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bachelor in business administration
Polytechnic State University Sanluis
Jan-2006 - Nov-2010
CPA
Polytechnic State University
Jan-2012 - Nov-2016
Professor
Harvard Square Academy (HS2)
Mar-2012 - Present
A method for determining the equivalent circuit of a transformer consists of two tests: the open-circuit test and the short-circuit test. The open-circuit test, shown in Figure P7.35 (a), is usually done by applying rated voltage to the primary side of the transformer while leaving the secondary side open. The current into the primary side is measured, as is the power dissipated.Â
The short-circuit test, shown in Figure P7.35(b), is performed by increasing the primary voltage until rated current is going into the transformer while the secondary side is short-circuited. The current into the transformer, the applied voltage, and the power dissipated are measured. The equivalent circuit of a transformer is shown in Figure P7.35(c), where rw and Lw represent the winding resistance and inductance, respectively, and rc and Lcrepresent the losses in the core of the transformer and the inductance of the core. The ideal transformer is also included in the model. With the open-circuit test, we may assume that P = S = 0. Then all of the current that is measured is directed through the parallel combination of rc and Lc. We also assume that |rc||jωLc| is much greater than rw + jωLw. Using these assumptions and the open-circuit test data, we can find the resistance rc and the inductance Lc. In the short-circuit test, we assume that  secondary is zero, so that the voltage on the primary side of the ideal transformer is also zero, causing no current flow through the rc − Lc parallel combination. Using thisassumption with the short-circuit test data, we are able to find the resistance rw and inductance Lw. Using the following test data, find the equivalent circuit of the transformer:Â
Â
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