SH/T 0101-1991 Determination of Dielectric Strength of Petroleum Waxes and Petrolatums

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Card type: Test method

1. Method number / full title / English name / replacement relationship

• Standard number: SH/T 0101-91 (confirmed in 1998)
• Chinese name: Determination of Dielectric Strength of Petroleum Waxes and Petrolatums
• English name: not provided in the available source
• Replacement relationship: not provided in the available source
• Reference adoption: IEC 243-1967 "Recommended Standard for Test Methods for Dielectric Strength of Solid Insulating Materials at Power Frequencies", IEC 156-1963 "Determination Method for Dielectric Strength of Insulating Oil"
• Approval/implementation: approved by China Petrochemical Corporation 1992-01-15, implemented on 1992-12-01

2. Scope of application and non-applicability

• This standard specifies the method for determining the dielectric strength of petroleum waxes and petrolatums under normal conditions.
• It is applicable to the determination of dielectric strength of petroleum waxes or petroleum wax blends that can be prepared into flat and smooth wax sheets, as well as petrolatums.
• Not applicable: not provided in the available source.

3. Method principle

Place the specimen between two electrodes and subject it to the action of an alternating electric field continuously increased at a certain rate until breakdown. Calculate the dielectric strength based on the breakdown voltage and the specimen thickness, i.e., the distance between electrodes.

• Petroleum wax or petroleum wax blend is made into wax sheets in transformer oil, and its dielectric strength is measured under the conditions of temperature 20℃±5℃ and relative humidity 65%±5%.
• The petrolatum specimen is placed in an electrode cup, melted, cooled to room temperature, and then its dielectric strength is measured under the condition of humidity less than 75%.

4. Reagents and materials (purity / preparation)

• 5.1 Mold: dimensions and technical requirements are shown in Figure 3, assembly is shown in Figure 4. Material is brass or stainless steel.
• 5.2 Wax scraping plate: stainless steel plate of length 220～240mm, width 30～40mm, thickness 2mm, its working edge is required to be straight and smooth.
• 5.3 Beakers: 125～150mL pieces.
• 5.4 Micrometer.
• 5.5 Annealed aluminum foil: thickness less than 0.01mm.
• 5.6 Refined petrolatum or silicone oil.
• 5.7 Silk cloth and absorbent cotton.
• 5.8 Transformer oil: breakdown voltage not less than 25 kV/2.5mm, used as medium.
• 5.9 Solvents: anhydrous gasoline and petroleum ether (60～90℃, analytical reagent), used for cleaning the electrode cup.

5. Instruments and equipment

• 4.1 Solid electrodes: upper and lower electrodes are both made of brass or stainless steel. Shape, dimensions and technical requirements are shown in Figure 1 and Table 1.
  • Table 1 Electrode dimensions: R=3, D=25, H=25 (unit not indicated in the source text, requires confirmation against the source standard (source-text extraction))
• 4.2 Electrode cup for petrolatum specimen
  • 4.2.1 The electrode cup consists of two parts: the cup body and the electrodes, as shown in Figure 2.
  • 4.2.2 The cup body of the electrode cup is a transparent container made of glass or plastic, or a container made of electrical ceramics, with an effective volume between 300～500mL, and the cup body is preferably sealed.
  • 4.2.3 The electrodes are made of polished copper, brass, bronze or stainless steel, spherical, diameter 12.5～13.0mm, and the electrode surface should be smooth. Once pits caused by discharge appear on the surface, the electrodes should be replaced.
  • 4.2.4 The two electrodes should be installed on the same horizontal axis, with a spacing of 2.5mm. The gap between electrodes is calibrated with gauge blocks, required to be accurate to 0.1mm. The depth of the electrode axis immersed in the specimen should be about 40mm.
• 4.3 High-voltage test transformer
  • 4.3.1 A step-up transformer powered by an AC 50Hz low-voltage power supply, capable of providing the test voltage required for specimen breakdown. The voltage should be an approximately sinusoidal waveform, and its peak factor should be within the range of √2±5% (the source text source-text extraction is "[unreadable factor]%t5%", requires confirmation against the source standard (source-text extraction)).
  • 4.3.2 For solid specimens, the transformer capacity should ensure that the secondary rated current is not less than 0.1 A.
  • 4.3.3 For petrolatum specimens, the transformer and matching device should be able to produce a minimum short-circuit current of 20mA when the voltage is greater than 15kV (the source text source-text extraction is "20m、", requires confirmation against the source standard (source-text extraction)).
• 4.4 Protective devices
  • 4.4.1 Protective resistor: resistance value about several thousand ohms. Used to prevent damage to the test equipment due to current and voltage fluctuations caused by breakdown.
  • 4.4.2 Overcurrent relay: requires sufficient sensitivity, the operating current should be selected appropriately to avoid failure to operate after breakdown or false operation when no breakdown occurs. For solid specimens, it should operate within 0.5s (the source text source-text extraction is "OAS", requires confirmation against the source standard (source-text extraction)) upon breakdown; for petrolatum specimens, it should operate within no more than 0.02s after breakdown due to the specimen breakdown current, and a no-voltage release coil should be connected to protect the equipment.
  • 4.4.3 Safety shielding door (cover) and safety door switch.
  • 4.4.4 The high-voltage equipment used for testing and the safety shielding door must be well grounded.
• 4.5 Voltage regulating device
  • 4.5.1 Voltage regulation can be achieved by one of the following devices: a. autotransformer; b. resistance divider; c. generator field regulation; d. induction voltage regulator.
  • 4.5.2 It is best to use an automatic voltage boosting system for voltage regulation, because manual regulation is not easy to achieve the required uniform voltage rise.
• 4.6 Voltage measuring device: measured by connecting a peak voltmeter or other type of voltmeter to the input or output of the test transformer. The measuring instrument used must be calibrated with a sphere gap to the full voltage expected to be measured. Its voltage measurement error shall not exceed ±4%. The voltage ratio obtained from the sphere gap and the voltage indicated by the auxiliary meter depends on whether the specimen and the sphere gap are connected. Therefore, it is important to connect a load equivalent to the specimen in the circuit during calibration. If it is known that the influence of the sphere gap connection on the voltage ratio is negligible, the sphere gap may not be connected during the test.
• 4.7 Constant temperature and humidity chamber: ensures room temperature 20℃±5℃, humidity 65%±5%.
• 4.8 Thermostatic oven: temperature control range 20～140℃, temperature control accuracy ±2℃ (the source text source-text extraction is "129 C0", requires confirmation against the source standard (source-text extraction)).
• 4.9 Thickness gauge: type XUT or other models, measuring range 0～10mm, minimum division of indication 0.01mm.
• 4.10 Oil bath: a container with a cover, its volume is required to accommodate the electrodes and the insulating material supporting the electrodes, and to facilitate loading and unloading of specimens.

6. Recommended operating conditions

• Solid wax specimen test environment (normal conditions): temperature 20℃±5℃, relative humidity 65%±5%.
• Petrolatum test environment: humidity not higher than 75%.
• Voltage rise rate (solid wax specimen): breakdown voltage below 10kV, 0.5kV/s; breakdown voltage between 10～20kV, 1kV/s; breakdown voltage value greater than 20kV, 2kV/s.
• Voltage rise rate (petrolatum): 2kV/s.
• Specimen pretreatment (solid wax sheet): temperature 20℃±5℃, relative humidity 65%±5%, placed for more than 24h; if the product standard has special provisions, proceed according to the specified requirements.
• Transformer oil (test medium): clean, breakdown voltage not less than 25kV/2.5mm; after vacuum filtration, placed in an oil bath, the oil bath should be placed under test conditions for more than 24h.

7. Sampling and specimen preparation

Solid wax specimen

• 6.1.1.1 Place the wax specimen to be tested in a thermostatic oven and melt it at a temperature 15～20℃ higher than the drop melting point of the specimen.
• 6.1.1.2 Assemble the mold, rotate the mold cap so that it is higher than the mold bottom by 0.5mm (measured with a micrometer). Preheat the assembled mold to a temperature slightly lower than that of the liquid specimen. Apply a layer of refined petrolatum or silicone oil on the working surface of the mold with a silk cloth. To facilitate demolding, attach a square annealed aluminum foil with side length 120mm onto it. The aluminum foil should be attached flat, without bubbles and wrinkles.
• 6.1.1.3 Pour the molten specimen into the mold while hot, so that the liquid level is slightly higher than the upper edge of the mold. Cool to a semi-solid state, and scrape off excess specimen with a preheated stainless steel wax scraping plate. If the specimen in the center of the mold is insufficient due to shrinkage caused by temperature drop, replenish by pouring specimen slightly higher than the upper edge of the mold. Cool to a semi-solid state and scrape the poured specimen flat again.
• 6.1.1.4 After slight cooling, gently remove the wax sheet and place it on a flat surface, cover with a layer of cellophane and press a copper plate or stainless steel plate with a diameter of 120mm and thickness of 10mm and a smooth surface on it to avoid deformation of the wax sheet.
• 6.1.2.1 The specimen wax sheet is a circular piece with a diameter of 100mm (the source text source-text extraction is "[unreadable character]OOmm", requires confirmation against the source standard (source-text extraction)) and a thickness of about 0.5mm. The wax sheet should be flat and smooth, free of bubbles and cracks, and uniform in thickness.
• 6.1.2.2 Each group of specimens consists of 5 or 10 wax sheets.
• 6.1.3 Measurement of wax sheet thickness: use a thickness gauge of type XUT or other models, measure at least three points along the radial direction in the area of the measuring electrode of the wax sheet, and take the arithmetic mean as the wax sheet thickness. The thickness measurement error is ±0.01mm.

Petrolatum

• 7.1.2.1 Take the petrolatum specimen to be tested into three electrode cups respectively, so that after melting the specimen can immerse the electrodes.
• 7.1.2.2 Place the electrode cups containing the specimen in a thermostatic oven, and melt all the specimen at about 80℃. After taking out, stir evenly with a glass rod. Avoid generating air bubbles during stirring. Measure the electrode spacing again with gauge blocks.
• 7.1.2.3 Test only after cooling to room temperature.

8. Analysis procedure

Solid wax specimen (6.2)

• 6.2.1 Place the vacuum-filtered transformer oil in an oil bath, and the oil bath should be placed under test conditions for more than 24h.
• 6.2.2 Use a KSZ-3 digital automatic breakdown device (if using other test devices that meet technical requirements, proceed according to the device instruction manual), turn on the power, and preheat for 30min. At this time, the status on the panel: zero return lamp and power lamp are on; the digital device is in 100.00 state.
• 6.2.3 Place the specimen wax sheet between the upper and lower electrodes of the oil bath, connect the electrode wires, and close the high-voltage door.
• 6.2.4 Turn the "range" switch to 50kV, and press the "single point" button.
• 6.2.5 According to the estimated value of the specimen breakdown voltage, determine the voltage rise rate selection switch (see Section 6 Recommended operating conditions).
• 6.2.6 Press the "start" switch, and the voltage begins to rise at the specified rate until breakdown failure of the specimen occurs.
• 6.2.7 Recording of readings: after the specimen breaks down, there is a signal sampling process of about 1～3s, and the breakdown display value can be recorded only after the reading indicator light is on.

Petrolatum (7.2)

• 7.2.1 The test is conducted under the condition of humidity not higher than 75%.
• 7.2.2 Use a a1-100A insulating liquid dielectric strength test device (if using other test devices that meet technical requirements, proceed according to the device instruction manual), after installation and debugging, confirm the equipment is normal before performing the following operations.
  • 7.2.2.1 Turn on the power, use the preset keys to input the test date and specimen batch number, and make the digital display show 00.00 state.
  • 7.2.2.2 Set the single test/multiple cycle test selector switch on the panel to the single test position (the source text source-text extraction is "[garbled instruction for selecting the next test position]", requires confirmation against the source standard (source-text extraction)).
  • 7.2.2.3 Set the voltage rise rate selector switch on the panel to 2kV/s.
  • 7.2.2.4 Place the electrode cup containing the sample on the high-voltage terminal, close the protective cover or close the safety door (the safety door must be reliably connected).
  • 7.2.2.5 Press the "Start" key to begin voltage rise until the sample breaks down. The digital display shows and prints the breakdown voltage value.
  • 7.2.2.6 Only after the voltage has been reduced until the "return to zero" lamp lights up may the safety door be opened to remove the electrode cup.
  • 7.2.2.7 After all prepared samples have been tested, cut off the power supply and end the test.
• 7.2.3 Cleaning of the electrode cup
  • 7.2.3.1 After the sample test is completed, place the electrode cup in a constant-temperature oven, wait until all the sample in the cup has melted, then remove it, pour out the sample, wash the cup body and electrodes with gasoline, disassemble the electrodes, wash them multiple times with gasoline, then rinse clean with petroleum ether and dry.
  • 7.2.3.2 When the electrode cup is not in use, it should be placed in a clean, dry, dust-proof place.

Electrode cup preparation (7.1.1)

• 7.1.1.1 Carefully reinstall the cleaned and dried electrodes, and use gauge blocks to measure the electrode spacing. Avoid direct contact with fingers during installation.
• 7.1.1.2 If the electrode cup has not been used for a period of time, it should be strictly cleaned and dried before use again.

9. Qualitative and quantitative determination and calculation formulas

Solid wax samples

Dielectric strength is calculated according to formula (1): E = U/d ……………………………………(1)

• E—— dielectric strength, MV/m;
• U—— breakdown voltage, kV;
• d—— wax sheet thickness, mm.

Petroleum grease

The dielectric strength of petroleum grease is calculated according to formula (2): E = U/2.5 ……………………………………(2)

• E—— dielectric strength, kV/mm;
• U—— breakdown voltage, kV;
• 2.5—— distance between electrodes, mm.

10. Precision

• Solid wax samples (6.4): The arithmetic mean of the test results of five wax sheets is taken as the dielectric strength of the sample. If the relative error of an individual wax sheet test value with respect to the mean exceeds 15% (the source text source-text extraction is "[unreadable value]%", requires confirmation against the source standard (source-text extraction)), then another five wax sheets are taken and the test is repeated, and the arithmetic mean of the test results of ten wax sheets is taken as the dielectric strength of the sample.
• Petroleum grease (7.4): Take the arithmetic mean of three breakdown voltages, calculate according to formula (2), and report.
• Other precision indicators: not provided in the available source.

11. Report

• Solid wax samples: The arithmetic mean of the test results of five wax sheets is taken as the dielectric strength of the sample; if the relative error of an individual wax sheet test value with respect to the mean exceeds 15%, then another five wax sheets are taken and the test is repeated, and the arithmetic mean of the test results of ten wax sheets is taken as the dielectric strength of the sample.
• Petroleum grease: Take the arithmetic mean of three breakdown voltages, calculate according to formula (2), and report.

12. Reference documents

• IEC 243-1967 "Recommended Standard for Test Methods for Dielectric Strength of Solid Insulating Materials at Power Frequency"
• IEC 156-1963 "Determination Method for Dielectric Strength of Insulating Oil"
• Other reference documents: not provided in the available source.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference for questions and answers