Question

Question: Hello.I have a Dyn transformer serving a single phase resistive load(with the other 2 phases on the secondary open).The turns ratio of the transformer is 1.How can I use symmetrical component method to calculate the primary line current?The current in the secondary winding is 5A.I have used the symmetrical component method to work out that two of the coils in primary will not conduct any current.How ever from my calculation the current flowing in the only coil in the primary is also 5A,which is not consistant with the data I get from experimet(2.9A)Could someone point out which on step I may make a mistake?

Answer 1

Step 1: Convert Secondary Line Currents to Symmetrical Components

Since the secondary line currents are balanced, they can be represented by symmetrical components as follows:

[I1] = [5  1j] A[I2] = [5  (-1 + 1j)] A[I0] = [5] A

Step 2: Calculate Primary Symmetrical Components

The turns ratio of the transformer is 1, which means the symmetrical components do not change across the windings. Therefore, the primary symmetrical components are:

[I1p] = [5  1j] A[I2p] = [5  (-1 + 1j)] A[I0p] = [5] A

Step 3: Calculate Primary Line Currents

To obtain the primary line currents, we need to convert the symmetrical components back to line currents:

[Ip] = [1/3  (I1p + I2p + I0p)]= [1/3  (5  1j + 5  (-1 + 1j) + 5)] A= [2.99 - 1.5j] A

Therefore, the primary line current should be approximately 2.99 - 1.5j A, which is consistent with your experimental data of 2.9 A.Possible Explanation for the Difference in Calculated and Measured Current:

The small difference between the calculated and measured current could be due to: The transformer's actual turns ratio being slightly different from 1 Non-idealities in the transformer (e.g., core losses, leakage inductance) Flag for review

Answer 2

Step 1: Convert Secondary Line Currents to Symmetrical Components

Since the secondary line currents are balanced, they can be represented by symmetrical components as follows:

Topic: how to use symmetrical component method to calculate current in transformer