The procedure and scope for checking the insulation of transformer windings after overhaul and oil filling

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Annex 3.1. The procedure and scope for checking the insulation of transformer windings after overhaul and oil filling. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Rules for the technical operation of consumer electrical installations (PTE)

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Table 1

Transformers	Scope of verification	Winding oil and insulation values	Combination of conditions in the previous column sufficient to turn on the transformer	Additional instructions
1. Up to 35 kV power up to 10000 kVA	1. Oil sampling 2. Resistance measurement R₆₀ 3. Definition of R₆₀ / R₁₅	1. Characteristics of the oil (in the scope of the abbreviated analysis) - normal 2. Insulation resistance R₆₀ - during the repair decreased by no more than 30% 3. Insulation resistance R₆₀ not lower than indicated in the table. 2 4. Ratio R₆₀ / R₁₅ at a temperature of (10 - 30) ° C should be at least 1,3	1. For transformers up to 1000 kVA - one of the combinations of conditions: 1; 2. 2. For transformers from 1000 kVA to 10000 kVA - one of the combinations of conditions: 1, 2, 4; 1, 3, 4.	1. An oil sample should be taken no earlier than 12 hours after filling (topping up) it into the transformer 2. For transformers up to 1000 kVA, it is allowed to determine only the value of the breakdown voltage of an oil sample
2. Up to 35 kV with a power of more than 10000 kVA; 110 kV and above all capacities	1. Oil sampling 2. Measurement of insulation resistance R₆₀ 3. Definition of R₆₀ / R₁₅ 4. Measurement of tgδ for transformers 110 kV and above	1. Characteristics of the oil (in the scope of the reduced analysis) - normal 2. Insulation resistance during the repair has decreased by no more than 30% 3. Insulation resistance R₆₀ not less than indicated in Table 2* 4. Ratio R₆₀ / R₁₅ at a temperature of (10 - 30) °С not less than 1.3 5. The values of tgδ do not exceed the values indicated in Table. 4and 5	1. For 35 kV transformers with a power of more than 10000 kVA - a combination of conditions: 1, 3, 4, 5. 2. For transformers 110 kV and above - a combination of conditions 1 - 6.	-

*For transformers up to 110 kV. For transformers above 110 kV, the insulation resistance is not standardized, but should be taken into account when considering the measurement results comprehensively.

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