则:
当时,
输入功率:
输出功率:
效率:
2、一台并励直流发电机,铭牌数据如下:
P
N
=6kW,U
N
=230V,n
N
=1450r/min,R
a
=0.57Ω(包括电刷接触电阻),励磁回路
总电阻 R
f
=177Ω,额定负载时的电枢铁损 P
Fe
=234W,机械损耗为 P
mec
=61W,求:
(1)额定负载时的电磁功率和电磁转矩。(2)额定负载时的效率。
解:(1)
'
1
324.75
Cua
Cub
mec
Fe
f
ad
P
P
P P
P
P
P
W
+
= −
−
−
−
=
10
a
I
A
=
10.5
a
f
I
I
I
A
= +
=
1
220 10.5
2310
P UI
W
W
=
=
=
ᄡ
2
2
1 10
100
Cua
a a
P
R I
W
W
=
=
=
ᄡ
110
f
P
W
=
2
2 1 10
20
Cub
b a
P
U I
W
W
= ∆
=
=
ᄡᄡ
2
1
1
(
) 1755.25
Cua
f
Cub
mec
Fe
P
P
P P P
P
P
P
P
W
= − Σ = −
−
−
−
+
=
2
1
100% 75.98%
P
P
η =
=
ᄡ
2
6
N
P
P
kW
=
=
220
1.3
177
f
f
f
U
I
A
A
R
=
=
=
2
299
f
f
f
P
R I
W
=
=
6000
26.1
230
N
N
N
P
I
A
A
U
=
=
=
27.4
a
N
f
I
I
I
A
=
+
=
3