Question

How to calculate transformer per unit values for different base?

Answer 1

Answer:distribution of electrical power are more economical in three phase system than single phase system. For three phase system three single phase transformers are required. Three phase transformation can be done in two ways, by using single three phase transformer or by using a bank of three single phase transformers. Both are having some advantages over other. Single 3 phase transformer costs around 15 % less than bank of three single phase transformers. Again former occupies less space than later. For very big transformer, it is impossible to transport large three phase transformer to the site and it is easier to transport three single phase transformers which is erected separately to form a three phase unit.

Step-by-step explanation:

Answer 2

Answer:Let’s move on and calculate the per unit impedance for transformer T2:

 

 

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Step 7: Calculate the Per Unit Current and Per Unit Voltage

Now that we have both per unit impedances let’s fill in the remaining values in our per unit impedance diagram.

Again, notice that both transformer per unit impedances are reactive terms and we had to add the “j” multiplier:

 

 

Now that we have all impedances converted to per unit values of the same base, it’s time to calculate the per unit current using Ohm’s law:

However, in order to calculate the per unit impedance, we will need to calculate the per unit voltage.

Luckily for us, the voltage on our input bus is equal to the base voltage selected in that zone which simplifies the math since both terms cancel:

 

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Step 8: Use Ohm’s Law to Calculate the Per Unit Current

Since the input voltage is equal to the base voltage in zone 1, the per unit voltage at the source of our per unit impedance diagram is equal to 1.

This greatly simplifies solving for the per unit current which will now equal the inverse of the total series per unit impedance of the system:

 

The per unit current will be the same value for each voltage zone.

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Step 9: Calculate the Base Current in Each Zone

Now that we know the per unit current, we can finally calculate the actual current in each voltage zone by multiplying by the per unit current by each base current:

 

 

However, this requires us to know what the base current in each voltage zone is equal to.

We can calculate it using the chosen base power and the chosen base voltage in each zone as shown below.

Notice the √3 multiplier since it is a three phase system:

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Step 10: Calculate the Actual Current in Each Zone

Now that we have each of the base current values we can complete the problem and solve for the actual current in each zone in amps:

Step-by-step explanation: