A fan detection device and temperature control system for a tank transformer

Abstract

The application discloses a fan detection device and a temperature control system of a box-type transformer. The fan detection device comprises a first switch assembly, a second switch assembly, a first current sampling unit, a second current sampling unit and a controller. The first end of the first switch assembly and the first end of the second switch assembly are respectively connected with a first power supply. The second end of the first switch assembly and the second end of the second switch assembly are respectively used for connecting a body fan and a box fan of the box-type transformer. The control end of the first switch assembly, the control end of the second switch assembly, the output end of the first current sampling unit and the output end of the second current sampling unit are connected with the controller. The first current sampling unit and the second current sampling unit are respectively used for acquiring the current of the body fan and the current of the box fan. In the embodiment of the application, the current collected by the current sampling unit corresponding to each fan is used to detect the fault of the fan, and the flexibility of the fan detection device is improved.

Description

Technical Field

[0001] This application relates to the field of power system technology, and in particular to a wind turbine detection device and a temperature control system for a box-type transformer. Background Technology

[0002] With the rapid development of new energy sources, the application of box-type transformers is becoming increasingly widespread. The main cooling system for box-type transformers consists of both the main body fan and the enclosure fan. Therefore, detecting and identifying the status of these fans is an essential part of the cooling system.

[0003] In related technologies, differential current is used to determine whether a fan is faulty. However, this method has certain requirements regarding the number of fans in the fan circuit, which leads to low flexibility of the fan detection device. Utility Model Content

[0004] To address the aforementioned issues, this application provides a temperature control system for a fan testing device and a box-type transformer, thereby improving the flexibility of the fan testing device.

[0005] The embodiments of this application disclose the following technical solutions:

[0006] In a first aspect, embodiments of this application provide a wind turbine detection device, comprising: a first switching assembly, a second switching assembly, a first current sampling unit, a second current sampling unit, and a controller;

[0007] The first end of the first switch assembly is used to connect to the first power source, and the second end of the first switch assembly is used to connect to the body fan of the box-type transformer; the first end of the second switch assembly is used to connect to the first power source, and the second end of the second switch assembly is used to connect to the box-type transformer's enclosure fan.

[0008] The control terminal of the first switching assembly, the control terminal of the second switching assembly, the output terminal of the first current sampling unit, and the output terminal of the second current sampling unit are connected to the controller; wherein, the first current sampling unit is used to acquire the current flowing through the main body fan, and the second current sampling unit is used to acquire the current flowing through the casing fan.

[0009] One possible implementation is that the first switching assembly includes a first contactor, and the second switching assembly includes a second contactor.

[0010] One possible implementation is that the first current sampling unit includes a first current transformer, and the second current sampling unit includes a second current transformer.

[0011] One possible implementation is a controller specifically configured to identify a fault in the main fan when the current of the main fan exceeds a first range, and to identify a fault in the casing fan when the current of the casing fan exceeds a second range.

[0012] Secondly, embodiments of this application provide a temperature control system for a box-type transformer, comprising: a processor, a temperature sampling unit, and a fan detection device as described in any embodiment of the first aspect; wherein the box-type transformer includes a dry-type transformer;

[0013] The output of the temperature sampling unit is connected to the processor;

[0014] Temperature sampling unit, used to obtain the winding temperature of dry-type transformer;

[0015] The processor is configured to, when the winding temperature of the dry-type transformer exceeds a first threshold, activate a first switching assembly connected to the main body fan of the dry-type transformer, or activate both the first switching assembly connected to the main body fan of the dry-type transformer and a second switching assembly connected to the enclosure fan.

[0016] One possible implementation is that the box-type transformer includes an oil-immersed transformer;

[0017] The temperature sampling unit is also used to obtain the oil surface temperature of the oil-immersed transformer;

[0018] The first current sampling unit is also used to obtain the operating current of the oil-immersed transformer;

[0019] The processor is also configured to determine the winding temperature of the oil-immersed transformer based on the operating current and the oil surface temperature, and to activate the first switching assembly connected to the main fan of the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than a second threshold and / or the oil surface temperature is greater than a third threshold.

[0020] One possible implementation is that the temperature control system is powered by a second power source, which includes an uninterruptible power supply.

[0021] One possible implementation is that the temperature sampling unit is also used to acquire the outdoor room temperature of the box-type transformer, and when the outdoor room temperature is greater than a fourth threshold, to activate the second switching assembly connected to the box-type fan.

[0022] One possible implementation is that the processor is also used to identify a cabinet fan failure when the outdoor room temperature is greater than a fifth threshold and the second switching component is turned on.

[0023] In one possible implementation, the temperature control system further includes: an alarm unit, the control terminal of which is connected to the processor;

[0024] The alarm unit is used to indicate that the dry-type transformer is overheating when the winding temperature of the dry-type transformer exceeds the sixth threshold; to indicate that the winding temperature of the oil-immersed transformer exceeds the seventh threshold; and to indicate that the oil surface temperature of the oil-immersed transformer exceeds the eighth threshold.

[0025] In one possible implementation, the temperature control system further includes: a protection unit, which is connected to the power supply of the dry-type transformer and the power supply of the oil-immersed transformer respectively, and the control terminal of the protection unit is connected to the processor.

[0026] The protection unit is used to cut off the power supply to the dry-type transformer when the winding temperature of the dry-type transformer is greater than the ninth threshold; and to cut off the power supply to the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than the tenth threshold, or when the oil surface temperature of the oil-immersed transformer is greater than the eleventh threshold; wherein the ninth threshold is greater than the sixth threshold, the tenth threshold is greater than the seventh threshold, and the eleventh threshold is greater than the eighth threshold.

[0027] Determining fan malfunction using differential current detection requires a certain number of fans in the fan circuit, resulting in low flexibility of the fan detection device. Therefore, this application provides a fan detection device comprising: a first switching assembly, a second switching assembly, a current sampling unit, and a controller; a first terminal of the first switching assembly is connected to a first power supply, and a second terminal is connected to the main fan of a box-type transformer; a first terminal of the second switching assembly is connected to the first power supply, and a second terminal is connected to the enclosure fan of the box-type transformer; the control terminals of the first and second switching assemblies, the output terminals of the first and second current sampling units are connected to the controller; wherein, the first current sampling unit is used to acquire the current of the main fan, and the second current sampling unit is used to acquire the current of the enclosure fan. In this application embodiment, by detecting the current of a single fan (main fan or enclosure fan), the controller can determine the status of the corresponding fan, without requiring a certain number of fans in the circuit, thus improving the flexibility of the fan detection device. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of a fan testing device;

[0030] Figure 2 This is a schematic diagram of another fan testing device provided in an embodiment of this application;

[0031] Figure 3 A schematic diagram of a temperature control system for a box-type transformer provided in this application embodiment;

[0032] Figure 4 A schematic diagram of another temperature control system for a box-type transformer provided in this application embodiment;

[0033] Figure 5 A schematic diagram of a temperature control system for a box-type transformer provided in an embodiment of this application. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0035] The terms "first" and "second," etc., used in the specification and claims of this application are used to distinguish different objects, not to describe a specific order of objects. For example, "first switch assembly" and "second switch assembly," etc., are used to distinguish different switch assemblies, not to describe a specific order of switch assemblies.

[0036] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0037] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0038] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application scenarios of the embodiments of this application will be described below with reference to the accompanying drawings.

[0039] like Figure 1As shown, the fan detection device includes a controller, contactor 1, contactor 2, and contactors CT1, CT2, CT3, and CT4. Contactors CT1 and CT2 measure the current in the main fan circuit, with I1 and I2 being two currents of equal magnitude but opposite directions. Contactors CT3 and CT4 measure the current in the casing fan circuit, with I3 and I4 being two currents of equal magnitude but opposite directions. When all main fans are operating normally, the differential current device KD detects zero current in the circuit. If one main fan fails, the differential current device KD detects a non-zero current in the circuit. Similarly, when all casing fans are operating normally, the differential current device KD detects zero current in the circuit. If one casing fan fails, the differential current device KD detects a non-zero current in the circuit. The fan detection device has certain requirements regarding the number of fans in the fan circuit. Specifically, the number of fans in the fan circuit must be even. Furthermore, if an even number of fans fail, the circuit current detected by the differential current device KD will be 0, and the fan failure cannot be correctly identified.

[0040] Therefore, in this embodiment of the application, the status of the corresponding fan is determined by detecting the current of a single fan (the main fan or the casing fan). There is no requirement for the number of fans in the circuit, which improves the flexibility of the fan detection device and avoids the problem of not being able to correctly identify the fan fault when an even number of fans fail, thereby improving the reliability of the fan detection device.

[0041] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, embodiments of this application will be described below in conjunction with the accompanying drawings.

[0042] See Figure 2 The figure is a schematic diagram of a fan testing device provided in an embodiment of this application.

[0043] like Figure 2 As shown, the fan detection device 1000 provided in this embodiment includes a first switch assembly 200, a second switch assembly 300, a first current sampling unit 400, a second current sampling unit 500, and a controller 100. The first end of the first switch assembly 200 is connected to a first power supply, and the second end of the first switch assembly 200 is connected to the main fan of the box-type transformer. The first end of the second switch assembly 300 is connected to the first power supply, and the second end of the second switch assembly 300 is connected to the enclosure fan of the box-type transformer. The control terminals of the first switch assembly 200 and the second switch assembly 300, the output terminals of the first current sampling unit 400 and the second current sampling unit 500 are all connected to the controller 100.

[0044] In this embodiment of the application, the type of controller is not specifically limited. For example, the controller 100 may be a digital signal processor (DSP), a field-programmable gate array (FPGA), or a microcontroller.

[0045] It should be understood that in the embodiments of this application, the main body fan is a fan installed on the transformer body, and the box-type transformer is a fan installed on the box.

[0046] In this embodiment, the form of the first switch component 200 and the second switch component 300 is not specifically limited. For example, the first switch component 200 and the second switch component 300 can be contactors or semiconductor switching devices.

[0047] In this embodiment, the box-type transformer may include a dry-type transformer, an oil-immersed transformer, or both. Correspondingly, the main fan of the box-type transformer may be the main fan of a dry-type transformer or the main fan of an oil-immersed transformer.

[0048] The first current sampling unit 400 is used to acquire the current Ia of the main fan.

[0049] In this embodiment, the method by which the first current sampling unit 400 collects current is not specifically limited. For example, the first current sampling unit may include a first current transformer, which is used to obtain the current Ia of the main fan. It should be understood that in this embodiment, the number of first current transformers corresponds to the number of main fans, and each first current transformer is used to obtain the current of the corresponding main fan.

[0050] The second current sampling unit 500 is used to acquire the current Ib of the casing fan.

[0051] In this embodiment, the method by which the second current sampling unit 500 collects current is not specifically limited. For example, the second current sampling unit may include a second current transformer, which is used to acquire the current Ib of the enclosure fan. It should be understood that in this embodiment, the number of second current transformers corresponds to the number of enclosure fans, and each second current transformer is used to acquire the current of the corresponding enclosure fan.

[0052] The controller 100 is used to identify a fault in the main fan when the current Ia of the main fan exceeds a first range, and to identify a fault in the casing fan when the current Ib of the casing fan exceeds a second range.

[0053] When the main fan is operating normally, its current varies within a first range; when the main fan malfunctions, its current may exceed the upper limit of the first range or fall below the lower limit. Similarly, when the enclosure fan is operating normally, its current varies within a second range; when the enclosure fan malfunctions, its current may exceed the upper limit of the second range or fall below the lower limit. It should be noted that the relationship between the first and second ranges is not limited in the embodiments of this application.

[0054] In this embodiment, the status of a single fan (either the main fan or the casing fan) is determined by detecting its current. There are no requirements regarding the number of fans in the circuit, thus improving the flexibility of the fan detection device. Furthermore, the solution in this embodiment avoids the problem of failing to correctly identify fan faults when an even number of fans fail, thereby improving the reliability of the fan detection device.

[0055] Based on the fan detection device provided in the above embodiments, this application also provides a temperature control system for a box-type transformer, which will be described in detail below with reference to the accompanying drawings.

[0056] See Figure 3 The figure is a schematic diagram of a temperature control system for a box-type transformer provided in an embodiment of this application.

[0057] like Figure 3 As shown, the temperature control system for the box-type transformer in this embodiment includes: a processor 3000, a temperature sampling unit 2000, and a fan detection device 1000; wherein, the box-type transformer in the fan detection device 1000 includes a dry-type transformer.

[0058] The output of the temperature sampling unit 2000 is connected to the input of the processor 3000.

[0059] Temperature sampling unit 2000 is used to obtain the winding temperature of dry-type transformer.

[0060] In this embodiment, the method by which the temperature sampling unit 2000 acquires the temperature is not specifically limited. For example, the temperature sampling unit can acquire the winding temperature of the dry-type transformer through a platinum resistance thermometer PT100.

[0061] For example, the temperature of phase A winding of dry-type transformer is obtained through PT100A, the temperature of phase B winding of dry-type transformer is obtained through PT100B, and the temperature of phase C winding of dry-type transformer is obtained through PT100C.

[0062] The processor 3000 is used to, when the winding temperature of the dry-type transformer is greater than a first threshold, turn on the first switching assembly connected to the main body fan of the dry-type transformer, or turn on the first switching assembly connected to the main body fan of the dry-type transformer and the second switching assembly connected to the casing fan.

[0063] In this application embodiment, the type of processor is not specifically limited. For example, the processor may be a digital signal processor (DSP), a field-programmable gate array (FPGA), or a microcontroller.

[0064] When the winding temperature (A-phase winding temperature, B-phase winding temperature, or C-phase winding temperature) of the dry-type transformer exceeds a first threshold, the first switching assembly connected to the main body fan of the dry-type transformer is turned on, so that the main body fan of the dry-type transformer dissipates heat from the dry-type transformer. Furthermore, when the winding temperature (A-phase winding temperature, B-phase winding temperature, or C-phase winding temperature) of the dry-type transformer exceeds the first threshold by a significant amount, the first switching assembly connected to the main body fan of the dry-type transformer and the second switching assembly connected to the enclosure fan of the dry-type transformer are turned on, so that the main body fan and the enclosure fan of the dry-type transformer dissipate heat from the dry-type transformer simultaneously, thereby accelerating the heat dissipation speed of the dry-type transformer.

[0065] In this embodiment, a temperature sampling unit is added to the existing fan detection device to form a temperature control system. This temperature control system leverages the advantages of the existing fan detection device and, based on these advantages, can provide heat dissipation for the box-type transformer.

[0066] In the preceding embodiments, the temperature control system was described for the case of a box-type transformer, including a dry-type transformer. The following section will describe the temperature control system for the case of a box-type transformer, including both dry-type and oil-immersed transformers.

[0067] In the case of a box-type transformer including an oil-immersed transformer, the temperature sampling unit 2000 is also used to acquire the oil surface temperature of the oil-immersed transformer; the first current sampling unit is also used to acquire the operating current of the oil-immersed transformer; the processor 3000 is used to obtain the winding temperature of the oil-immersed transformer based on the operating current and the oil surface temperature, and to conduct the first switching assembly connected to the main body fan of the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than a second threshold and / or the oil surface temperature is greater than a third threshold.

[0068] Depending on the manufacturer of the oil-immersed transformer, the winding temperature can be directly calculated using the oil surface temperature and the operating current. Alternatively, a first and second oil surface temperature can be obtained using a temperature sampling unit (the PT100 measuring the first and second oil surface temperatures are located at different points, with the second PT100 being closer to the winding). The winding temperature can then be calculated based on the second oil surface temperature and the operating current. It should be understood that calculating the winding temperature of an oil-immersed transformer from its oil surface temperature and operating voltage is a mature technique in this field, and the specific calculation method for the winding temperature will not be elaborated upon here.

[0069] In addition, in this embodiment, the temperature sampling unit 2000 is also used to obtain the outdoor room temperature of the box-type transformer. When the outdoor room temperature is greater than the fourth threshold, the second switch assembly connected to the box fan is turned on so that the box fan dissipates heat for the box-type transformer.

[0070] In this embodiment of the application, when the temperature sampling unit collects the outdoor room temperature, in addition to identifying the status of the box fan by the current of the box fan, the status of the box fan can also be identified by the outdoor room temperature.

[0071] For example, if the outdoor room temperature is greater than the fifth threshold and the second switch assembly connected to the enclosure fan is turned on, the processor 3000 can identify an enclosure fan malfunction and take corresponding measures for the enclosure fan malfunction.

[0072] In this embodiment, the temperature control system for the box-type transformer can simultaneously control the temperature of both dry-type and oil-immersed transformers. Furthermore, for the oil-immersed transformer, its internal fan can be controlled for heat dissipation. Compared to related technologies (where the temperature control systems for dry-type and oil-immersed transformers are independent), this embodiment uses a single temperature sampling unit to simultaneously collect winding temperature data for the dry-type transformer, as well as oil surface temperature and winding temperature data for the oil-immersed transformer. Data transmission between the temperature sampling unit and the processor requires only one communication channel, thus reducing the number of communication devices required.

[0073] To improve the stability of the temperature control system of the box-type transformer, in this embodiment, the main body fan (the main body fan of the dry-type transformer and the main body fan of the oil-immersed transformer) and the box fan are powered by a first power supply, while other units in the temperature control system (other electrical equipment besides the main body fan and the box fan, such as processors and temperature sampling units) are powered by a second power supply. The second power supply includes an uninterruptible power supply to prevent the temperature control system from shutting down due to external power failure, thereby improving the stability of the temperature control system.

[0074] Furthermore, to improve the safety of the temperature control system, such as Figure 4 As shown in the embodiment of this application, the temperature control system further includes: an alarm unit 4000, the control terminal of which is connected to the processor 3000; the alarm unit 4000 is used to indicate that the dry-type transformer is overheating when the winding temperature of the dry-type transformer is greater than a sixth threshold; to indicate that the winding temperature of the oil-immersed transformer is overheating when the winding temperature of the oil-immersed transformer is greater than a seventh threshold; and to indicate that the oil surface temperature of the oil-immersed transformer is overheating when the oil surface temperature of the oil-immersed transformer is greater than an eighth threshold.

[0075] In this embodiment, the alarm method of the alarm unit is not specifically limited. For example, the alarm unit can achieve alarm by means of hearing or vision. The hearing method can be achieved by a buzzer, and the visual method can be achieved by means of flashing indicator lights or display screen.

[0076] By incorporating an alarm unit into the temperature control system, maintenance personnel can be promptly notified to perform repairs.

[0077] Furthermore, such as Figure 5 As shown, the temperature control system further includes: a protection unit 5000, which is connected to the power supply of the dry-type transformer and the power supply of the oil-immersed transformer respectively, and the control terminal of the protection unit 5000 is connected to the processor 3000; the protection unit 5000 is used to cut off the power supply of the dry-type transformer when the winding temperature of the dry-type transformer is greater than the ninth threshold; and to cut off the power supply of the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than the tenth threshold and / or the oil surface temperature of the oil-immersed transformer is greater than the eleventh threshold; wherein the ninth threshold is greater than the sixth threshold, the tenth threshold is greater than the seventh threshold, and the eleventh threshold is greater than the eighth threshold.

[0078] By incorporating a protection unit into the temperature control system, the operation of the temperature control system can be stopped in a timely manner, reducing damage to the internal components of the temperature control system.

[0079] The above description is merely one specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A fan testing device, characterized in that, include: The system comprises a first switching assembly, a second switching assembly, a first current sampling unit, a second current sampling unit, and a controller. The first end of the first switch assembly is used to connect to the first power supply, and the second end of the first switch assembly is used to connect to the body fan of the box-type transformer; the first end of the second switch assembly is used to connect to the first power supply, and the second end of the second switch assembly is used to connect to the box-type transformer's enclosure fan. The control terminal of the first switch assembly, the control terminal of the second switch assembly, the output terminal of the first current sampling unit, and the output terminal of the second current sampling unit are connected to the controller; wherein, the first current sampling unit is used to acquire the current flowing through the main body fan, and the second current sampling unit is used to acquire the current flowing through the casing fan; The controller is configured to identify a fault in the main fan when the current of the main fan exceeds a first range.

2. The fan testing device according to claim 1, characterized in that, The first switching assembly includes a first contactor, and the second switching assembly includes a second contactor.

3. The fan testing device according to claim 1 or 2, characterized in that, The first current sampling unit includes a first current transformer, and the second current sampling unit includes a second current transformer.

4. The fan testing device according to claim 3, characterized in that, The controller is used to identify a fault in the enclosure fan when the current of the enclosure fan exceeds a second range.

5. A temperature control system for a box-type transformer, comprising: The processor, the temperature sampling unit, and the fan detection device according to any one of claims 1-4; wherein the box-type transformer includes a dry-type transformer; The output of the temperature sampling unit is connected to the processor; The temperature sampling unit is used to obtain the winding temperature of the dry-type transformer; The processor is configured to, when the winding temperature of the dry-type transformer is greater than a first threshold, activate a first switching assembly connected to the main body fan of the dry-type transformer, or activate both the first switching assembly connected to the main body fan of the dry-type transformer and the second switching assembly connected to the enclosure fan.

6. The temperature control system according to claim 5, characterized in that, The box-type transformer includes an oil-immersed transformer; The temperature sampling unit is also used to obtain the oil surface temperature of the oil-immersed transformer; The first current sampling unit is also used to acquire the operating current of the oil-immersed transformer; The processor is further configured to obtain the winding temperature of the oil-immersed transformer based on the operating current and the oil surface temperature, and to conduct the first switching assembly connected to the main fan of the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than a second threshold and / or the oil surface temperature is greater than a third threshold.

7. The temperature control system according to claim 5 or 6, characterized in that, The temperature control system is powered by a second power source, which includes an uninterruptible power supply.

8. The temperature control system according to claim 6, characterized in that, The temperature control system further includes an alarm unit, the control terminal of which is connected to the processor. The alarm unit is used to indicate that the dry-type transformer is overheating when the winding temperature of the dry-type transformer is greater than a sixth threshold; to indicate that the winding temperature of the oil-immersed transformer is overheating when the winding temperature of the oil-immersed transformer is greater than a seventh threshold; and to indicate that the oil surface temperature of the oil-immersed transformer is overheating when the oil surface temperature of the oil-immersed transformer is greater than an eighth threshold.

9. The temperature control system according to claim 8, characterized in that, The temperature control system further includes a protection unit, which is connected to the power supply of the dry-type transformer and the power supply of the oil-immersed transformer respectively, and the control terminal of the protection unit is connected to the processor. The protection unit is used to cut off the power supply to the dry-type transformer when the winding temperature of the dry-type transformer is greater than a ninth threshold; and to cut off the power supply to the oil-immersed transformer when the winding temperature of the oil-immersed transformer is greater than a tenth threshold, or when the oil surface temperature of the oil-immersed transformer is greater than an eleventh threshold; wherein the ninth threshold is greater than the sixth threshold, the tenth threshold is greater than the seventh threshold, and the eleventh threshold is greater than the eighth threshold.

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