Understanding Basic Transformer Concepts

  • Thread starter fred2028
  • Start date
  • Tags
    Transformer
In summary, the open circuit and closed circuit tests are used to determine the parameters, such as impedances and resistances, of a transformer. The closed circuit test measures the equivalent impedances while the open circuit test measures the core losses or iron losses. When testing a known transformer, the results can be compared to those of a known "good" transformer, but testing an unknown transformer may require more judgment. The purpose of the short circuit test is to determine the series branch parameters of the equivalent circuit. The term "isolation" refers to the ability of a transformer to isolate a power source from the load. The dominant harmonic in the current waveform is referring to the highest frequency present and it is important to consider when testing a transformer.
  • #1
fred2028
19
0
The questions in this pre-lab are pretty basic and conceptual, and have not yet been taught in class. However, I'd like to complete this prelab early since I will be busy later on. Because it is pretty conceptual, I don't have any attempt at them except Googling around. Quick explanations or links are appreciated.

- What is the purpose of the open circuit and closed circuit test?
- How do you judge if a transformer is good or bad?
- How is the term ‘isolation’ attributed to the transformers?
- What is the dominant harmonic present in the current waveform and why? (I'm unclear what a dominant harmonic is)

Thanks!
 
Physics news on Phys.org
  • #2
I can really only help you with the first one not too sure about the rest. Especially if the transformer is good or bad one.

Essentially the open ckt and closed ckt tests are used to get the parameters of the transformer, the impedances and resistances.

As with good or bad, I guess you'd need to measure how efficient it is.
 
  • #3
rock.freak667 said:
I can really only help you with the first one not too sure about the rest. Especially if the transformer is good or bad one.

Essentially the open ckt and closed ckt tests are used to get the parameters of the transformer, the impedances and resistances.

As with good or bad, I guess you'd need to measure how efficient it is.

Does impedance not include resistance (Z = R + X)? I'm logically thinking that the closed circuit test gets the impedance because all of the I flows back to the source, and any resulting V drop would be due to the impedance (real and imaginary) in the transformer right? How about the open circuit test?
 
Last edited:
  • #4
fred2028 said:
Does impedance not include resistance (Z = R + X)? I'm logically thinking that the closed circuit test gets the impedance because all of the I flows back to the source, and any resulting V drop would be due to the impedance (real and imaginary) in the transformer right?

It is to get the impedances yes, but the calculations you do would give you the values of R and X. The closed circuit test will give you the equivalent impedances (when you refer the impedances on the secondary side back to the primary side)
 
  • #5
rock.freak667 said:
It is to get the impedances yes, but the calculations you do would give you the values of R and X. The closed circuit test will give you the equivalent impedances (when you refer the impedances on the secondary side back to the primary side)

Oh, so what exactly does closed ckt test give you? R, or X?
And open ckt?

Thanks!
 
  • #6
It would be a waste to do this experiment before you have done it in class. You may be able to pick it up from the textbook, but give your teacher a chance to cover it in class.

A short circuit test is for finding the copper losses in a transformer. A very small voltage is applied to the primary of the transformer and the voltage is increased until the current in the short circuit is equal to the maximum load current of the transformer.
Then measure the power in. This is mostly copper loss because very there is very little magnetic core flux flowing to get this output.

The open circuit test tests for core losses or iron losses. Because there is little current flowing in the wires of the transformer, most of the power used is iron losses like eddy current loss.

Testing a known type of transformer for faults will be mostly a matter of comparing the results of the above tests against those of a known "good" transformer.

Testing an unknown transformer is more difficult and may be a matter of judgement.
Obviously, if it is known to run very hot or to blow fuses, then it is probably faulty.

If it runs hot without any load, then it is possibly faulty, or it may be a poor design.

If it draws a large primary current without any load (say, maybe more than 10 % of the rated full load primary current) then it may be a poor design or it may be faulty.
You might like to read the Wikipedia article about this:
http://en.wikipedia.org/wiki/Short_circuit_test
Here is a bit of it:

The purpose of short circuit test is to determine the series branch parameters of the equivalent circuit. as the name suggests, in this test primary applied voltage, the current and power input are measured keeping the secondary terminals short circuited. Let these values be Vsc, Isc and Wsc respectively.

The supply voltage required to circulate rated current through the transformer is usually very small and is of the order of a few percent of the nominal voltage. The excitation current which is only 1% or less even at rated voltage becomes negligibly small during this test and hence is neglected. The shunt branch is thus assumed to be absent. Wsc is the sum of the copper losses in primary and secondary put together. The reactive power consumed is that absorbed by the leakage reactance of the two windings.
 
  • #7
  • #8
I am unclear as to what the dominant harmonic is referring to in the last part.
 

FAQ: Understanding Basic Transformer Concepts

What is a transformer?

A transformer is a device that is used to transfer electrical energy from one circuit to another through the process of electromagnetic induction. It typically consists of two or more coils of wire wrapped around a core made of magnetic material.

What are the main components of a transformer?

The main components of a transformer include the primary and secondary coils, a core made of magnetic material (such as iron), and sometimes an additional component called a tap changer. The primary coil is connected to the power source and the secondary coil delivers the transformed energy to the load.

How does a transformer work?

A transformer works by utilizing the principles of electromagnetic induction. When an alternating current (AC) flows through the primary coil, it creates a constantly changing magnetic field that induces a current in the secondary coil. This causes the electrical energy to be transferred from the primary circuit to the secondary circuit.

What are the different types of transformers?

There are two main types of transformers: step-up transformers and step-down transformers. Step-up transformers increase the voltage level from the primary to the secondary circuit, while step-down transformers decrease the voltage level. Other types of transformers include isolation transformers, autotransformers, and three-phase transformers.

What are some common applications of transformers?

Transformers are commonly used in power transmission and distribution systems to step up the voltage for efficient transmission and then step it down for safe use in homes and businesses. They are also used in various electronic devices such as chargers, adapters, and power supplies. Additionally, transformers are used in industrial settings for welding, lighting, and other high-power applications.

Back
Top