Transformer Percent Impedance
Transformer Percent Impedance
(OP)
Hello,
I have a question regarding transformer %Z. The things that are known are as follows:
1. %Z is acquired through testing the transformer via a short circuit test.
2. %Z is the percentage of rated primary voltage that when applied, produces the full load current through the secondary.
3. %Z is a representation of a transformers leakage reactance (the flux produced by the primary windings that does not link with the secondary).
Now, if those statements above are true, can someone please shed light on the following:
1. Can you consider %Z to be the "impedance" of the transformer during steady state conditions (ie. does %Z only apply during transient events when the transformer is essentially short circuited)?
I have a question regarding transformer %Z. The things that are known are as follows:
1. %Z is acquired through testing the transformer via a short circuit test.
2. %Z is the percentage of rated primary voltage that when applied, produces the full load current through the secondary.
3. %Z is a representation of a transformers leakage reactance (the flux produced by the primary windings that does not link with the secondary).
Now, if those statements above are true, can someone please shed light on the following:
1. Can you consider %Z to be the "impedance" of the transformer during steady state conditions (ie. does %Z only apply during transient events when the transformer is essentially short circuited)?






RE: Transformer Percent Impedance
RE: Transformer Percent Impedance
explain it in detail.
www.jcmiras.net/jcm/item/117
www.jcmiras.net/jcm/item/116
RE: Transformer Percent Impedance
Under short circuit conditions, the load (i.e., a bolted fault) is negligible so the only impedance in the circuit is the transformer s-c impedance.
Under load conditions, the load impedance dominates and controls the amount of current and the resulting power factor.
Under load conditions, we're usually concerned with how the impedance affects the load voltage. The most commonly used equation is:
Voltage Drop = I * (R * cos theta + X * sin theta)
This incorporates the transformer R & X as well as the load current.
RE: Transformer Percent Impedance
Regards.
RE: Transformer Percent Impedance
First of all the "impedance" includes not only the reactance[series reactance that means inductive reactance]
but the resistance of the circuit-depending on temperature and frequency also.
Second this reactance it is of leakage magnetic flux of both-primary and secondary winding. You may understand this
using Steinmetz circuit diagram.
RE: Transformer Percent Impedance
I have gone over the transformer impedance models in my old power text over and over, and have made marginal headway. Actual impedance can be calculated using %Z and the transformer base impedance. This is constant under any condition.
Here is where I reach a contradiction, and if someone could point out the solution I would very much appreciate it:
When I use an old arc welder as a ballast for an induction heater, I can achieve two levels of impedance, one when I short the secondary windings and one where I open the secondary windings. I notice the impedance is much higher when the secondary is open. I can only assume (either correctly or incorrectly) this occurs from the magnetizing reactance.
Please elaborate if possible.
Thanks
RE: Transformer Percent Impedance
The short circuit impedance gives you the nameplate impedance in % or ohms. This is orders of magnitude lower than the magnetizing impedance.
RE: Transformer Percent Impedance
The impedance is a combination of resistance and reactance.
The transformer impedance is valid only under short circuit conditions, when only the transformer resistance and reactance are in the circuit.
Bill
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"Why not the best?"
Jimmy Carter
RE: Transformer Percent Impedance
The shunt magnetising impedance across input voltage, draws a current from primary current to magnetise the core so that secondary will have an induced voltage= primary voltage.Secondary current will be primary current minus the current through shunt magnetisng impedance.This loss in current as magnetising current is the price to be paid for transferring voltage from one circuit to other.
RE: Transformer Percent Impedance