Transformers 1 Final
What temperature does oil degrade?
140 C
how much oil should you discard before taking a sample?
2-4 liters or half gallon to a gallon
What temperature does paper degrade?
80 C
What phase shifts are expected?
A minimum of 30 degrees, increasing by 30 degree increments.
How does a transformer work?
An AC voltage is applied to the primary, the primary produces a magnetic flux in the core, the magnetic flux induces an AC voltage on the secondary
When will we have a phase shift between the primary and secondary windings?
Anytime there is two different configurations between the primary and secondary windings.
If it is moisture or water in the gas state, what test are you going to run?
DGA (dissolved gas analysis)
What determines the amount of inrush current that you will see?
How much magnetic field or flux is left in the transformer when we energize it
What are eddy currents?
Small currents induced in any conductor material by the alternating flux. They generate heat and waste energy
What is inrush current?
When a device(anything with a coil or core) is turned on, it draws a large amount of current during the first energization. It is the spike of current when the device is turned on.
What does make-before-break mean?
When you have 2 contacts, one must stay on the current tap while the other travels to the next tap. When the 2nd contact connects, the first one is now clear to disconnect from the current tap
What is a breather unit?
a device that pulls and pushes air into the transformer from the outside and filters for contaminants and moisture
What is a nitrogen blanketed transformer?
a transformer tank with a nitrogen bottle and regulating system attached to it 24/7
What cooling systems are available for liquid filled transformers?
air and water
name the two types of bushings
capacitance graded/condenser and solid/bulk
What are bushings?
connection points or conductors coming from the outside to the inside of the transformer
What are the test taps?
connection points to the outer layer of the capacitors inside the capacitor graded/condenser bushing
Where can we find grounds on our transformer?
core, tank, neutral
What are CT's?
current transformers
What are tap changers?
devices that vary the input or output voltage by regulating the amount of winding used
What are our top 3 priorities when taking an oil sample?
documentation, providing the best sample possible, preventing any spills/messes
Which winding temperature gauge is the most accurate?
fiber optic
What cooling systems are available for dry type transformers?
forced air(FA) and ambient air(AA)
what is an open conservator transformer?
has conservator tank without a bladder and a breather unit
What is interfacial tension?
how much force you need to break the barrier between oil and water
What is viscosity testing?
how thick the oil is
What does specific gravity determine?
if ice is present based upon density
How do we know when to replace silica gel/desiccant?
it changes color
what is a sealed tank transformer?
just a tank, sealed from the outside world. no conservator, N2 bottle, breather unit etc.
What does a PRD operate on?
long term or gradual increases in pressure
What is power factor testing?
looking at the losses of insulation
What is the visual examination test?
making sure that oil is bright in color, clear, and free of particles
What is oxidation inhibitor content oil testing?
measuring how many inhibitors are present in the oil
What is the neutralization number?
measuring the amount of alkaline/acidic materials inside of the oil
What is dissolved gas analysis (DGA)?
measuring what gases are present and how much of each to determine what has previously occurred, what is currently happening, and what will happen in the future
which liquid do we use the most inside our transformers?
mineral oil
What is dielectric breakdown testing?
minimum voltage at which flash over occurs in oil
What does a buchols relay operate on?
monitoring pressure systems, oils, and the different gases that cause faults
What does a high power factor percentage indicate?
more contamination and deterioration
What are harmonics?
multiples of the fundamental frequency. It causes distortion and reduces the efficiency of the system.
what position does the reversing switch have to be in to operate?
neutral
what is a free breathing transformer?
no conservator, just a breather unit attached to the transformer pushing and pulling air into the transformer from outside
What should you never do with a DETC?
operate it or change the tap while it is energized, or operate it immediately when the DETC has been sitting for a long time
What type of insulation do we use to insulate our conductors?
paper
What is the color test?
physically looking at the color of the oil
Where do we have losses in or transformers?
resistance in the windings, eddy currents in the core, hysteresis, harmonics, stray flux
What are the four liquids that we use inside transformers?
silicone, natural esters, synthetic esters, mineral oil
What does a rapid pressure rise relay operate on?
sudden increases of pressure inside of the transformer
What is the capacity of the transformer?
the amount of power that the transformer is able to withstand without damage
What is oil processing?
the filtration of oil
What is specific gravity?
the ratio of equal amounts of oil and water
When taking an oil sample, where should you fill your bottle too?
the shoulder
Why do we use CT's?
to lower current to safe and manageable levels, to be able to monitor the system for relays or for metering
Why do we ground the transformer tank?
to protect people and equipment
What kinds of winding temperature gauges can we find on our transformers?
top oil, fiber optic, and hot spot CT
What is a sealed conservator transformer?
transformer that has an conservator with a bladder
Why do we do oil sampling?
we want to understand what previously has happened with the oil and transformer, what is currently happening and what is possibly going to happen in the future
