I`m studying transformers equivalent circuit and encountered this term "referring" to primary or secondary and I was confused by this terminology. I tried to look for a definition but couldn't find any. Is it implying that, for example referring to primary, just means looking into the circuit from the primary coil?
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\$\begingroup\$ More precise context required. I think you might be missing a subtlety here that is quite significant. \$\endgroup\$– Andy akaCommented Mar 10, 2021 at 16:27
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1\$\begingroup\$ I think I understand what you're asking and could answer the question in a few hours when I get back from work, but right now I unfortunately need to get to work. If no one's answered it by the time I return, I'll give it a shot. \$\endgroup\$– HearthCommented Mar 10, 2021 at 16:42
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2 Answers
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"Referring" is a term used in simplifying the equivalent circuit. It is sometimes useful to view the transformer load and secondary impedance as if the ideal transformer is not part of the circuit and the load and impedance of the secondary winding are multiplied by the transformer ratio and shown as part of the primary circuit. There are also times when it is convenient to show the primary impedance as part of the secondary circuit. That process is called "referring." In a way, it does mean looking into the circuit from the primary side or the secondary side, but part of that is adjusting the impedance values so that you have an "accurate view."
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\$\begingroup\$ I believe that the term "referring" is generally used because in power system analysis (where impedances are expressed as 'per unit' or 'per cent') generally this conversion of impedances from one voltage base to another is done using the reference impedance. \$\endgroup\$ Commented Mar 10, 2021 at 18:09
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With an ideal transformer, looking at the secondary load 'referred to the primary' means transforming the load impedance by the N2 of the transformer.
A non-ideal transformer tends to have losses and parasitics that are due to one or the other winding, resistance and stray capacitance mostly, and those that are common to both, so leakage inductance, eddy currents and core losses.
For many applications, it's convenient to model our transformer as if it's ideal, and then to represent all the losses as a single resistor on just the primary side, or just the secondary side. This is almost as accurate, and a lot simpler, than showing the losses as one resistor in each. The same goes for leakage inductance.
This process of collecting up all the similar defects, transforming them if necessary, and putting them on one side of the transformer is known as 'referring' the parasitics to one or the other winding.
