GB/T 5654-1985 Measurement of power frequency relative dielectric constant, dielectric loss factor and volume resistivity of liquid insulating materials
Some standard content:
National Standard of the People's Republic of China
Measurement of relative dielectric constant, dielectric dissipation factor and volume resistivity of liquid insulating materials at power frequencyMeasurement of relative dielectric constant, dielectric dissipation factor and volume resistivity of insulating materials at power frequency UDC 621.315
. 615 : 621
.317.3
GB 5654—86
This standard applies to the measurement of relative dielectric constant, dielectric dissipation factor and volume resistivity of insulating materials that are liquid at the test temperature. This method is mainly used to test unused liquid insulating materials. However, it is also applicable to testing used insulating liquids in transformers, cables and other electrical equipment. For routine tests, the simplified method described in Appendix A may be used. This standard is formulated with reference to the international standard 1EC247 (1978) "Measurement of relative dielectric constant, dielectric loss factor and DC resistivity of insulating liquids".
1 Definition
1.1 Relative dielectric constant
The ratio of the capacitance between the two electrodes of a capacitor and the surrounding area when it is filled entirely with the test insulating material to the vacuum capacitance of the same electrode shape.
1.2 Dielectric loss factor
The dielectric loss tangent of the insulating material.
The dielectric loss angle of the insulating material is the complementary angle of the phase angle between the external AC voltage and the current flowing through it. 1.3 Volume resistivity
The quotient of the true current electric field strength and the steady-state density in the insulating material. In fact, the volume resistivity can be regarded as the volume resistance in a unit cubic volume.
2 Overview
2.1 Relative dielectric constant and dielectric loss factor The relative dielectric constant and dielectric loss factor of liquid insulating materials depend greatly on the test conditions, especially the temperature and the frequency of the applied voltage. The relative dielectric constant and dielectric loss factor are caused by dielectric polarization and conductivity. At the power frequency and the temperature recommended by this method, the losses are mainly due to the conductivity of the liquid, that is, to the presence of carriers in the liquid. The measured value depends on the following factors: 2.1.1 Impurities
The presence of micro-ionizable dissolved impurities or colloidal particles in the sample will strongly affect the dielectric loss factor value. Therefore: Measuring the dielectric properties of the liquid is very valuable to indicate the presence of ionized impurities. However, the impurity content has little effect on the relative dielectric constant. 2.1.2 Samples: (Sampling and Storage)
Sample contamination caused by improper sampling or operation methods, electrodes not cleaned or dried, etc., will make the test results unreliable. Long-term exposure to strong light during the cutting process will cause the sample to deteriorate and increase the test value; long-term exposure to a humid environment will increase its water content, which will affect the measured value. Therefore, the sample must be stored in a dry and light-proof place. Sampling rules must be strictly followed to prevent contamination of the sample. In order to obtain the correct test value, the maximum storage period of the sample should be specified. National Bureau of Standards Issued on November 25, 1985
Implementation on December 1, 1986
2.1.8 Temperature
GB 5654 --85
The dielectric loss factor changes exponentially with the inverse of absolute temperature. Therefore, it is necessary to measure it under fairly precise temperature conditions. However, at higher temperatures, the dielectric loss factor value will change with the heating and constant temperature time of the sample, even when no electric field is applied. It is generally believed that the initial value can better represent the actual state of the liquid, so it is required to measure the loss factor as soon as the temperature reaches equilibrium. 2.1.4 Electric field strength
Generally speaking, the test voltage has little effect on the test value. However, within the test voltage range commonly used in general power frequency bridges (equivalent to an electric field strength of 100~1000V/mm), the voltage has already affected the test value of the dielectric loss factor. When the electric field strength is too high, the test value will increase significantly due to the secondary effect of the electrode, sample discharge, etc. Therefore, the measurement should be carried out under the specified electric field strength. 2.2 Volume resistivity
The measured value of volume resistivity is related to the following factors: 2.2.1 Temperature
The volume resistivity changes exponentially with the inverse of absolute temperature. Therefore, it is necessary to measure under fairly precise temperature conditions. Just as the dielectric loss factor changes with the heating and constant temperature time of the sample, the volume resistivity also changes with the heating and constant temperature time of the sample. Therefore, it is also required to measure the volume resistivity as soon as the temperature reaches equilibrium. 2.2.2 Electric field strength
The volume resistivity can be affected by the applied electric field strength. For the comparability of the results, the measurement should be carried out under the specified electric field strength. 2.2.3 Charging time
If the charging time is different, the results cannot be compared. The charging time is generally specified to be 60s. 2.2.4 Impurities
Sample contamination can seriously affect the measurement of volume resistivity. Trace ionized impurities and colloidal impurities in the sample will greatly reduce the volume resistivity. Similarly, the presence of dispersed water will significantly reduce the volume resistivity. Dissolved water will only have a significant effect when it is close to saturation.
Although the above factors will affect its measured value, volume resistivity is still a useful indicator. 2.3 Measurement order
When measuring relative dielectric constant, loss factor and volume resistivity successively on the same sample, AC measurement should always be carried out before DC measurement. After AC measurement, the two electrodes should be short-circuited for 1 minute and then the volume resistivity measurement should be started immediately. 3 Instruments
3.1 Instruments for measuring relative dielectric constant and loss factor For use with a gauge, a variable current (power frequency) bridge with a dielectric loss factor resolution of 10- can be used. However, it is best to use a bridge with a resolution of 10-5 when the sample capacitance is 100pF. 3.2 Instruments for measuring volume resistivity
Use a high resistance meter or other instrument with a resolution of more than 10152 for measurement. The measurement error caused by the measuring instrument should be guaranteed to be less than 20%. 3.3 Electrode damage
The same electrode cup can be used to measure relative dielectric constant, dielectric loss factor and volume resistivity. When making precise measurements, a three-terminal electrode cup should be used. The three-terminal electrode cup has a protective electrode that is sufficient to shield the measuring electrode. Usually the lead shielding layer is connected to the protective electrode. If a two-terminal electrode cup is used to measure the volume resistivity, it should be ensured that the insulation resistance between the measuring electrode and the commercial voltage electrode is at least 100 times the resistance of the liquid being measured. Similarly, when measuring the dielectric loss factor under AC, there should also be a corresponding ratio. The loss factor of the empty cup after cleaning and drying should be close to zero. The electrode cup should also meet the following requirements:
a: The electrode cup can be easily disassembled and cleaned of all parts, and can be reassembled without significantly changing the capacitance of the empty cup. It should also be placed in a suitable constant temperature solvent or oven, and the temperature of the internal electrode can be measured. b. The material used to make the electrode cup should be free of pores and able to withstand the required temperature. The coaxiality between the electrodes should not be affected by temperature changes. The surface roughness of the electrode in contact with the test liquid should not be less than Ra0.16μm, making it easy to clean. There should be no chemical reaction between the liquid and the electrode during the test. The electrode is also not affected by the cleaning agent. Electrodes made of stainless steel are good for testing all types of insulating liquids. Aluminum and its alloys should not be used as electrode cups because they will be corroded by alkaline cleaning agents. Note: The surface conductivity of the electrode is not as good as that of a gold-plated one. But the surface is gold-plated. Nickel or, as long as it is well protected and remains free of corrosion, can also be used satisfactorily. It has good discrimination on steel and has the advantage of low thermal expansion. Nickel or gold plating on brass and nickel bonding on stainless steel are also used. The insulating material used to support the electrode should have a low loss factor, high resistivity and sufficient mechanical strength. This solid insulating material should not absorb the test liquid and cleaning agent, nor react physically and chemically with them. Note: The band considers fused quartz to be a suitable insulating material. High-frequency ceramics can also be used in three-terminal electrodes. The core, and the lead wires should use shielded wires. In order to resist the interference of external electromagnetic fields, a grounded shielding sleeve should be added to the outside of the electrode. Any electrode cup that meets the above requirements can be used. An example of a three-terminal electrode cup that can be used for low-viscosity liquids and an applied voltage not higher than 2000V is shown in the figure below. It is best to use one electrode cup for testing one type of liquid. 8.4 Test chamber
The test chamber should be able to maintain the temperature within ±0.5℃ of the specified value. It may consist of a forced-air oven or a temperature-controlled oil bath or heating jacket with an electrode cup. The test chamber shall have a shielded wire connected to the electrode cup. The electrode cup shall be well insulated from the grounded chamber shell. 3.5 Glassware
Ordinary chemical glassware made of borosilicate glass shall be used. All glassware used for pouring samples shall be cleaned and thoroughly dried as specified in Chapter 5. 8.6 Timer
Used to measure the charging time. It is accurate to 0.5s. 4 Cleaning solvent
The solvent used to clean the electrode cup shall at least meet the requirements of 1. Industrial purity and be stored in brown glass. Barreled solvents should be filtered and stored in brown glass bottles.
Hydrocarbon sleeves and silicone sleeves are usually cleaned with hydrocarbon solvents, such as solvent gasoline, n-heptane, toluene, petroleum ether, etc. Suitable solvents can be selected for other types of liquids.
5 Cleaning the electrode cup
When measuring dielectric properties, it is most important to clean the electrode cup. Because insulating liquids are extremely sensitive to the influence of very small contamination. Therefore, the following method points must be strictly followed: 1. Completely disassemble the electrode cup.
b. Thoroughly clean all components and replace. 2. Solvent. c. Wash with acetone first, then with mild soap or detergent. Abrasive particles and friction should not damage the roughness of the metal surface. d. Boil with 5% sodium phosphate distilled water for at least 5 minutes, and then wash with distilled water for several times. e. Boil with distilled water for 1 hour.
f. Bake each part in an oven at 105~110℃ for 60~90min.
Note: When using solvents, pay attention to preventing burning and toxicity to the human body. 6 Sampling
When sampling, follow the sampling method standard of the tested liquid to ensure that the sample is not contaminated by moisture. The sample should be sealed and stored in a light-proof container to prevent moisture. The storage time of the sample should be as short as possible, generally not more than two weeks. Unless otherwise specified, it will not be filtered, dried, etc. before the test. 7 Sample preparation
GB565485
7.1 Place the container containing the sample in the test room. The air in the test room should be clean and the relative humidity should not exceed 70%. 7.2 Tilt the container and rotate it slowly to make the sample uniform. Open the container mouth, wipe it with a clean lint-free cloth or fine filter paper, pour out a little liquid sample to rinse the surface of the container mouth. Then pour the required sample into a conical flask with a lid. 7.3 Put the conical flask containing the sample into an oven and heat the sample to 5-10℃ higher than the required test temperature. The time kept at this temperature should not exceed 1h.
8 Fill the electrode cup with the sample
8.1 Assemble the electrode cup (the electrode cup is still hot at this time), be careful not to touch the electrode or insulating surface directly with your hands, and put the assembled electrode cup in a heating box that is 5-10℃ higher than the specified test temperature. In order to check whether the electrode is clean and dry, it is usually necessary to measure the dielectric loss factor of the empty electrode (should be close to zero) and record the empty cup capacitance. 8.2 When the temperature of the inner electrode exceeds the test temperature, quickly remove the electrode cup and lift the inner electrode out (do not let it directly contact any surface). Fill the electrode cup with a portion of the heated sample and put the remaining heated sample back to the original position in the oven. Put in the inner electrode and lift and lower the inner electrode twice to rinse the electrode cup. Then remove the inner electrode, pour out the rinse liquid and immediately fill it with the second heated sample. Insert the electrode cup. 8.3 Install the electrode cup and place it in a test chamber that meets the test temperature, connect the circuit, and ensure that temperature equilibrium is reached within 15 minutes.
Note: To ensure that equilibrium is reached within 15 minutes, first select the preheating temperature of the sample, electrode cup and test chamber, and then quickly complete the two steps of 8.2 and 8.3. Slow operation can not only prevent the electrode from being overcooled. It can also prevent dust particles from gathering on the wet surface of the electrode. 9 Test temperature
This test method is suitable for testing absolute liquids in a wide range of overflow. Unless otherwise specified in the specification of the test liquid, the general test is carried out at 90°C.
10 Measurement of dielectric loss factor (middle)
10.1 Test voltage
The test adopts 50Hz Voltage. The voltage value is determined by the specifications of the test liquid. Usually, the electric field strength can be selected between 0.03 and 1 kV/mm according to the properties of the test instrument and the requirements of the test liquid. However, it must be noted that the electric field strength has an impact on the test value. Therefore, the results obtained by testing with different voltages cannot be compared. 10.2 Measurement
10.2.1 After 15 minutes after the sample is injected into the electrode cup, the difference between the internal electrode temperature and the required test temperature should not be greater than ±1°C. At this time, the dielectric loss factor is measured. Note that the instrument applies voltage during measurement. Since the heating time affects the measured value, the measurement should be completed as soon as possible.
10.2.2 Immediately after the measurement, pour out the first sample and inject the second sample into the electrode cup for measurement. The operation process is the same as the first time (but there is no need to rinse again). The two The difference between the two readings shall not be greater than 0.0001 plus 25% of the larger of the two values. 10.2.3 If the above repeatability requirements cannot be met, continue to measure the sample until the difference between the two consecutive readings does not exceed C.0001 plus 25% of the larger of the two values. The measured results are considered valid at this time. Note: Repeated measurements can be made in another electrode of the same type, but their repeatability must meet the above requirements. 10.3 Report
The smaller value of the two valid measurements is taken as the dielectric loss factor of the liquid sample. The report should also include:
a: Electrode cup type and capacitance when air is the medium; b. Test voltage and electrode gap; c. Test temperature; d. Number of measurements and each result.
11 Measurement of relative dielectric constant (e,)
GB 5654--85
Usually, the measurement of relative dielectric constant and dielectric loss factor is carried out simultaneously. 11.1 When using a well-designed and pre-calibrated three-terminal electrode cup, et
where: C—the capacitance of the electrode cup with the sample at the measurement temperature, pF, C. —the capacitance of the empty electrode cup at the measurement temperature, pF. 11.2 When using a two-terminal electrode or an uncalibrated three-terminal electrode cup (1)
11.2.1 First measure the capacitance of the clean electrode cup with dry air as the medium. Then measure the capacitance of a body with a known relative dielectric constant e. Calculate the electrode constant C. and the corrected capacitance Cg as follows: C.
G,=Ca-Ce
where: C—the capacitance of the electrode cup filled with a calibration solution with a known relative dielectric constant e, pF; C.—the capacitance of the electrode cup with air as the medium, pF. 11.2.2 Measure the capacitance Cz of the electrode cup containing the test liquid: Er
11.3 The difference between the values obtained from two repeated measurements shall not exceed 5% of the larger value. Otherwise, continue to measure the sample until this repeatability requirement is met. Only then is the measurement considered valid. 11.4 Report
The average value of the two valid measurements is used as the relative dielectric constant of the liquid sample. The report should include:
8. Electrode cup type and capacitance with air as the medium: b. Test voltage and electrode gap
c Test temperature.
12 Measurement of volume resistivity
12.1 Test positive
Unless otherwise specified, the DC test voltage is generally selected to subject the liquid to an electric field strength of 200 to 300 V/mm. 12.2 Charging time
Usually, the charging time is 60 s.
12.3 Measurement
If the loss factor has been measured on this sample, the two electrodes should be short-circuited for 1 minute and then the volume resistivity measurement should be started immediately. If only the volume resistivity is to be measured, the measurement should be started immediately after the sample has been filled into the electrode cup for 15 minutes. Connect the connecting wires of the measuring instrument and the power supply. Connect the positive pole of the power supply to the outer electrode of the electrode cup. Apply a DC voltage and record the resistance value immediately after charging for 60 seconds.
Note: An instrument with current reading can also be used, but the other basic requirements must still be observed. Short-circuit the two electrodes of the electrode cup for 5 minutes. Pour out the liquid on the electrode cup. Pour out the second sample from the sample and repeat the measurement. Calculate the volume resistivity using the following formula in m: Where: R - measured sample resistance, a
K - empty electrode constant, m.
GB 5654-85
The empty electrode constant is calculated according to the electrode cup capacitance when the medium is air. K=0.13Cg, pF
An Anlin
The difference between the two readings should not exceed 35% of the higher of the two values. Otherwise, continue to measure the sample. Until the difference between the two adjacent readings does not exceed 35% of the higher of the two values. Only then is the test valid. 12.4 Report
The higher value of the two valid measurements is used as the volume resistivity of the sample. The report should also include:
a, test voltage and electrode gap:
Number of measurements and each result;
Test temperature.
GB 5654—85
Example of three-terminal electrode cup
1—insulation, 2—high voltage electrode: 3—measuring electrode; 4—protective electrode, 5—thermometer hole
A.1 Overview
GB6654—85
Appendix A
Simplified method for routine test of dielectric loss factor and volume resistivity of liquid insulating materials
(Supplement)
This simplified method can be used to determine whether the dielectric loss factor and volume resistivity of insulating liquids in operation in electrical equipment and unused insulating liquids are worse than their specified values. The test method described in this appendix has a lower accuracy than the method described in the main text, but it can be measured faster and with acceptable accuracy.
A.2 Electrode cup
The electrode cup described in the main text can still be used. A flat three-terminal electrode cup can also be used. An example of a flat three-terminal electrode cup is shown in the figure below. It is best to use one electrode cup for each type of material. 172
Example of a flat three-terminal electrode cup
1 - Measuring electrode: 2 - Insulation: 3 - Preservation electrode: 4 - High voltage electrode, 5 - Insulation
A.8 Test chamber
The test chamber is a forced ventilation oven, heating jacket or oil bath that can maintain a sufficiently uniform test temperature of the electrode cup. It can make the difference between the temperature of the electrode in the electrode cup and the temperature required by the test not exceed 2°C. It cannot be heated by a hot plate, because it will cause too large a temperature difference in the electrode cup and lead to unreliable results. A,4 Test temperature
GB 5654-85bzxZ.net
Measurement can be carried out when the sample temperature is within ± 2°C of the specified temperature. A.5 Cleaning the electrode cup
When the cleaning method described in Chapter 5 of the main text cannot be used, in order to obtain repeatable and reasonable test results, the following cleaning method is used:
A.5.1 Ultrasonic cleaning method
a: Disassemble the electrode cup.
b. Rinse all parts with solvent.
c. Shake the parts with soapy water in an ultrasonic cleaner for 20 minutes, remove the parts, rinse them with tap water and distilled water, and then shake them with distilled water for 20 minutes.
A.5.2 Solvent cleaning method
a. Disassemble the electrode cup.
b. Thoroughly wash all parts with solvent and replace the secondary solvent. c. Wash all parts with acetone first, then with hot tap water. Then wash with distilled water. A.5.3 After cleaning, put the parts in an oven at 105-110℃ to fully dry for about 60-90 minutes. A.5.4 When testing a group of similar unused liquid samples, the same electrode cup can be used without intermediate cleaning as long as the performance of the last tested sample is better than the specified value of the oil to be tested. If the performance value of the previous sample tested is worse than the specified value of the oil to be tested, the electrode cup must be cleaned before the next test. A.6 Sample preparation, sample injection into the electrode cup and measurement The samples shall be sampled and stored in accordance with Chapters 6 and 7 of the main text. Prepare the preheated sample in accordance with Chapters 7 and 8 and inject it into the electrode cup. Install the electrode cup, put it in the test box, connect the circuit and wait for 15 minutes. The difference between the internal electrode temperature and the required test temperature should be ± 2°C. Start the measurement at this time.
For liquids with low viscosity, the liquid sample can also be injected into the unheated electrode cup at room temperature, and then the electrode cup with the sample is heated. It should not take more than 1 hour from the start of heating to the liquid reaching the test temperature. Connect the test circuit and measure when the difference between the internal electrode temperature and the required test temperature is ± 2°C.
When the electrode cup is used sequentially for different samples, although it is not necessary to clean it between each test, it is always necessary to fill the electrode cup with the next test sample and rinse it three times.
When the aged liquid is heated or stored at high temperature, special care should be taken to avoid further oxidation. The influence of suspended foreign matter can be judged by the test results of the samples before and after filtration using a porous melt filter with a pore size of 5 to 15 μm.
When AC and DC measurements are made on the same sample in succession, the AC measurement is always carried out before the DC measurement. Only one sample is required for each batch of samples.
Additional Notes:
This standard was proposed and managed by the National Insulation Material Standard Technical Committee. This standard was drafted by a working group composed of Guilin Electric Science Research Institute, Shanghai Refinery, Shanghai Resin Factory, Xi'an Thermal Engineering Research Institute and other units.
The main drafter of this standard is Yuan Mingzhen.
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