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When transformer secondary is short circuited & primary voltage is raised, current in the secondary winding increases from 0 to rated current (say, 667A at 433V), a small voltage appears at the secondary windings. This percentage of this voltage to the rated secondary voltage is expressed as %age impedance. IEC table 76-5 provides following details :
Rated KVA %impedance
Up to 630 4.0
631-1250 5.0
1251-3150 6.25
3151-6300 7.15
6301-12500 8.35
12501-25000 10.0
25001-200000 12.5
Also, it may vary from manufacturer to manufacturer. For example, for a transformer of 500kva, 4% impedance, rated current of 667A@433V , when secondary is short circuited & primary voltage is raised to drive a current of 667A in the secondary windings, 4% of 433V develops across it's secondary windings i.e. 17.32V.
Now, the impedance is calculated as
Z= V/I = 17.32/667 = 0.02596 ohms.
This percentage impedance also decides the amount of fixed KVAr compensation required at the secondary of transformer. This is
4% x 500KVA = 20 KVAr
Also, short circuit capability of transformer is calculated as
433/0.02596 = 16,679.50 Amps or approximately 17kA.
Hope this information is sufficient. Also, one may again find a good answer to the above question as I've seen a transformer of 500kva with % impedance of 5.13 also.
Regards,
Asif Mansoori, DEE, Mumbra-Thane, India.
asif_currents@hotmail.com
Wiki User
∙ 13y ago
Wiki User
∙ 11y agoWithout knowing the rated voltages, it's impossible to tell! And the symbol for kilovolt ampere is kV.A, not kva.
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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 are the advantages of Transformer coupling method?
transformer coupling ensures maximum power transfer is obtained even if the output impedance is not equal to the load impedance
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.
What is the relationship between frequency and the size of a transformer?
Basically the characteristics of a transformer depends on the impedance(resistance) and on the coupling of its primary and secondary coils. The impedance of a coil depends on the frequency, as the frequency increases you need less volume of iron core and less number of turns in the coil for a given impedance, then reducing the size of the transformer.
More the transformer impedance less the fault current... so is a high value of transformer impedance good for it?
It depends a lot on the application, i would go with low impedance transformers if am using the transformers for distribution as it will really increase the the maximum fault current. If am using the transformers as step up specially for generators or to charge capacitors, using a high impedance transformer is a good idea as it will decrease the inrush current of the system. you have to see your application and decide what fit that best. Mohammad Jaradat Power Generation Project Manager
How many amps can you get from a 500Kva transformer?
To answer this question a voltage must be given.
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 are the advantages of Transformer coupling method?
transformer coupling ensures maximum power transfer is obtained even if the output impedance is not equal to the load impedance
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 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.
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.
How a transformer can be used as impedance matching?
If the line impedance is Z0 and the load is ZL then connect the load using a transformer with N turns ration. N=sqrt(Z0/ZL)
What is the relationship between frequency and the size of a transformer?
Basically the characteristics of a transformer depends on the impedance(resistance) and on the coupling of its primary and secondary coils. The impedance of a coil depends on the frequency, as the frequency increases you need less volume of iron core and less number of turns in the coil for a given impedance, then reducing the size of the transformer.
What type of transformer configuration will you select to design a high input impedance and low output impedance amplifier?
main volage
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.
