Transformers 1 Final

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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


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