Density relay verification device

Abstract

The embodiment of the utility model discloses a density relay checking device. The density relay checking device comprises a cylinder, a piston, a transition cavity and a breather pipe, the piston is arranged in the air cylinder and is in sliding connection with the air cylinder, and a closed space defined by the piston and the air cylinder is a variable-pressure cavity; the piston is used for sliding in the air cylinder, so that the volume of the variable-pressure cavity is increased to reduce the gas pressure in the variable-pressure cavity, or the volume of the variable-pressure cavity is reduced to increase the gas pressure in the variable-pressure cavity; one end of the breather pipe is connected with a variable-pressure cavity of the air cylinder, and the other end of the breather pipe is connected with a density relay of equipment to introduce gas in the equipment into the variable-pressure cavity; the transition cavity is arranged in the air cylinder and communicates with the variable-pressure cavity through the air inlet and outlet channel, the air inlet and outlet channel is provided with a switch, and the transition cavity is used for collecting air in the variable-pressure cavity so as to supplement the pressure reduction amount to the variable-pressure cavity and meet the requirement that when the size of air in a pipeline is increased due to the fact that a long breather pipe is used and installed, the pressure reduction amount is increased. The step-down amount reaches a target verification value.

Description

Technical Field

[0001] This utility model relates to the field of density relay calibration, and in particular to a density relay calibration device. Background Technology

[0002] In power systems, SF6 gas is widely used in high-voltage electrical equipment (such as circuit breakers and GIS switchgear) due to its excellent insulation and arc-extinguishing properties. SF6 density relays, as key components for monitoring the SF6 gas density within equipment, directly affect the safe and stable operation of electrical equipment. Therefore, regular calibration of SF6 density relays is an important part of power equipment operation and maintenance. For example, existing patent document CN112924858B discloses a field density relay calibration device and method, which has a simple overall structure and is easy to operate.

[0003] In actual calibration operations, an SF6 density relay calibration device needs to be connected to the density relay to be calibrated, and the connecting pipeline needs to extend from the calibration device to the cabinet where the density relay is installed. However, due to differences in the design of different models and specifications of electrical equipment, the installation position of the density relay on the cabinet is not uniform. Some are installed in an easily accessible area on the front of the cabinet, while others are installed in more concealed positions on the side, back, or inside the cabinet. This directly leads to significant differences in parameters such as the length and diameter of the connecting pipeline between the calibration device and the density relay, resulting in different volumes of SF6 gas contained inside the pipeline.

[0004] Currently, the palm-sized SF6 density relay calibrator, commonly used in the industry, is widely applied in mobile field calibration due to its compact size and portability. However, limited by its compact design, the internal gas system capacity of this type of calibrator is fixed, resulting in a fixed gas intake volume and relatively small overall values ​​during a single calibration process. In calibration scenarios with large gas volumes in the pipeline, the fixed and limited gas intake of the palm-sized calibrator makes it difficult to ensure that the total gas volume in the pipeline and the calibrator's internal gas system reaches the target value required for calibration, leading to insufficient gas pressure drop during the calibration process. Since SF6 density relay calibration requires observing the relay's action values ​​(such as alarm values ​​and lockout values) during specific pressure drop processes to determine its performance, an insufficient pressure drop cannot trigger the relay to produce an action response that meets the calibration standards. Ultimately, this results in inaccurate calibration and fails to meet the effective testing requirements of SF6 density relays in the field. Utility Model Content

[0005] This utility model discloses a density relay calibration device to solve the problem that the pressure drop is too small due to the large gas volume in the pipeline, which cannot meet the effective testing requirements of SF6 density relays on site.

[0006] This utility model embodiment provides a density relay calibration device, including: a cylinder, a piston, a transition chamber, and a vent pipe;

[0007] The piston is disposed inside the cylinder and is slidably connected to the cylinder. The sealed space formed by the piston and the cylinder is a pressure-changing chamber. The piston is used to slide inside the cylinder to increase the volume of the pressure-changing chamber and decrease the gas pressure inside the pressure-changing chamber, or to decrease the volume of the pressure-changing chamber and increase the gas pressure inside the pressure-changing chamber.

[0008] One end of the vent pipe is connected to the pressure-changing chamber of the cylinder, and the other end is used to connect to the density relay of the equipment to introduce gas into the pressure-changing chamber.

[0009] The transition chamber is disposed inside the cylinder and is connected to the pressure transformer chamber through an inlet and outlet air passage. The inlet and outlet air passage is equipped with a switch. The transition chamber is used to collect the gas in the pressure transformer chamber to supplement the pressure reduction of the pressure transformer chamber.

[0010] Furthermore, the cylinder includes a first cylinder and a second cylinder that are interconnected, the piston includes a first plug and a second plug that are interconnected, the pressure-changing chamber includes a first chamber and a second chamber, and the sealed space formed by the first plug and the first cylinder is the first chamber.

[0011] The first plug is connected to the second plug via a side plug, the side plug being in contact with the side wall of the first cylinder, and the sealed space formed by the second plug, the side plug, and the second cylinder is the second cavity;

[0012] The area of ​​the first plug is larger than that of the second plug. One side of the second cavity is connected to the first cavity through a side air pipe, and a side switch is provided on the side air pipe. The other side of the second cavity is connected to the air pipe.

[0013] Furthermore, the first cavity and the second cavity are of equal height, so that when the first plug reaches the top of the first cylinder, the second plug also reaches the top of the second cylinder, and the gas in the transformer cavity is completely discharged out of the cylinder.

[0014] Furthermore, the transition cavity is disposed between the first plug and the second plug, the diameter of the transition cavity is equal to the diameter of the first plug, and the sealed space formed by the second plug, the outer wall of the transition cavity, and the second cylinder is the second cavity.

[0015] Furthermore, the transition cavity is connected to the first cavity through the air inlet / outlet channel.

[0016] Furthermore, the air inlet and outlet channels include an air inlet channel and an air outlet channel. The air inlet channel is used to introduce gas from the first cavity to the transition cavity, and the air outlet channel is used to output gas from the transition cavity to the first cavity. An air inlet switch is provided on the air inlet channel, an air outlet switch is provided on the air outlet channel, and a one-way air inlet valve is provided at the air outlet end of the air inlet channel.

[0017] Furthermore, both the intake switch and the exhaust switch include solenoid valves.

[0018] Furthermore, the vent pipe is equipped with a pressure measuring unit and a temperature measuring unit.

[0019] Furthermore, a ventilation switch is provided on the ventilation pipe.

[0020] Furthermore, the piston is connected to the motor via a push rod.

[0021] Based on the technical solution, the embodiments provided by this utility model have the following advantages: In this embodiment, the gas in the device is introduced into the transformer chamber and the transition chamber via a density relay and a vent pipe. The piston slides in the cylinder to adjust the gas pressure in the transformer chamber. The density relay is connected to the transformer chamber. By judging whether the gas pressure change in the transformer chamber is consistent with the gas pressure change obtained by the density relay, the density relay is verified. By setting the transition chamber to store and release gas in the transformer chamber, the pressure drop of the density relay verification device reaches the target verification value when the gas volume in the pipeline increases due to the use of a longer vent pipe, thus meeting the verification requirements. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this utility model 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 utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the overall structure of a density relay verification device provided in an embodiment of this utility model;

[0024] Figure 2 This is a schematic diagram of the piston and cylinder assembly of a density relay calibration device provided in an embodiment of this utility model;

[0025] Figure 3 This is a schematic diagram (II) of the piston and cylinder assembly of a density relay calibration device provided in this embodiment of the present invention.

[0026] Explanation of reference numerals in the attached drawings: 1. Cylinder; 11. First cylinder; 12. Second cylinder; 2. Piston; 21. First piston body; 22. Second piston body; 23. Side piston body; 3. Transition chamber; 4. Vent pipe; 5. Variable pressure chamber; 51. First chamber; 52. Second chamber; 6. Inlet / outlet air passage; 61. Inlet air passage; 62. Outlet air passage; 71. Inlet switch; 72. Outlet air switch; 73. One-way inlet valve; 8. Side air pipe; 9. Side switch; 10. Pressure measuring unit; 13. Temperature measuring unit; 14. Vent switch; 15. Push rod; 16. Motor; 17. Air circuit interface. Detailed Implementation

[0027] In the description of this utility model, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0028] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0029] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0030] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0031] This utility model discloses a density relay calibration device.

[0032] Please see Figures 1-2 This utility model provides a density relay calibration device including a cylinder 1, a piston 2, a transition chamber 3, and a vent pipe 4;

[0033] Piston 2 is disposed inside cylinder 1 and is slidably connected to cylinder 1. The sealed space enclosed by piston 2 and cylinder 1 is pressure-changing chamber 5. Piston 2 is used to slide inside cylinder 1 to increase the volume of pressure-changing chamber 5 and decrease the gas pressure inside pressure-changing chamber 5, or to decrease the volume of pressure-changing chamber 5 and increase the gas pressure inside pressure-changing chamber 5.

[0034] One end of the vent pipe 4 is connected to the pressure transformer chamber 5 of the cylinder 1, and the other end is used to connect to the density relay of the equipment to introduce gas into the pressure transformer chamber 5.

[0035] The transition chamber 3 is installed inside the cylinder 1. The transition chamber 3 is connected to the transformer chamber 5 through the inlet and outlet air passage 6. The inlet and outlet air passage 6 is equipped with a switch. The transition chamber 3 is used to collect the gas in the transformer chamber 5 in order to supplement the pressure reduction of the transformer chamber 5.

[0036] Understandably, in practice, the gas inside the equipment is introduced into the transformer chamber 5 and the transition chamber 3 via a density relay and a vent pipe 4. The piston 2 slides within the cylinder 1 to adjust the gas pressure inside the transformer chamber 5. The density relay is connected to the transformer chamber 5. The density relay is verified by determining whether the change in gas pressure inside the transformer chamber 5 matches the change in gas pressure obtained by the density relay. Furthermore, some density relays are installed at higher equipment positions, requiring a longer vent pipe 4 to connect the density relay to the verification device. The volume change of the transformer chamber 5 is fixed, while the length of the vent pipe 4 varies with the installation position. When the vent pipe 4 is long, the pressure drop inside the transformer chamber 5 may not reach the target verification value. Therefore, this embodiment uses a transition chamber 3 to store and release gas in the transformer chamber 5, ensuring that the pressure drop of the density relay verification device reaches the target verification value when a longer vent pipe 4 is installed, thus meeting the verification requirements.

[0037] It should be noted that when the vent pipe 4 is too long, the pressure drop in the transformer chamber 5 may not reach the target calibration value. Examples of such cases are as follows:

[0038] When the maximum volume change of the transformer chamber 5 is 10L and the shorter vent pipe 4 has a volume of 5L, the maximum overall volume change is 10 / (10+5) = 2 / 3. When the maximum volume change of the transformer chamber 5 is 10L and the longer vent pipe 4 has a volume of 8L, the overall volume change is 10 / (10+8) = 5 / 9. Since 5 / 9 < 2 / 3, and pressure change and volume change are positively correlated, the pressure drop will inevitably decrease when the vent pipe 4 is longer, failing to meet the calibration requirements. By collecting gas from the transformer chamber 5 through the transition chamber 3, the pressure drop of the transformer chamber 5 can be supplemented by releasing the gas from the transformer chamber 5 to the transition chamber 3, even when the volume change of the transformer chamber 5 is fixed.

[0039] In a more specific embodiment, cylinder 1 includes a first cylinder 11 and a second cylinder 12 that are connected to each other, piston 2 includes a first plug body 21 and a second plug body 22 that are connected to each other, and transformer chamber 5 includes a first chamber 51 and a second chamber 52. The sealed space formed by the first plug body 21 and the first cylinder 11 is the first chamber 51.

[0040] The first plug 21 is connected to the second plug 22 via the side plug 23. The side plug 23 is in contact with the side wall of the first cylinder 11. The sealed space formed by the second plug 22, the side plug 23 and the second cylinder 12 is the second cavity 52.

[0041] The area of ​​the first plug 21 is larger than that of the second plug 22. One side of the second cavity 52 is connected to the first cavity 51 through the side air pipe 8. A side switch 9 is provided on the side air pipe 8. The other side of the second cavity 52 is connected to the air pipe 4.

[0042] Understandably, in practical implementation, existing density relay calibration technologies present a significant contradiction: calibration at low speed throughout the entire process, while ensuring accuracy, is excessively time-consuming; calibration at high speed throughout the entire process, near the test point, is prone to errors due to rapid pressure changes (not meeting the requirement of GGDW 11921.3 that "the load change rate should not exceed 1% of the range per second"). The variable diameter setting, however, achieves "fast / slow speed switching" within the same drive mechanism through the following principle, balancing efficiency and accuracy.

[0043] The device synchronously drives the movement of the first plug 21 (adapted to the first cylinder 11, with a larger area) and the second plug 22 (adapted to the second cylinder 12, with a smaller area). The sealed space enclosed by the first plug 21 and the first cylinder 11 is the first cavity 51, and the sealed space enclosed by the second plug 22, the side plug 23, and the second cylinder 12 is the second cavity 52. ​​When the side switch 9 of the side air pipe 8 is opened, the first cavity 51 and the second cavity 52 are connected. The rate of change of gas volume compression / expansion is determined by the first plug 21. Due to its large area, the volume change per unit time is large, corresponding to a rapid pressure change, which is suitable for rapid pressure increase / decrease in the initial stage of calibration, shortening the overall time consumption. When approaching the test point, the side switch 9 is closed, and only the second cavity 52 participates in gas pressure increase or decrease. At this time, the rate of change of volume is determined by the second plug 22. Due to its small area, the volume change per unit time is reduced, and the rate of pressure change decreases accordingly, meeting the requirements of high-precision calibration.

[0044] In a more specific embodiment, the first cavity 51 and the second cavity 52 are of equal height, so that when the first plug 21 reaches the top of the first cylinder 11, the first plug 21 also reaches the top of the second cylinder 12, and the gas in the transformer cavity 5 is completely discharged.

[0045] Understandably, in practice, after the calibration is completed, it is necessary to discharge the SF6 gas in the calibration device. Since the first chamber 51 and the second chamber 52 are at the same height, that is, the first cylinder 11 and the second cylinder 12 are at the same height, the first plug 21 and the second plug 22 are also at the same height. When the first plug 21 reaches the top of the first cylinder 11, the second cylinder 12 also reaches the top of the second cylinder 12. The side plug 23 is in contact with the side wall of the first cylinder 11. At this time, the gas can be completely discharged to avoid the residual SF6 gas from causing harm to the environment.

[0046] In a more specific embodiment, the transition cavity 3 is disposed between the first plug 21 and the second plug 22, the diameter of the transition cavity 3 is equal to the diameter of the first plug 21, and the sealed space formed by the second plug 22, the outer wall of the transition cavity 3 and the second cylinder 12 is the second cavity 52.

[0047] Understandably, in specific implementation, the transition chamber 3 is placed on the piston 2, specifically between the first plug 21 and the second plug 22. On the one hand, this position directly relies on the structure of the piston 2 itself, without needing to open up additional installation space outside the cylinder 1, nor occupying other functional areas inside the cylinder 1, thus maximizing the use of the limited space inside the cylinder 1 and making the overall device structure more compact. On the other hand, the transition chamber 3 is independently located between the two plugs and does not occupy its internal volume with the pressure regulating chamber 5, ensuring that the transition chamber 3 and the pressure regulating chamber 5 always maintain the maximum effective volume, meeting the requirements for chamber space during gas pressure regulation.

[0048] In a more specific embodiment, the transition cavity 3 is connected to the first cavity 51 via the air inlet / outlet channel 6.

[0049] Understandably, in practice, since the first cavity 51 and the second cavity 52 have the same height and the area of ​​the first plug 21 is larger than that of the second plug 22, the volume of the first cavity 51 is larger than that of the second cavity 52. ​​Because the first cavity 51 has a larger volume, when the calibration device enters the pressure boosting stage after completing the pressure reduction compensation, it is necessary to introduce gas from the transition cavity 3 into the first cavity 51 to replenish the pressure, so that the pressure is more gradual and there will be no "pressure surge". However, when the same amount of gas is introduced into the smaller second cavity 52, the pressure changes more drastically and it is very easy to exceed the pressure range allowed by the system.

[0050] In a more specific embodiment, the inlet / outlet passage 6 includes an inlet passage 61 and an outlet passage 62. The inlet passage 61 is used to introduce gas from the first chamber 51 to the transition chamber 3, and the outlet passage 62 is used to output gas from the transition chamber 3 to the first chamber 51. An inlet switch 71 is provided on the inlet passage 61, and an outlet switch 72 is provided on the outlet passage 62. A one-way inlet valve 73 is provided at the outlet end of the inlet passage 61. It can be understood that, in specific implementation, when the piston 2 performs the pressure reduction action, in order to supplement the pressure reduction, when the inlet switch 71 is opened, the gas in the pressure-sensitive transformer chamber 5 enters the transition chamber 3 to reduce the pressure of the gas in the transformer chamber 5. Since the piston 2 moves away from the top of the cylinder during the pressure reduction process of the transformer chamber 5, the gas in the transition chamber 3 may not be able to remain stably in the transition chamber 3 under the suction force of the piston 2. By setting the one-way inlet valve 73, the gas in the transition chamber 3 can be stabilized in the transition chamber 3.

[0051] In a more specific embodiment, the air intake switch 71 and the air exhaust switch 72 are solenoid valves. Since the air intake switch 71 and the air exhaust switch 72 are located in the transition cavity 3, both the air intake switch 71 and the air exhaust switch 72 include solenoid valves to facilitate the control of air intake and exhaust.

[0052] It should be noted that the working principle of the calibration device for voltage reduction and voltage boost calibration using the transition cavity 3 is as follows:

[0053] Pressure Reduction: For cases where the vent tube 4 is relatively long, after the gas intake stage is completed, the pressures in the first chamber 51, the second chamber 52, and the transition chamber 3 are equal. First, the piston 2 is pushed to increase the pressure in the first chamber 51 and the second chamber 52. At this time, the pressure in the first chamber 51 is greater than that in the transition chamber 3. Then, the air intake switch 71 is opened, and gas enters the transition chamber 3 from the first chamber 51 to supplement the pressure reduction in the first chamber 51.

[0054] Pressure Boosting: When the vent pipe 4 is relatively long, after the pressure reduction stage is completed, the pressure in the transition chamber 3 is greater than that in the first chamber 51. At this time, the inlet switch 71 is closed and the outlet switch 72 is opened. Gas enters the first chamber 51 from the transition chamber 3. After the gas that entered the transition chamber 3 during the pressure boosting stage is discharged into the first chamber 51, the outlet switch 72 is closed. Then, the piston 2 is pushed to compress the gas in the first chamber 51 and the second chamber 52, thereby achieving pressure boosting and ensuring that the pressure boosting meets the requirements.

[0055] In a more specific embodiment, the air outlet switch 72 also includes a miniature air pump.

[0056] Understandably, during the actual implementation, when the verification is completed, the gas in the transition chamber 3 is extracted into the first chamber 51 by a micro air pump and then discharged through the vent pipe 4, thereby venting the gas in the transition chamber 3.

[0057] In a more specific embodiment, a pressure measuring unit 10 and a temperature measuring unit 13 are provided on the vent pipe 4. It is understood that, in practical implementation, the density relay works by sensing the pressure and temperature of the gas being measured through built-in components. After temperature compensation processing or calculation using the gas state equation, the pressure signal is corrected to a parameter that accurately reflects the gas density, thereby enabling monitoring of the gas density and triggering subsequent protection actions. In this embodiment, the pressure measuring unit 10 and the temperature measuring unit 13 are located on the vent pipe 4 to ensure that the detected data and the gas on the side of the density relay to be calibrated are "from the same source" to match the calibration target, avoid physical and spatial switching interference caused by the movement of the piston 2 within the cylinder 1, ensure data stability, adapt to on-site installation and maintenance requirements, and simplify the structure of the cylinder 1.

[0058] In a more specific embodiment, a ventilation switch 14 is provided on the ventilation pipe 4.

[0059] Understandably, in practice, the ventilation pipe 4 is equipped with a ventilation switch 14, which can accurately supply gas during calibration to ensure the orderly conduct of the calibration process, and can also cut off the gas path during non-calibration periods (such as when the device is calibrated, the pipeline is maintained, or the relay is repaired) to prevent gas leakage and avoid the entry of external impurities, while ensuring the safety of personnel operation and the stability of the equipment.

[0060] In a more specific embodiment, piston 2 is connected to motor 16 via push rod 15.

[0061] Understandably, in practical implementation, the piston 2 of the density verification device is connected to the motor 16 via the push rod 15. The core advantage lies in the ability to leverage the precise controllability of the motor 16 (such as the precise displacement of a stepper motor and the stable power output of a servo motor) to achieve fine-tuning of the stroke, speed, and thrust of the push rod 15 in pushing the piston 2. This allows for precise control of the piston 2's motion state, ensuring that the device can stably and uniformly change the gas volume within the sealed chamber to regulate pressure. This provides accurate and repeatable pressure parameters for density relay verification, while avoiding errors and instability caused by manual operation, thus improving the automation level and accuracy of the verification process.

[0062] The present invention will now be described in detail with reference to specific embodiments. The calculation methods involved in this technical solution are all existing technologies, and are used to further explain and demonstrate the beneficial effects of the density relay verification device provided by the present invention in the use of any of the above embodiments, so that those skilled in the art can understand the contribution of the solution. These embodiments are not limitations on the present invention, and those skilled in the art can adjust them according to the verification purpose in practical applications.

[0063] S1. Gas density relay calibration procedure:

[0064] The method for calibrating the SF6 gas density relay is mainly to increase or decrease the pressure by sliding the piston 2 relative to the cylinder 1, while detecting the gas temperature and pressure. The state equation of SF6 gas, namely the Beattie-Bridgman equation, as shown in formula (1), is used to convert the detected pressure into the pressure value corresponding to 20℃. Then, according to the method and requirements of the inspection procedure, it is compared with the displayed value of the SF6 gas density relay to determine whether the indication error, hysteresis error, set point deviation, switching error, etc. of the SF6 gas density relay are qualified.

[0065] (1)

[0066]

[0067] In the formula:

[0068] p — pressure, ×0.1MPa;

[0069] ρ—density, kg / m³ 3 ;

[0070] T—Temperature, K.

[0071] S2, Gas Extraction Stage:

[0072] 1) Conventional gas extraction procedure:

[0073] The palm-type density relay calibration device pushes piston 2 to the top, ensuring no gas remains inside. At this point, the first plug 21 is positioned on top of the first cylinder 11, and the second plug 22 is positioned on top of the second cylinder 12. The air inlet 17 is connected to the air inlet on one side of the density relay to be calibrated. The side switch 9 and the air vent switch 14 are opened, allowing a small amount of gas to fill the first chamber 51 and the second chamber 52. Simultaneously, the motor 16 is controlled to move the push rod 15 downwards a distance l. At this point, the pressure values ​​of the first chamber 51 and the second chamber 52 in cylinder 1 are equal to the chamber pressure.

[0074] After the gas extraction stage is completed, the volume V1 of the second cavity 52 is:

[0075] (2)

[0076] The volume V2 of the first cavity 51 is:

[0077] (3)

[0078] The palm-type density relay calibration device automatically detects the current gas pressure P0 and temperature T0, and automatically calculates the gas density ρ0 and the pressure P converted to 20℃ according to formula (1). 200 .

[0079] (4)

[0080] Based on formulas (2), (3), and (4), the total mass m0 of the gas is calculated as follows:

[0081] (5)

[0082] 2) Self-compressing gas extraction scheme:

[0083] If the density relays are installed in different locations, resulting in a long pipeline between the testing equipment and the density relays, the gas intake of the density relay calibration device needs to be adjusted according to the actual situation. If a large gas intake is required, a self-compressing gas intake scheme should be adopted. The specific operating steps are as follows:

[0084] The palm-type density relay calibration device pushes piston 2 to the top, ensuring no gas remains inside. At this point, the first plug 21 is positioned on top of the first cylinder 11, and the second plug 22 is positioned on top of the second cylinder 12. The air inlet 17 is connected to the air inlet on one side of the density relay to be calibrated. The side switch 9 and the air vent switch 14 are turned on, allowing a small amount of gas to fill the first chamber 51 and the second chamber 52. Simultaneously, the motor 16 is controlled to move the push rod downwards a distance l.

[0085] During self-compression, the ventilation switch 14 and the exhaust switch 72 are closed, while the side switch 9, the intake switch 71, and the one-way intake valve 73 are opened. The control motor 16 moves the push rod 15 upward, compressing the gas in the first chamber 51 and the second chamber 52 into the transition chamber 3. Due to the one-way intake, the gas cannot escape after entering the transition chamber 3, thus completing one compression cycle.

[0086] The number of compression cycles is determined based on the pressure reduction and gas intake requirements. Simultaneously, based on the volume V3 within the transition chamber 3 and the automatic detection of the current gas pressure P1 and temperature T1 by the palm-type density relay calibration device, the gas density ρ1 and the pressure P converted to 20℃ are automatically calculated according to formula (1). 200 .

[0087] Based on formulas (2), (3), and (4), the total mass of the gas, m0', is calculated as follows:

[0088] (6)

[0089] S3, Pressure Reduction Phase:

[0090] 1) Rapid blood pressure reduction phase:

[0091] Motor 16 controls the push rod to drive piston 2 to move downward at a constant speed v. The total mass of the gas remains unchanged, and the volume of the pressure-changing chamber 5 increases, thereby causing its pressure to decrease smoothly.

[0092] Combining equations (1) and (4), we get:

[0093] (7)

[0094] The depressurization process is relatively short, and the gas temperature remains essentially constant. Differentiating equation (7) with respect to time t yields the relationship between the rate of pressure change and the rate of volume change:

[0095] (8)

[0096] In the formula:

[0097] —Pressure change rate, ×0.1MPa / s;

[0098] — Rate of change of volume, m 3 / s;

[0099] The gas pressure is monitored in real time by the pressure measuring unit 10. When the pressure point to be verified is far away, a rapid pressure reduction is adopted. The side switch 9 is in the open state, and the first cavity 51 and the second cavity 52 are connected. Let the distance between the push rod 15 and the top of the cylinder 1 be l1. Substitute it into equations (2) and (3) to obtain the volume V1' of the second cavity 52 and the volume V2' of the first cavity 51. Add them to obtain the total volume V3' of the transformer cavity 5.

[0100] (9)

[0101] Differentiating equation (9) with respect to time t yields the rate of volume change. Relationship with the velocity v of push rod 15:

[0102] (10)

[0103] Formulas (6), (7), (8), (9), and (10) are used simultaneously to calculate the rapid blood pressure drop rate. , where p3 is the gas pressure change value during the rapid depressurization phase of the transformer chamber 5.

[0104] 2) Slow blood pressure reduction phase:

[0105] When approaching the pressure point to be calibrated, the side switch is automatically closed. At this time, although the movement speed v of the push rod 15 remains unchanged, only the second cavity 52 is connected to the density relay to be calibrated. The rate of increase in volume slows down, and the rate of decrease in pressure also decreases accordingly. The rate of pressure change should not exceed 1% of the range per second. The current gas pressure P1 and temperature T1 are detected in real time. The palm-type density relay calibration device automatically calculates the gas density ρ1 and the pressure P converted to 20℃ according to formula (1). 201The value is compared with the actual displayed value of the density relay. Let the distance from the push rod to the top of the cylinder be l2.

[0106] At this time, the volume V4 of the second cavity 52 is:

[0107] (11)

[0108] Differentiating equation (11) over time t yields the rate of volume change. Relationship with the velocity v of push rod 15:

[0109] (12)

[0110] (13)

[0111] At the instant the side switch 9 is closed, the gas density in the second chamber 52 remains unchanged. V1' is the volume of the second chamber 52 when the side switch 9 is closed after rapid pressure reduction (the distance between the push rod 15 and the top of the cylinder 1 is l1). m4 is the mass of the gas in the second chamber 52 when the side switch 9 is closed and after the side switch 9 is closed.

[0112] Formulas (7), (8), (11), (12), and (13) are used simultaneously to calculate the slow voltage drop rate. p4 is the gas pressure change value during the slow depressurization phase of the second chamber 52.

[0113] 3) Calculation of the slowdown factor for pressure transformation rate:

[0114] At the instant the side switch 9 switches, the gas density inside the second chamber 52 remains unchanged. At this time:

[0115] (14)

[0116] Jointly established (14) , Solving for the rate of decrease in pressure transformation (n):

[0117] (15)

[0118] As can be seen from equation (15), during the pressure reduction process, after the side switch 9 is closed, the pressure reduction rate slows down, and the closer r2 is to r1, the greater the rate of decrease n of the pressure change rate.

[0119] 4) Calculation of the lower limit of pressure verification:

[0120] Motor 16 controls push rod 15 to move downwards at a constant speed v to the bottom, with a moving distance of h. At this point, the total gas volume in transformer chamber 5 reaches its maximum value V.max :

[0121] (16)

[0122] like Figure 3 As shown, h = h1 = h2 = h3.

[0123] V max Substituting m0' into equation (7), the lower limit of pressure verification P for the palm density relay verification device can be obtained. min (Temperature is 20℃).

[0124] S4, Boost Phase:

[0125] The boosting verification process is similar to the depressurization verification process. The motor 16 drives the piston 2 to move at a constant speed to the top. The opening and closing of the control side switch 9 controls the rate of volume change, thereby realizing the change of the boosting rate.

[0126] Motor 16 controls push rod 15 to move upwards at a constant speed v to the top, the total mass of gas m0' remains unchanged, and the total volume reaches the minimum value V. min :

[0127] (17)

[0128] V min Substituting m0' into equation (7), the upper limit of pressure verification P of the palm density relay verification device can be obtained. max (Temperature is 20℃).

[0129] According to the principle in this section, the pressure points of the density relay can be tested by variable speed pressure reduction / increase, and the indication error, hysteresis error, set point deviation, and switching error of the SF6 gas density relay can be judged to be qualified. In summary, this utility model adopts a variable displacement cylinder 1 structure, and the motor 16 drives the piston 2 to reciprocate in the cylinder 1 with different radii. Through pressure speed adjustment, the set point pressure is output accurately and stably, so that the pressure change rate is faster when it is far from the set point and slower when it is close to the set point. This ensures the calibration speed while improving the calibration accuracy. The SF6 gas density relay can be calibrated across its entire range in about 4 minutes without disassembly.

[0130] This invention directly uses the gas inside the gas chamber as the calibration gas source, eliminating the need to carry other external gas sources on site and reducing the size of traditional box-type or benchtop density relay calibrators.

[0131] The device uses a self-compression structure to allow for a large and adjustable gas intake, which can adapt to the gas volume differences caused by different actual working conditions, ensuring that the target value is reached during the detection process and that the pressure drop is sufficient to fully meet the detection requirements.

[0132] It should be noted that the terms used to describe positional relationships in the above examples and accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. The various embodiments of this utility model described above are merely examples for clearly illustrating this utility model, and are not intended to limit the implementation of this utility model. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the scope of protection of the claims of this utility model.

Claims

1. A density relay calibration device, characterized in that, include: Cylinder, piston, transition chamber, and vent pipe; The piston is disposed inside the cylinder and is slidably connected to the cylinder. The sealed space formed by the piston and the cylinder is a pressure-changing chamber. The piston is used to slide inside the cylinder to increase the volume of the pressure-changing chamber and decrease the gas pressure inside the pressure-changing chamber, or to decrease the volume of the pressure-changing chamber and increase the gas pressure inside the pressure-changing chamber. One end of the vent pipe is connected to the pressure-changing chamber of the cylinder, and the other end is used to connect to the density relay of the equipment to introduce gas into the pressure-changing chamber. The transition chamber is disposed inside the cylinder and is connected to the pressure transformer chamber through an inlet and outlet air passage. The inlet and outlet air passage is equipped with a switch. The transition chamber is used to collect the gas in the pressure transformer chamber to supplement the pressure reduction of the pressure transformer chamber.

2. The density relay calibration device according to claim 1, characterized in that, The cylinder includes a first cylinder and a second cylinder that are connected to each other. The piston includes a first plug and a second plug that are connected to each other. The pressure-changing chamber includes a first chamber and a second chamber. The sealed space formed by the first plug and the first cylinder is the first chamber. The first plug is connected to the second plug via a side plug, the side plug being in contact with the side wall of the first cylinder, and the sealed space formed by the second plug, the side plug, and the second cylinder is the second cavity; The area of ​​the first plug is larger than that of the second plug. One side of the second cavity is connected to the first cavity through a side air pipe, and a side switch is provided on the side air pipe. The other side of the second cavity is connected to the air pipe.

3. The density relay calibration device according to claim 2, characterized in that, The first cavity and the second cavity are of equal height, so that when the first plug reaches the top of the first cylinder, the second plug also reaches the top of the second cylinder, and the gas in the transformer cavity is completely discharged out of the cylinder.

4. The density relay calibration device according to claim 3, characterized in that, The transition cavity is disposed between the first plug and the second plug, and the diameter of the transition cavity is equal to the diameter of the first plug. The sealed space formed by the second plug, the outer wall of the transition cavity, and the second cylinder is the second cavity.

5. A density relay calibration device according to claim 4, characterized in that, The transition cavity is connected to the first cavity through the air inlet and outlet channels.

6. A density relay calibration device according to claim 5, characterized in that, The air inlet and outlet channels include an air inlet channel and an air outlet channel. The air inlet channel is used to introduce gas from the first cavity to the transition cavity, and the air outlet channel is used to output gas from the transition cavity to the first cavity. An air inlet switch is provided on the air inlet channel, an air outlet switch is provided on the air outlet channel, and a one-way air inlet valve is provided at the air outlet end of the air inlet channel.

7. A density relay calibration device according to claim 6, characterized in that, Both the air intake switch and the air outlet switch include solenoid valves.

8. A density relay calibration device according to any one of claims 1-7, characterized in that, The vent pipe is equipped with a pressure measuring unit and a temperature measuring unit.

9. A density relay calibration device according to claim 8, characterized in that, A ventilation switch is installed on the ventilation pipe.

10. A density relay calibration device according to claim 9, characterized in that, The piston is connected to the motor via a push rod.

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