Relay protection circuit for hydropower station

Abstract

The utility model relates to the technical field of circuit protection, and discloses a relay protection circuit for a hydropower station, which aims to solve the problem of poor protection sensitivity in the prior art, and adopts the scheme that the hydropower station comprises a power grid, a main transformer, a generator motor, a static frequency converter, a station transformer, a first reactor and a second reactor, the circuit comprises a main transformer protection module, a first reactor protection module, a second reactor protection module, a first current transformer, a second current transformer, a third current transformer, a fourth current transformer, a fifth current transformer, a sixth current transformer, a seventh current transformer, an eighth current transformer, a first circuit breaker and a second circuit breaker. And a third circuit breaker and a fourth circuit breaker. According to the utility model, each reactor is independently provided with a corresponding protection module, so that the protection sensitivity can be improved when the rear end of the reactor is short-circuited.

Description

Technical Field

[0001] This utility model relates to the field of circuit protection technology, specifically to a relay protection circuit for hydropower stations. Background Technology

[0002] According to the relevant requirements of pumped storage power stations, in order to limit the short-circuit current when a short-circuit fault occurs in the plant power supply or the static frequency converter branch, series reactors will be installed on the branch.

[0003] For protection after adding reactors, the existing solution is to use the protection devices of the main transformer, mainly the main transformer differential protection and main transformer overcurrent protection. By separately detecting the current values ​​at the grid side, generator / motor side, static inverter side, and stationary transformer side, the currents at the four detection points are normally balanced. When a short-circuit fault occurs in the reactor, a fault current is generated, which can then trip the corresponding circuit breaker based on the detected current value, thus interrupting the fault current. Specifically, when the imbalance of the collected current reaches the set operating threshold, the differential protection will trip the circuit breaker on the static inverter side, the stationary transformer side, the grid side, and the generator / motor side. When the collected current on the grid side and the generator / motor side exceeds the set operating threshold, the overcurrent protection will trip the grid side circuit breaker and the generator / motor side circuit breaker.

[0004] This approach has at least the following problems: First, the purpose of setting up reactors is to limit fault short-circuit currents and create conditions for the selection of conductors, circuit breakers, and other equipment downstream of the reactor. The short-circuit current at the reactor's upstream end (closer to the grid side) is far greater than the short-circuit current at the reactor's downstream end (closer to the static inverter side and the plant service transformer side), with a difference of more than five times. Second, the operating thresholds for both the main transformer differential protection and the main transformer overcurrent protection are calculated based on the main transformer capacity. Taking a standardized pumped storage design as an example, the main transformer capacity is typically around 300 MW, the static inverter capacity is typically 20 to 30 MW, and the plant service transformer capacity is typically around 8 MW. It can be seen that the capacities of each piece of equipment vary significantly, and the operating thresholds set based on the main transformer's capacity will be relatively large. When a short-circuit fault occurs from the low-voltage side branch point of the main transformer to the front end of the reactor, the fault current is not limited, and the sensitivity of the differential protection and overcurrent protection is very high. When a short-circuit fault occurs at the rear end of the reactor, the fault current is significantly limited, which will greatly reduce the protection sensitivity and may make it impossible to reliably isolate the fault point, causing the accident to escalate. Utility Model Content

[0005] This invention aims to solve the problem of poor protection sensitivity in existing relay protection methods for hydropower stations, and proposes a relay protection circuit for hydropower stations.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is:

[0007] A relay protection circuit for a hydropower station, the hydropower station including a power grid, a main transformer, a generator motor, a static frequency converter, a stationary transformer, a first reactor, and a second reactor, the circuit including: a main transformer protection module, a first reactor protection module, a second reactor protection module, a first current transformer, a second current transformer, a third current transformer, a fourth current transformer, a fifth current transformer, a sixth current transformer, a seventh current transformer, an eighth current transformer, a first circuit breaker, a second circuit breaker, a third circuit breaker, and a fourth circuit breaker;

[0008] The power grid is connected to the primary side of the main transformer via a first circuit breaker. The secondary side of the main transformer is connected to the generator motor via a second circuit breaker. The secondary side of the main transformer is also connected to the static inverter via a first reactor and a third circuit breaker, and further connected to the stationary transformer via a second reactor and a fourth circuit breaker. The first current transformer is located at the end of the first circuit breaker near the main transformer; the second current transformer is located at the end of the second circuit breaker near the main transformer; the third and fifth current transformers are located at the end of the third circuit breaker near the static inverter; the fourth and sixth current transformers are located at the end of the fourth circuit breaker near the stationary transformer; the seventh current transformer is located at the end of the first reactor near the main transformer; and the eighth current transformer is located at... The second reactor is located near the main transformer. The first, second, third, and fourth current transformers are connected to the signal input terminals of the main transformer protection module. The signal output terminals of the main transformer protection module are connected to the control terminals of the first, second, third, and fourth circuit breakers. The fifth and seventh current transformers are connected to the signal input terminals of the first reactor protection module. The signal output terminals of the first reactor protection module are connected to the control terminals of the first, second, and third circuit breakers. The sixth and eighth current transformers are connected to the signal output terminals of the second reactor protection module. The signal output terminals of the second reactor protection module are connected to the control terminals of the first, second, and fourth circuit breakers.

[0009] Furthermore, it also includes a ninth current transformer and a static inverter protection module. The ninth current transformer is located at the end of the third circuit breaker near the first reactor. The ninth current transformer is connected to the signal input terminal of the static inverter protection module, and the signal output terminal of the static inverter protection module is connected to the control terminal of the third circuit breaker.

[0010] Furthermore, it also includes a tenth current transformer and a plant transformer protection module. The tenth current transformer is located at the end of the fourth circuit breaker near the second reactor. The tenth current transformer is connected to the signal input terminal of the plant transformer protection module, and the signal output terminal of the plant transformer protection module is connected to the control terminal of the fourth circuit breaker.

[0011] The beneficial effects of this utility model are as follows: The relay protection circuit for hydropower stations provided by this utility model adds a set of protective current transformers at the front end of the reactor, and adds a set of protective current transformers at the static inverter and the stationary transformer side, and configures corresponding reactor protection modules. The action threshold of the reactor protection module is set separately, which can be set according to the magnitude of the short-circuit current at the rear end of the reactor, combined with the capacity of the static inverter and the stationary transformer. The action threshold can be reduced to one-fifth or even less than the original value, which can improve the sensitivity of protection when a short circuit occurs at the rear end of the reactor. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the main circuit structure of a relay protection circuit in the prior art;

[0013] Figure 2 This is a schematic diagram of the protection circuit structure of the main transformer protection module in the prior art;

[0014] Figure 3 A schematic diagram of the structure of a relay protection circuit for a hydropower station provided as an example;

[0015] Figure 4 A schematic diagram of the protection circuit structure of the first reactor protection module provided in the embodiment;

[0016] Figure 5 A schematic diagram of the protection circuit structure of the second reactor protection module provided in the embodiment;

[0017] Figure 6 A schematic diagram of the protection circuit structure of the static inverter protection module provided in the embodiment;

[0018] Figure 7 A schematic diagram of the protection circuit structure of the plant transformer protection module provided for the embodiment;

[0019] Explanation of reference numerals in the attached figures:

[0020] T1 - Main transformer; L1 - First reactor; L2 - Second reactor; d1 - Reactor front end; d2 - First reactor rear end; d3 - Second reactor rear end; CT1 - First current transformer; CT2 - Second current transformer; CT3 - Third current transformer; CT4 - Fourth current transformer; CT5 - Fifth current transformer; CT6 - Sixth current transformer; CT7 - Seventh current transformer; CT8 - Eighth current transformer; CT9 - Ninth current transformer; CT10 - Tenth current transformer; Q1 - First circuit breaker; Q2 - Second circuit breaker; Q3 - Third circuit breaker; Q4 - Fourth circuit breaker. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] Figure 1 A schematic diagram of the main circuit structure of a prior art relay protection circuit is shown. Please refer to [link / reference]. Figure 1 It includes the power grid, main transformer T1, generator motor, static frequency converter, plant transformer, first reactor L1, second reactor L2, main transformer protection module, first current transformer CT1, second current transformer CT2, third current transformer CT3, fourth current transformer CT4, first circuit breaker Q1, second circuit breaker Q2, third circuit breaker Q3 and fourth circuit breaker Q4.

[0023] Please see Figure 1 Under normal circumstances, the generator motor and the power grid are the power supply end, and the static inverter and the plant transformer are the load end. The current flows from the generator motor and the power grid to the branch, then to the first reactor L1 and the second reactor L2, and then to the static inverter and the plant transformer.

[0024] Please see Figure 2 The first current transformer CT1, the second current transformer CT2, the third current transformer CT3, and the fourth current transformer CT4 are respectively connected to the signal input terminals of the main transformer protection module. The signal output terminals of the main transformer protection module are respectively connected to the control terminals of the first circuit breaker Q1, the second circuit breaker Q2, the third circuit breaker Q3, and the fourth circuit breaker Q4. Based on the above relay protection circuit, its corresponding protection functions include main transformer differential protection and main transformer overcurrent protection.

[0025] Main transformer differential protection: The main transformer protection module acquires the current values ​​collected by the first current transformer CT1, the second current transformer CT2, the third current transformer CT3, and the fourth current transformer CT4. Under normal circumstances, the currents at the four acquisition points are balanced. When a short circuit fault occurs at the front end d1 of the reactor, the rear end d2 of the first reactor, or the rear end d3 of the second reactor, a fault current will be generated, causing an imbalance in the four acquisition currents. The currents collected by the first current transformer CT1 and the second current transformer CT2 will increase, while the currents collected by the third current transformer CT3 and the fourth current transformer CT4 will decrease. When the imbalance reaches the set operating threshold, the differential protection will trip the first circuit breaker Q1, the second circuit breaker Q2, the third circuit breaker Q3, and the fourth circuit breaker Q4 to cut off the fault current.

[0026] Overcurrent protection of the main transformer: The protection module of the main transformer obtains the current value collected by the first current transformer CT1 and the second current transformer CT2. Under normal circumstances, the current value collected by the first current transformer CT1 and the second current transformer CT2 will not exceed the rated current of the main transformer. When a short circuit fault occurs at the front end d1 of the reactor, the back end d2 of the first reactor, or the back end d3 of the second reactor, a fault current will be generated. The current collected by the first current transformer CT1 and the second current transformer CT2 will increase and exceed the rated current of the main transformer. When it exceeds the set operating threshold, the overcurrent protection will trip the first circuit breaker Q1 and the second circuit breaker Q2 to cut off the source of the fault current.

[0027] The inventors discovered the following problems with the above scheme: First, the purpose of setting up the first reactor L1 and the second reactor L2 is to limit the fault short-circuit current and create conditions for the selection of conductors, circuit breakers, and other equipment after the reactors. The short-circuit current at the reactor front end d1 is much greater than the short-circuit current at the first reactor back end d2 or the second reactor back end d3, with a difference of more than 5 times. Second, the operating thresholds of the main transformer differential protection and the main transformer overcurrent protection are calculated based on the main transformer capacity. Taking the standardized design of pumped storage as an example, the capacity of the main transformer T1 is usually around 300 MW, the capacity of the static frequency converter is usually 20 to 30 MW, and the capacity of the plant service transformer is usually around 8 MW. It can be seen that the capacity of each piece of equipment varies greatly, and the operating threshold set based on the main transformer T1 capacity will be relatively large. When a short-circuit fault occurs from the secondary side branch point of the main transformer T1 to the front end d1 of the reactor, the fault current is not limited, and the sensitivity of the differential protection and overcurrent protection is very high. When a short-circuit fault occurs at the rear end d2 of the first reactor or the rear end d3 of the second reactor, the fault current is significantly limited, which will greatly reduce the protection sensitivity and may make it impossible to reliably isolate the fault point, causing the accident to escalate.

[0028] To improve protection sensitivity and reliability, the technical solution of this utility model is proposed. Please refer to [link / reference]. Figure 3 The relay protection circuit for a hydropower station provided in this embodiment includes a power grid, a main transformer T1, a generator motor, a static frequency converter, a plant transformer, a first reactor L1, and a second reactor L2. The circuit also includes: a main transformer protection module, a first reactor protection module, a second reactor protection module, a first current transformer CT1, a second current transformer CT2, a third current transformer CT3, a fourth current transformer CT4, a fifth current transformer CT5, a sixth current transformer CT6, a seventh current transformer CT7, an eighth current transformer CT8, a first circuit breaker Q1, a second circuit breaker Q2, a third circuit breaker Q3, and a fourth circuit breaker Q4.

[0029] The power grid is connected to the primary side of the main transformer T1 via a first circuit breaker Q1. The secondary side of the main transformer T1 is connected to the generator motor via a second circuit breaker Q2. The secondary side of the main transformer T1 is also connected to the static frequency converter via a first reactor L1 and a third circuit breaker Q3, and further connected to the station service transformer via a second reactor L2 and a fourth circuit breaker Q4. The first current transformer CT1 is located at the end of the first circuit breaker Q1 closest to the main transformer T1. The second current transformer... CT2 is located at the end of the second circuit breaker Q2 near the main transformer T1. The third current transformer CT3 and the fifth current transformer CT5 are located at the end of the third circuit breaker Q3 near the static frequency converter. The fourth current transformer CT4 and the sixth current transformer CT6 are located at the end of the fourth circuit breaker Q4 near the plant service transformer. The seventh current transformer CT7 is located at the end of the first reactor L1 near the main transformer T1. The eighth current transformer is located at the end of the second reactor L2 near the main transformer T1.

[0030] Please see Figure 2 In this embodiment, the protection circuit connection method of the main transformer protection module is the same as that of the prior art, that is, the first current transformer CT1, the second current transformer CT2, the third current transformer CT3 and the fourth current transformer CT4 are respectively connected to the signal input terminal of the main transformer protection module, and the signal output terminal of the main transformer protection module is respectively connected to the control terminal of the first circuit breaker Q1, the second circuit breaker Q2, the third circuit breaker Q3 and the fourth circuit breaker Q4.

[0031] Please see Figure 3 and Figure 4In this embodiment, a first reactor protection module and a second reactor protection module are added. The corresponding protection circuit connection method is as follows: the fifth current transformer CT5 and the seventh current transformer CT7 are respectively connected to the signal input terminal of the first reactor protection module. The signal output terminal of the first reactor protection module is respectively connected to the control terminals of the first circuit breaker Q1, the second circuit breaker Q2 and the third circuit breaker Q3. The sixth current transformer CT6 and the eighth current transformer CT8 are respectively connected to the signal output terminal of the second reactor protection module. The signal output terminal of the second reactor protection module is respectively connected to the control terminals of the first circuit breaker Q1, the second circuit breaker Q2 and the fourth circuit breaker Q4.

[0032] The relay protection circuit provided in this embodiment adds a seventh current transformer CT7 and an eighth current transformer CT8 at the front end of the first reactor L1 and the second reactor L2. A fifth current transformer CT5 and a sixth current transformer CT6 are added on the static inverter and the plant service transformer side. The first reactor protection module is configured to be connected to the fifth current transformer CT5 and the seventh current transformer CT7, and the second reactor protection module is configured to be connected to the sixth current transformer CT6 and the eighth current transformer CT8. Simultaneously, the trip interface of the first reactor protection module is connected to the circuit breaker on the static inverter side, the grid side circuit breaker, and the generator motor side circuit breaker; the trip interface of the second reactor protection module is connected to the circuit breaker on the plant service transformer side, the grid side circuit breaker, and the generator motor side circuit breaker. In the event of a fault, the power supply can be disconnected, and the fault current can be interrupted.

[0033] The first reactor protection module is equipped with differential protection and overcurrent protection. The differential protection collects the current values ​​from the fifth current transformer CT5 and the seventh current transformer CT7. Under normal circumstances, the current values ​​on both sides are balanced. When a fault occurs at the downstream end d2 of the first reactor, an unbalanced current is generated. When the unbalanced current exceeds the set threshold, a trip signal is issued. The overcurrent protection collects the current value from the seventh current transformer CT7. Under normal circumstances, the current value is matched to the rated current of the first reactor L1. When a fault occurs at the downstream end d2 of the first reactor, the current value will greatly exceed the rated current. When it exceeds the set operating threshold, a trip signal is issued. After issuing the trip signal, the first circuit breaker Q1, the second circuit breaker Q2, and the third circuit breaker Q3 are disconnected.

[0034] Similarly, the second reactor protection module is configured with differential protection and overcurrent protection. The differential protection collects the current values ​​from the sixth current transformer CT6 and the eighth current transformer CT8. Under normal circumstances, the current values ​​on both sides are balanced. When a fault occurs at the downstream end d3 of the second reactor, an unbalanced current is generated. When the unbalanced current exceeds the set threshold, a trip signal is issued. The overcurrent protection collects the current value from the eighth current transformer CT8. Under normal circumstances, the current value is matched to the rated current of the second reactor L2. When a fault occurs at the downstream end d3 of the second reactor, the current value will greatly exceed the rated current. When it exceeds the set operating threshold, a trip signal is issued. After issuing the trip signal, the first circuit breaker Q1, the second circuit breaker Q2, and the fourth circuit breaker Q4 are disconnected.

[0035] After configuring the reactor protection module separately, the operating thresholds of the first reactor protection module and the second reactor protection module can be set independently. They can be set according to the magnitude of the short-circuit current at the end of the first reactor (d2) and the end of the second reactor (d3), combined with the capacity of the static frequency converter and the plant transformer. This can significantly reduce the operating threshold to one-fifth or even less of the original value, and improve the sensitivity of the protection when a short circuit occurs at the end of the first reactor (d2) and the end of the second reactor (d3).

[0036] Please see Figure 3 and Figure 6 In this embodiment, a ninth current transformer CT9 and a static inverter protection module are also included. The ninth current transformer CT9 is located at the end of the third circuit breaker Q3 near the first reactor L1. The ninth current transformer CT9 is connected to the signal input terminal of the static inverter protection module, and the signal output terminal of the static inverter protection module is connected to the control terminal of the third circuit breaker Q3.

[0037] The static inverter protection module is equipped with overcurrent protection, which means that it collects the current value of the ninth current transformer CT9. When the current value is greater than the action threshold, it sends a trip signal to control the disconnection of the third circuit breaker Q3 to achieve circuit protection.

[0038] Please see Figure 3 and Figure 7 In this embodiment, the system also includes a tenth current transformer CT10 and a plant transformer protection module. The tenth current transformer CT10 is located at one end of the fourth circuit breaker Q4 near the second reactor L2. The tenth current transformer CT10 is connected to the signal input terminal of the plant transformer protection module, and the signal output terminal of the plant transformer protection module is connected to the control terminal of the fourth circuit breaker Q4.

[0039] The plant transformer protection module provides overcurrent protection by collecting the current value of the tenth current transformer CT10. When the current value exceeds the action threshold, a trip signal is issued to control the disconnection of the fourth circuit breaker Q4 to achieve circuit protection.

[0040] As can be seen from the circuit principle described above, the protection module in this embodiment includes a main transformer protection module, a first reactor protection module, a second reactor protection module, a static inverter protection module, and a plant service transformer protection module. The function of these protection modules is to acquire the current values ​​collected by the current transformers, compare the current values, and control the corresponding circuit breakers to open. Therefore, the protection module can be implemented using simple combinations of digital circuits such as comparators, OR gates, and AND gates, without the need for a computer program. Of course, the protection module can also be a controller loaded with a computer program. This computer program is used to implement current comparison; it is a conventional computer program in the art and not an improvement of this embodiment, so it will not be elaborated upon here.

[0041] In summary, the relay protection circuit for hydropower stations provided in this embodiment adds a set of protective current transformers at the front end of the reactor and another set of protective current transformers at the static inverter and the stationary transformer side, and configures corresponding reactor protection modules. The operating threshold of the reactor protection module is set independently, according to the magnitude of the short-circuit current at the rear end of the reactor, and in combination with the capacity of the static inverter and the stationary transformer. This can reduce the operating threshold to one-fifth or even less of the original value, thereby improving the sensitivity of the protection when a short circuit occurs at the rear end of the reactor.

[0042] It should be noted that the present invention provides only a specific structure for a relay protection circuit for hydropower stations. The relevant modules involved are all hardware system modules or functional modules that combine computer software programs or protocols with hardware in the prior art. The computer software programs or protocols involved in these functional modules are technologies known to those skilled in the art and are not improvements to this circuit, so they will not be described in detail here. The improvement of this circuit is the interaction or connection relationship between the components, that is, the improvement of the overall structure of the circuit, in order to solve the corresponding technical problems to be solved by this circuit.

Claims

1. A relay protection circuit for a hydroelectric power plant, the hydroelectric power plant comprising a power grid, a main transformer, a generator motor, a static frequency converter, a station service transformer, a first reactor and a second reactor, characterized in that, The circuit comprises a main transformer protection module, a first reactor protection module, a second reactor protection module, a first current transformer, a second current transformer, a third current transformer, a fourth current transformer, a fifth current transformer, a sixth current transformer, a seventh current transformer, an eighth current transformer, a first circuit breaker, a second circuit breaker, a third circuit breaker, and a fourth circuit breaker; The power grid is connected with a primary side of the main transformer through the first circuit breaker, a secondary side of the main transformer is connected with the generator motor through the second circuit breaker, the secondary side of the main transformer is connected with the static frequency converter through the first reactor and the third circuit breaker in sequence, the secondary side of the main transformer is connected with the auxiliary transformer through the second reactor and the fourth circuit breaker in sequence, the first current transformer is arranged at one end of the first circuit breaker close to the main transformer, the second current transformer is arranged at one end of the second circuit breaker close to the main transformer, the third current transformer and the fifth current transformer are arranged at one end of the third circuit breaker close to the static frequency converter, the fourth current transformer and the sixth current transformer are arranged at one end of the fourth circuit breaker close to the auxiliary transformer, the seventh current transformer is arranged at one end of the first reactor close to the main transformer, and the eighth current transformer is arranged at one end of the second reactor close to the main transformer; the first current transformer, the second current transformer, the third current transformer, and the fourth current transformer are connected with a signal input end of the main transformer protection module respectively, a signal output end of the main transformer protection module is connected with control ends of the first circuit breaker, the second circuit breaker, the third circuit breaker, and the fourth circuit breaker respectively, the fifth current transformer and the seventh current transformer are connected with signal input ends of the first reactor protection module respectively, a signal output end of the first reactor protection module is connected with control ends of the first circuit breaker, the second circuit breaker, and the third circuit breaker respectively, the sixth current transformer and the eighth current transformer are connected with signal output ends of the second reactor protection module respectively, and signal output ends of the second reactor protection module are connected with control ends of the first circuit breaker, the second circuit breaker, and the fourth circuit breaker respectively.

2. The relay protection circuit for a hydroelectric power plant according to claim 1, characterized in that, The circuit further comprises a ninth current transformer and a static frequency converter protection module, the ninth current transformer is arranged at one end of the third circuit breaker close to the first reactor, the ninth current transformer is connected with a signal input end of the static frequency converter protection module, and a signal output end of the static frequency converter protection module is connected with a control end of the third circuit breaker.

3. The relay protection circuit for a hydroelectric power plant according to claim 1, characterized in that, The circuit further comprises a tenth current transformer and an auxiliary transformer protection module, the tenth current transformer is arranged at one end of the fourth circuit breaker close to the second reactor, the tenth current transformer is connected with a signal input end of the auxiliary transformer protection module, and a signal output end of the auxiliary transformer protection module is connected with a control end of the fourth circuit breaker.

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