Transformer Connection Diagrams (Full Lecture)

In this lecture we'll examine transformer winding polarity, transformer power ratings, rated voltage, rated current, parallel winding configurations, series aiding and series opposing winding configurations, tapped transformers, and briefly introduce the autotransformer. (Full Lecture)
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[@johnlam8538]

thank you for spending your time and sharing your knowledge

[@spelunkerd]

Another thought provoking lecture, which naturally leads to the following question. Suppose you have a transformer with two secondary windings, one turn ratio 5:1, the second 5:2. What would happen if the tech made a mistake when wiring the secondary, by wiring the two in parallel, with the "in phase" dotted arms joined directly together? I'm guessing that the 5:2 arm would exert its higher secondary voltage on the lower arm, trying to force current back through the 5:1 windings so the voltage drop was equalized. My first thought was that it might set up a countercurrent circular flow that could burn out the windings, but then I wondered if the contrary voltage drop would limit flow to that arm because of the magnetic field....

[@pokerface550]

22:45 it remains somewhat unclear for me: are power & number of turns the anchors? There are no loads on the right side but you drew 24V and 5A for the uppermost winding (for example). Does it mean that in order to get the current we have just to take the power of 120VA and divide it by 24V (due to 5:1 ratio)? Will 5A be the constant current supply in this case? Another nuance - the 360VA of the primary part seems to be distributed equally among 3 windings on the secondary part. Is it always the case?

[@bigbadtech]

Yes rated power divided by rated voltage equals rated current (among other algebraic permutations). The secondary would not be constant current. 5A is the "rated" current, meaning the transformer secondary can handle a load drawing 5A or less (ie: 4.8ohm load or greater). Ohm's Law applies at all times. Lower impedances on the 24V secondary will draw more current. Larger impedances on the 24V secondary will draw less current. As long as you stay below 5A you won't smoke the winding. Evenly distributed power ratings among the secondaries is generally (though not always) the case. You'll commonly see transformers with two identical secondaries (ex: a 240VA, 120V, 2A primary with two 120VA, 24V, 5A secondaries) allowing the secondaries to be placed in series (240VA, 48V, 5A max) or parallel (240VA, 24V, 10A max) without worrying about exceeding the maximum of an unequally rated winding.

[@pokerface550]

ok, thanks again for the concise explanation. And one more question: if we put, let's say, 2 Ohm impedance on the secondary, it will increase the current I = 24v/2 Ohm = 12A and subsequently the apparent power would be 12A*24V = 288VA. Will it influence in any way the primary via magnetic field or all the power will be dissipated on the 2 Ohms secondary resistor burning out the resistor itself and winding?

[@bigbadtech]

The resistor might survive provided it was rated to handle 288W however it would be a rough day for both the primary and secondary. Assuming we're using a single secondary (secondary rating: 120VA, 24V, 5A) the 12A current drawn by a load consuming 288VA would kill it. On the primary side (primary rating: 240VA, 120V, 2A) to yield the desired 288VA it would experience 2.4A of current slightly in excess of the 2A rated current. One way to make this a slightly less awful experience would be to place the two secondary windings in parallel with one another. 24V, 5A each for 10A total. The 12A demand is still greater however much less of a mismatch than a single 5A winding being asked to provide all 12A.