Y. LI ET AL.

1106

3) Material of iron core is according to rolling direc-

tion and orthogonal opposite treated. The material of tank,

draw plate and clamping part are treated according to

each direction same treated. The basic magnetization

characteristic curve is used here and hysteresis charac-

teristic is neglected.

4) The Newton-Raphson algorithm is used to solve the

magnetization characteristic of core silicon steel sheet

and tank steel plate for their characteristic are nonlinear

relation.

5) The eddy zone produce skin effect, and mesh gen-

eration should take current density radial distance.

1

f

(6)

where

is penetration depth,

is frequency,

is

conductivity,

is permeability. According to field

value some gradient descent discipline to stratify, pene-

tration depth chooses 0.22, 0.51, 0.92, 1.6 and 5 times to

mesh generation.

3. Field Analysis

To analysis short-circuit electromagnetic force, the flux

leakage magnetic distribution should be studied first.

As shown in Figure 2 that winding average flux den-

sity along circumferential distribution, winding end

magnetic density is affected by upper and lower iron yok,

the inner magnetic density is higher than the outers’. The

radiation component Br value is impacted greatly from

24.35mT to 27.8mT. The axis component Bz value varies

from 58.4mT to 61.6mT, and both of their two sides are

more than that at the middle part. The middle of the

winding does not change greatly for its far distant form

clamping part and iron yoke.

For the anglicizing of the structure eddy current loss,

the surface field and eddy current distribution are the

emphases.

As shown in Figure 3 that the magnetic curve of outer

tank side winding end part is bend, and the vortex center

is formed for the leakage flux concentrated into the tank

surface.

tank

Draw

Plate Pp

champing

Figure 1. Transformer calculation model.

Figure 2. Winding average fl ux density along circumferential

distribution.

Vo rtex

center ble

stress

requireme

nts g7

Figure 3. The surface of the oil tank eddy current distribu-

tion.

According to the CIGRE recommended document , the

transformer metal structure of local overheating criteria,

through calculation, the tank surface magnetic field

strength of the tangential component maximum value

was 48.22A • cm-1, does not exceed the standard value of

60 A • cm-1, therefore, the additional fuel tank shield is

not necessary.

4. Short Circuit Strength

The national standard GB1094.5-2008, in the new ver-

sion, the allowable stress requirements of .conventional,

non - viscous, sticky wire and CTCs (continuous trans-

posed conductor) are different from the original design.

Now, take average ring stress t1

, warping free limit

stress cr

, the inner winding radial bending stress sav

,

axial compressive stress act

, conductor axial bending

stress AL

, and wire inclination critical stress _cr tilt

for example [3,4]

According to the national standard GB1094.2-2008,

the first peak of asymmetric short-circuit current is

2

k

ik

IU

峰 (7)

where, i is rated current effective value, k

U is short

circuit impedance, 2k is peak factor, in this paper

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