Question

1 A standard transformer has a rating of 60 kVA. The primary and secondary voltages are rated respectively at 600 V and 120 V. (4) a. What is the rated current for each winding?

Answer 1

Given Information:

Apparent power = S = 60 kVA

Primary Voltage = V₁ = 600 V

Secondary Voltage = V₂ = 120 V

Required Information:

Primary Current = I₁ = ?

Secondary Current = I₂ = ?

Answer:

Primary Current = I₁ = 100 A

Secondary Current = I₂ = 500 A

Step-by-step explanation:

Transformer: an electrical device that works on the principle of electromagnetic induction to either step up or step down the voltages. There is no physical connection between the primary and secondary winding.

The apparent power in primary and secondary winding is given by

S = V₁I₁

S = V₂I₂

Current in Primary winding:

I₁ = S/V₁

I₁ = 60,000/600

I₁ = 100 A

Current in Secondary winding:

I₂ = S/V₂

I₂ = 60,000/120

I₂ = 500 A

Bonus:

Please note that the voltage is stepped down from 600 V primary to 120 V secondary but at the same time the current is stepped up from 100 A primary to 500 A secondary. This is due to the fact that the power must be conserved.

Answer 2

The rated current for the 600V side is I = 100 A and the rated current for the 120 V side is 500 A.

Step-by-step explanation:

For standard transformers they step up or down the level of voltage while maintaning the power output (ideally). So the same power output should be seen on both sides, since the equation for apparent power is P = V*I we can solve for I on both sides and find the rated current. So we have:

600 V side:

P = V*I

I = P/V = (60*10^3)/600 = 100 A

120 V side:

P = V*I = (60*10^3)/120 = 500 A