Once, I was walking down the road. There I saw some people establishing a new transformer. I became curious and went towards it to see how it is done. Then, I took a look at the plate. I saw something written like Dny11 on its body. Then, I wondered, what does it mean by Dny11 written on a transformer body? Now, I will discuss what is meant by it. Let us at first notice how many characters are here. Here are 4 signs. They are D, n, y, 11.

What does it mean by Dny11 written on a transformer body?

D stands for Delta connection, n for neutral, y for Star connection, the number 11 indicates leading/lagging angle. Let me clear it up for you. Up to now, we learned what the symbols imply. Now, let us discuss these.

Definition of D, y: What does it mean by Dny11 written on a transformer body?

Now, let us see that D is a capital letter and y is of the small letter. By the capital D letter, it is meant Delta connection on the side of high voltage (HV). Again, y being a small letter character stands for Star connection on the side of low voltage(LV). The common point of the Star connection works as neutral and it has been grounded. Right now, each and every one of you might have caught up to the formula. The capital characters D/Y indicates HV side whereas the small characters d/y indicate the LV side. Now, let us move to interesting part.

What does it mean by Dny11 written on a transformer body? The meaning of 11

11 indicates the leading angle/ lagging angle. And, to find it out we have to take the help of a clock.


A clock
A clock

Let us assume, it is 11 pm on your clock. Then answer me, how long is it till midnight? The answer is 1 hour to go. In this case, I will say, the hour hand will have to go forward by one pace to strike midnight. And, each pace stands for 30 degrees. 

The math behind

What does it mean by Dny11 written on a transformer body? A Protractor
A Protractor

One whole rotation of the hour hand along the clock is 360 degrees. In total there are 12 paces. As a result, each pace = 360 รท 12 = 30 degrees. In the end, we can easily say that LV leads HV by 30 degrees. Because the hour hand has to pass by one pace only. Thus, 30 x 1 = 30. And, the engineering term for forwarding ahead is leading. Similarly, we can also express this same concept using lagging. The hour hand that is right now at 11 pm has passed 11 pace. And, the engineering term for passing by is lagging. In this case, we can say that LV lags HV by 330 degrees.

Why is the high voltage of the transformer connected to the side delta and the low voltage of the transformer is connected to the side star?

What does it mean by Dny11 written on a transformer body? A Voltmeter
A Voltmeter

We all know that star connections always tend to suppress high current level.

We also have learned this while learning about the star delta connection of the motor. 

Usually, in order to suppress the LV side’s excess current star connection is used.

Why there is more current in LV side?

It is very easy to explain. We know that transformer increase or decrease voltage remaining fix the power. The pressure of LV side voltage is comparatively less.

As a result, the current will increase a lot in order to fix the power. And, to suppress this excess current, the use of star connection is evident.

In a different concept, the pressure of voltage is more on the HV side. But, the current is less. As a result, the use of delta connection is evident here.

Courtesy: Iqbal Mahmood

If you want to read more such interesting articles, check these:

1. Direction of current flow and electron flow | Why are they opposite to each other? Mystery behind opposite direction of electron & current flow

2. Why stones are used in Substation instead of Sand or Grass? | Silent protector of substation


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