UHV Converter Transformer Emergency Oil Drainage and Nitrogen Injection Device, Control System and Method

Abstract

Ultra-high voltage converter transformer emergency oil drainage and nitrogen injection device, control system and method, belonging to the field of ultra-high voltage converter transformer emergency oil drainage, including a main body three-way, a shut-off valve, a main body oil tank oil drainage device, an oil conservator oil drainage device, a nitrogen injection device and an accident oil pool; the main body three-way is arranged between the upper part of the main body oil tank and the bottom of the oil conservator, the first port of the main body three-way is connected to the bottom of the oil conservator through a pipeline, the second port is connected to the oil conservator oil drainage device through a pipeline, a shut-off valve is arranged at the third port, the output port of the shut-off valve is connected to the main body oil tank through a pipeline, the main body oil tank oil drainage device is connected to the bottom of the main body oil tank through a pipeline, and the output ends of the main body oil tank oil drainage device and the oil conservator oil drainage device are respectively connected to the accident oil pool through pipelines; an inflation port is opened on the main body oil tank and connected to the nitrogen injection device; when an initial fire occurs, the oil inside the main body oil tank and the oil conservator can be quickly, safely and reliably discharged to avoid air entering the main body oil tank and causing the fire to spread.

Description

Technical Field

[0001] The present invention belongs to the field of emergency oil drainage for UHV converter transformers, and particularly relates to an emergency oil drainage and nitrogen injection device, a control system and a method for UHV converter transformers. Background Art

[0002] UHV refers to voltage levels of 1000 kV and above for alternating current and ±800 kV and above for direct current. The main characteristics of UHV power transmission are high voltage, large transmission capacity, and narrow line corridors, which are suitable for high-power and long-distance power transmission.

[0003] A converter station is a system for mutual energy conversion between direct current and alternating current in a UHV power transmission project. In addition to equipment similar to those in an AC substation such as an AC yard, a converter station also has the following equipment: converters, converter transformers, AC / DC filters, reactive power compensation equipment, smoothing reactors, etc.

[0004] A converter transformer is a crucial key equipment in a UHV power transmission project and is the core equipment at the rectifying and inverting ends of the AC and DC power transmission systems. A converter transformer belongs to an oil-immersed transformer. The transformer oil filled in the oil tank of an oil-immersed transformer is a hydrocarbon liquid mixture mainly composed of naphthenic base refined from crude oil, usually divided into No. -25 (pour point) and No. -45 transformer oil, and No. -25 is commonly used. The initial boiling point of the transformer oil is greater than 300 °C. When leaving the factory, its flash point is above 140 °C. After being filled into the transformer and working for a long time, due to local high temperature and high voltage cracking, a small amount of hydrogen and light hydrocarbons will be generated, making the gas phase space mixed with gaseous combustibles.

[0005] By summarizing and analyzing several oil-immersed transformer fire cases at home and abroad, the oil-immersed transformer fire modes can be divided into three categories: initial insulator root burst fire, local oil tank burst fire, and overall oil tank burst fire. Among them, the initial insulator root burst fire is the main one, the local oil tank burst fire is mostly developed from the insulator root fire, and the overall oil tank burst fire is relatively rare.

[0006] Since the gas phase space in the insulator is most likely to generate electric sparks, and the insulator is the weakest part of the oil-immersed transformer, the initial fire of the oil-immersed transformer mostly shows an explosion and ignition at the root of the insulator. When the oil of the oil-immersed transformer catches fire, the oil product is mostly at a relatively high temperature, and when the fire extinguishing system operates, it has often burned for a certain period of time, causing the metal structure to be heated to a relatively high temperature. Therefore, the main characteristics of an oil-immersed transformer fire are the combined action of oil fire and high-temperature metal structure.

[0007] The converter transformers used in the UHV power transmission field contain a large amount of transformer oil. The oil storage volume inside the main body tank of the in-service UHV converter transformer in China is about 130 - 200 tons, and the oil storage volume in the conservator is generally 10 - 30 tons. The model is mostly Kunlun KI50X. The conservator is connected to the main body tank through a valve. Therefore, the total oil storage volume inside the entire converter transformer is about 140 - 230 tons. When an explosion and fire occur at the root of the bushing insulator on the grid side, it will cause secondary damage to the main body tank of the UHV converter transformer, blast a gap in the main body tank of the converter transformer, and a large amount of transformer oil will overflow through the gap of the transformer under the action of gravity, flow through the complex surface of the transformer and be partially ignited, forming a complex vertical flow, providing continuous fuel supply for the external fire source of the transformer and resulting in continuous combustion. At the same time, the externally ignited transformer oil fire has a heating effect on the transformer body, increasing the oil temperature inside the transformer. The transformer oil expands in volume due to thermal expansion and contraction, further increasing the amount of oil leaking out, leading to the further deterioration and loss of control of the fire, and it is almost impossible to be covered by the fire extinguishing agent. This is one of the fundamental reasons why it is difficult to extinguish the fire of the converter transformer in UHV power transmission.

[0008] Therefore, when a fire accident occurs in the UHV converter transformer, it is very necessary to drain a large amount of transformer oil inside the converter transformer into the accident oil pool, so as to reduce the possibility of the fire getting out of control, weaken the difficulty of fire fighting, and improve the fire extinguishing success rate.

[0009] In the prior art, the Chinese patent application "High-temperature flame-retardant combined valve control system for accident oil drainage pipeline of UHV transformer" with the application publication date of November 13, 2018 and the application publication number of CN108806932A discloses a high-temperature flame-retardant combined valve control system for accident oil drainage pipeline of UHV transformer. By setting a pipeline comprehensive control mechanism and a one-way valve, it realizes the blocking of the oil drainage pipeline at low oil level and the opening of the pipeline for oil drainage at high oil level, and realizes the real-time control of the oil level in the oil drainage pipeline. The valve in the annular cross-section of the oil drainage pipeline rotates left and right around the axis to realize the connection of the pipeline.

[0010] The disadvantages of the above Chinese patent application are as follows:

[0011] (1) The conservator and the main body tank of the transformer share a set of oil drainage system. Since the main body tank of the converter transformer is forced to drain oil, there is a certain pressure in its oil drainage pipeline, while the oil in the conservator is drained by the natural pressure of the oil surface height. If the oil drainage of the conservator is connected to the oil drainage pipeline of the transformer body, it will cause the oil drainage time of the conservator to be too long, or due to the pressure effect, the oil in the conservator cannot be drained at all.

[0012] (2) Only the fire prevention design is carried out from the oil accumulation and drainage tank to the accident oil tank, without the fire prevention design for the overall system. During the oil drainage process, the flame will enter the emptied oil pipe together with a large amount of unburned combustible vapor and un-premixed reaction air, resulting in the spread of the fire in the oil pipe.

[0013] (3) All valves are in serial design, and the system reliability is not high. If a single valve fails to open, the system cannot drain oil.

[0014] Moreover, during emergency oil drainage, as the oil level in the main tank of the converter transformer drops, the air outside the main tank of the converter transformer will enter the main tank of the converter transformer through the transformer notch. The entry of air into the emptied main tank of the converter transformer will cause the spread of the fire inside the main tank of the converter transformer. In the prior art, while draining the oil from the main tank of the converter transformer, nitrogen is injected into the main tank of the converter transformer to solve this problem. This method has a high fire extinguishing efficiency, the non-re-ignition fire extinguishing time is less than 2 minutes, and the fire extinguishing time during the test is only 22 seconds. The continuous nitrogen injection time is greater than 30 minutes, and the tank temperature can be reduced to below 0°C. Compared with the foam spray fire extinguishing device, this device does not require the construction of a fire protection room and a spraying pipeline network. The foam tank and the nitrogen cylinder group are large in volume and high in cost, and the disassembly of the transformer is affected during the maintenance of the spraying pipeline network. The foam fire extinguishing agent has a service life limit, while the nitrogen fire extinguishing agent has no timeliness and is low in cost.

[0015] Experimental studies have shown that if the ignited insulating material inside the transformer is not protected and cooled by nitrogen, it can still radiate the transformer oil to form combustion, causing re-ignition of the transformer oil inside. The injected nitrogen plays a controlling role in the combustion of the transformer oil inside. When the flow rate of the injected nitrogen is greater than the loss flow rate at the outlet of the transformer bushing base, the combustion of the transformer oil inside can be completely suffocated (when the oil drainage stops, the remaining transformer oil level is about one-third of the original liquid level).

[0016] For example, in the prior art, the Chinese invention patent "Combined distribution type oil drainage and nitrogen filling fire extinguishing system and fire extinguishing method" with the authorization announcement number CN104721992B and the authorization announcement date of June 9, 2017, discloses a combined distribution type oil drainage and nitrogen filling fire extinguishing system, including a nitrogen gas source, a control cabinet, a fire detector arranged on the top of each transformer, a transformer oil storage control system with a gas relay, a transformer oil drainage system with an oil drainage control valve, a transformer nitrogen filling system with a nitrogen filling control valve arranged on each transformer. The transformer nitrogen filling systems are all connected to the nitrogen gas source; the fire detector, the gas relay, the oil drainage control valve, and the nitrogen filling control valve are all electrically connected to the control cabinet; the nitrogen filling system further includes a one-way throttle valve, a nitrogen filling pipeline, and a constant temperature valve. The nitrogen filling pipeline is connected to the nitrogen gas source, the nitrogen filling pipeline passes through the transformer wall at the lower side of the conservator and extends into the conservator, the constant temperature valve is arranged on the nitrogen filling pipeline inside the conservator, and the one-way throttle valve is arranged on the nitrogen filling pipeline between the nitrogen filling control valve and the transformer.

[0017] Although the above-mentioned Chinese invention patent solves the technical problem that after the fire detector and the gas relay are used for a period of time, the false alarm rate increases with the increase of the use time, and the false alarm will cause the oil-draining and nitrogen-filling device to malfunction, resulting in the tripping of the main transformer and causing a large-scale sudden power outage accident. However, in addition to the aforementioned disadvantages of the "Ultra-high Voltage Transformer Accident Oil-draining Pipeline High-temperature Flame-retardant Combined Valve Control System", the above-mentioned Chinese patent also has the following disadvantages: nitrogen is injected from the bottom of the main body oil tank of the converter transformer, and the fire extinguishing effect is poor.

[0018] Therefore, when a fire occurs in the early stage of the ultra-high voltage converter transformer, how to quickly, safely and reliably drain a large amount of transformer oil inside the main body oil tank and the conservator and prevent the air outside the main body oil tank of the converter transformer from entering the main body oil tank of the converter transformer through the transformer gap is an urgent problem to be solved. Summary of the Invention

[0019] The technical problem to be solved by the present invention is how to quickly, safely and reliably drain a large amount of transformer oil inside the main body oil tank and the conservator and prevent the air outside the main body oil tank of the converter transformer from entering the main body oil tank of the converter transformer when a fire occurs in the early stage of the ultra-high voltage converter transformer.

[0020] The present invention solves the above technical problems through the following technical solutions.

[0021] An emergency oil-draining and nitrogen-injecting device for an ultra-high voltage converter transformer, which is used for draining the oil of the main body oil tank (1) and the conservator (10) of the converter transformer, includes a main body three-way (11), a cut-off valve (12), a main body oil tank oil-draining device, a conservator oil-draining device, a plurality of nitrogen-injecting devices and an accident oil pool; the main body three-way (11) is arranged between the upper part of the main body oil tank (1) and the bottom of the conservator (10), the first port of the main body three-way (11) is connected to the bottom of the conservator through a pipeline, the second port is connected to the conservator oil-draining device through a pipeline, a cut-off valve (12) is arranged at the third port, the output port of the cut-off valve (12) is connected to the main body oil tank (1) through a pipeline, the main body oil tank oil-draining device is connected to the bottom of the main body oil tank (1) through a pipeline, and the output ends of the main body oil tank oil-draining device and the conservator oil-draining device are respectively connected to the accident oil pool through pipelines; a plurality of air-inflating ports are opened at the middle and upper positions on both sides of the main body oil tank (1), and the plurality of nitrogen-injecting devices are connected to the plurality of air-inflating ports; when draining oil, the cut-off valve (12) is closed to cut off the oil supply pipeline from the conservator (10) to the main body oil tank (1), the main body oil tank oil-draining device and the conservator oil-draining device independently drain oil to the accident oil pool respectively, and at the same time, the plurality of nitrogen-injecting devices inject nitrogen into the main body oil tank (1).

[0022] When the emergency oil drainage device of the UHV converter transformer receives the oil drainage start signal, it closes the shut-off valve, cuts off the oil drainage pipeline from the conservator to the explosion-proof and fire-retardant arrester of the main tank, and the main tank and the conservator each adopt a set of oil drainage systems to drain oil independently. The oil in the conservator no longer enters the main tank, greatly shortening the oil drainage time. At the same time of emergency oil drainage, the nitrogen injection device fills nitrogen into the main tank to prevent the spread of fire inside the emptied main tank of the converter transformer due to the entry of air.

[0023] As a further improvement of the technical solution of the present invention, the oil drainage device of the main tank includes a maintenance valve (2), a first oil flowmeter (3), a first dual-redundancy configured electric valve group (4), a plurality of main tank leakage alarm devices (5), and a plurality of main tank butterfly valves (6). The main tank (1), the maintenance valve (2), the first oil flowmeter (3), the first dual-redundancy configured electric valve group (4), the plurality of main tank leakage alarm devices (5), and the plurality of main tank butterfly valves (6) are sequentially connected to the accident oil pool through pipelines along the negative x-axis direction.

[0024] As a further improvement of the technical solution of the present invention, the oil drainage device of the conservator includes a second dual-redundancy configured electric valve group (13), a second oil flowmeter (14), a plurality of conservator leakage alarm devices (15), and a plurality of conservator butterfly valves (16). The second dual-redundancy configured electric valve group (13), the second oil flowmeter (14), the plurality of conservator leakage alarm devices (15), and the plurality of conservator butterfly valves (16) are sequentially connected to the accident oil pool through pipelines along the negative y-axis direction.

[0025] As a further improvement of the technical solution of the present invention, the nitrogen injection device includes a plurality of nitrogen cylinder groups (21), a gas collecting valve (22), an injection pipeline (23), a control valve (24), and a nitrogen injection port (25). The plurality of nitrogen cylinder groups (21) are connected to one end of the injection pipeline (23) through the gas collecting valve (22). The other end of the injection pipeline (23) is connected to the nitrogen injection port (25). A control valve (24) is provided between the injection pipeline (23) and the nitrogen injection port (25). The nitrogen injection port (25) is connected to the inflation ports at the upper-middle positions on both sides of the main tank (1).

[0026] As a further improvement of the technical solution of the present invention, the calculation formula for the number of nitrogen cylinders in the nitrogen cylinder group (21) is:

[0027] s = V2 / V1 (1)

[0028]

[0029] Where s is the number of nitrogen cylinders, P1 is the pressure of nitrogen in the main body oil tank after nitrogen filling, P2 is the pressure of nitrogen in the nitrogen cylinders, V1 is the volume occupied by a single nitrogen cylinder filled into the main body oil tank at a pressure of P1, V2 is the volume of transformer oil in the main body oil tank, φ is the diameter of the nitrogen cylinder, and h is the height of the nitrogen cylinder.

[0030] As a further improvement of the technical solution of the present invention, the first dual-configured electric valve group (4) includes two normally closed butterfly valves. After the two normally closed butterfly valves are connected in parallel, one end is connected to the first oil flowmeter (3) through a pipeline, and the other end is connected to the main body oil tank leakage alarm (5) through a pipeline. The power supply circuit and control circuit of each normally closed butterfly valve are independently powered.

[0031] As a further improvement of the technical solution of the present invention, the second dual-configured electric valve group (13) includes two normally closed butterfly valves. After the two normally closed butterfly valves are connected in parallel, one end is connected to the second oil flowmeter (14) through a pipeline, and the other end is connected to the conservator leakage alarm (15).

[0032] As a further improvement of the technical solution of the present invention, the pipeline adopts an explosion-proof and deflagration-proof type flame arrester oil discharge pipeline.

[0033] A control system applied to the above-mentioned UHV converter transformer emergency oil discharge and nitrogen injection device includes an oil discharge control cabinet, a first control center, and a second control center. The oil discharge control cabinet integrates a first oil discharge control unit and a second oil discharge control unit; the oil discharge control cabinet integrates a first oil discharge control unit, a second oil discharge control unit, and a nitrogen injection control unit; the first control center is respectively connected to the first oil discharge control unit, the second oil discharge control unit, and the nitrogen injection control unit; the second control center is respectively connected to the first oil discharge control unit, the second oil discharge control unit, and the nitrogen injection control unit; the first oil discharge control unit is respectively connected to the main body oil tank oil discharge device, the conservator oil discharge device, and the shut-off valve (12) by hard wiring; the second oil discharge control unit is respectively connected to the main body oil tank oil discharge device, the conservator oil discharge device, and the shut-off valve (12) by hard wiring; the nitrogen injection control unit is connected to the nitrogen injection device by hard wiring.

[0034] As a further improvement of the technical solution of the present invention, the first control center or the second control center issues an oil drainage start signal, which is simultaneously transmitted to the first oil drainage control unit, the second oil drainage control unit, and the nitrogen injection control unit; the first oil drainage control unit transmits the signal to the main body oil drainage device, the conservator oil drainage device, and the cut-off valve (12) respectively; the second oil drainage control unit transmits the signal to the main body oil drainage device, the conservator oil drainage device, and the cut-off valve (12) respectively; the nitrogen injection control unit sends the signal to the nitrogen injection device; the cut-off valve (12) is controlled to close, and the main body oil drainage device, the conservator oil drainage device, and the nitrogen injection device are opened to drain the converter transformer oil to the accident oil pool, and nitrogen is injected into the main body oil tank (1).

[0035] As a further improvement of the technical solution of the present invention, the hard wiring is a high-temperature resistant and flame-retardant armored shielded cable.

[0036] A control method based on the above-mentioned control system, characterized by comprising the following steps:

[0037] 1) The first control center or the second control center powers on the system and issues an oil drainage start signal to the oil drainage control cabinet. At this time, the oil drainage control cabinet controls the cut-off valve (12) to close, cutting off the pipeline for the conservator (10) to supply oil to the main body oil tank (1);

[0038] 2) After the main body oil tank oil drainage device receives the oil drainage start signal sent by the oil drainage control cabinet, the main body oil tank (1) starts to drain oil. At this time, the oil drainage control cabinet starts timing;

[0039] 3) After accumulating the timing for 10s, the oil drainage control cabinet sends an oil drainage start signal to the conservator oil drainage device. After the conservator oil drainage device receives the oil drainage start signal, it starts to drain oil;

[0040] 4) After accumulating the timing for another 15s, the oil drainage control cabinet sends a signal, and the nitrogen injection device is opened to start injecting nitrogen into the main body oil tank (1);

[0041] 5) When the oil level of the converter transformer main body oil tank (1) reaches the oil drainage end threshold, the oil drainage processes of the main body oil tank oil drainage device and the conservator oil drainage device end, and at the same time, the nitrogen injection device is closed, and the nitrogen injection process ends.

[0042] As a further improvement of the technical solution of the present invention, the method for generating the oil drainage start signal includes the following steps:

[0043] 1) The oil drainage control cabinet receives the heavy gas signal, the fire alarm signal, and the transformer power-off signal, and outputs the logical "AND" of the three signals; the output logical "AND" signal is sent to the first control center and the second control center;

[0044] (2) Based on the on-site situation, after excluding interference situations such as false alarms and small-scale fire alarms, the first control center or the second control center reports for instructions. After comprehensive judgment and processing, the first control center or the second control center issues an oil drainage start signal and transmits it to the oil drainage control cabinet.

[0045] As a further improvement of the technical solution of the present invention, the oil drainage start signal adopts a remote manual electrical start mode.

[0046] The advantages of the present invention are as follows:

[0047] (1) When the UHV converter transformer emergency oil drainage device receives the oil drainage start signal, it closes the shut-off valve, cuts off the oil drainage pipeline from the oil conservator to the explosion-proof and flame-retardant type flame arrester of the main body oil tank. The main body oil tank and the oil conservator each adopt a set of oil drainage systems to drain oil independently. The oil in the oil conservator no longer enters the main body oil tank, greatly shortening the oil drainage time. At the same time of emergency oil drainage, the nitrogen injection device fills nitrogen into the main body oil tank to prevent the entry of air into the emptied converter transformer main body oil tank, which may cause the spread of fire inside the converter transformer main body oil tank.

[0048] (2) The dual-configured electric valve groups of the main body oil tank oil drainage device and the oil conservator oil drainage device are opened successively for oil drainage. Even if a single valve fails, the oil drainage system can still drain oil normally, with high reliability.

[0049] (3) The use of an explosion-proof and flame-retardant type flame arrester oil drainage pipeline effectively prevents the flame from entering the emptied oil pipe together with a large amount of unburned combustible vapor and un-premixed reaction air during the oil drainage process, resulting in the spread of fire in the oil pipe, with high safety.

[0050] (4) The first oil drainage control unit, the second oil drainage control unit are cross-connected with the dual first control center and the second control center. The dual-configured electric valve groups of the main body oil tank oil drainage device and the oil conservator oil drainage device are controlled through hard wiring. The two sets of oil drainage control units operate independently, without a primary and backup distinction, to prevent the situation where the dual-configured electric valve groups cannot be started due to the failure of one of the oil drainage control units.

[0051] (5) The oil drainage start signal adopts a remote manual electrical start mode. When it is necessary to start the oil drainage system, the on-site situation is confirmed by the operating personnel and double-checked through the remote control panel or the operation box before starting. This prevents huge losses caused by misoperation of the system due to interference signals such as false alarms and small-scale fire alarms.

[0052] (6) The oil drainage pipeline passes through the cobblestone layer and directly leads into the accident oil pool. Through oil drainage test verification, it will not inject the oil with fire into the accident oil pool.

[0053] (7) The monitoring circuit of the oil draining system for the converter transformer has a powerful function. The monitoring signals include the power failure signals of the power supply and control power supply of the electric ball valve, the open / close status signal, the oil leakage signal of the oil draining pipeline, etc., and real-time monitoring is carried out.

[0054] (8) The cable is designed with fire-resistant cable plus a fire protection cover, and the electric ball valve is fully protected by a fire protection cover, which can ensure that the oil can still be drained remotely after direct combustion for 1 hour. Brief Description of the Drawings

[0055] Figure 1 Structural diagram of the main body oil tank oil draining device for the embodiment of the present invention;

[0056] Figure 2 Structural diagram of the conservator oil draining device for the embodiment of the present invention;

[0057] Figure 3 Structural diagram of the nitrogen injection device for the embodiment of the present invention;

[0058] Figure 4 Block diagram of the emergency oil draining and nitrogen injection system for the embodiment of the present invention;

[0059] Figure 5 Control system diagram of the emergency oil draining and nitrogen injection system for the embodiment of the present invention;

[0060] Figure 6 Logic diagram of the emergency oil draining and nitrogen injection start signal generation for the embodiment of the present invention;

[0061] Figure 7 Emergency oil draining and nitrogen injection system start-up process for the embodiment of the present invention;

[0062] Figure 8 Test effect diagram of top nitrogen injection of the emergency oil draining and nitrogen injection system for the embodiment of the present invention;

[0063] Figure 9 Test effect diagram of bottom nitrogen injection of the emergency oil draining and nitrogen injection system for the embodiment of the present invention. Detailed Embodiment

[0064] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0065] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0066] Embodiment

[0067] As shown Figures 1-3 in the figure, the UHV converter transformer emergency oil drainage and nitrogen injection device includes a main body oil tank 1, a maintenance valve 2, a first oil flowmeter 3, a first dual-configuration electric valve group 4, multiple main body oil tank leakage alarm devices 5, multiple main body oil tank butterfly valves 6, an accident oil pool, an oil conservator 10, a main body three-way pipe 11, a cut-off valve 12, a second dual-configuration electric valve group 13, a second oil flowmeter 14, multiple oil conservator leakage alarm devices 15, multiple oil conservator butterfly valves 16, and multiple nitrogen injection devices.

[0068] The first port of the main body three-way pipe 11 is connected to the oil conservator 10 through an explosion-proof and flame-retardant type oil drainage pipeline, the second port is connected to the second dual-configuration electric valve group 13 through an explosion-proof and flame-retardant type oil drainage pipeline, a cut-off valve 12 is arranged at the output port of the third port, and the output port of the cut-off valve 12 is connected to the main body oil tank 1 through an explosion-proof and flame-retardant type oil drainage pipeline.

[0069] As shown Figure 1 in the figure, the main body oil tank 1, the maintenance valve 2, the first oil flowmeter 3, the first dual-configuration electric valve group 4, multiple main body oil tank leakage alarm devices 5, and multiple main body oil tank butterfly valves 6 are sequentially connected to the accident oil pool through an explosion-proof and flame-retardant type oil drainage pipeline along the negative x-axis direction.

[0070] The first dual-configuration electric valve group 4 includes two normally closed butterfly valves. After the two normally closed butterfly valves are connected in parallel, one end is connected to the first oil flowmeter 3 through an explosion-proof and flame-retardant type oil drainage pipeline, and the other end is connected to the main body oil tank leakage alarm device 5 through an explosion-proof and flame-retardant type oil drainage pipeline.

[0071] Preferably, 2 main body oil tank leakage alarm devices 5 and 2 main body oil tank butterfly valves 6 are alternately connected through an explosion-proof and flame-retardant type oil drainage pipeline along the negative x-axis direction.

[0072] As shown Figure 2 in the figure, the oil conservator 10, the main body three-way pipe 11, the second dual-configuration electric valve group 13, the second oil flowmeter 14, multiple oil conservator leakage alarm devices 15, and multiple oil conservator butterfly valves 16 are sequentially connected to the accident oil pool through an explosion-proof and flame-retardant type oil drainage pipeline along the negative y-axis direction.

[0073] The second dual-configuration electric valve group 13 includes two normally closed butterfly valves. After the two normally closed butterfly valves are connected in parallel, one end is connected to the second oil flowmeter 14 through an explosion-proof and flame-retardant type oil drainage pipeline, and the other end is connected to the oil conservator leakage alarm device 15 through an explosion-proof and flame-retardant type oil drainage pipeline.

[0074] Preferably, 2 oil conservator leakage alarm devices 15 and 2 oil conservator butterfly valves 16 are alternately connected through an explosion-proof and flame-retardant type oil drainage pipeline along the negative x-axis direction.

[0075] The described oil flowmeter is used to monitor the flow rate of the converter transformer oil in the oil discharge pipeline of the explosion - resistant and deflagration - suppressing type flame arrester in real time.

[0076] For the described dual - configured electric valve group, after the control system sends a signal to the main body oil tank oil discharge device and the conservator oil discharge device, the dual - configured electric valve group changes from normally closed to normally open and enters the oil discharge mode; each of the two normally closed butterfly valves in each dual - configured electric valve group includes 1 independent power supply circuit and control circuit. The power supply of the power supply circuit of each normally closed butterfly valve uses 220V single - phase AC power, which is respectively taken from different busbars of the station - used AC system, and the control power supply of the control circuit of each normally closed butterfly valve is respectively taken from DC section 1 and DC section 2 of 110V of the station - used, to avoid the situation that the two normally closed butterfly valves cannot work properly at the same time due to the loss of voltage of one DC busbar or DC grounding.

[0077] The described main body oil tank leakage alarm 5 is used to monitor in real time whether there is leakage in the oil discharge pipeline of the explosion - resistant and deflagration - suppressing type flame arrester during the normal operation of the converter transformer or during emergency oil discharge.

[0078] The oil discharge pipeline of the explosion - resistant and deflagration - suppressing type flame arrester has wall effect, heat conduction effect, and flame obstruction effect, preventing the flame from entering the emptied oil pipe together with a large amount of unburned combustible vapor and un - premixed reaction air during the oil discharge process, resulting in the spread of fire in the oil pipe.

[0079] As Figure 3 shown, the described nitrogen injection device includes multiple nitrogen cylinder groups 21, a gas collecting valve 22, an injection pipeline 23, a control valve 24, and a nitrogen injection port 25. The multiple nitrogen cylinder groups 21 are connected to one end of the injection pipeline 23 through the gas collecting valve 22, the other end of the injection pipeline 23 is connected to the nitrogen injection port 25, and a control valve 24 is arranged between the injection pipeline 23 and the nitrogen injection port 25.

[0080] At the upper - middle positions on both sides of the main body oil tank 1 of the described converter transformer, multiple gas - filling ports are arranged at a height of 500mm - 600mm from the tank top. The nitrogen injection ports 25 of the multiple nitrogen injection devices are connected to the multiple gas - filling ports at the upper - middle positions on both sides of the main body oil tank 1. The control valve 24 of the nitrogen injection device is normally closed in the normal state. After the main body oil tank 1 of the converter transformer discharges oil for a period of time, after the control system issues an instruction, the control valve 24 changes to normally open for nitrogen filling. The control system of the nitrogen injection device is integrated with the main body oil discharge control system and the conservator oil discharge control system.

[0081] The calculation formula for the number of nitrogen cylinders in the described nitrogen cylinder group 21 is:

[0082] s = V2 / V1 (1)

[0083]

[0084] Wherein, s is the number of nitrogen cylinders, P1 is the pressure of nitrogen in the main body oil tank after nitrogen filling, P2 is the pressure of nitrogen in the nitrogen cylinders, V1 is the volume occupied by a single nitrogen cylinder filled into the main body oil tank under the pressure of P1, V2 is the volume of transformer oil in the main body oil tank, φ is the diameter of the nitrogen cylinder, and h is the height of the nitrogen cylinder.

[0085] As Figure 4 shown, the UHV converter transformer emergency oil drainage and nitrogen injection system includes a control system, a main body oil tank oil drainage device, an oil conservator oil drainage device, a nitrogen injection device, and a shut-off valve 12. The control system controls the start and stop of the main body oil tank oil drainage device, the oil conservator oil drainage device, the nitrogen injection device, and the shut-off valve 12 according to the oil drainage start signal.

[0086] As Figure 5 shown, the control center A is respectively connected to the oil drainage control unit A and the oil drainage control unit B through IEC61850 communication; the control center B is respectively connected to the oil drainage control unit A and the oil drainage control unit B through IEC61850 communication; the oil drainage control unit A is respectively connected to the first dual-configured electric valve group 4 of the main body oil tank oil drainage device, the second dual-configured electric valve group 13 of the oil conservator oil drainage device, and the shut-off valve 12 by hard wiring; the oil drainage control unit B is respectively connected to the first dual-configured electric valve group 4 of the main body oil tank oil drainage device, the second dual-configured electric valve group 13 of the oil conservator oil drainage device, and the shut-off valve 12 by hard wiring; the nitrogen injection control unit is connected to the control valve 24 of the nitrogen injection device by hard wiring.

[0087] Based on the on-site situation, after excluding interferences such as false alarms and small-scale fire alarms, the control center A or the control center B reports and requests instructions. After comprehensive judgment and processing, the control center A or the control center B remotely manually issues an oil drainage start signal, which is simultaneously transmitted to the oil drainage control unit A, the oil drainage control unit B, and the nitrogen injection control unit. The oil drainage control unit A transmits the signal to the first dual-configured electric valve group 4 of the main body oil drainage device, the second dual-configured electric valve group 13 of the oil conservator oil drainage device, and the shut-off valve 12 respectively; at the same time, the oil drainage control unit B transmits the signal to the first dual-configured electric valve group 4 of the main body oil drainage device, the second dual-configured electric valve group 13 of the oil conservator oil drainage device, and the shut-off valve 12 respectively; the nitrogen injection control unit transmits the signal to the control valve 24 of the nitrogen injection device; the shut-off valve 12 is controlled to close, the first dual-configured electric valve group 4 and the second dual-configured electric valve group 13 are started, the converter transformer oil is drained into the accident oil pool, and the control valve 24 is started to inject nitrogen from multiple nitrogen cylinder groups 21 into the main body oil tank 1.

[0088] The oil drainage control unit A and the oil drainage control unit B are cross-connected with the dual control centers A and B. The dual-configured electric valve groups of the main tank oil drainage device and the conservator oil drainage device are controlled through hard wiring. The two oil drainage control units operate independently without a primary or standby distinction, preventing the situation where the dual-configured electric valve groups cannot be started due to a failure of one of the oil drainage control units.

[0089] The main tank oil drainage device and the conservator oil drainage device are both equipped with monitoring circuits for monitoring the power supply loss signal, control power supply loss signal, valve open / close status signal, and oil leakage signal of the oil drainage pipeline of the dual-configured electric valve groups.

[0090] As Figure 6 shown, the method for generating the oil drainage and nitrogen injection start signal includes the following steps:

[0091] 1) The oil drainage control cabinet receives the heavy gas signal (two out of three), the fire alarm signal (at least two fire alarm signals), and the transformer power-off signal, and outputs the logical "AND" of the three signals; the output logical "AND" signal is sent to the control center A and the control center B.

[0092] 2) According to the on-site situation, the control center A or the control center B excludes interference situations such as false alarms and small-scale fires, reports and requests instructions, and after comprehensive judgment and processing, the control center A or the control center B remotely manually issues an oil drainage start signal and transmits it to the oil drainage control cabinet.

[0093] The oil drainage start signal adopts a remote manual electrical start method to prevent huge losses caused by system misoperation due to interference signals such as false alarms and small-scale fires.

[0094] As Figure 7 shown, the start-up process of the main tank oil drainage device, the conservator oil drainage device, and the nitrogen injection device of the UHV converter transformer emergency oil drainage and nitrogen injection system is as follows: The control center A or the control center B powers on the system and issues an oil drainage start signal to the oil drainage control cabinet. At this time, the oil drainage control cabinet controls the shut-off valve (12) to close, cutting off the pipeline for the conservator (10) to supply oil to the main tank (1); after the main tank oil drainage device receives the oil drainage start signal sent by the oil drainage control cabinet, the main tank (1) starts to drain oil. At this time, the oil drainage control cabinet starts timing; after accumulating 10s, the oil drainage control cabinet sends an oil drainage start signal to the conservator oil drainage device. After the conservator oil drainage device receives the oil drainage start signal, it starts to drain oil; after accumulating another 15s, the oil drainage control cabinet sends a signal to open the nitrogen injection device, and starts to inject nitrogen into the main tank (1); when the oil level of the converter transformer main tank (1) reaches the oil drainage end threshold (the oil level gauge in the converter transformer main tank reaches the limit value), the oil drainage process of the main tank oil drainage device and the conservator oil drainage device ends, and at the same time, the nitrogen injection device closes and the nitrogen injection process ends.

[0095] Figure 8 This is the test effect diagram of nitrogen injection from the top of the emergency oil drainage and nitrogen injection system in the embodiment of the present invention. 5 liters of 93# gasoline is added to the base of the transformer bushing as an auxiliary fuel agent. After ignition for about 1 minute, the color and concentration of the rising flue gas begin to change. The transformer oil is radiantly heated and evaporated to form oil and gas that continues to burn. After 3 minutes, through the first thermocouple arranged on the transformer oil surface, the flame temperature is read to be about 750°C, which is close to the flame temperature when the transformer oil burns stably. Thus, it is determined that the transformer oil reaches a stable combustion state.

[0096] At the 4th minute, the oil drainage starts. The flame burning at the base of the bushing observed from the video provided by the drone follows the liquid level down into the transformer cavity. Combining with the fact that the temperature of the thermocouple on the original liquid surface remains stable at about 750°C, and at the same time, the second thermocouple 480 mm away from the original liquid surface rises from the oil temperature to nearly the flame temperature of about 700°C. From this, it is judged that the burning flame has followed the decline of the liquid level into the transformer and continues to burn stably (when the oil drainage stops, the transformer oil level is about three-fifths of the original liquid level).

[0097] Starting from the injection of nitrogen after the 5th minute, after about 2 minutes, white smoke emerges from the position of the transformer bushing seat. This indicates that the nitrogen starts to take effect at this time. Observing the base of the bushing from the drone video, it is observed that the flame inside the transformer becomes smaller. Thus, it is judged that the injected nitrogen plays a role in controlling the combustion of the transformer oil inside.

[0098] About 8 minutes after starting to inject nitrogen, the flue gas at the top of the transformer basically disappears, and what remains is white smoke and a slight updraft of temperature difference. Observing the inside through the base of the bushing with the drone video, no flame can be seen, and the thermocouple temperature data returns to about 60°C. Therefore, it is judged that the open fire inside the transformer has gone out.

[0099] About 15 minutes after starting to inject nitrogen, the valve of the nitrogen pipeline is closed to stop injecting nitrogen into the transformer. Observing the inside of the transformer through the drone video, no burning flame is seen, and the thermocouple temperature data on the liquid surface remains at about 60°C. From this, it is judged that there is no situation of smoldering inside the transformer and no re-ignition occurs.

[0100] Figure 9This is the test effect diagram of bottom nitrogen injection for the emergency oil drainage and nitrogen injection system in the embodiment of the present invention. 5 liters of 93# gasoline was added to the base of the transformer bushing as an auxiliary fuel agent. At the initial stage of igniting the gasoline, the combustion was limited to the gasoline acting within the area of the transformer bushing base. After about 1 minute, the rising smoke gradually changed from thick black smoke to light black smoke, indicating that the auxiliary fuel gasoline was completely burned. The transformer oil was radiantly heated and evaporated to form oil gas that continued to burn. After 3 minutes, the first thermocouple arranged on the transformer oil surface read a flame temperature of about 780 °C, which was close to the flame temperature during the stable combustion of the transformer oil. Thus, it was determined that the transformer oil reached a stable combustion state.

[0101] After the oil drainage started, the transformer oil level dropped. It was observed from the video provided by the drone that there was a flame burning inside the base of the bushing. Combining with the fact that the temperature of the first thermocouple remained stable at about 780 °C, and at the same time, the second thermocouple 480 mm away from the original liquid level rose from the oil temperature to nearly the flame temperature of about 550 °C. It was thus judged that the burning flame had followed the drop of the liquid level into the transformer and continued to burn stably.

[0102] Starting from the calculation after nitrogen injection began at the 5th minute, after about 3 minutes, white smoke emerged from the position of the transformer bushing seat opening, indicating that the nitrogen had then floated and filled the fire position in the upper cavity of the transformer. Part of the nitrogen followed the smoke and emerged from the ignition opening. Observing the base of the bushing through the drone video, it was observed that the flame inside the transformer became smaller. Thus, it was judged that the injected nitrogen played a role in controlling the combustion of the transformer oil inside. However, due to the fact that the flow rate of the injected nitrogen was less than the loss flow rate at the outlet of the transformer bushing base, it could not completely suffocate the combustion of the transformer oil inside (when the oil drainage stopped, the remaining transformer oil level was about one-third of the original liquid level).

[0103] Starting from the calculation about 15 minutes after nitrogen injection began, the smoke at the top of the transformer basically disappeared, and what remained were white smoke and a slight updraft due to temperature difference. Observing the inside through the drone video at the base of the bushing, no flame was visible, and the thermocouple temperature data returned to about 200 °C, indicating that there was no burning flame inside. Therefore, it was judged that the open fire inside the transformer was extinguished, but the insulating parts of the transformer winding had been burned and carbonized and were smoldering inside.

[0104] About 15 minutes after the calculation starting from nitrogen injection began, the valve of the nitrogen pipeline was closed to stop injecting nitrogen into the transformer. After about 10 minutes, black smoke began to emerge from the base of the bushing at the top of the transformer. Observing the inside of the transformer through the drone video, partial burning flames could be seen, and the thermocouple temperature data returned to about 300 °C. It was thus judged that the smoldering insulating material inside the transformer could still radiate the transformer oil to form combustion and cause the re-ignition of the transformer oil inside without the protection and cooling of nitrogen at this time.

[0105] By Figure 8 and Figure 9From the test results, it can be known that nitrogen injection helps to reduce the internal fire, and the degree depends on the nitrogen injection rate. Moreover, the nitrogen injection effect at the top of the transformer is better than that at the bottom.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. UHV converter transformer emergency oil drainage and nitrogen injection device, which is used for draining oil from the main body oil tank (1) and the oil conservator (10) of the converter transformer, and is characterized in that, It includes a main body three-way joint (11), a shut-off valve (12), an oil drainage device for the main body oil tank, an oil drainage device for the conservator, multiple nitrogen injection devices, and an accident oil pool; the main body three-way joint (11) is arranged between the upper part of the main body oil tank (1) and the bottom of the conservator (10). The first port of the main body three-way joint (11) is connected to the bottom of the conservator through a pipeline, the second port is connected to the oil drainage device of the conservator through a pipeline, the third port is provided with a shut-off valve (12), and the output port of the shut-off valve (12) is connected to the main body oil tank (1) through a pipeline. The oil drainage device of the main body oil tank is connected to the bottom of the main body oil tank (1) through a pipeline. The output ends of the oil drainage device of the main body oil tank and the oil drainage device of the conservator are respectively connected to the accident oil pool through pipelines; multiple gas filling ports are opened at the upper-middle positions on both sides of the main body oil tank (1), and multiple nitrogen injection devices are connected to the multiple gas filling ports; when draining oil, the shut-off valve (12) is closed to cut off the oil supply pipeline from the conservator (10) to the main body oil tank (1). The oil drainage device of the main body oil tank and the oil drainage device of the conservator independently drain oil to the accident oil pool respectively, and at the same time, multiple nitrogen injection devices inject nitrogen into the main body oil tank (1). The nitrogen injection device includes multiple nitrogen cylinder groups (21), a gas collecting valve (22), an air injection pipeline (23), a control valve (24), and a nitrogen injection port (25). Multiple nitrogen cylinder groups (21) are connected to one end of the air injection pipeline (23) through the gas collecting valve (22). The other end of the air injection pipeline (23) is connected to the nitrogen injection port (25). A control valve (24) is arranged between the air injection pipeline (23) and the nitrogen injection port (25). The nitrogen injection port (25) is connected to the gas filling ports at the upper-middle positions on both sides of the main body oil tank (1). The calculation formula for the number of nitrogen cylinders in the nitrogen cylinder group (21) is: s = V2 / V1 (1) Where s is the number of nitrogen cylinders, P1 is the pressure of nitrogen in the main body oil tank after nitrogen filling, P2 is the pressure of nitrogen in the nitrogen cylinder, V1 is the volume occupied by a single bottle of nitrogen in the main body oil tank when the pressure is P1, V2 is the volume of transformer oil in the main body oil tank, φ is the diameter of the nitrogen cylinder, and h is the height of the nitrogen cylinder.

2. The emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 1, characterized in that, The oil drainage device of the main body oil tank includes a maintenance valve (2), a first oil flowmeter (3), a first dual-redundancy configured electric valve group (4), multiple main body oil tank leakage alarm devices (5), and multiple main body oil tank butterfly valves (6). The main body oil tank (1), the maintenance valve (2), the first oil flowmeter (3), the first dual-redundancy configured electric valve group (4), multiple main body oil tank leakage alarm devices (5), and multiple main body oil tank butterfly valves (6) are sequentially connected to the accident oil pool through pipelines along the negative x-axis direction.

3. The emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 1, wherein The oil drainage device of the conservator includes a second dual-redundancy configured electric valve group (13), a second oil flowmeter (14), multiple conservator leakage alarm devices (15), and multiple conservator butterfly valves (16). The second dual-redundancy configured electric valve group (13), the second oil flowmeter (14), multiple conservator leakage alarm devices (15), and multiple conservator butterfly valves (16) are sequentially connected to the accident oil pool through pipelines along the negative y-axis direction.

4. The emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 2, characterized in that, The described first dual-configured electric valve group (4) includes two normally-closed butterfly valves. After the two normally-closed butterfly valves are connected in parallel, one end is connected to the first oil flowmeter (3) through a pipeline, and the other end is connected to the body oil tank leakage alarm instrument (5) through a pipeline. The power supply circuit and control circuit of each normally-closed butterfly valve are independently powered.

5. The emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 3, wherein The described second dual-configured electric valve group (13) includes two normally-closed butterfly valves. After the two normally-closed butterfly valves are connected in parallel, one end is connected to the second oil flowmeter (14) through a pipeline, and the other end is connected to the conservator leakage alarm instrument (15).

6. The emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 1, characterized in that The pipeline adopts an explosion-proof and deflagration-resistant flame arrester oil discharge pipeline.

7. A control system for the UHV converter transformer emergency oil drainage and nitrogen injection device according to any one of claims 1-6, characterized in that, It includes an oil discharge control cabinet, a first control center, and a second control center. The oil discharge control cabinet integrates a first oil discharge control unit and a second oil discharge control unit; the oil discharge control cabinet integrates a first oil discharge control unit, a second oil discharge control unit, and a nitrogen injection control unit; the first control center is respectively connected to the first oil discharge control unit, the second oil discharge control unit, and the nitrogen injection control unit; the second control center is respectively connected to the first oil discharge control unit, the second oil discharge control unit, and the nitrogen injection control unit; the first oil discharge control unit is respectively connected to the body oil tank oil discharge device, the conservator oil discharge device, and the shut-off valve (12) by means of hard wiring; the second oil discharge control unit is respectively connected to the body oil tank oil discharge device, the conservator oil discharge device, and the shut-off valve (12) by means of hard wiring; the nitrogen injection control unit is connected to the nitrogen injection device by means of hard wiring.

8. The control system of the emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 7, characterized in that, When the first control center or the second control center issues an oil discharge start signal, the signal is simultaneously transmitted to the first oil discharge control unit, the second oil discharge control unit, and the nitrogen injection control unit; the first oil discharge control unit transmits the signal to the body oil discharge device, the conservator oil discharge device, and the shut-off valve (12) respectively; the second oil discharge control unit transmits the signal to the body oil discharge device, the conservator oil discharge device, and the shut-off valve (12) respectively; the nitrogen injection control unit sends the signal to the nitrogen injection device; the shut-off valve (12) is controlled to close, the body oil discharge device, the conservator oil discharge device, and the nitrogen injection device are opened, the converter transformer oil is discharged to the accident oil pool, and nitrogen is injected into the body oil tank (1).

9. The control system of the emergency oil draining and nitrogen injection device for UHV converter transformer according to claim 8, characterized in that, The hard wiring is a high-temperature resistant, flame-retardant, armored, and shielded cable.

10. A control method for a control system according to any one of claims 7-9, characterized in that, It includes the following steps: 1) The first control center or the second control center powers on the system and issues an oil discharge start signal to the oil discharge control cabinet. At this time, the oil discharge control cabinet controls the shut-off valve (12) to close, cutting off the pipeline for the conservator (10) to supply oil to the body oil tank (1); 2) After the body oil tank oil discharge device receives the oil discharge start signal sent by the oil discharge control cabinet, the body oil tank (1) starts to discharge oil. At this time, the oil discharge control cabinet starts timing; 3) After accumulating the timing for 10s, the oil discharge control cabinet sends an oil discharge start signal to the conservator oil discharge device. After the conservator oil discharge device receives the oil discharge start signal, it starts to discharge oil; 4) After accumulating the timing for another 15s, the oil discharge control cabinet sends a signal, and the nitrogen injection device is opened to start injecting nitrogen into the body oil tank (1); 5) When the oil level in the main tank (1) of the converter transformer reaches the oil drainage end threshold, the oil drainage processes of the main tank oil drainage device and the conservator oil drainage device end. At the same time, the nitrogen injection device is closed and the nitrogen injection process ends.

11. The control method of the control system according to claim 10, characterized in that, The method for generating the oil drainage start signal includes the following steps: 1) The oil drainage control cabinet receives the heavy gas signal, the fire alarm signal and the transformer power-off signal, and outputs the logical "AND" of the three signals; the output logical "AND" signal is sent to the first control center and the second control center; 2) According to the on-site situation, the first control center or the second control center eliminates interference situations such as false alarms and small-scale fires, reports for instructions, and after comprehensive judgment and processing, the first control center or the second control center issues an oil drainage start signal and transmits it to the oil drainage control cabinet.

12. The control method of the control system according to claim 10, characterized in that, The oil drainage start signal adopts a remote manual electrical start mode.

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