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GB/T 1408.1-2016: PDF in English (GBT 1408.1-2016) GB/T 1408.1-2016
Insulating materials--Test methods for electric strength--Part 1. Test at power frequencies
ICS 29.035.99
K15
National Standards of People's Republic of China
Replace GB/T 1408.1-2006
Insulation material electrical strength test method
Part 1. Test under power frequency
Released on December 13,.2016
2017-07-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
China National Standardization Administration issued
Content
Foreword I
1 range 1
2 Normative references 1
3 Terms and Definitions 2
4 Test significance 2
5 electrodes and sample 3
6 Conditional treatment before test 6
7 surrounding medium 7
8 Electrical equipment 7
9 Test procedure 8
10 boost mode 8
11 breakdown judgment 10
12 trials 10
13 Test report 10
Appendix A (informative) Test data and processing 18
Reference 19
Foreword
GB/T 1408 "Insulation Material Electrical Strength Test Method" is divided into the following three parts.
--- Part 1. Test under power frequency;
--- Part 2. Additional requirements for the application of DC voltage tests;
--- Part 3. 1.2/50μs impact test supplementary requirements.
This part is the first part of GB/T 1408.
This part replaces GB/T 1408.1-2006 "Insulation material electrical strength test method Part 1. Test under power frequency". versus
The main technical changes compared with GB/T 1408.1-2006 are as follows.
---Modified "normative references" (see Chapter 2, Chapter 2 of the.2006 edition);
--- Increased the test requirements for "ball plate electrodes" (see 5.2.1.3);
--- Increased the test requirements for "elastomers" (see 5.2.6.2.4);
--- Added "test in solid materials" (see 7.4);
--- Added schematic diagram of "ball plate electrode" [see Figure 1c)];
--- Removed Appendix B (see Appendix B of the.2006 edition).
This part uses the translation method equivalent to IEC 60243-1.2013 "Insulation material electrical strength test method Part 1. Power frequency
Test" (3rd edition).
The documents of our country that have a consistent correspondence with the international documents referenced in this part are as follows.
Paints for electrical insulation - Part 2. Test methods (IEC 60464-2.2001, MOD)
---GB 2536-2011 Unused mineral insulating oil for electrical liquid transformers and switches (IEC 60296.2003,
MOD)
---GB/T 5471-2008 Compression molding of plastic thermosetting plastic samples (ISO 295.2004, IDT)
Insulated hoses - Part 2. Test methods (IEC 60684-2.2003, MOD)
---GB/T 9352-2008 Compression molding of plastic thermoplastic materials (ISO 293.2004, IDT)
---GB/T 10580-2015 Standard conditions for the use of solid insulating materials before and during testing (IEC 60212.2010,
IDT)
GB -T 15022.2-2007 Resin-based reactive composites for electrical insulation - Part 2. Test methods (IEC 60455-2.
1998, MOD)
Plastics -- Thermoplastics -- Preparation of injection mouldings - Part 3 . slabs ( ISO )
294-3.2002, IDT)
---GB/T 21218-2007 Unused silicon insulating liquid for electrical (IEC 60836.2005, IDT)
This part was proposed by China Electrical Equipment Industry Association.
This part is under the jurisdiction of the National Technical Committee for Standardization of Electrical Insulation Materials and Insulation Systems (SAC/TC301).
This section drafted by. Suzhou Taihu Electric New Materials Co., Ltd., Yantai Minstar Special Paper Co., Ltd., mechanics
Beijing Institute of Electrical and Mechanical Technology, Shanghai Cable Research Institute, Zhuzhou Times Electric Insulation Co., Ltd., Guilin Electric Apparatus Research Institute
Limited.
The main drafters of this section. Chen Yu, Zhang Chunqi, Guo Zhenyan, Wang Dianxin, Xu Xiaofeng, Xia Junfeng, Liu Yali, Zeng Zhi, Zhang Junhua, Wang Yizhen,
Wu Bin, Wang Xianfeng.
The previous versions of the standards replaced by this section are.
---GB/T 1408-1978, GB/T 1408-1989, GB/T 1408.1-1999, GB/T 1408.1-2006.
Insulation material electrical strength test method
Part 1. Test under power frequency
1 Scope
This part of GB/T 1408 proposes a test method for determining the short-term electrical strength of a solid insulation material at a power frequency (ie 48 Hz to 62 Hz).
This section specifies the impregnating agent or surrounding medium when testing liquids and gases as solid insulating materials, but not for liquids and gases.
Body test.
Note. This section includes methods for determining the breakdown voltage of a solid insulating material.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
ISO 293 plastic thermoplastic compression molded specimen (Plastics-Compressionmouldingoftestspecimensof
Catalyst materials)
Plastics -- Thermoplastic injection mouldings - Part 1 . General principles and versatile mouldings and strips (Plas-
tics-Injectionmouldingoftestspecimensofthermoplasticmaterials-Part 1.Generalprinciples,and
Mouldingofmultipurposeandbartestspecimens)
ISO 294-3 Plastics -- Thermoplastic injection molded specimens - Part 3. Plastics-Injectionmouldingof
testspecimensofthermoplasticmaterials-Part 3.Smalplates)
ISO 295 plastic thermoset compression molded specimen (Plastics-Compressionmouldingoftestspecimensof
Thermosettingmaterials)
ISO 10724 (all parts) Plastic thermosetting powder molding composite injection molded specimens (Plastics-Injectionmoulding
Oftestspecimensofthermosettingpowdermouldingcompounds)
Standard conditions for the use of IEC 60212 solid electrical insulating materials during testing and before testing (Standardconditionsforuseprior
Toandduringthetestingofsolidelectricalinsulatingmaterials)
IEC 60296 Unused mineral insulating oil for liquid transformers and switchgear used in electrical engineering (Fluidsforelectrotech-
nicalapplications-Unusedmineralinsulatingoilsfortransformersandswitchgear)
Specification for solvent-free polymerizable resin compounds for electrical insulation - Part 2. Test method (Specification for
solvent-lesspolymerizableresinouscompoundsusedforelectricalinsulation-Part 2.Methodsoftest)
Paints for electrical insulation - Part 2. Test methods (Varnishesusedforelectricalinsulation-Part 2.
Methodsoftest)
IEC 60684-2 insulating flexible bushings - Part 2. Test methods (Flexibleinsulatingsleeving-Part 2.Methods
Oftest)
IEC 60836 Specification for unused silicon-insulated liquids for electrical equipment (Specificationsforunusedsiliconeinsulating
Liquidsforelectrotechnicalpurposes)
IEC 61099 Insulating Liquids for Electrically Unused Synthetic Organic Ester Specifications (Insulatingliquids-Specificationsfor
Unusedsyntheticorganicestersforelectricalpurposes)
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
Electrical breakdown electricalbreakdown
When the sample is subjected to electrical stress, its insulation performance is seriously lost, thereby causing the test loop current to promote the corresponding circuit breaker.
action.
Note. Breakdown is usually caused by partial discharge in the gas or liquid medium around the sample and the electrode, and makes the small electrode (or two electrodes if the two electrodes are straight
If the diameter is the same, the sample at the edge is destroyed.
3.2
Flashover flashover
Under the action of electrical stress, the insulation properties of the gas or liquid medium around the sample and the electrode are lost, and the resulting test loop current is promoted.
Responsive loop breaker action.
Note. A carbonization channel or a perforation in the sample indicates a breakdown, otherwise it is a flashover.
3.3
Breakdown voltage breakdownvoltage
3.3.1
(In the continuous boost test) The voltage at which the sample breaks under the specified test conditions.
3.3.2
(In the step-up test) the highest voltage that the sample withstands, at which the sample does not break down throughout the time.
3.4
Electrical strength electircstrength
The quotient of the distance between the breakdown voltage and the two electrodes applying the voltage under the specified test conditions.
Note. Unless otherwise specified, it is recommended to determine the distance between the two test electrodes as specified in 5.5.
4 Test significance
The electrical strength test results obtained in this section can be used to detect changes in process, aging conditions or other manufacturing or environmental conditions.
The resulting performance changes or deviations from normal values are generally not recommended for direct determination of the performance of insulating materials in practical applications.
status.
The electrical strength measurements of materials may be affected by a number of factors, including.
a) Sample status.
1) the thickness and uniformity of the specimen and the presence of mechanical stress;
2) pretreatment of the sample, especially the drying and impregnation process;
3) Whether there is air gap, moisture or other impurities.
b) Test conditions.
1) the frequency, waveform and boosting speed or pressurization time of the applied voltage;
2) ambient temperature, pressure and humidity;
3) electrode shape, electrode size and thermal conductivity;
4) Electrical and thermal properties of the surrounding medium.
All of these influential factors should be considered when researching new materials that have no practical experience. This section specifies some specific
Conditions to quickly identify materials and can be used for quality control and similar purposes.
The results obtained by different methods are not directly comparable, but each result provides information on the electrical strength of the material. most
The electrical strength of the material decreases as the thickness of the sample between the electrodes increases, and decreases as the voltage application time increases.
The electrical strength measured by most materials is significantly affected by the surface discharge intensity and time before breakdown. Designed for boosting straight
Electrical equipment that does not undergo partial discharge during the test voltage, should know the electrical strength of the material before discharge, but the method of this part
This information is generally not available.
Materials with high electrical strength may not be resistant to prolonged degradation processes such as heat aging, corrosion or chemical reactions due to partial discharges.
Electrochemical corrosion under corrosive or humid conditions, all of which can cause the material to fail at much lower electric field strength during operation.
5 electrodes and samples
5.1 General
Metal electrodes should always be smooth, clean and free of defects. When testing sheets and sheets, the electrode assembly shall be perpendicular to the surface of the specimen.
see picture 1.
Note. Maintenance of the electrodes is especially important when testing thin samples. In order to minimize electrode damage during breakdown, stainless steel electrodes are preferred.
The wire attached to the electrode should neither tilt or otherwise move the electrode or cause pressure changes on the sample, nor should it cause the sample to be surrounded
The electric field distribution is significantly affected.
When testing very thin films (for example, thickness less than 5.0 μm), the product standards for these materials should specify the electrodes and operating tools used.
The preparation procedure of the body program and the sample.
5.2 Test perpendicular to the surface of the non-laminated material and perpendicular to the layer of the laminate
5.2.1 Sheets and sheet materials (including cardboard, paper, fabric and film)
5.2.1.1 unequal diameter electrodes
The electrode consists of two metal cylinders whose edges are rounded to an arc of a radius of (3.0 ± 0.2) mm. One of the diameters of the electrodes
It is (25.0 ± 1.0) mm and has a height of about 25.0 mm; the other electrode has a diameter of (75.0 ± 1.0) mm and a height of about 15.0 mm. The two electrodes are coaxial,
The error is within 2.0 mm, as shown in Figure 1a).
Note. The radius of the sample that is not in contact with the electrode is not critical to the result, but partial discharge in the surrounding medium should be avoided.
5.2.1.2 Equal diameter electrode
If a device that allows the upper and lower electrodes to be accurately centered (with an error within 1.0 mm) is used, the diameter of the lower electrode can be reduced to
(25.0 ± 1.0) mm, the difference between the diameters of the two electrodes is not more than 0.2 mm, as shown in Figure 1b). The results measured in this way are not necessarily the same as 5.2.1.1.
The results measured by the radial electrodes are the same.
5.2.1.3 Ball plate electrode
The electrode consists of a sphere and a metal plate, wherein the upper electrode is a sphere of diameter (20.0 ± 1.0) mm and the lower electrode is of diameter
A metal plate of (25.0 ± 1.0) mm has an edge rounded to an arc of a radius of 2.5 mm. The upper and lower electrodes are coaxial, and the error is within 1.0mm, such as
Figure 1c) is shown.
5.2.1.4 Test of thick samples
When specified, sheets and sheets with a thickness exceeding 3.0 mm shall be machined from one side to a thickness of (3.0 ± 0.2) mm. Then try
The high voltage electrode is placed on the unmachined surface during the test.
In order to avoid flashover or limited by existing equipment, the thickness of the sample can be thinner by mechanical means if necessary.
5.2.2 Belts, films and strips
The two electrodes are two metal rods, each having a diameter of (6.0 ± 0.1) mm, mounted vertically in the fixture so that one electrode is at the other electrode
Above, the sample is sandwiched between the two end faces of the rod.
The upper and lower electrodes should be coaxial with an error of 0.1 mm. The end faces of the two electrodes should be perpendicular to their axial directions, and the edge radius of the end faces is (1.0±
0.2) mm. The upper electrode has a mass of (50.0 ± 2.0) g and should be free to move in the vertical direction inside the fixture.
Figure 2 shows a suitable device. If the specimen needs to be tested under tension, the specimen should be clamped in the rack so that
The sample is placed at the specified position as shown in FIG. In order to achieve the desired stretching, a convenient method is to wrap one end of the sample around a rotating circle.
On the stick.
In order to prevent flashover of the edges of the strips, a thin film or other thin strip of insulating material may be used to cover the edges of the strips and clamp the sample. In addition,
An arc-proof sealing ring can also be used around the electrode as long as an annular gap of 1.0 mm to 2.0 mm is left between the electrode and the sealing ring. Lower electrode
The gap between the sample and the sample (before the upper electrode is in contact with the sample) should be less than 0.1 mm.
Note. For testing of films, see IEC 60674-2.
5.2.3 Hose and soft casing
Tested in accordance with IEC 60684-2.
5.2.4 Hard tube (inner diameter 100mm and below)
The outer electrode is a metal foil tape (25.0 ± 1.0) mm wide. The inner electrode is a conductor that fits tightly with the inner wall, such as a round bar, tube, foil or
Fill the metal ball with a diameter of 0.75mm~2.0mm to make good contact with the inner surface of the pipe. Each end of the inner electrode should extend at least externally
Extreme 25mm.
When there is no adverse effect, Vaseline can be used to attach the metal foil to the inner and outer surfaces of the sample.
5.2.5 Pipes and hollow cylinders (inner diameter greater than 100mm)
The outer electrode is a metal foil strip (75.0±1.0) mm wide, and the inner electrode is a circular metal foil with a diameter of (25.0±1.0) mm. The metal foil should be
It is quite soft enough to accommodate the curvature of the cylinder, as shown in Figure 3.
5.2.6 Casting and molding materials
5.2.6.1 Casting materials
Sample preparation and testing in accordance with IEC 60455-2.
5.2.6.2 Molding materials
5.2.6.2.1 General
Apply a pair of ball electrodes, each ball has a diameter of (20.0 ± 0.1) mm. When arranging the electrodes, make them share the axis and sample.
The plane is vertical (see Figure 4). If the specimen is an elastomer, the plate electrode in 5.2.1.3 should be used [see Figure 1c)].
5.2.6.2.2 Thermosetting materials
Specimens with a thickness of (1.0 ± 0.1) mm, either compression molded according to ISO 295 or injection molded according to ISO 10724, side dimensions
Should be sufficient to prevent flashover (see 5.4).
If a (1.0 ± 0.1) mm thick specimen cannot be applied, a (2.0 ± 0.2) mm thick specimen can be used.
5.2.6.2.3 Thermoplastic materials
The sample was injection-molded according to ISO 294-1 and ISO 294-3, and the dimensions were 60 mm × 60 mm × 1 mm. If that
Insufficient size to prevent flashover (see 5.4) or compression molded specimens as required by the relevant material standards, in which case it shall be compression molded according to ISO 293
The formed flat specimen has a diameter of at least 100.0 mm and a thickness of (1.0 ± 0.1) mm.
See the relevant material standards for the conditions of injection molding or compression molding. If there are no applicable material standards, these conditions should be negotiated between the supplier and the buyer.
5.2.6.2.4 Elastomer
Apply specimens with a thickness of (1.0 ± 0.1) mm. These specimens are formed according to standard conditions and their side dimensions should be sufficient to prevent flashover.
(see 5.4). If there are no valid standards, these conditions should be negotiated between the supplier and the buyer.
For electrode devices, the plate electrode in 5.2.1.3 should be used [see Figure 1c)]. As for the low hardness elastomer, such as silicone rubber, it should be divided
Do not use the appropriate casting material as the filling material or the surrounding medium.
5.2.7 Hard molded parts
For molded insulators that cannot be placed between planar electrodes, opposed equal-diameter ball electrodes should be used. Usually used as electricity for such tests
The pole diameter is 12.5mm or 20.0mm (see Figure 5).
5.2.8 Varnish
Tested in accordance with IEC 60464-2.
5.2.9 Filling glue
The electrodes are two metal balls, each having a diameter of 12.5 mm to 13.0 mm. Horizontally placed coaxially, separated from each other unless otherwise specified
(1.0 ± 0.1) mm and embedded in the filler. Care should be taken to avoid voids, especially to avoid voids between the two electrodes. Due to the use of different
The results obtained from the electrode distance cannot be directly compared, so the gap length should be noted in the material specification and test report.
5.3 Test parallel to the surface of the non-laminated material and parallel to the layer of the laminate
5.3.1 General
If it is not necessary to distinguish whether the breakdown is through the breakdown of the sample or the breakdown along the surface of the sample, the electrodes of 5.3.2 or 5.3.3 can be used, and
The electrodes of 5.3.2 should be used with priority.
When it is required to prevent surface damage, the electrode of 5.3.3 should be used.
5.3.2 Parallel plate electrodes
5.3.2.1 Sheets and sheets
When testing sheets and sheets, the thickness of the sample is the thickness of the test material. The sample is rectangular, long (100 ± 2) mm, and wide (25.0 ± 0.2) mm.
The long sides of the specimen should be cut into two parallel planes perpendicular to the surface of the material. The sample is sandwiched between metal parallel plates and the distance between the two metal plates
25 mm, the thickness is not less than 10 mm, and as two electrodes, a voltage is applied to the metal plate. For thin materials, two or three samples can be used.
Placed locally, even if their long sides are at an appropriate angle to support the upper electrode. The electrode should be of sufficient size to cover the sample
The edge should be at least 15 mm from each side of the specimen. Care should be taken to ensure that the entire area of both sides of the specimen is in good contact with the electrode. Edge of the electrode
It should be properly rounded with a radius of 3mm~5mm to avoid flashover between the edges and sides of the electrode (see Figure 6).
If the existing equipment does not allow the sample to break down, the sample width can be reduced to (15.0 ± 0.2) mm or (10.0 ± 0.2) mm. test
This reduction in the width of the sample shall be specified in the report.
This electrode is only suitable for testing hard materials with a thickness of at least 1.5 mm.
5.3.2.2 Pipe and cylinder
When testing pipes and cylinders, the specimen shall be a complete ring or a segment of a circular arc length of 100 mm with an axial length of (25 ±
0.2) mm. Both ends of the specimen shall be machined into two parallel faces perpendicular to the tube or cylinder axis. Place the sample between two parallel plates according to 5.3.2.1
The test methods for the sheets and sheets described are tested. If necessary, 2 to 3 samples can be used to support the upper electrode. The electrode should have a large enough ruler
In order to make the electrode cover the sample at least 15mm beyond the sides of the sample, the entire area of both sides of the sample should be in good contact with the electrode.
5.3.3 Cone pin electrode
Two parallel holes are drilled on the surface of the vertical sample on the sample, and the center distance between the two holes is (25 ± 1) mm. The diameter of the two holes is so
Fixed. The diameter of the larger end of each hole after reaming with a reamer with a taper of about 2% is not less than 4.5 mm and not more than 5.5 mm.
The two holes of the drill hole completely penetrate the sample, or if the sample is a large pipe, the hole only runs through one pipe wall and is hinged over the entire length of the hole
The knife is reamed.
When drilling and reaming, the material around the hole should not be damaged in any way, such as splitting, crushing or carbonization.
The tapered pin used as the electrode has a taper of (2.0 ± 0.02)% and is pressed in, but do not hammer the two holes so that they fit tightly, and
Highlight the specimen at least 2 mm on each side (see Figure 7).
These electrodes are only suitable for testing hard materials with a thickness of at least 1.5 mm.
5.3.4 Parallel cylindrical electrode
When testing a sample with high electrical strength greater than 15 mm, cut the sample into 100 mm × 50 mm, and as shown in Figure 8.
Two holes are drilled as shown, each having a diameter that is 0.1 mm or less larger than the diameter of the cylindrical electrode. The diameter of the cylindrical electrode is (6.0 ±
0.1) mm with a hemispherical end. The bottom of each hole is hemispherical to fit the electrode end such that the end of the electrode and the bottom of the hole
The gap does not exceed 0.05 mm at any point. If not otherwise specified in the material specification, the distance between the sides of the two holes along their length shall be
(10 ± 1) mm, each hole should extend to within the opposite surface (2.25 ± 0.25) mm. Two optional forms of ventilation electrodes are shown in Figure 8.
Show. When using electrodes with small grooves, the positions of these small grooves should be exactly opposite to the spacing between the electrodes.
5.4 Sample
In addition to the conditions described in the above-mentioned articles, it is usually necessary to pay attention to the following points.
a) When preparing a solid material sample, it should be noted that the two surfaces of the sample in contact with the electrode should be parallel and should be as smooth and smooth as possible;
b) for tests perpendicular to the surface of the material, the specimen is required to have a large enough area to prevent flashover during the test;
c) For tests perpendicular to the surface of the material, the results for specimens of different thicknesses cannot be directly compared (see Chapter 4).
5.5 Distance between electrodes
The distance between the two electrodes used to calculate the electrical strength shall be one of the following (as specified in the material to be tested).
a) nominal thickness or distance between two electrodes (this value is generally used unless otherwise specified);
b) for tests parallel to the surface, the average thickness of the specimen or the distance between the two electrodes;
c) The thickness directly measured near the breakdown point on each specimen or the distance between the two electrodes.
6 Conditional treatment before test
The electrical strength of the insulating material varies with temperature and moisture content. If the test material has been specified, it should be followed. Unless another
There are agreed conditions, the sample should be at a temperature of (23 ± 2) ° C, relative humidity of (50 ± 5)%, that is, the standard ring specified in IEC 60212
The treatment in the atmosphere is not less than 24h.
7 surrounding medium
7.1 General
The material should be tested in the surrounding medium selected to prevent flashover. Transformer oil according to IEC 60296, silicone fluid of IEC 60836
The ester liquid of IEC 61099 or a suitable casting material can be used as a suitable medium. And the surrounding medium should not have any materials and materials during the test.
Significant interactions, such as swelling during the test process.
For samples with a relatively low breakdown voltage, they can be tested in air, especially if the test is to be carried out at high temperatures.
At moderate test voltages, discharge at the edge of the electrode can also have a large effect on the test value.
This medium can be applied if an attempt is made to test the performance of a material in another medium.
Select the medium that has the least impact on the test material.
The surrounding medium may have a great influence on the test results, especially for easily absorbed materials such as paper and cardboard, so it should be in the sample preparation process.
All necessary steps (eg, drying and dipping) are determined in the sequence, as well as the state of the surrounding medium during the test.
Sufficient time is required for the sample and electrode to reach the desired temperature, but some materials may be affected by prolonged exposure to high temperatures.
7.2 Test in high temperature air
When tested in high temperature air, it can be carried out in any well-designed oven. The oven must have a large enough volume to accommodate the sample and electricity.
Extremely so that they do not flash during the test. The oven should be equipped with an air circulation device so that the temperature around the sample is within ±2 °C of the specified temperature.
Generally, keep it even, and measure the temperature by placing a thermometer, thermocouple or other temperature measuring device near the test point.
7.3 Liquid test
When the test is to be carried out in an insulating liquid, the insulating liquid should be of sufficient electrical strength to avoid flashover. In the case of variable pressure
Samples tested in liquids with higher relative dielectric constants of oil may exhibit higher electrical strength than those measured in transformer oil.
The impurity content of transformer oil or other liquids may affect the measured electrical strength.
The test at high temperature can be carried out in a liquid container in an oven (see 7.1) or in a thermostatic control with insulating oil as the heat transfer medium.
In a prepared oil bath. In this case, appropriate liquid circulation measures should be used to make the temperature around the sample approximately uniform and maintain
Within ±2 °C of the specified temperature.
7.4 Test in solid materials
For slab-shaped soft elastomer samples, a suitable casting material should be used, which is preferably cured at room temperature and has a dielectric constant.
Similar to the test elastomer. During the casting process, voids should be avoided, especially in cylindrical electrodes and test panels that are vacuum treated.
Between the volumes. The potting material should have sufficient adhesion to the electrode and the surface of the test plate.
For silicone elastomers, it can be a low viscosity silicone rubber that is cured by two-component room temperature vulcanization.
8 electrical equipment
8.1 Voltage source
A variable voltage low voltage sinusoidal power supply is used to supply a step-up transformer to obtain the test voltage. Transformer and its power supply and its regulating device
It should have the following characteristics.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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