The test method is to subject the test sample placed in a special equipment to the effect of an alternating electric field that is continuously boosted at a certain rate until the oil breaks down. The measured values â€‹â€‹are very much related to the measuring equipment used and the method used.
2, the instrument
2.1 Transformer 2.1.1 The test voltage is obtained from a boost converter powered by an AC (50 Hz) low voltage power supply. The primary coil voltage is gradually increased by manual or automatic control means, and the boosted secondary coil voltage is applied to the electrode of the test cup. The voltage should be an approximately sinusoidal waveform with a crest factor in the range of 2 Â± 5% Â°C.
2.1.2 Transformers and matched devices shall be capable of generating a minimum short-circuit power of 20 mA at a voltage greater than 15 kV.
2.2 Transformer oil pressure tester protection device 2.2.1 The device should be well grounded.
2.2.2 When testing, try to prevent high-frequency oscillations. Capacitance inductance tester has the characteristics of small measurement workload, quick and simple, stable performance, accurate measurement, and high failure detection rate. Can also double as CVT, arrester and other electrical equipment for measurement purposes.
2.2.3 In order to protect the equipment and to avoid breakdown of the test oil at the moment of breakdown, a resistor may be connected in series with the test cup to limit the breakdown current.
2.2.4 A circuit breaker is connected to the primary circuit of the high-voltage transformer. The circuit breaker can be operated by the breakdown current of the sample within 0.02 seconds after the breakdown of the sample. The breaker is connected to a non-voltage release coil to protect the equipment.
2.3 Voltage regulation 2.3.1 Voltage regulation can be achieved with one of the following devices;
188.8.131.52 Transformer ratio autotransformer.
184.108.40.206 Resistive Voltage Divider.
220.127.116.11 Generator magnetic field regulation.
18.104.22.168 Induction regulator.
2.3.2 Voltage regulation It is best to use an auto-boost system because the manual adjustment is not the desired uniform boost.
2.4 dielectric strength of dielectric oil test voltage test voltage value is the voltage RMS, that is, the peak voltage divided by 2. The voltage can be measured with a peak voltmeter or other type of meter connected to the input or output of the test transformer. The measuring instrument used must be calibrated with the ball gap to the full voltage that it is desired to measure with it. The ratio of the voltage obtained from the ball gap to the voltage indicated by the auxiliary device is related to the access of the test cup or ball gap. Therefore, the test cup should be connected to the circuit during the calibration process. If it is known that the effect of the insertion of the ball gap on the voltage ratio is negligible, then the ball gap may not be received during the measurement.
2.5 Test Oil Cup 2.5.1 The test oil cup consists of a cup body and an electrode. The two types of test cups are shown in Figure 1 and Figure 2.
2.5.2 Oil cup The cup body is a transparent container made of glass or plastic or a container made of electric ceramics. The effective volume is between 300 and 500 milliliters. The cup body is preferably closed.
2.5.3 Electrodes are made of polished copper, brass, bronze or stainless steel. It is spherical and 12.5-13 mm in diameter, as shown in Figure 1. The ball cap shape is shown in Figure 2. The electrode surface should be smooth. The electrodes should be replaced whenever there are pits on the electrode surface due to discharge.
2.5.4 The electrodes should be mounted on the horizontal axis 2.5 mm apart. The gap between the electrodes is calibrated with a block gauge and is required to be roughly 0.1 mm. The depth of the electrode shaft immersed in the test oil should be about 40 mm.
3.1 Insulating oil Dielectric strength sampling The dielectric strength test is very sensitive to the slight contamination of the sample, it is easy to absorb moisture when sampling, so the sample should be cleaned and dried with a special sampler strictly according to GB4758-84 "stone and liquid Sampling method for petroleum products (manual method). Samples for drum or oil should be drawn from the bottom of the container.
3.2 Preparation of Samples 3.2.1 Gently shake the container containing the sample so that the impurities in the oil are evenly distributed without the formation of air bubbles.
3.2.2 Slowly pour the sample into the prepared oil cup and avoid the formation of air cannon when pouring the sample (by means of a clean, dry glass rod). The operation should be carried out in a dust-proof and dry place so as not to contaminate the sample.
3.2.3 The oil temperature at the time of the test shall be the same as the room temperature. Arbitration trials should be conducted between 15 and 20 Â°C.
3.3 Preparation of the oil cup 3.3.1 When the oil cup is not in use, it should be filled with dry oil and placed in a dry, dust-proof clean place.
3.3.2 The oil cup has not been used for a period of time. Strict cleaning should be performed when it is reused.
22.214.171.124 Remove and wash the electrode, then wash it with fresh dry oil.
126.96.36.199 Carefully reinstall the upper electrode and avoid direct contact with it during installation.
3.3.3 Flush the oil cup with the sample (at least twice) before filling the sample according to 3.2.2.
4, dielectric oil dielectric strength test steps
4.1 The test is conducted at a humidity of no more than 75%.
4.2 In the measuring device, a 50 Hz AC voltage is applied to both ends of the electrode containing the sample, and the voltage is raised from zero at a uniform speed of 2 kV/sec to a value at which the sample breaks down. Breakdown voltage is the voltage that is reached when the first spark occurs between electrodes, regardless of whether the spark is instantaneous or constant.
If a momentary spark (audible or visible) occurs between the electrodes, the circuit is manually disconnected. If a constant arc occurs, the circuit breaker on the primary circuit of the high voltage transformer can automatically disconnect the circuit. An automatic circuit breaker that opens the circuit can cut off the voltage within 0.02 seconds.
The sample is loaded into the oil cup. Apply the first voltage as soon as possible after ensuring that there are no more air bubbles in the sample (at the latest 10 minutes after loading).
4.3 After the sample is broken down, the sample is gently stirred with a clean, dry glass rod between the electrodes, and the air cannon is avoided as much as possible during stirring.
4.4 One minute after air bubbles disappear, apply the second voltage according to the requirements of 4.1. If it is impossible to observe the disappearance of air bubbles, it is necessary to wait 5 minutes for the breakdown test. The above tests were performed six times for each test, and the arithmetic mean of the six results was taken as the dielectric strength of the sample.
5.1 Record the six breakdown voltage values â€‹â€‹obtained from the test and calculate their arithmetic mean, expressed in kilovolts.
5.2 The test report should also describe the type of electrode used and the oil temperature.
Thank you for your attention to our products. In addition to this product introduction, the company also has insulation ladders, high-voltage insulation mats, cable fault testers, high-voltage measuring instruments, insulation boots gloves pressure test equipment, power safety equipment cabinets, etc. Introduction, if you are interested in our products, welcome to inquire. Thank you!
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