Transformer turns ratio

[Mohammed Ahmed]

Hi Gents,

Referring to the below example, when we multiply the secondary phase current in wye side by transformer turn ratio, shall we get phase current in primary (Delta side)? 

Is given answer correct when he got on tge line current in primary after multiplication of turn ratio? 

 

[akyip]

When you use the single-phase or per-phase turns ratio (a 1-ph), that is the ratio of the secondary phase (wye or line) current to the primary phase (delta) current.

When you use the overall 3-phase turns ratio of the 3-phase transformer as a whole (a 3-ph), it is the ratio of the secondary line current to the primary line current.

Single-phase ratio: a 1-ph = V1 ph / V2 ph = I2 ph / I1 ph (this depends on how the windings are connected)

3-phase turns ratio: a 3-ph = V1 LL / V2 LL = I2 L / I1L (this does not depend on how the windings are connected)

Give me a few minutes to draw an illustration to try to help you understand this better.

 

[akyip]

Attached is how I broke down this 3-phase transformer into the individual phases on both sides of the transformers.

I have one more illustration coming up, give me a few more minutes.

 

[akyip]

I took some time to draw out the transformer phase diagrams, both for just 1 phase and for the 3-phase transformer as a whole. Hope this helps.

 

[Mohammed Ahmed]

GREAT, thank you so much for your help