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Choice of the dimension type of transformer’s magnetic conductor
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When the magnetic conductor configuration is chosen with respect to part 2 of the problem №1, its dimension type is defined by the Addition B or [3,11,14] according to value of product S c S 0 that is calculated in the fallowing way:
(3.1)
where P PSR, f n, B m, j, k cs, k 0 are defined in the table 1.6, η T is coefficient of efficiency of transformer is defined in the table 3.1 with respect to the value of total power of the secondary windings 
is for single phase transformer and 
is for three phase transformer.
The calculation according to the formula (3.2)…(3.7) should be made if it is impossible to define S c S 0 from the Addition B or from [3, 11, 14].
The values of magnetic core for non standard core are defined from the following expression:
(3.2)
Table 3.1 – The initial data
| Frequency of the network f c, Hz | Defined parameters | Total power of the secondary windings P 2, VA | ||
| 150…300 | 300…1000 | 1000…2500 | ||
| ηT cos φ1 | 0,9…0,93 0,95…0,93 | 0,93…0,95 0,93 | 0,95 0,93 |
To define these expressions it is necessary to calculate the width a of the magnetic core:
, sm (3.3)
The rest geometric sizes of magnetic core such as H and C and its weigh G are defined by the following formula:
mm; 
mm; 
sm2; (3.4)
, kg (3.5)
The weigh of the magnetic core is defined by the formula (3.5) that corresponds to the plane 0,15 mm. If it is used the plane with another weigh then it is used the following formula to define the weigh:
kg (3.6)
The construction parameters of chosen and calculated sizes have to be shown in the table 3.2.
Table 3.2 – Construction parameters of magnetic core
| Parameters |  , sm4
|  ,
sm2
| a, mm | b, mm | c, mm | h, mm | C, mm | H, mm | G, kg |
| Results of calculation |
Calculation of electrical parameters of transformer
With respect to the calculated parameters of magnetic core it is define the power of losses in the steel
(3.7)
power of magnetization
(3.8)
Using Bm (from the table 2.14) it is possible to define the specific losses in the magnetic core p c and specific power of magnetization p μ:
(3.9)
(3.10)
(3.11)
where 
corresponds to the armored magnetic core;
corresponds to the steel magnetic core.
The total value of current under the open circuit is defined by
(3.11)
To calculate the expression (3.11) it is necessary to define the current in the primary windings according to the expression
(3.12)
where Un = Uc for the single-phase transformers and Un = 
is used for three-phase transformer (
is linear voltage);
and 
are defined from the table 2.14.
Then it is necessary to check the values 
and the obtained value Bm from the table 2.4.
If the calculation of the specific current with respect to current in the open circuit is more than 50% then it is necessary to take the smaller value of magnetic inductance Bm and recalculate. If the calculation of the specific current with respect to current in the open circuit is less than 10% then it is necessary to increase the value of magnetic inductance Bm in the range Bm < Bs, where Bs = 1,6T and recalculate to obtain the value that correspond to the condition:
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10% < < 50% (3.13)
The number of cells in the primary winding and secondary winding are calculated by the formula:
, (3.14)
where i is the number of the winding, Sc [ sm 2] for the corresponding values of EMF E1 and E2.
These values are defined by the following formulas:
(3.15)
(3.16)
where 
and 
are the specific values of voltage drop in the windings.
For the double winding transformer with working voltage up to 1000 V and the temperature in the winding is 
the orientated values are shown in the table 3.3.
Table 3.3 – The specific voltage drop in the winding of transformer
| Construction of magnetic core |  , V
| The total power of the secondary winding P 2, VA | ||
| 150…300 | 300…1000 | 1000…2500 | ||
| Armored |
| 0,45…0,03 0,08…0,06 | 0,03…0,01 0,06…0,02 | - |
| Steel |
| 0,04…0,03 0,06…0,04 | 0,03…0,01 0,04…0,02 | 0,01…0,008 0,00…0,01 |
The calculated results should be shown in the table 3.4
Table 3.4 – The parameters of transformer
| Parameters of transformer |  , W
|  , VA
| I0, A | I0Л, A | I0P, A | I1, A | , %
| E1, W | E2, W | W1, un | W2, un |
| Calculated results |
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