# Transformers Basic

Discussion in 'Homework Help' started by chyadesh, Jan 18, 2010.

Apr 10, 2009
19
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Q)what is the clear cut definition of RESISTOR?
In my view, Resistor opposes the flow of current.
But while solving problems , we are considering that the current entering the resistor is same as the current leaving the resistor.

It is quite opposite to the definition,,,, SO.,please clarify my doubt.

Last edited: Jan 20, 2010
2. ### sawanepd New Member

Jan 18, 2010
2
0
1.
because,ironloss is depends in voltage and cu_loss is
depends in current.so the transformer ratings in kva.
Both the losses of the transformer is independent of the
power factor (cos phi), which means a transformer would not
make any change in the power factor, since both the losses
viz copper loss(depends on current) and iron loss(depends
on voltage) are independent of power factor, that is why a
Transformers rating is not on kW, but on KVA.
Transformer is not a load and having
no effect on P.F and it only transfer the constant power
from one voltage level to another voltrage level without
changing frequency thats why transformer are rated in KVA
or MVA

3. ### zgozvrm Member

Oct 24, 2009
115
2
1. Transformers are rated by VA, because they typically can handle a range of voltages. Therefore the amount of current you can obtain from the transformer is based on the power (the VA) that the xfmr can handle on the input side (power in = power out). So, if you have a 12 kVA (12,000 VA) transformer fed by a 480V source, the transformer can draw on its primary side at most 25A (12kVA / 480 V). At the same time, it can only supply 12 kVA on its secondary side. So, if the xfmr's winding ratio is 4:1, then the 480V on the primary will be transformed into 120V on the secondary side, this allows for up to 100A to be drawn from the secondary side (12 kVA / 120V).

2. A resistor does oppose the flow of current, you are forgetting that the resistance actually defines the amount of current. All things being equal, if the total resistance is the only thing changed, the current also changes inversely.

4. ### Audioguru New Member

Dec 20, 2007
9,411
896
A device is rated in Watts when it uses Watts. A transformer does not use Watts, instead it passes Volt-Amperes.

A resistor reduces current flow.

Nov 12, 2009
14
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the resistor doesnt reduce current in the sense that the current leaving the resistor is less than the current that enters. Think about what would happen if the resistor wasnt there, the current flowing through the circuit would be much greater. if you replaced it with a larger resistor the current would be even less.

6. ### retched AAC Fanatic!

Dec 5, 2009
5,201
313
If a human resistor existed, it would be a turnstile. You know, those things you have to walk through to get into a train depot.

The thousand people behind it are the current. The resistor doesn't make people smaller when they go through it. It slows down the amount of people that can pass. So all of the people can pass, but it takes longer.

Same with electricity. The battery may have 1000 amps but with a resistor only so many can get through in a set time. Eventually ALL the electrons will get through, draining the battery.

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