CC BY
4УДК 621.75 Safiyev E.S., Pashayev S.S.
Safiyev E.S.
Azerbaijan State Oil and Industry University (Baku, Azerbaijan)
Pashayev S.S.
Azerbaijan State Oil and Industry University (Baku, Azerbaijan)
INVESTIGATION OF TRANSFORMER CIRCUIT INSULATION CHARACTERISTICS
Аннотация: evaluation of transformer insulation wear is one of the main conditions for their normal and long-term operation. Abrasion directly depends on the operating temperature of the equipment, external influences on it and working time. The main drawback during operation is that the insulation loses its quality due to wear and tear. This increases the humidity of the transformer during the aging process, further accelerating the aging process. By knowing the moisture content of solid insulation, you can get an idea of its wear rate and subsequent use. Various methods of frequency spectroscopy (FS) are known.
Ключевые слова: insulation materials, winding of transformer, insulation resistance, increase, temperature.
Insulation materials used in sewage systems are classified according to how long they can withstand heat. As we know, whenever the load increases, the temperature of the circuit increases due to the flow of current. For every 11 degrees increase in temperature, the service life of the insulation decreases by 50%. Depending on the temperature factor, the insulation composition is divided into classes. In general, during normal operation, the temperature of the windings of electrical machines should not exceed the insulation class specified in their passports.
Otherwise, for every 10% increase in temperature, the operating time of the electric machine is halved. For example: If the temperature of the electrical machine circuit rises to 1800C. The most common failure is damage to the winding insulation and a short circuit of one phase to ground. Deterioration of insulation is one of the main causes of soil shortage. Insulation resistance is measured with a megometer at a voltage of 1000...2500V. The measurement is carried out at a temperature of the top layer of oil not lower than +100C. They measure the insulation resistance between the conductors, as well as between the turns of each turn. When measuring, the megometer readings are taken 15 and 60 seconds after voltage is applied. In this case, the absorption coefficient is defined as Kab. The insulation grade refers to the heat resistance class of the insulation materials used for the windings of the motor (or transformer). Motors and transformers typically use insulation materials a, e, B, F, and H. Each insulation class of insulation material has a corresponding maximum operating temperature (the temperature of the hottest point of the motor or transformer winding). When the motor or transformer is running, the temperature of the hottest point of the winding should not exceed the standards, otherwise it will lead to rapid aging of the insulation materials and shorten the service life of the motor or transformer; If the temperature significantly exceeds the permissible value, the insulation will be damaged and the motor or transformer will burn. The insulation class of the transformer refers to the heat-resistant class of the insulation material used, divided into classes A, e. , B, F and H. Permissible temperature rise refers to the temperature rise limit of the transformer compared to the ambient temperature. The test of the longitudinal insulation of the transformer (between the windings, layers and sections) is carried out with a high voltage induced in the transformer itself. This test is carried out in the no-load mode by applying a voltage equal to 1.3 nominal for one minute to the outputs of one of the circuits (usually AG). Each transformer coming out of repair must pass a verification test. Before testing, the transformer is externally inspected and the windings are checked for proper connection. During the external inspection, the insulation quality of the windings of the transformer is carefully checked, the connection of the output ends to the clamp plate and marking
are reviewed. In the external inspection process, the general condition of the transformer core, the flat stacking of the sheets, the insulation quality of the winding studs and the quality of the steel sheet retention are evaluated. According to the current standards, small power transformers must undergo the following inspection tests after repair:
1) checking the transformation ratio at all outputs.
2) measuring the insulation resistance of the circuit.
3) measuring resistance of the wires of windings with direct current.
4) checking the electrical strength of the circuit insulation.
5) measurement of no-load losses and transformer current.
6) measurement of short circuit voltage and transformer losses.
The insulation resistance of the transformer windings to the housing should be checked with a megger with a voltage of up to 500V. The measured value is compared with previous results. The minimum insulation resistance value must be at least 5 MOhm. The loop insulation value, measured in a cold state during operation, should not be lower than 1 MQ. To check the insulation between the housing and the winding by applying test voltage in single-phase low-power transformers, checking the electrical strength of the winding insulation is carried out according to the following scheme (Fig. 2).
Fig. 2. Electrical scheme of the test stand.
The trial period is considered to be 1 minute. The test voltage is found from the following expression.
Usm = 2Un + 1000
where Un is the nominal voltage of the tested circuit of the transformer. The test result is considered positive if the indication of the devices does not change sharply during the test process, and short-circuiting does not occur.
Conclusion. In article on the insulation classes of transformer windings, the strength of their insulation is studied using several methods. A number of factors influencing the transformer windings during operation have been studied. The advantages and disadvantages of different methods for measuring the quality of circuit insulation are studied.
СПИСОК ЛИТЕРАТУРЫ:
1. Aslam, M.; Arbab, M.N.; Basit, A.; Ahmad, T.; Aamir, M. A review on fault detection and condition monitoring of power transformer. Int. J. Adv. Appl. Sci. 2019, 6, 100-110. [Google Scholar]
2. Bagheri, M.; Phung, B.T.; Blackburn, T. Influence of moisture content variation on Frequency Response Analysis of transformer winding. In Proceedings of the EIC 2014 32nd Electrical Insulation Conference, Philadelphia, PA, USA, 8-11 June 2014; Volume 21, pp. 333-337. [Google Scholar]
3. Ansari, M.A.; Martin, D.; Saha, T.K. Investigation of Distributed Moisture and Temperature Measurements in Transformers Using Fiber Optics Sensors. IETrans. Power Deliv. 2019, 34, 1776-1784. [Google Scholar] [CrossRef]
4. Martin, D.; Perkasa, C.; Lelekakis, N. Measuring paper water content of transformers: A new approach using cellulose isotherms in nonequilibrium conditions. IETrans. Power Deliv. 2013, 28, 1433-1439. [Google Scholar] [CrossRef]
5. Martin, D.; Saha, T.; Gray, T.; Wyper, K. Determining Water in Transformer Paper Insulation: Effect of Measuring Oil Water Activity at Two Different Locations. IEElectr. Insul. Mag. 2015, 31, 18-25. [Google Scholar] [CrossRef]
6. García, B.; Valecillos, B.; Burgos, J.C. Determination of Water Content in Transformer Solid Insulation by Frequency Domain. Spectroscopy 2005, 2005, 1823. [Google Scholar]
7. Martin, D.; Saha, T.; Krause, O.; Clarkson, V. Improving the online water content measurement of transformer insulation paper using low pass filters. In Proceedings of the IEPES Innovative Smart Grid Technologies Conference Europe, Ljubljana, Slovenia, 9-12 October 2016; pp. 1043-1048. [Google Scholar]
8. Gizzatova, I.D.; Kozlov, V.K.; Valiullina, D.M. Determination of the true water content, the nature of the impurities and their concentration in transformer oil. E3S Web Conf. 2019, 124, 10-13. [Google Scholar] [CrossRef] [Green Version]
9. Gradnik, T.; Koncan-Gradnik, M.; Petric, N.; Muc, N. Experimental evaluation of water content determination in transformer oil by moisture sensor. In Proceedings of the IEInternational Conference on Dielectric Liquids, Trondheim, Norway, 26-30 June 2011. [Google Scholar]
