Condition Monitoring of 132kv Transformers
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CONDITION MONITORING OF 132 kV TRANSFORMERS M K Domun
EA Technology, UK
1.
INTRODUCTION
Approximately 3 0 % of the 132 kV grid transformers in the UK are over 40 years old. Some 8 0 % are over 20 years old. To date, performance has been satisfactory with negligible occurrence of serious failure. However, transformer loads are increasing and reserved capacities are decreasing. Consequently, it is imperative to have some simple and practical means of assessing the insulation integrity of high voltage power transformers. Historically, diagnostic tests include dc resistance and ac dielectric loss of the winding insulation. The electric strength and moisture content of the oil are also measured. When a fault occurs samples of oil are sent to a laboratory for dissolved gas analysis (DGA). This technique is effective in identifying fault characteristics from the measurement of concentrations of hydrogen, hydro-carbon and carbon oxide gases (1). It is also possible to define the type of fault by means of gas ratio codes (2). The three gas ratios, acetylene/ethylene (discharge fault), ethylene/ethane (high temperature thermal fault) and methane/hydrogen (low temperature thermal fault) have been very useful parameters in determining the cause of fault
acids and moisture. The hydrolytic effect is to cleave the glucosidic bond, yielding free glucose. Cellulose is susceptible to oxidation, which leads to the formation of carbonyl and carboxyl acid groups. Secondary reactions can eventually occur, to molecular chain scission. leading The degradation of oil results in high acid content, which exacerbates the chemical deterioration of the paper insulation even further. Consequently, condition monitoring of the properties of the paper insulation is more important than an analysis of the properties of the oil. Methods of Monitoring Insulating Paper Properties of
The direct relation between mechanical strength and the degree of polymerisation (DP) has been
CONDITION MONITORING OF 132 kV TRANSFORMERS M K Domun
EA Technology, UK
1.
INTRODUCTION
Approximately 3 0 % of the 132 kV grid transformers in the UK are over 40 years old. Some 8 0 % are over 20 years old. To date, performance has been satisfactory with negligible occurrence of serious failure. However, transformer loads are increasing and reserved capacities are decreasing. Consequently, it is imperative to have some simple and practical means of assessing the insulation integrity of high voltage power transformers. Historically, diagnostic tests include dc resistance and ac dielectric loss of the winding insulation. The electric strength and moisture content of the oil are also measured. When a fault occurs samples of oil are sent to a laboratory for dissolved gas analysis (DGA). This technique is effective in identifying fault characteristics from the measurement of concentrations of hydrogen, hydro-carbon and carbon oxide gases (1). It is also possible to define the type of fault by means of gas ratio codes (2). The three gas ratios, acetylene/ethylene (discharge fault), ethylene/ethane (high temperature thermal fault) and methane/hydrogen (low temperature thermal fault) have been very useful parameters in determining the cause of fault
acids and moisture. The hydrolytic effect is to cleave the glucosidic bond, yielding free glucose. Cellulose is susceptible to oxidation, which leads to the formation of carbonyl and carboxyl acid groups. Secondary reactions can eventually occur, to molecular chain scission. leading The degradation of oil results in high acid content, which exacerbates the chemical deterioration of the paper insulation even further. Consequently, condition monitoring of the properties of the paper insulation is more important than an analysis of the properties of the oil. Methods of Monitoring Insulating Paper Properties of
The direct relation between mechanical strength and the degree of polymerisation (DP) has been
References: 1. Rogers, R R, et al, 1973, "CEGB experience of the analysis of dissolved gas in transformer oil for the detection of incipient faults", IEE Conf Pub, No 94. Montsinger, transformers Trans, 49. -V M, 1930, "Loading by temperature", AIEE 2.