Fault interpretation for power transformer using dissolved gas
- 1. FAULT INTERPRETATION FOR POWER TRANSFORMER USING DISSOLVED GAS ANALYSIS
- 2. IMPORTANCE OF TRANSFORMERS IN A POWER SYSTEM • ONE OF THE MOST IMPORTANT COMPONENT OF A POWER SYSTEM • STEPPING UP AND DOWN OF VOLTAGE • VERY EXPENSIVE • TRANSPORTATION OF TRANSFORMER IS VERY TEDIOUS AND TIME TAKING PROCESS. • fault in a transformer can have a huge repercussion • as the number of old transformers and of those that are difficult to operate in overload conditions is on the rise, it is important to detect incipient faults in a transformer and forecast and prevent failures
- 3. Classification of faults in a Transformer • Partial Discharge (PD) • Discharges of Low energy (D1) • Discharges of High energy (D2) • Thermal fault, (T1) • Thermal fault, (T2) • Thermal fault, (T3) • Thermal & Electrical fault (DT)
- 4. • Partial Discharge (PD): The temperature plays a less important role in the chemical reaction occurring in the PD since the vapour temperature in the discharge zone is not higher than 60150°C. Hydrocarbon cracking in the partial discharges occurs as a result of excitation of molecules and their subsequent dissociation by collision with high energy electrons, atomic hydrogen, ions and also free radicals. It often generates large amounts of hydrogen. • Discharges of Low energy (D1): Partial discharges of the sparking type, inducing pinholes, carbonized small punctures in paper. Low energy arcing results in surface tracking of paper or the formation of small amount of carbon particles in oil. • Discharges of High energy (D2): Discharges in paper or oil, with power follow- through, resulting in extensive damage to paper or large formation of carbon particles in oil, metal fusion, tripping of the equipment and gas alarms. • Thermal fault (T1): These types of faults occur below . These are evidenced by paper turning brownish (> 200 °C) or carbonized (> 300 °C).
- 5. • Thermal fault (T2): These types of faults occur in between to . These are evidenced by carbonization of paper, formation of carbon particles in oil. • Thermal fault (T3): The high temperature faults whose temperature is more than falls in this kind of fault. These are evidenced by extensive formation of carbon particles in oil, metal coloration (800 °C) or metal fusion (>1000 °C). • Thermal & Electrical fault (DT): Sometime both thermal and electrical fault occurs inside the transformer. These faults accelerate the decomposition of dielectric fluid and solid insulation.
- 6. FORMATION OF GASES IN THE TRANSFORMER OIL • ALL ELECTRICAL DEVICES GIVES OFF WASTE HEAT AS A BYPRODUCT • HEAT THEREFORE , RISE IN TEMPERATURE • OVERLOADING • MOISTURE • POOR QUALITY OIL OR PAPER (insulating meterial)
- 7. DIAGNOSTIC METHODS • Key Gas • Rogers ratio • Dornenberg • logarithmic nomograph • IEC ratio • Duval triangle
- 8. IEC RATIO • This method is widely used as a guideline and a standard for diagnosis of the transformer fault.This approach consist of three gas ratios and ten fault cases are identified corresponding to the suggested fault diagnosis method.However these faults are mainly categorized from the original fault types TH,DA and PD.
- 9. Dornenberg Method • This method utilizes the gas concentration from ratio of CH4/H2, C2H2/CH4, C2H4/C2H6 and C2H2/C2H4. • If at least one of the gas concentrations exceeds twice the values for limit L1(see table 7) and one of the other three gases exceeds the values for limit L1, the unit is considered faulty . Table 7
- 10. ROGER’S RATIO METHOD This method takes into consideration industrial experience , laboratory tests and further theoretical assessment. It follows the same procedure as Dornenburg method except for the three ratios (R1,R2 and R5).
- 11. The Duval Triangle method: • Micheal Duval in 1973. • Concentration of methane ,ethylene and acetylene in percentages . • Plotted on a triangular chart (subdivided different fault regions ). • Should not be applied unless the gas concentrations are well above the detection limit, because of the relative inaccuracy of gas-in-oil concentration measurements at low concentrations. The faults which are detected by Duval triangle are expressed as follows; 1. Partial Discharge (PD) 2.Discharges of Low energy (D1) 3.Discharges of High energy (D2) 4. Thermal fault (T1) 5.Thermal fault (T2) 6.Thermal fault, (T3) 7. Thermal & Electrical fault (DT) Figure 3.1 Classical Duval’s Triangle
- 12. Various faults produce certain gases and the percent of some gases have been found to indicate fault types, such as overheated oil and cellulose, corona in oil and arching in oil. The diagnostic interpretations applying various gases are given below in the Table 4.1. KEY GAS RATIO METHOD
- 13. Nomograph Method • This method was developed by J. O. Church. • It combines the fault gas ratio concept with the Key Gas threshold value to improve the accuracy of fault diagnosis. • It provides both a graphic presentation of fault-gas data and the means to interpret its significance.
Editor's Notes
- #2: DGA is a sensitive and reliable technique for the detection of incipient faults occurring in oil-immersed transformers ,wherein we sample oil to measure concentrations of different gases to predict the type of fault that might be occurring.
- #3: ** T/F are used to step up the voltage >>transmission >> distribution ** Various types of gen according to ratings *** cost ? *** speak on it *** p/s connected n/w , 1 neeche jaayega toh load badhega doosre pe , who bhi neeche chala jaayega. *** obvious
- #7: ** efficiency not 1 **