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Introduction to the Delta Wye transformer connection, Part 3.

In part of the series, we illustrated the relationship between line-to-line voltage and phase voltage. In part 3, we'll cover the relationship between line current and phase current for the delta wye transformer connection.

Check out the resources section under this video for helpful comments, suggestions, and clarifications.

Let's pick up where we left of on the secondary of the transformer connection, where our transformer is connected in wye with neutral grounded. We understand that line-current or line-to-line current as I like to call it – is a current that flow through the lines or conductor. Since we've assumed the secondary side is our load side, we understand that the line current will flow through our lines to our load. So line-to-line current a will flow through line a, line-to-line current be will flow through line b, and line-to-line current c will flow through line c. And they will all feed our load.

We have decided to call our line currents line-to-line current. Now it may sound misleading. But it helps my brain to point out clearly, that we're talking about the actual line currents for a particular line. So if labeling this current as line current or some other names helps you, by all means do so. As long as we clearly define our variables, we should be alright.

So our transformer is connected in delta in our primary side or source side. So this is where our source current will come from. The line-to-line current A will flow through line A, line-to-line current B will flow through line B. And line-to-line current C will flow through line C respectively.

Remember, this line current comes from the source like a generator, the utility, or the grid. Let's now talk about phase currents. We understand that phase current flow through transformer windings. Let's start on the secondary side where our transformer is connected in wye. We should expect phase a current to come from winding a and flow to our load. Similarly phase b current comes from winding and flows to our load. And phase c current comes from winding c and flows to our load.

For a Wye connected transformer, we should expect phase a current and line-to-line current to be the same. Checkout the resources section for more information. Since our phase currents flows through transformer windings, the delta transformer connection is no exception. Let's begin with winding A. Since we know that secondary phase a current flows out of the dot on the secondary side that simply means that the primary phase a current must flow into the dot on the primary side. So primary phase a current will flow into the dot and secondary phase a current will flow out of the dot. 

That makes sense right? We're simply following the dot convention. If current flows into the dot on one side means that current must flow out of the dot on the other side. Similarly, phase B current must flow into must flow into the dot on the primary side to make secondary phase b current flow out of the dot on the secondary. And lastly, phase C current must flow into the dot on the primary side to make secondary phase b current to flow out of the dot on the secondary side.

And that my friends is how we describe phase current and line currents for the delta wye transformer connection. For me personally, I found it more difficult to intuitively understand the relationship between line current and phase current for the delta connected transformer. However, this difficulty can be easily overcome with a simple yet intuitive explanation. In part 4, we'll cover this relationship.

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