Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems. Группа авторов

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Thermal faults of temperatures < 150 °C 0 0 1 7 Thermal faults of temperatures between 150 and 300 °C 0 2 0 8 Thermal faults of temperatures between 300 and 700 °C 0 2 1 9 Thermal faults of temperatures >700 °C 0 2 2

Table 2.7 Doernenburg gas ratio method.

Key gases	Minimum concentration L1 (ppm)
Hydrogen (H2)	100
Methane (CH4)	120
Carbon monoxide (CO)	350
Acetylene (C2H2)	1
Ethylene (C2H4)	50
Ethane (C2H6)	65

Table 2.8 Types of faults by Doernenburg ratio method.

No.	Type of fault	R1	R2	R3	R4
1	No fault	Conc. (H2 or CH4 or C2H2 or C2H4)>2L1 and Conc. (C2H6 and CO) <L1] or [Conc. (H2 or CH4 or C2H2 or C2H4)< 2L1]
2	Thermal decomposition	R1 > 1	R2 < 0.75	R3 < 0.3	R4 > 0.4
3	Low‐intensity partial discharge	R1 < 0.1	R2 = ND	R3 < 0.3	R4 > 0.4
4	High‐intensity arcing	0.1 < R1 < 1	R2 > 0.75	R3 > 0.3	R4 < 0.4

      2.6.1.3 Rogers Ratio Method

In this technique, three gas ratios R1, R2, and R5 are used for the explanation of the incipient faults in a transformer. The boundaries of the gas ratios suggesting a specific fault type is given in Table 2.9. Rogers method is not dependent on specific gas concentrations for the analysis to be valid. This technique is not always suitable as the accuracy is not very good in identifying faults.

      2.6.1.4 Duval’s Triangle

The Duval Triangle uses three hydrocarbon gases only, namely methane (CH₄), ethylene (C₂H₄), and acetylene (C₂H₂), to detect the fault types [75, 76]. The concentration of the gases is plotted in a triangular coordinate system. The types of faults detected by the Duval’s triangle method are given in Table 2.10. The coordinates of the fault are denoted by the points A1=%p1, A2=%p2, A3=%p3 for the percentage concentration of CH₄, C₂H₄, and C₂H₂ gases, respectively. The concentration of gases in ppm are considered for CH₄ = p₁, C₂H₄ = p₂, and C₂H₂ = p₃ and are converted to triangular coordinates. The relative proportion of the three gases is calculated as below:

      (2.18)

Table 2.9 Types of faults by Rogers ratio method.

No.	Type of fault	R1	R5	R2
1	No fault	0.1 < R1 < 1	R5 < 1	R2 < 0.1
2	Partial Discharge with low energy density	R1 < 0.1	R5 < 1	R2 < 0.1
3	Arcing with high energy discharge	0.1 ≤ R1 ≤ 1	R5 > 3	0.1 ≤ R2 ≤ 3
4	Low temperature thermal faults	0.1 < R1 < 1	1 ≤ R5 ≤ 3	R2 < 0.1
5	Thermal faults of temperatures < 700 °C	R1 > 1	1 ≤ R5 ≤ 3	R2 < 0.1
6	Thermal faults of temperatures >700 °C	R1 > 1	R5 > 3	R2 < 0.1

Table 2.10 Types of faults.

No.	Type of fault	Symbol
1	Partial discharge with low energy density	PD
2	Discharge (arc) with Скачать книгу В начало < 21 22 23 24 25 26 27 28 29 30 > В конец e-mail: [email protected]