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Power Transformers have an impedance (Z) rating that is listed in %. So the nameplate might state 5% Z for example. What this means is that when the secondary conductors are bolted together then 5% of the rated primary voltage is applied and will generate 100% current in flow in the secondary.
Example: you have a 75KVA Delta-Wye 5% Z transformer with a 480V primary rating and 208/12 secondary rating. The amp rating of the secondary is 208A [75,000/(1.732x208)]
So if you applied 24VAC to the primary with the secondary bolted together with busbar then you would have 208A of current flow.
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The purpose of transformer percentage impedance?
Inherently, the actual impedance seen at the secondary voltage will be different than that seen at the primary voltage. To make things easy, we use symmetrical components, where transformers are reduced to a p.u. (per unit) impedance. 100 x p.u. is equivalent to the percentage impedance you are referring to. When converted to per unit, a transformer has one impedance, not two, so it does not matter whether you are looking through the transformer from the secondary or the primary.
What are three requirement for connecting the transformer in paralle?
Transformer capacity (kvA) shall be identical, Both transformer impedance, secondary voltage and frequency shall be identical.
What is percentage impedance?
In electrical engineering, the percentage impedance of a transformer is the voltage drop on a full load, which is expressed as a percentage of the specified rated voltage. It's measured by conducting a short circuit test.
Why LV side is shorted in short circuit test?
Transformer short circuit tests are used to determine the impedances (positive and zero sequence) of the transformer. A simple explanation: to do this one winding is shorted, and voltage is applied to another winding to circulate the normal full load current of the transformer. The impedance of the transformer is the applied voltage divided by the induced current. If one winding was not shorted, the voltage divided by induced current would not give the impedance of the transformer - the induced current would be much lower, giving a much higher impedance measurement that would be essentially meaningless.
HOW TO CALCULATE THE IMPEDANCE FOR THE TRANSFORMER?
The term, 'percentage impedance', is a little misleading, as it is defined as 'the value of primary voltage that will cause rated current to flow in the secondary winding, expressed as a percentage of the rated primary voltage'. So, the test is carried out as follows: the secondary winding is short-circuited through an ammeter capable of reading the rated secondary current. A variable voltage is applied to the primary winding. The primary voltage is gradually increased until the ammeter indicates rated secondary current. That primary voltage is then expressed as a percentage of the rated primary voltage -and that value is the transformer's 'percentage impedance'.
What is the effect of transformer impedance on regulation?
The lower the impedance, the lower the voltage drop across the transformer as it is loaded. This means regulation is better, since voltage variance is smaller.
How do you convert percent impedance of transformer to impedance value?
The apparent impedance looking into a transformer from one side will not be the same as looking in it from the other, which is why percent impedance is used. If you are looking from the high voltage winding (I'm labeling #1) to the low voltage winding (#2), you must scale the percent impedance as follows: (% impedance) x (Winding #1 nominal voltage)^2 / (transformer base VA)
What is the effect of low impedance transformer on regulation?
The lower the impedance, the lower the voltage drop across the transformer as it is loaded. This means regulation is better, since voltage variance is smaller.
The purpose of transformer percentage impedance?
Inherently, the actual impedance seen at the secondary voltage will be different than that seen at the primary voltage. To make things easy, we use symmetrical components, where transformers are reduced to a p.u. (per unit) impedance. 100 x p.u. is equivalent to the percentage impedance you are referring to. When converted to per unit, a transformer has one impedance, not two, so it does not matter whether you are looking through the transformer from the secondary or the primary.
What is impedance of transformer?
The transformer impedance is the amount of voltage applied for transformer during the load test.Answer.I really don't agree with the answer given by the previous user.Impedance is the total vector opposition offered by the transformer to the flow of current i.e the vector sum of its pure resistance (R) and it's inductive reactance (XL). http://en.wikipedia.org/wiki/Electrical_impedanceAnother AnswerThe 'impedance' of a transformer is usually expressed as a 'percentage impedance', which is defined (perhaps rather confusingly!) as the ratio of the primary voltage that will result in the full rated current flowing through the secondary, to the rated primary voltage.
What are three requirement for connecting the transformer in paralle?
Transformer capacity (kvA) shall be identical, Both transformer impedance, secondary voltage and frequency shall be identical.
What is percentage impedance?
In electrical engineering, the percentage impedance of a transformer is the voltage drop on a full load, which is expressed as a percentage of the specified rated voltage. It's measured by conducting a short circuit test.
What is the impedance of a transformer?
Impedance (Z) voltage is the amount of voltage applied to the primary side to produce full load current in the secondary side. It is usually listed on the transformer nameplate, expressed as a percent, and measured by conducting a short circuit test.
Why LV side is shorted in short circuit test?
Transformer short circuit tests are used to determine the impedances (positive and zero sequence) of the transformer. A simple explanation: to do this one winding is shorted, and voltage is applied to another winding to circulate the normal full load current of the transformer. The impedance of the transformer is the applied voltage divided by the induced current. If one winding was not shorted, the voltage divided by induced current would not give the impedance of the transformer - the induced current would be much lower, giving a much higher impedance measurement that would be essentially meaningless.
What should be the short circuit setting of the feeder breaker of a transformer so that it does not trip on short circuit fault in secondary side?
You need to model this - the line impedance and transformer impedance, and the voltage will determine this. There is no "one size fits all".
HOW TO CALCULATE THE IMPEDANCE FOR THE TRANSFORMER?
The term, 'percentage impedance', is a little misleading, as it is defined as 'the value of primary voltage that will cause rated current to flow in the secondary winding, expressed as a percentage of the rated primary voltage'. So, the test is carried out as follows: the secondary winding is short-circuited through an ammeter capable of reading the rated secondary current. A variable voltage is applied to the primary winding. The primary voltage is gradually increased until the ammeter indicates rated secondary current. That primary voltage is then expressed as a percentage of the rated primary voltage -and that value is the transformer's 'percentage impedance'.
Why is a transformer necessary?
A transformer is not 'necessary'. The human race evolved, and developed cultures, societies, disease resistance, and technology, without ever seeing a transformer. But there are specific situations in which desirable things can be accomplished much more effectively and efficiently with a transformer than with any other device or method. Here are a couple of examples: -- If the voltage you have available is not the voltage you need, then you can use a transformer to make the change. (But that only works for AC.) -- You can use a transformer to change the output impedance of an amplifier to the impedance of the speaker or earbuds you want to use with it.
