Parameter of 3 windings transformer 1

[tiewrc]

Anyone familiar with Neplan? I got a 3 windings transformer rated at
1. 7.6/6.8/0.8MVA,
2. 18/11/0.415kV,
3. Uk(H/X)=12% to 6.8MVA base
4. Uk(H/Y)=5% to 0.8MVA base
5. Uk(X/Y)=7.5% to 0.8MVA base

May i know how to translate this to

Rated power in MVA.
12: primary-secondary,=6.8?
23: secondary-tertiary,=?
31: tertiary-primary.=0.8?

Rated positive sequence short-circuit voltage with
respect to Sr12, Sr23, Sr31 and Ur1, Ur2, Ur3.
12rimary-secondary,= ?
23: secondary-tertiary,=?
31: tertiary-primary.=?

 

[tonyjony]

The rated power is the winding power, so the minor rated power in the power flow is the one you are looking for (0.8MVA).

Z12=12%
z23=7.5%
Z13=5%

 

[pwrtran]

Just be careful on the base. You indicated none of MVA values are on the primary base.
So, check the transformer test report to make sure.

 

[tonyjony]

Using 7.6MVA as base:

z12(7.6) 0.05pu 5%
Z13(7.6) 0.0003pu 0.03%
z23(7.6) 0.0004pu 0.04%

 

[davidbeach]

I don't think so. When going from a lower MVA base to a higher MVA base the per unit impedance of the same ohmic value goes up. Someplace something that should have be multiplied was divided.

 

[pwrtran]

Agree with David. You may want to refer everything to HV kV and MVA base.

 

[PHovnanian]

Anyone familiar with Neplan?

No.

Rated positive sequence short-circuit voltage with
respect to Sr12, Sr23, Sr31 and Ur1, Ur2, Ur3.
12rimary-secondary,= ?
23: secondary-tertiary,=?
31: tertiary-primary.=?

Voltage where? On the unfaulted winding?

You'll have to convert the winding-to-winding impedance figures to an equivalent star circuit. With a little simultaneous linear equation chicken scratch on the back of an envelope, I get:

Zh-o = 0.0475 pu
Zx-o = 0.0725 pu
Zy-o = 0.0025 pu

Now, for a source of 1.0V pu on H and a balanced fault on X,
the voltage on the unfaulted winding, Vy is:

Vy = Vh ( Zh-o / ( Zh-o + Zx-o ) ) = 0.604 pu

Hint: If you draw the one-line diagram for the fault, it looks like a simple voltage divider.

If this is NOT what you were after, then ignore everything I've said.

 

[tonyjony]

let me know if I'm wrong:

Z=Zpu1*Zb1=Zpu2*Zb2 Z=U^2/S

Zpu2=Zpu1*(Ub1^2/Sb1)/(Ub2^2/Sb2)

If the impedance in pu it's higher or lower depends of U^2/S ratio

Anyway, I think those values are odd, so maybe the Uk given are not in the base you are saying

 

[BSEE1980]

Typically 3 winding xmfs (US standards...don't know your brand) the M/Kva ratings are of the winding. You can look at it like it has 2 secondaries. One you "put in" 7.6M, one you "can get" 6.8M from and one you "can get" .8M from.

We used to use these in remote substations: the third winding was for station power.

As far as the Z calcs go, these other guys are right on.

Steve

 

[tonyjony]

Tha calcs are Ok, but not the values.

3. Uk(H/X)=12% to 6.8MVA base
4. Uk(H/Y)=5% to 0.8MVA base
5. Uk(X/Y)=7.5% to 0.8MVA base

I thought the "to" was the base of the impedance after the pwrtran post.

I think that my first post is the right one

 

[tiewrc]

agreed. i think tonyjony first post is the right one.