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Single phase transformer question

  • #1

Homework Statement


A 100 kVA, 2300/230V, single phase transformer has the following parameters: Rp = 0.30Ω, Rs = 0.0030Ω, Rc = 4.5 kΩ, Xp = 0.65Ω, Xs = 0.0065Ω, Xm = 1.0 kΩ The transformer delivers 75 kW at 230 V at 0.85 power factor lagging, find:
a) The input current.
b) The input voltage.

Homework Equations




The Attempt at a Solution


[/B]
Referred to primary
IMG_20160427_002407.jpg


I'm confused with the part where the transformer delivers 75kW. Then will the secondary current be 0.75*Israted ?
 

Answers and Replies

  • #2
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
I'm confused with the part where the transformer delivers 75kW. Then will the secondary current be 0.75*Israted ?
You know the power and the PF so you can determine the secondary's VA output.
 
  • #3
You know the power and the PF so you can determine the secondary's VA output.
So,
cos(∅) = P/S
S = P/cos(∅)
= 75/0.85
= 88.24 kVA

So would the secondary current be
Is = 88.24/230 = 383.65A ?
 
  • #4
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
So,
cos(∅) = P/S
S = P/cos(∅)
= 75/0.85
= 88.24 kVA

So would the secondary current be
Is = 88.24/230 = 383.65A ?
That should be right.
 
  • #5
Ok, so to find the input current, Ip, would this be right ?

From my schematic:

Ip = Io + Is/a..................1

Io = 2300(1/4.5k + 1/1k)

Is/a = 383.65∠-31.79 / 10
= 38.365∠-31.79

Therefore,

Ip = 2300(1/4.5k + 1/1kj) + 38.365∠-31.79
= 40.05∠-34.2
 
  • #6
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
Ok, so to find the input current, Ip, would this be right ?

From my schematic:

Ip = Io + Is/a..................1

Io = 2300(1/4.5k + 1/1k)

Is/a = 383.65∠-31.79 / 10
= 38.365∠-31.79

Therefore,

Ip = 2300(1/4.5k + 1/1kj) + 38.365∠-31.79
= 40.05∠-34.2
That looks right.
 
  • #7

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