Single-phase large-current generating device and generating method and large-current transformer test system

Abstract

The invention discloses a single-phase large-current generating device and method and a large-current transformer test system, a station-used three-phase 380V line is used as a power supply, a rectification filtering loop and an inversion loop are combined, the current is boosted to a large current required by a test through N current boosters, the large current is added to a primary copper conductor of a large-current test device, and the large-current transformer is connected with the primary copper conductor of the large-current test device. After the primary copper conductor passes through the inner window hole of the tested piece, a large current or an ultra-large current can be directly applied to the physical center of the plane of the tested piece or a position deviating from the physical center, so that the operation effect and state of related electric power and electrical equipment under the direct large current or ultra-large current can be tested and detected; the method is called a'direct method 'large current test detection method, and thoroughly overcomes the defects of inaccuracy, large deviation and the like in the conventional'simple connection method' test detection in which'equal ampere turns' formed by combining multiple turns of small currents is adopted to replace direct large current or ultra-large current.

Description

Technical Field

[0001] The present invention relates to the field of large current to ultra-large current electrical complete sets or equipment, and in particular to a special electrical test device for performing temperature rise or error test on large current or ultra-large current transformers for testing power electrical equipment by a direct method. Background Art

[0002] At present, the domestic and international demands for power equipment and technical requirements are getting higher and higher, and the power generation capacity of generator sets is getting larger and larger, especially large-scale hydropower, thermal power and even nuclear power units, with a power generation capacity of more than 1000MW. At present, the highest nuclear power unit has reached more than 1400MW, which requires corresponding large-capacity or ultra-large-capacity power equipment to match. These supporting power and electrical equipment, such as ultra-large test generators, ultra-large test transformers, ultra-large current circuit breakers, generator export insulating sleeves and generator export insulating busbars, etc., are all world-wide problems in production and manufacturing. It is required that their conductive performance can be guaranteed for more than 10 minutes when the current value is 50,000A or even above 55,000A, and their long-term stable current-carrying performance is 45,000A or even above 50,000A. According to searches, such a large current value indicator has not appeared at home or abroad. After the production and manufacture of these power equipment, they are subject to large current and ultra-large current testing, inspection and acceptance. However, there is currently no corresponding device or equipment that can output ultra-large current to directly test power and electrical equipment at home and abroad, that is, the direct large current method. For the testing and inspection of these power equipment with ultra-large current performance requirements, all of them adopt a scheme of winding a small current conductor into multiple turns and combining them together to be equivalent to a turn of conductor through which a large (or ultra-large) current directly passes, also known as the "equiampere-turn method". This "equiampere-turn method" is relative to the "direct method" scheme of directly passing a large current through a turn of conductor for testing, also known as the "indirect method" scheme, in order to achieve an approximately equivalent situation. This "indirect method" is used to replace the "direct method" of directly passing a large (or super large) current or super large current through a conductor (turn) for testing. The test data will have a certain deviation and is not completely equivalent to the test data under actual operation. At the same time, when the number of winding turns is large, the capacity of the current output transformer will need to be increased due to increased impedance, and a larger capacity transformer will be required, which will also impose certain restrictions on the test. In order to achieve more accurate test data, the direct method, that is, passing a large (or super large) current or super large current through a conductor (turn) for testing, will be the best option. Summary of the invention

[0003] In view of the deficiencies in various aspects of the existing technology and equipment, the present invention provides a technical solution for a single-phase 50kA ultra-large current generating device and a complete set of devices or equipment. This complete set of test equipment can directly test and detect the operating effect and status of related power and electrical equipment under direct large current or ultra-large current. It has a simple structure, low manufacturing cost, and reliable performance. It can realize a current source that can output a stable ultra-large current and a corresponding test detection device in a 380V power system of normal city power or factory power.

[0004] The technical solution adopted by the present invention is a single-phase large current generating device, including a basic power supply unit and a steady-state current boosting unit. The basic power supply unit includes a rectifier circuit and an inverter circuit. The rectifier circuit converts the three-phase AC input power supply into a DC power supply, and the inverter circuit converts the DC power supply into an AC power supply. The output AC power supply with a relatively large current value is then connected in parallel through N current boosting transformers (abbreviated as: current boosters) in the steady-state current boosting unit to boost the current, where N is greater than or equal to 1. The high current after the boost is added to the high current bus conductor of the high current test device.

[0005] A large current transformer test system, when N is greater than 1, N current risers are symmetrically arranged with a large current collecting conductor as the center, the large current experimental device comprises a large bracket of a frame structure, the large current transformer to be tested is placed at the center position of the lower part of the large bracket, the upper end of the large bracket is provided with an upper collecting plate, the lower end of the large current transformer to be tested is provided with a lower collecting plate, the current riser is electrically connected to the upper collecting plate and the lower collecting plate through the upper current collecting conductor and the lower current collecting conductor respectively, the top of the large bracket is connected with a lifting motor support frame, the lifting motor and the gearbox are connected to the lifting motor support frame, the gearbox is connected to the large current collecting conductor through a lead screw, driving the large current collecting conductor to move up and down, lift and put down, and pass through the inner cavity of the large current transformer to be tested, and contact and conduct with the upper collecting plate and the lower collecting plate.

[0006] Preferably, the large bracket is made of non-magnetic material, and the non-magnetic material is a hard aluminum alloy material or a non-magnetic stainless steel material.

[0007] Preferably, the large current bus conductor is a cylindrical structure and is made of T2 copper. The large current bus conductor has a stable and long-term current carrying capacity of more than 55,000A.

[0008] Preferably, a liquid cooling channel is added inside the large current bus conductor, and the cooling liquid is output into the bus conductor through an external cooling liquid conduit, and the cooling liquid injected into the large current bus conductor is then output through an external liquid guide tube on the other side to form flowing liquid cooling.

[0009] A single-phase large current generation method combines the three-phase 380V AC power of the factory transformer with the principles of rectification, filtering and inverter to output a larger current value I 1 , I 1 Greater than 1000A, voltage not less than U1, this current is output from N parallel wires to N current boosters, N is greater than or equal to 1, as the current input source of the ultra-large current test system device, when N is greater than 1, N current boosters are evenly distributed in a central symmetric manner. Each current booster has a capacity of U1*I 1 / N, each of these N current boosters outputs I 2 The large current is then connected in parallel and combined to supply the large current bus conductor in the transformer test system device for input current for large current transformer testing.

[0010] The invention discloses a method for applying a large current transformer test system to a temperature rise and error test of a large current transformer.

[0011] A large current transformer test system is applied to large current circuit breakers, bushings, busbars and other power equipment in large current related test detection.

[0012] The beneficial effects of the present invention are as follows: 1. By using the principle of energy conversion superposition, a basic starting power supply capable of outputting a single-phase large-capacity ultra-large current can be easily completed by using conventional 380V three-phase electricity for factory use, without the need for high-capacity transformers or large-capacity power supplies and other high, large, advanced and difficult equipment. The conventional three-phase 380V line of the factory power supply system is used as the power supply, which ensures that the capacity of each phase meets 150kW or more (the total capacity of the three phases reaches more than 450kW). If you want to output a larger ultra-large current, the power supply capacity will be increased accordingly. Through the widely used technical solution of combining rectifier and filter circuits with inverters of corresponding capacity, three-phase AC power is converted into single-phase DC power, and then the inverter converts the single-phase DC power into single-phase AC power. Through this technical solution, the total capacity of the three-phase power supply is superimposed and connected to a single phase. At this time, the output capacity is about three times the original capacity (about 450kVA). If the voltage value at this time is set at 400V (it can be adjusted high or low according to the needs of the circuit when conducting ultra-large current tests), the current can reach more than 1000A (estimated at 150kVA), which provides a necessary power supply capacity and a basic starting current source for the subsequent output of ultra-large current.

[0013] If a larger current is required, the capacity of the plant transformer can be increased accordingly, the capacity of the rectifier and filter circuits and the inverter can be increased, the capacity or number of current boosters can be increased, and the current carrying capacity of the conductors related to the bus conductor can be increased.

[0014] 2. Through the control device and N current-boosting transformers, the current of the previous basic starting current source is increased to a relatively small current that can ensure long-term stable ultra-large current through a current booster alone or multiple current boosters in parallel, reaching the required value of the tested power and electrical equipment, and realizing the requirement of changing small to large.

[0015] 3. According to the power and electrical equipment being tested for ultra-large current related tests, a corresponding special test and detection device that can meet the requirements of ultra-large current related tests is specially designed. Taking the temperature rise and error test of ultra-large current transformer as an example, a set of special devices that can perform temperature rise and error tests on ultra-large current transformers is designed to achieve ultra-large current temperature rise or error tests. Such special devices can be specially designed and manufactured according to the conditions of the tested equipment and products and local conditions.

[0016] 4. Through comprehensive testing and control system, the different units and the units are controlled to ensure accurate control, testing and inspection of each equipment unit and between units, as well as the coordinated cooperation between different units of the complete set of testing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the basic circuit principle of the special electrical test device of the present invention.

[0018] Figure 2 It is a schematic diagram of a large current or ultra-large current transformer test detection system of the present invention.

[0019] Figure 3 The schematic diagram of the present invention is that N (8) current boosters are evenly and symmetrically arranged around the single-phase primary super-large current conductor as the center. The markings in the figure are: 1-large bracket, 2-lower current collector, 3-lower current collector, 4-support frame of the tested large current transformer, 5-current booster, 6-tested large current transformer, 7-upper current collector, 8-large current collector, 9-upper collector, 10-lifting motor support frame, 11-screw, 12-gearbox, 13-lifting motor, 14-pipe for input or output of cooling liquid. DETAILED DESCRIPTION

[0020] In order to make the purpose, 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 drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0021] One of the purposes of the present invention is to provide a device with a simple structure, low manufacturing cost, reliable performance, and an ultra-large current source device capable of outputting a stable output in a 380V power system of a normal mains electricity.

[0022] The present invention does not require a dedicated ultra-high power power system or power line, nor does it require a dedicated ultra-high current power generation equipment or a high current output transformer. Instead, on a conventional factory-produced conventional three-phase 380V line, under the condition that the transformer capacity is ≥150kVA, a relatively simple method for manufacturing a power supply complete set of equipment that can stably output ultra-high current (up to 50,000A or more) can be developed. The method includes the following technical units: The schematic diagrams are shown in FIG. Figures 1 to 3 .

[0023] 1. Basic power supply part of the ultra-large current generation test device: The conventional three-phase 380V line of the factory power supply system is used as the power supply, which ensures that the capacity of the three phases meets 150kVA or more. If you want to output a larger ultra-large current, the power supply capacity must be increased. Through the technical solution of combining the widely used rectifier filter circuit and the corresponding capacity inverter, the three-phase AC is converted into single-phase DC, and then the inverter converts the single-phase DC into single-phase AC. Through this solution, the total capacity of the three-phase power supply is superimposed and combined into a single phase. At this time, the output capacity is about three times the original (about 450kVA). If the voltage value at this time is set at 400V (it can be adjusted according to the needs of the circuit when conducting ultra-large current tests), the current can reach more than 1000A (estimated at 150kVA), which provides a necessary power supply capacity and a basic current for the subsequent output of ultra-large current. In addition to being related to the extremely large current value that needs to be output, the power capacity value is also related to the impedance value of the entire output large current loop. The wire (conductor) that outputs large current and the total length of the loop (affected by the distance between the test device and the power supply) will affect the power capacity required for the entire device.

[0024] 2. Steady-state ultra-large current boost unit,

[0025] The steady-state current boost unit device uses a single-phase current boost transformer (referred to as current booster 5) with a certain capacity to boost the required current output by the inverter to the required large current or ultra-large current. Figure 1 .

[0026] According to the overall test device, multiple current boosters 5 with larger capacity (this current booster 5 can be a single-phase current booster with large capacity or multiple single-phase current boosters with small capacity connected in parallel to form a single-phase current booster with large capacity) are connected in correspondence with the number of inverters. The AC current output by multiple inverters is increased to a certain required value through multiple current boosters 5 of corresponding number. The current is concentrated and applied to the large current bus conductor 8 through the inner window of the large current transformer to perform the corresponding large current transformer test. This steady-state current boosting unit device is first supported mainly by the large bracket 1. The large bracket 1 is a three-dimensional frame structure made of square columnar hard aluminum alloy, non-magnetic stainless steel or other high-strength insulating non-metallic materials. Other auxiliary devices are also made of hard aluminum alloy, non-magnetic stainless steel or other high-strength insulating The frame is composed of non-metallic materials (such as epoxy glass fiber, polycarbonate, polytetrafluoroethylene), etc. The large current collecting conductor 8 is set in the middle position of this frame. The large current collecting conductor 8 is a cylindrical structure and is made of T2 copper. It meets the temperature rise requirements when passing ultra-large current to conduct related tests of large current transformers. It is collected in the upper collector plate 9 through the upper current collecting conductor 7 (generally a soft wire conductor or a jointable rotatable connection type), and then added to the large current collecting conductor 8 (generally a copper column) through the upper collector plate 9, and then through the lower collector plate 2 (whose plane is in close contact with the end face of the collector conductor 8 to form a conductive loop) and the lower current collecting conductor 3 (generally a soft wire conductor or a jointable rotatable connection type first). The large current returns to the current booster 5, thereby forming a current loop in the steady-state current boosting unit device. The liquid cooling channel is added inside the large current bus conductor 8, and the cooling liquid is output into the bus conductor 8 through the external cooling liquid conduit 14, and the cooling liquid injected into the large current bus conductor 8 is output through the external liquid guide tube 14 on the other side to form a flowing liquid cooling. To reduce the temperature of the large current bus conductor 8 itself during the test. This solution can reduce the conductive cross-section of the large current bus conductor 8, reduce the copper cost, and reduce the oxidation intensity of the conductor surface, ensuring that the contact resistance of the conductor surface is as small as possible.

[0027] At the same time, there is a related electric lifting device on this conductor, and there is a small supporting lifting motor support frame 10 on it. The lifting motor support frame 10 is provided with a lifting motor 13 for lifting the bus conductor 8, a gearbox 12, and a lead screw 11 for lifting the large current bus conductor 8. The large current bus conductor 8 can be lifted and lowered a certain distance by rotating the lead screw 11, and this conductor can be moved so as to pass through the center of the busbar type or through-type super-large current transformer to conduct large current tests, so as to ensure that the tested large current transformer 6 (which has no primary conductor itself) can be put on this super-large current conductor. The ultra-large current conductor is equivalent to the primary conductor of the large current transformer 6 under test. After some related test and detection equipment are assembled, associated, and regulated to form a comprehensive control system, a complete set of ultra-large current test and detection system is formed. The large current or ultra-large current transformer is mounted on the current-carrying conductor 8 of the special test and detection device. This conductor 8 is the primary winding of the transformer (equivalent to one turn of the primary winding). The comprehensive control system is operated to increase the current from a small current at a uniform speed to the current value required for the test and detection, and then the relevant large current or ultra-large current test and detection can be carried out. During the test or operation process, cooling liquids such as water or oil are injected and output into the bus conductor 8 through the external cooling liquid conduit 14, and the flowing liquid is used to reduce the temperature generated by the large current bus conductor 8 when a large current flows through it during the test. The current carrying capacity of the conductor set in this test device can be guaranteed to last for more than 10 minutes when it is 50000A or even above 55000A, and its long-term stable current carrying performance is 45000A or even above 50000A.

[0028] If a larger current is required, the capacity of the plant transformer can be increased accordingly, the capacity of the rectifier and filter circuits and the inverter can be increased, the capacity or number of current boosters can be increased, and the current carrying capacity of the conductors related to the bus conductor can be increased.

[0029] In the ultra-large current complete test device system described in the present invention, the special test device designed for the temperature rise and error test of ultra-large current transformers is to ensure that the steady-state single-phase large current of 50,000A or above is reached. A large-capacity current booster 5 can be used to increase the current output from the inverter to a certain large current or ultra-large current, which is equivalent to a large-capacity constant current source to supply power to the transformer test detection device. Another method can also be used to divide the current into multiple parts, each of which is connected to a certain capacity current booster 5. In this way, the current is increased by multiple current boosters 5 and then collected on the same conductor with ultra-large current flow capacity, so as to input large current or ultra-large current to the relevant power and electrical equipment. However, for the ultra-large current system, if a large-capacity current booster 5 is used, an anti-interference partition can be used to prevent the bias magnetic field and the large leakage reactance of the output current device itself, so it is recommended to use multiple current boosters 5. When multiple current boosters 5 are used, the current output from the inverter can be divided into multiple parts by passing through a parallel conductor structure that divides the current into multiple parts, and each part is connected to a current booster 5 of a certain large capacity. In this way, the current is boosted by multiple current boosters 5 and then collected on the same conductor with super-large current carrying capacity, so as to input large current or super-large current to the relevant power and electrical equipment. (If the capacity of the current booster 5 is insufficient, multiple existing small-capacity boosters can be combined in parallel, which is equivalent to forming a large current booster 5). When multiple current boosters 5 are used in parallel, the current boosters 5 should be evenly and symmetrically set or arranged relative to the input current conductor in the special test device, which can reduce the influence of the bias magnetic field on the tested equipment and reduce the leakage reactance, and improve its effect of outputting large current.

[0030] 3. This scheme takes the temperature rise and error test of super-large current transformer as an example to explain the special test and detection device.

[0031] Before the invention of this complete set of test equipment (including the power supply part), all domestic and foreign production, research and development, testing and application units used indirect methods when conducting temperature rise tests and error (including composite errors) tests on large current, especially ultra-large current transformers. Because the indirect method test is not carried out under the actual operating state of the transformer in the actual working conditions, there may be a certain amount of deviation, which is not completely equivalent to the test and detection data under the actual operating conditions (not the true value). At the same time, when the number of winding turns is large, the capacity of the current output transformer needs to be increased due to the increase in impedance, and a larger capacity transformer is required, which will also impose certain restrictions on the test. It is now necessary to use the direct method to carry out temperature rise test and error (including composite error) test of through-hole large current or ultra-large current. For this purpose, the special test device for temperature rise and error of ultra-large current transformer designed and manufactured can simulate the actual operating conditions of the transformer. After the test, the real data under the maximum limit and the most severe conditions can be obtained, so as to provide more accurate digital basis or reference for various related links such as research and design, production and manufacturing, quality control, procurement acceptance, installation and operation.

[0032] The design scheme adopts 8 current-boosting transformers running in parallel (see Figure 3 ), the 8 current-boosting transformers are arranged evenly and symmetrically in 8 directions with the large current collecting conductor 8 of the ultra-large current transformer test device as the center, so as to improve the current transmission efficiency and effect as much as possible. At the same time, due to the use of 8 current boosters 5, the output capacity and size of each current booster will not be too large, and it is also relatively easy to purchase in the current market, and the total cost will not be higher than the price of a large capacity. And because the size of the 8 units is relatively small, it is also easy to occupy the smallest possible site when arranging them in the test site. Therefore, it is also a better solution to use multiple current boosters 5 in parallel and arranged in a central symmetrical manner.

[0033] 4. Comprehensive control system for ultra-large current complete test and detection equipment consisting of the initial rectifier inverter source to the large current special test equipment.

[0034] 1. This control system can be placed in a large control cabinet or divided into multiple different control cabinets, depending on the on-site spatial layout, user requirements or habits. It can ensure that different equipment or devices can coordinate with each other during the test and detection, so that their technology, efficiency, etc. can reach the best state or effect.

[0035] 2. This integrated control system includes the following components:

[0036] 1) Adjust the current to rectify and filter the 380V three-phase circuit and convert it into a single-phase DC circuit control system;

[0037] 2) Control system of inverter system;

[0038] 3) Control system of current boosting transformer;

[0039] 4) It consists of a special electrical test device system for temperature rise or error test of large current or ultra-large current transformers and a loading and unloading control system for transformers and special large current devices;

[0040] 5) Auxiliary systems, including mutual coordination control and protection devices between systems.

[0041] The above-mentioned units are combined to form a complete set of integrated control system for ultra-large current testing.

[0042] 5. Auxiliary equipment of complete set of equipment

[0043] The auxiliary device includes the connection conductors between the control systems, temperature measuring equipment, standard transformers used in error tests, error testers, power factor compensation devices, water cooling systems added for special tests of ultra-large current transformers, auxiliary electric loading and unloading equipment required for the test products, and other related auxiliary servo equipment and systems.

[0044] If large current or ultra-large current related tests and inspections are carried out on other electrical power equipment, it is only necessary to replace the special test and inspection devices for the temperature rise and error tests of the ultra-large current transformer described in the above three items with special test and inspection devices suitable for the tested equipment. According to the structural form of the tested equipment (such as ultra-large current circuit breakers, ultra-large capacity current-boosting transformers, ultra-large current bushings, ultra-large current enclosed busbars and other electrical and power equipment), a special test and inspection device should be designed to adapt to the testing and inspection of the tested equipment in all aspects.

[0045] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. Single-phase high current generating device, characterized in that: The invention comprises a basic power supply unit and a steady-state current boosting unit. The basic power supply unit comprises a rectifier circuit and an inverter circuit. The rectifier circuit converts a three-phase AC input power supply into a DC power supply. The inverter circuit converts the DC power supply into an AC power supply. The output AC power supply is then boosted in parallel by N current boosters (5) in the steady-state current boosting unit, wherein N is greater than or equal to 1. The boosted high current is added to a high current collecting conductor (8) of a high current test device.

2. A high current transformer test system using the single-phase high current generating device according to claim 1, characterized in that: When N is greater than 1, N current boosters (5) are symmetrically arranged with the large current collecting conductor (8) as the center. The large current experimental device comprises a large support (1) of a frame structure, a large current transformer (6) to be tested is placed at the center position of the lower part of the large support (1), an upper collector plate (9) is arranged at the upper end of the large support (1), a lower collector plate (2) is arranged at the lower end of the large current transformer (6) to be tested, and the current boosters (5) are connected to the upper collector plate (7) and the lower collector plate (3) respectively through the upper current collecting conductor (7) and the lower current collecting conductor (3). The plate (9) is electrically connected to the lower busbar (2), and a lifting motor support frame (10) is connected to the top of the large bracket (1). The lifting motor support frame (10) is connected to the lifting motor (13) and the gearbox (12). The gearbox (12) is connected to the large current busbar (8) through a lead screw (11), driving the large current busbar (8) to move up and down, lift and lower, and pass through the inner cavity of the tested large current transformer (6), and contact and conduct with the upper busbar (9) and the lower busbar (2).

3. The large current transformer test system according to claim 2, characterized in that: The large bracket (1) is made of non-magnetic material, such as hard aluminum alloy material, non-magnetic stainless steel material or other non-metallic insulating material.

4. The large current transformer test system according to claim 2, characterized in that: The large current collecting conductor (8) is of cylindrical structure and made of T2 copper. The large current collecting conductor (8) has a stable and long-term current carrying capacity of more than 55,000A.

5. The large current transformer test system according to claim 2, characterized in that: A liquid cooling channel is added inside the large current collecting conductor (8), and cooling liquid is output into the collecting conductor (8) through an external cooling liquid conduit (14), and the cooling liquid injected into the large current collecting conductor (8) is then output through an external liquid guide tube (14) on the other side, thereby forming flowing liquid cooling.

6. A single-phase high current generation method, characterized in that: The three-phase 380V AC power of the factory transformer is combined with the principles of rectification, filtering and inverter to output a relatively large current value I1, I1 is greater than 1000A, and the voltage is not less than U1. This current is output from N parallel wires to N current boosters (5), N is greater than or equal to 1, as the current input source of the ultra-large current test system device. When N is greater than 1, the N current boosters (5) are respectively distributed in a centrally symmetrical manner. Each current booster (5) has a capacity of U1*I1 / N. The large current I2 output by each of the N current boosters is then connected in parallel and aggregated to supply the large current bus conductor (8) in the transformer test system device for the input current for the large current transformer test.

7. A method of applying the large current transformer test system described in claim 2 to temperature rise and error tests of large current transformers.

8. A method of applying the high current transformer test system described in claim 2 to high current circuit breakers, bushings, busbars and high current related tests.

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