Transformer Calculations - determining turns/current/maximum flux

In summary, we have a single phase transformer with a rating of 120 kVA, 2000 V/100 V, 60 Hz and 1000 primary turns. To determine the secondary number of turns, we use the equations NP = VP and NS = VS to get 50 turns. The rated currents on the primary and secondary are 60 A and 1200 A, respectively. To calculate the maximum flux, we use the equation emf = -dPHI/dt. Given a maximum flux density of 0.25 T, the cross sectional area of the core can be determined using the previously mentioned equations.
  • #1
Angusbrooks
2
0
The Question
A single phase transformer has the following rating: 120 kVA,
2000 V/100 V, 60 Hz with 1000 primary turns.

Determine:

(A) the secondary number of turns
(B) the rated currents on the primary and secondary
(C) The maximum flux
(D) given a maximum flux density of 0.25 T, the cross sectional area of the core.

Equations used

NP (primary number of turns) VP (primary voltage) IS (Secondary current)
NS (Secondary number of turns) VS (secondary voltage) IP (primary current)

I (current) = P (Power)
V (Voltage)

The attempt at a solution

(A) NP = VP
NS = VS

1000 Turns = 2000V
NS 100V

NS = 100V
2000V

= 0.05V X 1000 Turns

= 50 Turns

(B)i I (current) = P (power)
VP (primary voltage)

I = 120000VA
2000V

= 60 A on the primary

ii I (current) = P (power)
VS (seconday voltage)

I = 120000VA
100V

= 1200 A on the Secondary



(C) I am struggling with this question i understand that I must calculate the maximum flux but am completely lost could someone please advise me in the correct direction?!

(D) as above



Any help would be great thanks!
 
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  • #2
Part C: Remember emf = -dPHI/dt?
Part D follows immediately.
 

FAQ: Transformer Calculations - determining turns/current/maximum flux

1. How do I determine the number of turns needed in a transformer?

The number of turns in a transformer can be determined by using the formula N = V/I, where N is the number of turns, V is the voltage and I is the current. This formula assumes that the core material has a high permeability and the flux density is constant.

2. How do I calculate the maximum flux in a transformer?

The maximum flux in a transformer can be calculated using the formula B = μNI/A, where B is the maximum flux, μ is the permeability of the core material, N is the number of turns, I is the current, and A is the cross-sectional area of the core. This formula assumes that the core material has a high permeability and the magnetic field is uniform.

3. What factors affect the number of turns needed in a transformer?

The main factors that affect the number of turns needed in a transformer are the input voltage, output voltage, and the core material. A higher input voltage will require fewer turns, while a higher output voltage will require more turns. The type of core material used also affects the number of turns needed, as different materials have different permeabilities.

4. How does the frequency of the input signal affect transformer calculations?

The frequency of the input signal does not directly affect transformer calculations, as long as the core material has a high permeability and the magnetic field is uniform. However, a higher frequency may cause more losses in the transformer due to eddy currents and hysteresis, which should be taken into consideration in the design process.

5. Can transformer calculations be used for all types of transformers?

The basic transformer calculations for determining turns, current, and maximum flux can be used for most types of transformers. However, for specialized transformers such as auto-transformers or multi-winding transformers, additional calculations may be necessary to account for their unique configurations. It is important to consult the specific design guidelines for these types of transformers.

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