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# What is the line current of this transformer?

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## What is the line current of this transformer?

1. A given 1000kVA wye-wye transformer has a secondary rated voltage of 480/277V, what is the line current of this transformer?
Help: First find transformer FLA and then calculate line current.
1. FLA = VA / L-L Voltage x 1.732
2. Balanced Wye: Line Current = Phase Current, Line Voltage = 1.732 Phase Voltage

I guessed the wrong answer on purpose on this one because the formula used does not fully explain how to calculate 3 power. It should actually be this:

KVA/(3 * phase voltage)

Why would you take the line voltage and multiply it by the sqrt(3) when it is already the product of the phase voltage * sqrt(3)?

2. Originally Posted by mattj77
1. A given 1000kVA wye-wye transformer has a secondary rated voltage of 480/277V, what is the line current of this transformer?
Help: First find transformer FLA and then calculate line current.
1. FLA = VA / L-L Voltage x 1.732
2. Balanced Wye: Line Current = Phase Current, Line Voltage = 1.732 Phase Voltage

I guessed the wrong answer on purpose on this one because the formula used does not fully explain how to calculate 3 power. It should actually be this:

KVA/(3 * phase voltage)

Why would you take the line voltage and multiply it by the sqrt(3) when it is already the product of the phase voltage * sqrt(3)?
Single Phase Transformer Full-Load Current (Amps)= kVA × 1000 / V
Three Phase Transformer Full-Load Current (Amps) = kVA × 1000 / (1.732 × VL-L)
Three Phase Transformer Available Fault Current (Amps) = kVA × 1000 / (1.732 × VL-L x %IMP)

https://goodcalculators.com/transformer-calculator/

To derive the equation: S (measured in VA, or KVA)
S=sqrt(3) * V * I
I= S/(sqrt(3) * V)
=> FLA = VA / (1.732 * V L-L)
Last edited by Kalbi_Rob; January 20, 2021 at 08:05 PM.

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## multiply sqrt of 3 by 480 again?

Originally Posted by mattj77
1. A given 1000kVA wye-wye transformer has a secondary rated voltage of 480/277V, what is the line current of this transformer?
Help: First find transformer FLA and then calculate line current.
1. FLA = VA / L-L Voltage x 1.732
2. Balanced Wye: Line Current = Phase Current, Line Voltage = 1.732 Phase Voltage

I guessed the wrong answer on purpose on this one because the formula used does not fully explain how to calculate 3 power. It should actually be this:

KVA/(3 * phase voltage)

Why would you take the line voltage and multiply it by the sqrt(3) when it is already the product of the phase voltage * sqrt(3)?