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Introduction to the Wye Wye Transformer connection: Part 1 and the introduction to the infamous square root 3.
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Let's begin by drawing a single phase transformer with two windings – we'll assume that the winding on the left is the primary side, or the high voltage side, or the source side. And we'll assume that the winding on the right is the secondary side or the low voltage side or the load side. We'll indicate polarity side of the winding by nice round dots and lastly, we'll draw two parallel lines in the middle to illustrate magnetic coupling. And for the sake of simplicity, we'll assume that the primary voltage is 4160V and the secondary voltage is 480V.
What we have so far is a single phase transformer and we'll assigning a capital "A" to the primary side and lowercase "a" to the secondary side. To make a three phase transformer, we'll simply add winding B and winding C.
The wye connected transformer is distinguished by a "common wire" which is also referred to as the "4th wire" or "neutral wire". This common wire can be connected in various ways to achieve very specific results.
The wye connection is almost always found with the common wire connected to the non-polarity side of the windings. That's how we'll configure our transformer in this example. We're going to take a wire and connect the non-polarity side of winding A, B, and C together – and this wire will be referred as a "common wire" or "neutral wire" or "4th wire".
The primary windings are connected in the wye connection. We're going to connect the non-polarity side of the secondary windings together, which will make also make a wye connection on the secondary side. This here my friends, is a wye-wye connected, 3 phase transformer. Again, the "wye" connection is distinguished by a "common wire" which connects all three windings to a "common point" or "neutral point".
There are many names for a Wye connected 3 phase transformers. It's sometimes spelled as "Wye" it's sometimes referred as the letter "Y" it's sometimes called a "star" connection and sometimes referred as a "4 Wire" system. Different names, but they all mean the same thing.
There are many ways to configure the Wye connection and each method gives us a unique characteristic. We may find the "neutral wire" or "neutral point" to be grounded like this. And sometimes we may find it un-grounded. When ungrounded, it's simply a connection between all three winding – and it's referred as "YY connection with the neutral wire ungrounded".
When the 4th wire is grounded, it's sometimes referred as "effectively grounded" or "solidly grounded" system. Sometimes the 4th wire is grounded with a very large impedance like this. And sometimes its grounded with a small impedance. Nonetheless, a 4 wire system is distinguished by a common wire that connects all three windings do a common point.
In our example, we'll keep out discussion simple and solidly ground both sides of the transformer.
Okay – so now that we've drawn our YY connected transformer in this particular way, let's draw our lines or conductors. We'll begin by drawing Line A and line A is connected to the bushing of winding A which is illustrated by this small box. Let's also draw line B and line C on the primary side. And line a, b, c on the secondary side.
This my friends is our YY connected 3 phase transformer. If we were to describe this particular transformer connection to someone, we'd say – "We have a 4160 to 480V 3 phase transformer – it has Y-grounded Y-grounded connection – both the primary side and secondary side is solidly grounded with no neutral impedance."
We'll cover voltage and current quantities in the next module! Thanking you watching!
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