Next, these percentages are plotted on a triangular coordinate system, called Duval triangle, shown right.
This triangle is (empirically) pre-divided into 'fault zones'.
The PPM data is plotted as a point on the Duval triangle and (to a rough first degree), the zone in which it falls on indicates the faulty area.
PD fault zone is the partial discharge.
T1, T2 and T3 indicate a thermal fault.
D1 zone indicates a low-energy discharge, such as hot spots in the paper and paper/oil insulation.
D2 zone is the high-energy discharge zone.
DT - is an indterminate zone, attributed to a thermal fault or electrical discharge.
All in all, Duval mapped about 170 different faults into the fault zones, including application of the method to faults in the load tap changer.
Today DGA is considered a comprehensive method of assesing the state of a transformer. Still, it has its share of problems, and is open for interpretation somewhat. Because of the relative inaccuracy of gas-in-oil concentration measurements at low concentrations, DGA diagnostic methods, including the Duval Triangle, should not be applied unless the gas concentrations are well above the detection limit.
Megawatt Transformers performs DGA analysis in-house. We employ a veteran in the field with more than 20 years of field experience. This experience, combined with our advanced analysis lab allows us to assess the condition of a transformer beyond the mere threshold numbers given by the gas analysis. This is especially important when the numbers are inconclusive, as is sometimes the case with these measurements.
Contact us with all your transformer maintenance and repair needs.
Friday, October 30, 2009
Dissolved Gas Analysis in power transformers
Power transformers, being key components in any electrical network, require mindful operation and maintenance, in order to obtain safe and optimum working life. As transformers age, monitoring of their condition becomes more vital, with surveillance and diagnostic techniques being needed to prevent the possibility of surprise failures. Dissolved Gas Analysis (DGA) is a fundamental technique in establishing fault mechanisms in oil-filled power transformers.
In its simplest form, DGA analyzes the relative amount of three gasses in transformer oil: CH4, C2H4 and C2H2 (methane, ethylene and acetylene )
These gases are discharged from the insulation system (paper, wire) to the oil under detrimental conditions.
Empirical measurements of the relative percentage of these gasses in the oil have been mapped to specific problems in the transformer.
So the first step is collection of oil and measurement of the content of the gasses in the oil.
Next, these percentages are plotted on a triangular coordinate system, called Duval triangle, shown right.
This triangle is (empirically) pre-divided into 'fault zones'.
The PPM data is plotted as a point on the Duval triangle and (to a rough first degree), the zone in which it falls on indicates the faulty area.
PD fault zone is the partial discharge.
T1, T2 and T3 indicate a thermal fault.
D1 zone indicates a low-energy discharge, such as hot spots in the paper and paper/oil insulation.
D2 zone is the high-energy discharge zone.
DT - is an indterminate zone, attributed to a thermal fault or electrical discharge.
All in all, Duval mapped about 170 different faults into the fault zones, including application of the method to faults in the load tap changer.
Today DGA is considered a comprehensive method of assesing the state of a transformer. Still, it has its share of problems, and is open for interpretation somewhat. Because of the relative inaccuracy of gas-in-oil concentration measurements at low concentrations, DGA diagnostic methods, including the Duval Triangle, should not be applied unless the gas concentrations are well above the detection limit.
Megawatt Transformers performs DGA analysis in-house. We employ a veteran in the field with more than 20 years of field experience. This experience, combined with our advanced analysis lab allows us to assess the condition of a transformer beyond the mere threshold numbers given by the gas analysis. This is especially important when the numbers are inconclusive, as is sometimes the case with these measurements.
Contact us with all your transformer maintenance and repair needs.
Next, these percentages are plotted on a triangular coordinate system, called Duval triangle, shown right.
This triangle is (empirically) pre-divided into 'fault zones'.
The PPM data is plotted as a point on the Duval triangle and (to a rough first degree), the zone in which it falls on indicates the faulty area.
PD fault zone is the partial discharge.
T1, T2 and T3 indicate a thermal fault.
D1 zone indicates a low-energy discharge, such as hot spots in the paper and paper/oil insulation.
D2 zone is the high-energy discharge zone.
DT - is an indterminate zone, attributed to a thermal fault or electrical discharge.
All in all, Duval mapped about 170 different faults into the fault zones, including application of the method to faults in the load tap changer.
Today DGA is considered a comprehensive method of assesing the state of a transformer. Still, it has its share of problems, and is open for interpretation somewhat. Because of the relative inaccuracy of gas-in-oil concentration measurements at low concentrations, DGA diagnostic methods, including the Duval Triangle, should not be applied unless the gas concentrations are well above the detection limit.
Megawatt Transformers performs DGA analysis in-house. We employ a veteran in the field with more than 20 years of field experience. This experience, combined with our advanced analysis lab allows us to assess the condition of a transformer beyond the mere threshold numbers given by the gas analysis. This is especially important when the numbers are inconclusive, as is sometimes the case with these measurements.
Contact us with all your transformer maintenance and repair needs.
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