Transformer Schematics, Orientation, And Phase Identifiers

                                    Written By : Marc V Belanger

For some, transformer schematics are troublesome due to the knowledge of specific indicating markers on a schematic. For one, the indication of the proper flow of current to a transformer for proper phasing is vital, especially if the transformer circuit is unconventional, or built in a way where specific output waveforms or phasing is intended.

The dot, indicating the flow of current, or the feed of the transformer is to indicate where the designer intends the feed current to be given of the originating waveform so a particular phase of the signal is given in the output. For a standard transformer, it is easily recognized by the winding drawn, as the winding can be drawn to be expressed as a clockwise or counter-clockwise winding. For those who do not generally understand the theory behind the schematic, or, for a particular output that may be desired, the dot is taken into consideration as the "phase indicator", not as an electrical phase , but, as the desired current's feed location. For example, if one of the terminals of the transformer's winding is the ground, the other would be considered as the feed or "current feed" as the hot leg, or however one would consider the input. 
This is only done to give the builder of the circuit an indication of how the input and output are oriented in a particular situation. For the standard transformer shown below, the input coil's feed wire from the source must be the exact opposite of the secondary in winding which would be wound clockwise on one side of the transformer to give the same phase orientation as the output. The dot indicates the same phasing so the builder or installer can determine which is cw and ccw if the circuit diagram does not indicate winding orientation any other way than a dot, however, our schematic diagram does show winding orientation, as well, shows a dot. In some cases, the winding is shown oriented but an unconventional output may be desired, so, the dot could indicate reverse phase and it is shopwn purposely so the desired output has been correctly connected, even though the builder or installer may think otherwise, it is part of the instructional design criteria and should be followed to get the working result.

The above figure indicates a connection of a reversed polarity. Pay close attention to the winding of the coils. This is the standard orientation of the winding to correctly induce from primary to secondary, but, the phase dots indicate a reversing polarity which is not commonly used for power applications unless it is a specially assigned orientation., or, for some reason corrective.

In the figure above, the phase orientation is standard and is the same at the input as the output. Follow the winding diagram to see the windings and their feeds are oriented in the same manner as they should be exact opposite to make the phasing the same. Unfortunately in some instances, the schematic does not indicate the winding orientation clearly as our schematic diagram does, so, if this is the case, it is best to follow the dots as they are the intended method of connection desired by the circuit designer, pretty much ensuring the correct output if the interpretation or design criteria is in fact correct.

A lot of experimental circuitry is critically labeled so you could determine the correct connection, so, it is sometimes detrimental to include the dots, especially if the coils are drawn by hand where sometimes it is difficult to determine the correct winding orientation.

In the figure, the orientation of the windings are clearly shown as clockwise to the left and counter-clockwise to the right. In the figure below, there are other indicating factors that will show designer's indicating factors that may show their own interpretation of the orientation, so, we will show a pointer that may assist with these determining factors when following a circuit diagram, however, testing with an oscilloscope would be critical as the circuit diagram can be a misprint, or, copies may be bad enough to the point where a misunderstanding can easily arise.

In the above vertical representation of the transformer coil, the left side is shown as clockwise, right side as counter-clockwise orientation.

In the above horizontal coil representation, the upper is considered to be counter-clockwise, and the bottom is clockwise. The orientation of winding for the "loop type" schematic diagram is similar but it shows the actual wire rotation when this diagram type shows it a slight bit different than this method, however, it is easy to tell if you look and compare to how it is wound. In regards to mistaken drawings, always follow the dots to feed the system, and, to output the current in the correct manner, as well as the correct phasing. If the coil orientation does not follow how you would normally wire the transformer, there may be an error in the diagram, or, the circuit is made so it is specifically designed to operate in the  manner that is indicated in the drawing. For instance, I have designed a circuit that will eliminate Lenz's theory, which will not induce as a normal transformer, but, will eliminate loading created by opposing coils, and, the coils would be shown in the below orientation, with feeds as described. The picture shows the positive of a dc system entering the transformer, as well, exiting with jumpers, but, in a dc system, current flows from negative to positive. How would i do this if the system is not ac and flow both ways? Well, this would be simple if we ground the terminals of the coils as well connect to the battery -, the only connection left would be the positive, which can be the only feed to the system. Ground the intended coil terminals without the dot, then, connect the positive as the feed on the primary side, and, the output will be the secondary with the dot to give the desired effect.

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