GB/T 507-2002 Insulating oil breakdown voltage determination method

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Card type: Test method

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

• Standard number: GB/T 507-2002
• Chinese name: Insulating oil breakdown voltage determination method
• English name: Insulating liquids—Determination of the breakdown voltage at power frequency
• Adoption relationship: eqv IEC 156:1995
• Replacement relationship: replaces GB/T 507-1986 (including the 1986(91) version expression; the source text contains both "GB/T 507-1986" and "GB/T 507 1986(91)", requires confirmation against the source standard (source-text extraction))
• First publication: 1965 year 1 month; first revision: 1986 year 6 month (the source text "[garbled revision wording]" is source-text extraction noise and should be "revision")
• Publication/implementation: published on 2002-10-10, implemented on 2003-04-01 (the source text "2002[unreadable separator]0[unreadable separator]0 published" and "2003[unreadable separator]04[unreadable separator]01 implemented" are source-text extraction noise)
• Proposed by/under the jurisdiction of: proposed by China Petroleum & Chemical Corporation; under the jurisdiction of the Sinopec Research Institute of Petroleum Processing
• Drafting unit: Refinery of Sinopec Shanghai Gaoqiao Branch (the source text "[garbled Shanghai Gaoqiao name]" is source-text extraction noise)
• Main drafters: Gu Zhenyan, Lu Lihua

2. Scope of application and non-applicability

• Applicable to the determination of various insulating oils with a viscosity of 40 ℃ not greater than 350 mm²/s (the source text "40 C viscosity not greater than 350 mm'/s", unit requires confirmation against the source standard (source-text extraction), should be mm²/s).
• Applicable to handover tests of unused insulating oil.
• Applicable to the evaluation of sample condition during equipment monitoring and maintenance.
• Not applicable: no explicit non-applicability clause is provided in the available source.

3. Method principle

An alternating electric field with continuously increasing voltage at a certain rate is applied to the test sample placed in the specified apparatus until the sample breaks down. (Source text: "Method summary")

4. Reagents and materials (purity / preparation)

• Acetone: analytical reagent.
• Petroleum ether: analytical reagent, 60 ℃～90 ℃ (source text "60 C[unreadable separator]90C").
• Preparation method: not provided in the available source.

5. Apparatus and equipment

5.1 The electrical equipment consists of the following parts: a) voltage regulator; b) step-up transformer; c) switching system; d) energy-limiting device. Two or more of the above devices may be used in the system in an integrated manner.

5.1.1 Voltage regulator

• Voltage regulation should adopt an automatic control system (manual regulation is unlikely to achieve the required uniform voltage rise).
• Automatic control implementation methods: a) autotransformer; b) electronic regulator; c) generator excitation regulation; d) induction regulator; e) resistive voltage divider.

5.1.2 Step-up transformer

• 5.1.2.1 The test voltage is obtained from a step-up transformer supplied by an AC power source (48 Hz～62 Hz); the voltage increment (such as that produced by an autotransformer) shall not exceed 2% of the expected breakdown voltage.
• 5.1.2.2 The voltage applied to the electrodes of the insulating oil cell is approximately sinusoidal, and the peak factor should be within the range "[unreadable peak factor and sign]7%" (the source text is source-text extraction noise, requires confirmation against the source standard (source-text extraction)); the center point of the transformer secondary coil should be grounded.

5.1.3 Current-limiting resistor

• A resistor needs to be connected in series in the sample cup circuit to limit the breakdown current.
• When the voltage is greater than 15 kV, the short-circuit current of the transformer and related circuits should be within 10 mA～25 mA.

5.1.4 Switching system

• 5.1.4.1 Basic requirements: the circuit automatically disconnects when a constant arc is reached; when the sample breakdown current is reached, the primary coil of the step-up transformer should be connected to the circuit breaker and the voltage should be disconnected within 10 ms; if a transient spark occurs between the electrodes (audible or visible), the circuit should be manually disconnected.
  • Note: The sensitivity of the current-sensing element depends on the energy-limiting device; usually the current-triggered cut-off of 4 A cannot exceed 5 ms (the source text "sms" requires confirmation against the source standard (source-text extraction)), and when the instantaneous current is 1 A (according to 5.1.4.2), the current-triggered cut-off time is preferably 1 s (the source text "1 t 1so" requires confirmation against the source standard (source-text extraction)).
• 5.1.4.2 Special requirements for silicone oil: when arc discharge occurs, silicone oil may produce solid decomposition products leading to errors; the energy consumed by the breakdown discharge should be minimized; low-impedance transformer primary coil short-circuiting equipment or low-voltage equipment capable of detecting breakdown within a few microseconds may be used (analog devices such as modulated amplifiers, or switching types such as thyristors); when such equipment is used, the output voltage of the step-up transformer should be reduced to zero within 1 ms of breakdown detection, and the voltage must not be increased before proceeding to the next test in the test sequence.

5.2 Measuring instruments

• 5.2.1 The test voltage value is defined as the peak voltage divided by √2 (the source text "J[unreadable character]" is source-text extraction noise).
• 5.2.2 Voltage measurement may be performed by connecting a peak voltmeter or other type of voltmeter to the input or output of the test transformer, or to a dedicated coil; when in use, it should be calibrated according to a standard, and the standard should cover the full scale of the required measurement.
• 5.2.3 A satisfactory calibration method is the transfer standard method: place the auxiliary measuring device in the position of the sample cup connected between the high-voltage electrodes, so that it has the same impedance as the sample cup containing the sample; the auxiliary measuring device can be independently calibrated according to the primary standard. Such as IEC 52 (see also IEC 60).

5.3 Test assembly

• 5.3.1 Sample cup
  • 5.3.1.1 The volume of the sample cup is between 350 mL～600 mL.
  • 5.3.1.2 The sample cup is made of insulating material, should be transparent, and chemically inert to insulating oil and the cleaning agents used.
  • 5.3.1.3 The sample cup should have a lid, and the design should take into account that the electrodes can be easily removed during cleaning and maintenance.
  • See Figure 1 and Figure 2 for the sample cup (the source text does not provide dimensional details within the figures, only the illustrations).
• 5.3.2 Electrodes
  • 5.3.2.1 The electrodes are made of polished copper, brass, or stainless steel, spherical (diameter 12.5 mm～13.0 mm) as shown in Figure 1, and spherical cap-shaped as shown in Figure 2. The electrode axis should be horizontal, and the electrodes should be immersed in the sample to a depth of at least 40 mm. Any part of the electrode should be no less than 12 mm from the cup wall or stirrer, and the electrode gap is 2.5 mm±0.05 mm.
  • 5.3.2.2 The electrodes should be frequently checked for damage or dents, and if any are found, they should be repaired or replaced immediately.
• 5.3.3 Stirrer (optional)
  • 5.3.3.1 Stirring may be determined according to test needs; whether stirring is performed or not makes no obvious difference to the test results; for automated instruments, a stirrer is more convenient.
  • 5.3.3.2 The stirrer consists of two-blade rotor blades, with an effective diameter of 20 mm～25 mm, an immersion depth of 5 mm～10 mm, and rotates at a rate of 250 r/min～300 r/min. Stirring should not introduce air bubbles and should make the insulating oil flow vertically downward. The design should take into account ease of cleaning.
  • 5.3.3.3 If no magnetic particles are scraped off the magnetic bar, a magnetic bar (length: 20 mm～25 mm, diameter: 5 mm～10 mm) may be used instead for stirring.

6. Recommended operating conditions

• Power supply frequency: 48 Hz～62 Hz (5.1.2.1).
• Voltage increment: cannot exceed 2% of the expected breakdown voltage (5.1.2.1).
• Peak factor: the source text is "[unreadable peak factor and sign]7%", requires confirmation against the source standard (source-text extraction).
• Voltage application rate: 2.0 kV/s±0.2 kV/s (8.3.1).
• Difference between sample temperature and ambient temperature: not greater than 5 ℃; for arbitration tests, the sample temperature should be 20 ℃±5 ℃ (Chapter 8).
• Standing before the first voltage application: after the sample is loaded and it is checked that there are no visible bubbles between the electrodes, proceed after 5 min (8.3.1).
• Pause after breakdown: after reaching the breakdown voltage, pause for at least 2 min before applying voltage again, repeat 6 times (8.3.2).
• Stirring rate (if used): 250 r/min～300 r/min (5.3.3.2).

7. Sampling and sample preparation

7.1 Sample container

• 7.1.1 The sample volume is approximately 3 times the capacity of the sample cup.
• 7.1.2 The sample container is preferably a brown glass bottle; if a transparent glass bottle is used, it should be stored away from light before testing; a plastic container that does not react with insulating oil may also be used, but it must not be reused. To seal, a threaded stopper with a polyethylene or polytetrafluoroethylene gasket should be used.
• 7.1.3 The container and stopper should first be cleaned with an appropriate solvent to remove residual liquid from the previous use, then cleaned with acetone, and finally blown dry with hot air.
• 7.1.4 Immediately cover the lid after cleaning for later use.

7.2 Sampling

• 7.2.1 New oil or used insulating oil should be sampled in accordance with the requirements of GB/T 4756.
• 7.2.2 When sampling, leave 3% of container space.
• 7.2.3 The breakdown voltage test is quite sensitive to trace amounts of water or other impurities in the sample, and a dedicated sampler is required to prevent contamination; unless otherwise required, this work should be performed by trained or experienced personnel. The place most likely to introduce impurities when taking insulating oil is generally the bottom of the container.

8. Analysis procedure

• Unless otherwise specified, the sample is generally not dried or degassed; during the entire test process, the difference between the sample temperature and the ambient temperature is not greater than 5 ℃; for arbitration tests, the sample temperature should be 20 ℃±5 ℃ (Chapter 8).
• 8.1 Sample preparation: before pouring the sample into the sample cup, gently shake and invert the container holding the sample several times so that impurities in the sample are distributed as evenly as possible without forming bubbles, avoiding unnecessary contact between the sample and air.
• 8.2 Sample loading: Before the test, the original insulating oil in the sample cup should be poured out, and the cup walls, electrodes, and other parts should be immediately cleaned with the sample to be tested; then the sample should be slowly poured in, avoiding the generation of bubbles. Place the sample cup on the measuring instrument; if stirring is used, turn on the stirrer. Measure and record the sample temperature.
• 8.3 Pressurization operation
  • 8.3.1 The first pressurization is carried out after the sample has been loaded and it has been checked that there are no visible bubbles between the electrodes 5 min; slowly pressurize between the electrodes at a rate of 2.0 kV/s±0.2 kV/s until the sample breaks down; the breakdown voltage is the maximum voltage value when the circuit automatically disconnects (producing a constant arc) or manually disconnects (audible or visible discharge).
  • 8.3.2 Record the breakdown voltage value. After reaching the breakdown voltage, pause for at least 2 min, then pressurize again, repeating 6 times. Note that there should be no bubbles between the electrodes; if stirring is used, it should be maintained throughout the entire test.
  • 8.3.3 Calculate the average value of 6 breakdown voltages.

9. Qualitative and quantitative and calculation formulas

• Test result: Report the average value of the breakdown voltage, expressed in kilovolts (kV) (Chapter 9).
• Calculation formula: The source text does not provide an explicit formula; it only specifies "calculate the average value of 6 breakdown voltages" (8.3.3).
• Definition of test voltage value: voltage peak divided by √2 (5.2.1).

10. Precision

• The source text does not provide repeatability/reproducibility limit clauses.
• Chapter 10 "Dispersion of test data": The distribution of individual breakdown voltages depends on the numerical value of the test results; Figure 3 is a functional relationship between the coefficient of variation (standard deviation/average) and the average value obtained from a large amount of data measured by several laboratories using transformer oil. The solid line in the figure shows the functional distribution of the median value of the coefficient of variation and the average value, and the dashed line shows the functional distribution of the coefficient of variation and the average value within the 95% confidence interval.
• Specific numerical values: not provided in the available source (Figure 3 is a graphic and no extractable numerical values are given).

11. Report

Report the average value of the breakdown voltage as the test result, expressed in kilovolts (kV). The report should also include: sample name, each breakdown value, electrode type, voltage frequency, oil temperature, and the model of the stirrer used (if selected).

12. Reference documents

• GB/T 4756 Petroleum liquids—Manual sampling
• IEC 52 Voltage measurement method using sphere gaps (one sphere earthed) (the original text "sphere gap (one sphere earthed), electrical F T A9 [garbled measurement title]" is source-text extraction noise)
• IEC 60 High-voltage test techniques (the original text "high voltage [garbled title]" is source-text extraction noise, requires confirmation against the source standard (source-text extraction))

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