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powersys
Joined: 29 Nov 2005
Posts: 423
Helped: 1
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 25 Feb 2008 9:07 [URGENT] 3-phase transformer calculation - confusing |
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Hello,
Turn ratio, a = 2300/230 = 10 (for each transformer)
Let's look at Figure E2.7, do u think the value of V'2 is correct?
In my opinion, V'2 should be (√3) x 230 x 10 = 3984 V. What do you reckon?
Last edited by powersys on 26 Feb 2008 4:07; edited 1 time in total |
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FvM
Joined: 22 Jan 2008
Posts: 1759
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Location: Bochum, Germany
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| 25 Feb 2008 9:20 Re: 3-phase transformer calculation - confusing |
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| I don't see the problem V1=2300, V2=230. However, you must consider the transformer circuit Yd5.
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powersys
Joined: 29 Nov 2005
Posts: 423
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| 25 Feb 2008 9:25 Re: 3-phase transformer calculation - confusing |
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| FvM wrote: |
| I don't see the problem V1=2300, V2=230. However, you must consider the transformer circuit Yd5. |
In the PC Sen textbook, for a Y-D transformer, the 'effective' turn ratio a' = √3 x a
... where a is the turn ratio of individual single-phase transformer used to form the 3-phase transformer. Kindly correct me if I'm wrong...
Let's look at another example from the textbook as below. Kindly focus on the calculation in the 'blue rectangular' box. Say a = 1300/230, and a' = √3 x a
I'm confused when to use a and a' ... If we look at examples 2.7 and 2.8, a is used in 2.7, whilst a' is used in 2.8. Kindly advise.
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FvM
Joined: 22 Jan 2008
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Location: Bochum, Germany
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| 25 Feb 2008 10:02 Re: 3-phase transformer calculation - confusing |
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| I think, there may be confusion in defining the transformer voltage, you could either specify the mains (linked) voltage or the winding voltage. The latter is equal to mains voltage only for D circuit.
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KoRGeNeRaL
Joined: 08 Mar 2006
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Location: Turkey
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| 26 Feb 2008 1:00 Re: 3-phase transformer calculation - confusing |
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| powersys wrote: |
Hello,
Let's look at Figure E2.7, do u think the value of V'2 is correct?
In my opinion, V'2 should be (√3) x 230 x 10 = 3984 V. What do you reckon?
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2300V is correct, since the voltage in the equivalent circuit is the phase voltage, not the line voltage. But if it weren't so, 2300V would be correct again because in your first example the secondary of the 3f transformer is connected in delta, not wye.
I can't see anything wrong with these examples. In both examples, a' is first multiplied with the turn ratio to get a, then multiplied or divided by √3 (depending on the connection) to get the value of the line voltage.
I think it's the relation between the phase and line voltages which makes you frustrated.
Regards.
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powersys
Joined: 29 Nov 2005
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| 26 Feb 2008 3:03 Re: 3-phase transformer calculation - confusing |
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| KoRGeNeRaL wrote: |
2300V is correct, since the voltage in the equivalent circuit is the phase voltage, not the line voltage. But if it weren't so, 2300V would be correct again because in your first example the secondary of the 3f transformer is connected in delta, not wye.
I can't see anything wrong with these examples. In both examples, a' is first multiplied with the turn ratio to get a, then multiplied or divided by √3 (depending on the connection) to get the value of the line voltage.
I think it's the relation between the phase and line voltages which makes you frustrated. |
I think you see my confusions. Appreciate!
Let's look at Ex. 2.8. It gives that "The equivalent impedance of one transformer referred to the low-voltage side is 0.12 + j0.25 Ω." Can we label each transformer winding at the Δ side as 0.12 + j0.25 Ω? If it's so, can we use impedance transformation to convert the Δ to Y, i.e. (0.12 + j0.25)/3 ?
Thanks.
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