ABB REG316 4 Series - Page 279

REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-241
Design example:
U18kV
Gen
=
N
N
14.4 kV
240 V
60
1
2
==
Assumed: I 6.6 A
Emax
£
Determination of the grounding resistors:
Condition 1:
R' R'
18 kV
36.6A
1
60
440 m
Es Ps
2
+³
´
´
æ
è
ç
ö
ø
÷
=W
Condition 2: R' 130
1
60
36 m
Ps
2
³´
æ
è
ç
ö
ø
÷
=WW
Assumed: R' 42 m
Ps
=W
Condition 3: R' 4.5 42 m 189 m
Es
³´ =WW
Condition 4: R' 700
1
60
194 m
Es
2
³´
æ
è
ç
ö
ø
÷
=WW
In order to fulfil Conditions 1, 3 and 4:
R' 400 m
Es
=W
Determination of the v.t.:
Assumed:
N'
N'
18 kV
3100V
1
60
173.2 V
100 V
3
12
11
=
´
´= =
Condition 5 is fulfilled because:
1.2 n
N'
N'
0.8 n = 1.88 1.732 1.254
12
11
´³ ³ ´ ³ ³
where n
18 kV
3100V
1
60
400 m
400 m 42 m
1.567=
´
´´
+
=
W
WW
The following values are permissible:
R' = 42 m
Ps
W
R' = 400 m
Es
W
N N 173 V 100 V
12 11
=