15.
_, . ( _, ). P
P = UI
. R 3 . , I , P , _, .
P , E I
P = EI
_, , _, .
Δ P r
Δ P = rI 2
_, , _,
Δ P = P P
η = R /(r + R)
(R = 0) η = 0.
, , (R = r). η = 0,5. , , , (r << R). (, , , . .).
l, ( ) , :
r = ρ l / s,
r ( ), ;
ρ , ·;
l , ;
s , 2.
, 1 ( ) .
r = r 0 l,
r 0 1 , ;
l , .
1. 20 1,5 2.
ρ = 17,2 · = 17,2 · 10 9 ·; s =1,5 2 = 1,5·10 6 2;
|
|
r = 17,2·10 9 · 20 / 1,5·10 6 = 0,229 .
r 0 = 11,5 /; l = 0,02 ; r = 11,5·0,02 = 0,23 .
( _) . , U U , U .
Δ U = U U = 2 lr 0 I,
I = P / U .
Δ P = P P = 2 lr 0 I 2.
.
( ) . , , . , . , . . , 19 . . 220/380 . 6 , 10 , 20 , 35 . 110 , 220 , 330 , 500 , 750 .
2. 100 24 1.
Δ u % = 2·0,02·11,5·100/242 ·100% = 8%.
, 4-5%. , , .
, 48
Δ u % = 2·0,02·11,5·100/482 ·100% = 2%.
4 .
.
. . . .
, . , . , . , , .
, . , , .
.