the current transformer is consistent with the current rating of the transformer to which it is connected. The current rating of the current transformer can be determined according to the full rated current of the transformer to which it is connected and the transformer turns ratio.

[0094] Optionally, since current transformer ratios are currently available on the market with uniform ratings, there may be inconsistencies with the calculated expected ratings of the current transformer. Therefore, the primary current transformer ratio is usually limited to current transformers with standard ratios currently available on the market. For a CT ratio (N) that matches the transformer rating, there is usually only one turn (1) on the primary side and more turns on the secondary side. The primary CT turns ratio is usually between 120% and 150% of the load current. Therefore, the formula Pri / Sec Ratio =(137%) (I FL-W(Pri / Sec) )Calculate the primary CT ratio (Pri Ratio ) and secondary CT ratio (Sec Ratio ).

[0095] Furthermore, in an embodiment of the present invention, the current protection circuit based on differential protection further includes:

[0096] The full rated current of the first transformer is determined by the rated capacity and rated voltage of the first transformer, specifically:

[0097]

[0098] In the formula, I FL-(Pri / Sec) is the full rated current of the first transformer; S (VA) is the rated capacity of the first transformer; V P / S is the rated voltage of the first transformer.

[0099] In the embodiment of the present invention, the full rated current of the transformer can be calculated according to the rated capacity and rated voltage of the transformer, and the rated voltage can be the primary side rated voltage or the secondary side rated voltage.

[0100] Optionally, the current transformer ratio does not always correspond to the transformer winding ratio, so the current transformer correction factor can be selected according to the rated current of the transformer:

[0101]

[0102] Where TAP HV / LV(Pri / Sec) is the current transformer correction factor; N Pri / Sec-stardard is the rated turns ratio of the transformer; N Pri / Sec-Calculated is the actual transformation ratio of the transformer.

[0103] After determining the current transformer correction coefficient, the primary current ratio and secondary current ratio of the current transformer can be further adjusted to ensure that the actual measured current matches the rated current of the transformer, thereby reducing the current imbalance caused by inaccurate current transformer ratio and avoiding false operation of the differential protection device.

[0104] Further, in the embodiments of the present invention, see Figure 4 , is a third structural schematic diagram of the current protection circuit based on differential protection provided by the present invention, the current protection circuit based on differential protection further includes: a second transformer, a second relay protection module, a third circuit breaker and a fourth circuit breaker;

[0105] The first end of the third circuit breaker is electrically connected to the power supply module;

[0106] The second end of the third circuit breaker is electrically connected to the first end of the second transformer;

[0107] The second end of the second transformer is electrically connected to the first end of the fourth circuit breaker;

[0108] The second end of the fourth circuit breaker is electrically connected to the load;

[0109] The first end of the second relay protection module is electrically connected to the first end of the second transformer;

[0110] The second end of the second relay protection module is electrically connected to the second end of the second transformer.

[0111] In the embodiment of the present invention, if there is only one transformer in the circuit, when the transformer fails, power supply to the load will stop. However, if two transformers are arranged in parallel in the circuit, when one transformer fails, the other transformer can continue to supply power to the load, thereby improving the reliability of the circuit. By connecting two transformers in parallel in the current protection circuit, the cost of maintaining spare parts can be reduced.

[0112] Further, in the embodiments of the present invention, see Figure 5 , is a fourth structural schematic diagram of a current protection circuit based on differential protection provided by the present invention, wherein the second relay protection module comprises: a second differential relay, a third current transformer and a fourth current transformer;

[0113] The first end of the third current transformer is electrically connected to the third circuit breaker;

[0114] The second end of the third current transformer is electrically connected to the first end of the second differential relay;

[0115] The second end of the second differential relay is electrically connected to the first end of the fourth current transformer;

[0116] The second end of the fourth current transformer is electrically connected to the fourth circuit breaker.

[0117] In an embodiment of the present invention, the relay protection module includes a differential relay and two current transformers, the two current transformers are connected in series at both ends of the differential relay and in parallel with the transformer. The two current transformers are used to collect the primary winding current and the secondary winding current of the transformer respectively, and the primary winding current and the secondary winding current of the transformer are analyzed by the differential relay. When it is judged that there is an imbalance in the current, the differential relay will be activated and the circuit breaker corresponding to the transformer in the circuit will be turned on and off. As the main protection of the transformer, the differential relay can provide reliable and fast protection for the transformer.

[0118] In the embodiment of the present invention, two transformers are connected in parallel in the current protection circuit, and when one transformer fails, the other transformer can be used to supply power to the load. A relay protection module is connected in parallel to each of the two transformers, and when an electrical fault occurs in the transformer, a trip signal can be generated in time to control the circuit breakers at both ends of the corresponding transformer to disconnect, thereby protecting the safety of the transformer and the circuit.

[0119] Accordingly, see Figure 6 , is a flow chart of an embodiment of a control method of a current protection circuit based on differential protection provided by the present invention, the method includes steps 101 to 102, each step is specifically as follows:

[0120] Step 101: Utilize a first relay protection module to calculate a first differential current and a first braking current of a first transformer in real time, and determine whether the first transformer is faulty based on a comparison between the first differential current and the first braking current.

[0121] In the embodiment of the present invention, the primary winding current and the secondary winding current are theoretically of the same amplitude and opposite phase angle. However, due to the loss in the differential protection zone, the CT excitation current and the difference in the primary / secondary transformation ratio, in practice, there will be only a slight difference between the primary winding current and the secondary winding current. The principle of the control method of the current protection circuit based on differential protection is: by receiving the primary winding current input and the secondary winding current input of the transformer, the transformer is protected from the influence of internal faults. Under normal circumstances or in the event of an external fault, the phase sum of the primary winding current and the secondary winding current is zero, but it is not zero in the event of a fault. In the event of a fault, the trip signal sent by the differential relay causes the circuit breaker in the circuit to disconnect, thereby protecting the transformer and the circuit.

[0122] Further, in an embodiment of the present invention, the first relay protection module is used to calculate the first differential current and the first braking current of the first transformer in real time, and according to the comparison relationship between the first differential current and the first braking current, it is determined whether the first transformer is faulty, specifically:

[0123] obtaining a starting current of the first transformer;

[0124] Using a first current transformer to collect the primary winding current of the first transformer in real time;

[0125] Using the second current transformer to collect the secondary winding current of the first transformer in real time;

[0126] Calculating the differential current and the braking current of the first transformer respectively according to the primary winding current and the secondary winding current of the first transformer;

[0127] When the differential current of the first transformer is greater than the starting current of the first transformer and greater than a preset multiple value of the braking current of the first transformer, it is determined that the first transformer is faulty.

[0128] In the embodiment of the present invention, two current transformers connected in series with the protected transformer can be used to collect the primary winding current and the secondary winding current of the protected transformer respectively, and the differential current (also called the working current) of the protected transformer can be calculated using the phase sum of the primary winding current and the secondary winding current. Only when the calculated differential current is greater than the starting current and greater than the preset slope percentage of the braking current, it is determined that the protected transformer has a fault.

[0129] Further, in the embodiment of the present invention, the differential current and the braking current of the first transformer are calculated respectively according to the primary winding current and the secondary winding current of the first transformer, specifically:

[0130] Calculating the differential current of the first transformer using a preset differential current calculation formula according to the primary winding current and the secondary winding current of the first transformer;

[0131] The preset differential current calculation formula is specifically:

[0132] I OP =(|I W1 |+|I W2 |)

[0133] In the formula, I OP is the differential current; I W1 is the primary winding current; I W2 is the secondary winding current;

[0134] Calculating the braking current of the first transformer using a preset braking current calculation formula according to the primary winding current and the secondary winding current of the first transformer;

[0135] The preset braking current calculation formula is specifically:

[0136]

[0137] In the formula, I RT is the braking current; I W1 is the primary winding current; I W2 is the secondary winding current; θ is the angle between the primary winding current and the secondary winding current.

[0138] In the embodiment of the present invention, the braking current of the protected transformer can be calculated according to the formula: Calculated, where K is the preset compensation coefficient, generally set to 0.5 or 1. This braking current calculation method is relatively simple, but the accuracy is not high, so it can be improved to use the formula Calculate the braking current of the protected transformer.

[0139] In the embodiment of the present invention, after the braking current of the protected transformer is calculated, it is compared with the starting current and the braking current respectively, and when the differential current is greater than the starting current and greater than the preset multiple value of the braking current, it is determined that the protected transformer is faulty. D >SLP(I RT ), the differential current is determined to be greater than the preset multiple of the braking current. The SLP in the formula is the ratio braking coefficient, which is used to determine whether the differential current exceeds the set fault current. The ratio braking coefficient is preset according to the specific operating conditions, equipment characteristics and requirements of the protected transformer to ensure that the differential protection operates correctly in the event of a fault and does not malfunction due to external disturbances.

[0140] Step 102: When it is determined that the first transformer fails, the first circuit breaker and the second circuit breaker are switched to an open state.

[0141] In the embodiment of the present invention, when it is determined that the protected transformer is faulty, the differential relay generates a trip signal to control the two circuit breakers connected to the protected transformer to be disconnected, thereby protecting the circuit and the faulty transformer.

[0142] Further, in the embodiments of the present invention, see Figure 7 , is a flow chart of another embodiment of a control method of a current protection circuit based on differential protection provided by the present invention, the method further includes steps 201 to 202, each step is specifically as follows:

[0143] Step 201: Utilize a second relay protection module to calculate in real time a second differential current and a second braking current of a second transformer, and determine whether the second transformer is faulty based on a comparison between the second differential current and the second braking current.

[0144] Step 202: When it is determined that the second transformer fails, the third circuit breaker and the fourth circuit breaker are switched to an open state.

[0145] In an embodiment of the present invention, the control principle of the second relay protection module is the same as the control principle of the first relay protection module. The current transformer connected to the second transformer is used to collect the primary winding current and the secondary winding current of the second transformer in real time, and then the differential current and the braking current of the second transformer are calculated by the formula. According to the magnitude relationship between the differential current and the braking current of the second transformer and the starting current, it is determined whether the second transformer is faulty. When it is determined that the second transformer is faulty, the second differential relay in the second relay protection module is controlled to generate a tripping signal to disconnect the third circuit breaker and the fourth circuit breaker connected to the second transformer, thereby protecting the second transformer and the circuit.

[0146] As an example of an embodiment of the present invention, see Figure 8 , is a structural schematic diagram of an embodiment of the operation network model of the current protection circuit based on differential protection provided by the present invention. Considering the system CT, CT mismatch, CT saturation, CT polarity, vector group and CT star connection configuration, the IEC standard uses vector groups to classify the high voltage (HV) and low voltage (LV) winding configurations in three-phase transformers. The IEEE9 standard has been modified at bus 6 to add a secondary transmission and distribution part, which consists of 10 buses (nodes), one load, two lines and three transformers. Among them, two transformers (PTRF5 and PTRF6) are connected in parallel and have the same parameters such as voltage ratio / turns ratio and vector group. Using two parallel transformers with specifications of 110 / 22kV and 56MVA and two IEDs (SEL-487E and ALSTOM MiCOM-P645 relays) for differential protection, the relay can respond to faults in less than 20 milliseconds and have communication functions that comply with the IEC 61850 standard.

[0147] The operation network model of the above-mentioned current protection circuit based on differential protection can be used to simulate the hardware-in-the-loop test of the transformer under different fault conditions in real time, which can verify the effect of the current protection circuit under various fault scenarios. This simulation can be combined with CMS156 and CMS 356Omicron amplifiers and completed through RTDS's RSCAD software.

[0148] The current transformers are tested in hardware-in-the-loop in a real-time transformer simulation, which can be tested for different external faults, internal faults, CT saturation and inrush current. During the simulation run, the power system needs to maintain voltage and calculate current.

[0149] For parallel or single transformer simulation, the status of transformer 5 (TRF5) circuit breakers (CB1 and CB2), transformer 6 (TRF6) circuit breakers (CB3 and CB4), and selected busbar circuit breakers (SCB1 to SCB4) are used to determine whether the transformers are connected individually or in parallel. In parallel mode, all circuit breakers will be closed. The following table gives the simulation results of the transformer status when the circuit breakers are internally or externally faulted to determine whether the transformers are connected individually or in parallel. Where 1 = closed and 0 = open.

[0150]

[0151] For external fault simulation, in order to check whether the relay will trip in the event of an external fault, an external fault can be applied to the low-voltage side of the external transformer. The voltage and current waveforms, and all circuit breakers are in the closed state, prove that the system is in parallel mode.

[0152] For internal fault simulation, internal faults often occur, such as phase-to-phase faults, ground faults, turn-to-turn faults, etc. These faults may bring significant risks, so a fast and accurate response mechanism is required to ensure the safety and reliability of the system. In this case, the protection relay must identify the fault and send a trip signal to the CB, instructing it to disconnect and isolate. By introducing an internal fault in the low-voltage core winding of the transformer, the behavior of the protection system in detecting the fault can be analyzed.

[0153] In addition, by evaluating the ability of the SEL487E and MiCOMP645 IED relays to communicate using the IEC61850 standard and send GOOSE-based trip signals when a fault occurs, the effectiveness of the current protection circuit configuration in various fault scenarios can be verified.

[0154] In summary, the embodiment of the present invention provides a current protection circuit based on differential protection and a control method thereof, the circuit comprising: a power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load; the first end of the first circuit breaker is electrically connected to the power supply module; the second end of the first circuit breaker is electrically connected to the first end of the first transformer; the second end of the first transformer is electrically connected to the first end of the second circuit breaker; the second end of the second circuit breaker is electrically connected to the load; the first end of the first relay protection module is electrically connected to the first end of the first transformer; the second end of the first relay protection module is electrically connected to the second end of the first transformer. By connecting the relay protection module in parallel to the transformer, the faulty component can be isolated from the rest of the circuit in the event of a fault, thereby achieving effective protection of the parallel power transformers under various fault conditions, and communicating in the circuit based on the IEC61850 standard, thereby improving the response speed, thereby improving the efficiency of circuit fault processing, and improving the reliability of the circuit.

[0155] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A current protection circuit based on differential protection, characterized in that: include: A power supply module, a first transformer, a first relay protection module, a first circuit breaker, a second circuit breaker and a load; The first end of the first circuit breaker is electrically connected to the power supply module; The second end of the first circuit breaker is electrically connected to the first end of the first transformer; The second end of the first transformer is electrically connected to the first end of the second circuit breaker; The second end of the second circuit breaker is electrically connected to the load; The first end of the first relay protection module is electrically connected to the first end of the first transformer; The second end of the first relay protection module is electrically connected to the second end of the first transformer.

2. The current protection circuit based on differential protection according to claim 1, characterized in that: The first relay protection module comprises: a first differential relay, a first current transformer and a second current transformer; The first end of the first current transformer is electrically connected to the first circuit breaker; The second end of the first current transformer is electrically connected to the first end of the first differential relay; The second end of the first differential relay is electrically connected to the first end of the second current transformer; The second end of the second current transformer is electrically connected to the second circuit breaker.

3. The current protection circuit based on differential protection according to claim 2, characterized in that: Also includes: The current ratings of the first current transformer and the second current transformer are determined by the full rated current of the first transformer and the transformer turns ratio, specifically: In the formula, I Max_Load(Pri / Sec) I is the current rating of the first current transformer and the second current transformer; FL-(Pri / Sec) is the full rated current of the first transformer; N (Pri / Sec) is the transformer turns ratio of the first transformer.

4. The current protection circuit based on differential protection according to claim 3, characterized in that: Also includes: The full rated current of the first transformer is determined by the rated capacity and rated voltage of the first transformer, specifically: In the formula, I FL-(Pri / Sec) is the full rated current of the first transformer; S (VA) is the rated capacity of the first transformer; V P / S is the rated voltage of the first transformer.

5. The current protection circuit based on differential protection according to claim 1, characterized in that: Also includes: a second transformer, a second relay protection module, a third circuit breaker, and a fourth circuit breaker; The first end of the third circuit breaker is electrically connected to the power supply module; The second end of the third circuit breaker is electrically connected to the first end of the second transformer; The second end of the second transformer is electrically connected to the first end of the fourth circuit breaker; The second end of the fourth circuit breaker is electrically connected to the load; The first end of the second relay protection module is electrically connected to the first end of the second transformer; The second end of the second relay protection module is electrically connected to the second end of the second transformer.

6. The current protection circuit based on differential protection according to claim 5, characterized in that: The second relay protection module comprises: a second differential relay, a third current transformer and a fourth current transformer; The first end of the third current transformer is electrically connected to the third circuit breaker; The second end of the third current transformer is electrically connected to the first end of the second differential relay; The second end of the second differential relay is electrically connected to the first end of the fourth current transformer; The second end of the fourth current transformer is electrically connected to the fourth circuit breaker.

7. A control method for a current protection circuit based on differential protection, characterized in that: A current protection circuit based on differential protection for controlling any one of claims 1 to 6, comprising: Calculating a first differential current and a first braking current of a first transformer in real time by using a first relay protection module, and judging whether the first transformer is faulty according to a comparison relationship between the first differential current and the first braking current; When it is determined that the first transformer fails, the first circuit breaker and the second circuit breaker are switched to an open state.

8. The control method of the current protection circuit based on differential protection according to claim 7, characterized in that: The first relay protection module is used to calculate the first differential current and the first braking current of the first transformer in real time, and according to the comparison relationship between the first differential current and the first braking current, it is determined whether the first transformer is faulty, specifically: obtaining a starting current of the first transformer; Using a first current transformer to collect the primary winding current of the first transformer in real time; Using the second current transformer to collect the secondary winding current of the first transformer in real time; Calculating the differential current and the braking current of the first transformer respectively according to the primary winding current and the secondary winding current of the first transformer; When the differential current of the first transformer is greater than the starting current of the first transformer and greater than a preset multiple value of the braking current of the first transformer, it is determined that the first transformer is faulty.

9. The control method of the current protection circuit based on differential protection according to claim 8, characterized in that: The differential current and the braking current of the first transformer are calculated respectively according to the primary winding current and the secondary winding current of the first transformer, specifically: Calculating the differential current of the first transformer using a preset differential current calculation formula according to the primary winding current and the secondary winding current of the first transformer; The preset differential current calculation formula is specifically: I OP =(|I W1 |+|I W2 |) In the formula, I OP is the differential current; I W1 is the primary winding current; I W2 is the secondary winding current; Calculating the braking current of the first transformer using a preset braking current calculation formula according to the primary winding current and the secondary winding current of the first transformer; The preset braking current calculation formula is specifically: In the formula, I RT is the braking current; I W1 is the primary winding current; I W2 is the secondary winding current; θ is the angle between the primary winding current and the secondary winding current.

10. The control method of the current protection circuit based on differential protection according to claim 9, characterized in that: Also includes: Calculate the second differential current and the second braking current of the second transformer in real time by using the second relay protection module, and determine whether the second transformer is faulty according to the comparison relationship between the second differential current and the second braking current; When it is determined that the second transformer fails, the third circuit breaker and the fourth circuit breaker are switched to an open state.

Images