Impact of load ramping on power transformer dissolved gas analysis
- Authors: Cui, Huize , Yang, Liuging , Li, Shengtao , Qu, Guanghao , Wang, Hao , Abu-Siada, Ahmed , Islam, Syed
- Date: 2019
- Type: Text , Journal article
- Relation: IEEE Access Vol. 7, no. (2019), p. 170343-170351
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- Description: Dissolved gas in oil analysis (DGA) is one of the most reliable condition monitoring techniques, which is currently used by the industry to detect incipient faults within the power transformers. While the technique is well matured since the development of various offline and online measurement techniques along with various interpretation methods, no much attention was given so far to the oil sampling time and its correlation with the transformer loading. A power transformer loading is subject to continuous daily and seasonal variations, which is expected to increase with the increased penetration level of renewable energy sources of intermittent characteristics, such as photovoltaic (PV) and wind energy into the current electricity grids. Generating unit transformers also undergoes similar loading variations to follow the demand, particularly in the new electricity market. As such, the insulation system within the power transformers is expected to exhibit operating temperature variations due to the continuous ramping up and down of the generation and load. If the oil is sampled for the DGA measurement during such ramping cycles, results will not be accurate, and a fault may be reported due to a gas evolution resulting from such temporarily loading variation. This paper is aimed at correlating the generation and load ramping with the DGA measurements through extensive experimental analyses. The results reveal a strong correlation between the sampling time and the generation/load ramping. The experimental results show the effect of load variations on the gas generation and demonstrate the vulnerabilities of misinterpretation of transformer faults resulting from temporary gas evolution. To achieve accurate DGA, transformer loading profile during oil sampling for the DGA measurement should be available. Based on the initial investigation in this paper, the more accurate DGA results can be achieved after a ramping down cycle of the load. This sampling time could be defined as an optimum oil sampling time for transformer DGA.
Dissolved gas analysis for power transformers within distributed renewable generation-based systems
- Authors: Cui, Huize , Yang, Liuqing , Zhu, Yuanwei , Li, Shengtao , Abu-Siada, Ahmed , Islam, Syed
- Date: 2021
- Type: Text , Journal article
- Relation: IEEE Transactions on Dielectrics and Electrical Insulation Vol. 28, no. 4 (2021), p. 1349-1356
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- Description: In this paper, a series of laboratory experiments are conducted to investigate the effect of momentary small variations in the transformer operating temperature on the dissolved gas analysis (DGA) measurement. With the increased penetration level of renewable energy sources of intermittent characteristics into electricity grids, operating power transformers are expected to experience frequent temperature variations. Sampling transformer oil during such temperature variation leads to inaccurate diagnosis. Experimental results reveal that gas evolution in transformer oil is greatly affected by the small variations in the operating temperature. Such small variation can be a result of the intermittent generation characteristics of renewable energy sources. Hence, false analysis may be reported if oil is sampled during generation or load fluctuation events. Experimental results are explained through chemical equilibrium constant theory, which indicates that dissolved gases reflect the change in aging rate of the transformer oil-paper insulation system. These results suggest a new paradigm for DGA process through correlating measurements with the transformer operating temperature through the generation and load profiles at the instant of oil sampling. © 1994-2012 IEEE.
A comprehensive analyses of aging characteristics of oil-paper insulation system in HVDC converter transformers
- Authors: Cui, Huize , Yang, Liuqing , Zhu, Yuanwei , Li, Shengtao , Abu-Siada, Ahmed , Islam, Syed
- Date: 2020
- Type: Text , Journal article
- Relation: IEEE Transactions on Dielectrics and Electrical Insulation Vol. 27, no. 5 (2020), p. 1707-1714
- Full Text: false
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- Description: This paper investigates the dissolved gases evolution in transformer oil under combined DC/AC electrical-Thermal stress. Dissolved gases detected in transformer aged insulation oil reveal that oil under AC electric field combined with thermal stress can produce more dissolved gases than oil under DC electric field with thermal stress but less than the gases produced in oil under distorted AC or combined AC/DC voltage stress. This is attributed to the divergent migration properties of the charged components under different types of electric fields. To further understand this behavior, carrier recombination coefficient is proposed to explain the oil DGA results under various aging stresses. Results show that diagnostic parameters such as breakdown voltage, oil interfacial tension, and moisture content in pressboard should be used along with DGA results in order to accurately diagnose the insulation condition within converter transformers that impose a combined AC/DC voltage stress on the insulation system. © 1994-2012 IEEE.
- Description: This work has been supported by the National Key Research and Development Program of China (2017YFB0902705), State Key Laboratory of Electrical Insulation and Power Equipment (EIPE20210), the National Natural Science Foundation of China (51907148), the Youth Fund of State Key Laboratory of Electrical Insulation and Power Equipment (EIPE19308), the Foundation Project of State Grid in Shaanxi province section, China (SGSNKY00SPJS1900302). The authors thank the Natural Science Basic Research Plan in Shaanxi Province of China (2019JQ-070).