CHAPTER FOUR be transformer clock system vector nomenclature. The main purpose of power transformers in the system is to change voltage levels, that is to convert the magnitude of the voltage either up or down depending on the requirements. For example, distribution utilities may want to take the high voltage transmission levels of 500 to 1300 and 15 kV to voltage levels say 25 kV for ease of retail sales to customers or an independent power producer may want to step the generation voltage up to the level for the that could be connected to the transmission utility. If we were dealing with a single face quantity, the choice of connections would be simple would it be a simple matter of using the correct turns ratio. However, when dealing with three phases quantities, which are the ideal for economical transmission and distribution, not only the turns ratio has to be taken into consideration, but also the variety and permeability of connections.

That is why transformer clock system vector nomenclature was developed. With every power transformer installation we will have a primary system connected to the primary side of the transformer and a secondary system connected to the secondary side of the transformer. For simplicity sake, we can assume that the primary side is energized by a three phase balanced set of voltages rotating counterclockwise and having a phasor separation of 120 degrees. Depending on the transformer connections, the secondary voltages can either be rotating in a clockwise or a counterclockwise direction, assuming however that we are still dealing with a balanced system. The secondary voltages are equal in magnitude and 120 degrees apart, but may lead or lag the associated primary voltages. But in all systems, it is desired to have both primary and secondary systems rotating in the same direction.

And that as a standard is usually counterclockwise. This of course goes for the phase two phase voltages as well. Specifically when we're dealing with a Delta Delta Connection. Take for example a star star or a yy connected transformer. We have already looked at this connection, and it is fairly straightforward. However, if we reverse the connection of each of the secondary windings, it would still be yy connected.

But certainly the secondary phasers would have to be different. As is the case for a delta delta connected transformer. Again, we have already looked at this connection edit to seems fairly straightforward. However, once again if we reverse the connections of each secondary winding, it would still be delta delta connected, but certainly the secondary phasers would have have to be different. Another example would be this star Delta connected transformer which we also have studied. And we use these secondary connections as you see in the diagram we could have just as easily used the secondary windings connections that you see here now, and it would still be a star Delta transformer.

So how do we simply convey the configuration along with the connections? The answer is transformer clock system vector nomenclature. As its name suggests, we use the clock face as a reference for relating the secondary voltage to the primary voltage, the digits 01234 etc relate to the phase displacement between the high voltage and low voltage windings using the clock face notation. The phasor representing the high voltage winding is taken as a reference and set at 12 o'clock it is assumed that the phasers are rotating in a counterclockwise rotation. We use the our indicator as the indicating phase displacement angle. Low Voltage lags the high voltage by 30 degrees in this instance because there are 12 hours on the clock and a circle consists of 360 degrees, each hour represents 30 degrees.

For example, two o'clock is 60 degrees, three o'clock is 90 degrees, four o'clock is 125 is 156 o'clock is 180 Seven is to 10. Eight o'clock is 249 o'clock is 270 10 is 311 is 330. And 360 puts us back at the 12 o'clock position. This could also be referenced as zero degrees, so it could be zero. We're now going to look at some examples of the workings of a clock face nomenclature. And I'm going to start with the why, why connected transformer and we've seen this connection before.

And believe it or not, there are six different ways to connect up the secondary windings of this transformer. Number one, starting with our previously stated connection. The secondary phasers would look like this, showing that the secondary voltages are in phase with the respective primary voltages. using just one set of phasers, the red one, in this case, the clock system of vector nomenclature would tell us that there is zero degree displacement displacement from the secondary to the primary windings. The clock system nomenclature would be then why why y zero, we could have also said y y 360. But normally we just choose zero instead of 360.

It's much easier to write on a piece of paper I guess. Notice also that the primary side is designated with a capital Y, where the secondary is designated with a lowercase Why followed by the displacement which is zero. The second yy connection would look like this, the red winding x one terminal is connected to the secondary blue phase bus, the white winding x one terminal is connected to the secondary red phase bus, the blue winding x one terminal is connected to the secondary white phase bus and all of the x two winding terminals are connected together to form a secondary neutral. The secondary phasers looked like this showing the secondary voltages are 120 degrees lagging their respective primary voltages. Again, just using the read phase vectors, the clock system of vector nomenclature would tell us that there is 120 degrees displacement of the secondary voltage the clock system nomenclature would be y y for.

For the third connection, the yy connections would look like this. The red winding x one terminal is connected to the secondary white phase bus, the white winding x one terminal is connected to the secondary blue phase bus and the blue winding x one terminal is connected to the secondary red phase bus and all of the x two terminals are connected together to form a secondary neutral. The secondary phasers look like this showing that the secondary voltages are 120 degrees leading their respective primary voltages. Again, just using read phase vectors the clock system of Vector nomenclature would tell us that there is 120 degree displacement leading of the secondary voltage the clock system not nomenclature would be why why eight the fourth connection of the yy configuration would look like this. The x one terminals are connected together this time to form the secondary neutral and the x two winding terminals are connected to their respective red, white and blue phases on the secondary bus.

The secondary phasers would look like this showing that in the secondary voltages are 180 degrees out of phase with the respective primary voltages. The clock system of vector nomenclature would tell us that there is 180 degree displacement of the secondary voltage, the clock system would say why why six for the fifth connection of the yy configuration, the x one terminals again would be connected together to form a secondary neutral. The red winding x two terminal is connected to the secondary blue phase bus, the white winding x two terminal is connected to the secondary red phase bus and the blue winding x two terminal is connected to the secondary white phase bus. The secondary phasers would look like this showing that in the secondary voltages are 60 degrees leading the respective primary voltages. The clock system would tell us that there is a 60 degree leading displacement of the secondary voltage, meaning the clock system nomenclature would be y y 10.

The sixth and final connection of a yy configuration would look like this, the x one terminals again would be connected together to form a secondary neutral while the red winding x two terminal is connected to the white phase bus. The white x two terminal is connected to the blue phase bus, the blue x two terminal is connected to the red phase bus. The secondary phasers would look like this, showing that the secondary voltages are 60 degrees lagging the respective primary voltages. The clock system of vector nomenclature would tell us that there is a 60 degree to plate displacement in the secondary voltages and the clock system would then read y y two. Now let's look at a Delta two Delta configuration. We have already studied this configuration with the primary windings connected like this, it would it would produce these phase two phase voltages on the primary side.

With the secondary windings connected in a similar fashion, it would produce voltages that would look like this. The red to white primary voltage is in phase with a secondary red to white voltage. The white to blue is in phase with the white to blue and the blue the red is in phase with the blue the red primary to secondary Of course. In general terms we might say that the primary is in phase with the SEC So the clock face nomenclature would tell us that these the primary isn't face a with the secondary, such that this Delta Delta Connection would be the the zero. Now this Delta Delta Connection could have a variation of six different secondary connections if you wanted to go through them all I'm not going to do this at this point, because we've already done that exercise with a star star connection. However, I will look at one which is fairly simple, what would happen if we reversed the secondary terminals of this Delta Delta Connection.

The phasers of the second area would be reversed giving us this phasor configuration, meaning that the red to white primary voltage is 180 degrees out of phase with the red to white secondary, the white to blue is 180 degrees out of phase with the light to blue primary, the secondary as is the blue to red primary 180 degrees out of phase with the blue to red secondary and in general terms we would say that the primary is 180 degrees out of phase with a secondary. The clock phase nomenclature would then be DD six indicating this hundred and 80 degree phase shift. For the Y Delta Connection we have been through this exercise before and we saw that the red to white secondary is in phase with the red to neutral primary and that The red to white primary voltage is leading the red to neutral primary voltage by 30 degrees.

Meaning that the red the white primary voltage is leading the secondary red to white voltage by 30 degrees. And again in general terms we can say that the secondary is lagging the primary by 30 degrees. The clockface nomenclature would then be y d one indicating this 30 degree lightning phase shift. This ends the chapter on transformer clock system vector nomenclature