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Transformers Faults And Detection
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Transcript of Transformers Faults And Detection
- 1. -276225-390525Transformer Fault and
Detection26955751934210
In order to maximize the lifetime and efficacy of a transformer, it is important to be aware of possible faults that may occur and to know how to catch them early. Regular monitoring and maintenance can make it possible to detect new flaws before much damage has been done.
The four main types of transformer faults are:
Arcing, or high current break down
Low energy sparking, or partial discharges
Localized overheating, or hot spots
General overheating due to inadequate cooling or sustained overloading
- Techniques for finding faults:Buchholz Relay safety deviceDissolved gas analysisTests to detect oil contaminants and oil qualityThese faults can all lead to the thermal degradation of the oil and paper insulation within the transformer. One way to detect them is by evaluating the quantities of hydrocarbon gases, hydrogen and oxides of carbon present in the transformer. Different gases can serve as markers for different types of faults. For instance,
Large quantities of hydrogen and acetylene (C2H2) can indicate
heavy current arcing. Oxides of carbon may also be found if the
arcing involves paper insulation.
The presence of hydrogen and lower order hydrocarbons can be a sign
of partial discharge
Significant amounts of methane and ethane may mean localized
heating or hot spots.
CO and CO2 may evolve if the paper insulation overheats; which can
be a result of prolonged overloading or impaired heat
transfer.
Techniques to Detect Faults
Techniques to detect transformer faults include the Buchholz Relay
safety device, dissolved gas analysis (DGA) tests and a range of
tests for detecting the presence of contaminants in the oil, as
well as for measuring indicators of oil quality such as electric
strength and resistivity.
Buchholz Relay
A Buchholz Relay is also called a gas detection relay. It is a
safety device generally mounted at the middle of the pipe
connecting the transformer tank to the conservator. A Buchholz
Relay may be used to detect both minor and major faults in the
transformer.
This device functions by detecting the volume of gas produced in
the transformer tank. Minor faults produce gas that accumulates
over time within the relay chamber. Once the volume of gas produced
exceeds a certain level, the float will lower and close the
contact, setting off an alarm.
Major faults can cause the sudden production of a large quantity of
gas. In this case, the abrupt rise in pressure within the tank will
cause oil to flow into the conservator. Once this is detected the
float will lower to close the contact, which causes the circuit
breaker to trip or sets off the alarm.
Dissolved gas analysis (DGA)
Dissolved gas analysis, or DGA, is a test used as a diagnostic and
maintenance tool for machinery. Under normal conditions, the
dielectric fluid present in a transformer will not decompose at a
rapid rate. However, thermal and electrical faults can accelerate
the decomposition of dielectric fluid and solid insulation. Gases
produced by this process are all of low molecular weight, and
include hydrogen, methane, ethane, acetylene, carbon monoxide and
carbon dioxide. These gases will dissolve in the dielectric fluid.
Analyzing the specific proportions of each gas will help in
identifying faults. Faults detected in such a way may include
processes such as corona, sparking, overheating and arcing.
Abnormal functioning within a transformer can be caught early by
studying the gases that accumulate within it. If the right
countermeasures are taken early on, damage to equipment can be
minimized.
Other oil tests
Other oil tests used to detect faults include acidity tests,
electric strength tests, fiber estimation tests, color tests, water
content tests, Polychlorinated Biphenyl Analysis (PCB) tests,
furfuraldehyde analysis tests, metal in oil analysis tests and
resistivity tests.
Acidity test: The acidity of transformer fluid should be monitored
regularly. High acidities can hasten the degradation of paper
insulation and cause steel tanks to corrode.
Electric Strength: The electric strength of an insulating fluid is
its capacity to withstand electrical stress without failing. The
lower the dielectric strength of a fluid, the less it will be able
to insulate. Transformer failure can result if the dielectric
strength drops too low.
Fiber estimation: If fibers or other contaminants are present in a
transformer's oil, they may reduce the oil's electric strength. Wet
fibers in particular can be drawn into an electrical field,
resulting in arcing. Passing polarized light through an oil sample
can make fibers and other sediments visible, making it possible to
estimate the fiber content of the sample. Sampling should be done
carefully, since both fibers and moisture may be picked up during
the process of sampling itself.
Color: Obvious changes in oil color (for instance, light oil
abruptly growing dark) may indicate deeper changes within the oil
itself that need to be examined further.
PCB Test: A Polychlorinated Biphenyl Analysis (PCB) test calculates
the concentration or presence of polychlorinated biphenyl within
the oil. Capillary column chromatography can be used for this
process. While the presence of PCBs is not an indication of oil
quality, PCBS are a banned substance, no longer allowed in new
liquid filled transformers.
Metal in oil analysis: The concentrations of various metals in a
transformer's oil can be calculated by using methods such as atomic
absorption spectroscopy (AA) and inductive coupled plasma
spectrometry (ICP).
Furfuraldehyde Analysis: The concentration of furfuraldehyde in an
oil sample can be used as a measure of paper degradation.
Furfuraldehyde is one of the byproducts of paper degrading and
growing weaker, a process which sets a natural limit on a
transformer's life. Monitoring its concentration levels can help
determine the remaining service life of a transformer.
Moisture: Excess moisture in the oil can cause the oil's electric
strength to plummet, leading to transformer failure. It is
therefore very important to monitor moisture levels in the
transformer.
Resistivity Test: High resistivity indicates low levels of free
ions and ion-forming particles, as well as low levels of conductive
contaminants. Resistivity tests are generally carried out at
ambient temperature. It can also be useful, however, to carry out
tests at much higher temperatures, the results of which can be
compared to results at ambient temperature.