User manual

35
VDE 0100-compliant demonstration case
5.4 Line impedance (mains internal resistance)
Starting conditions:
  &RQQHFWWKHPDLQVSOXJDQGVZLWFKRQWKH5&'
  DOOIDXOWVZLWFKHVLQ2.SRVLWLRQ
Switch position at the BENNING IT 110 / IT 120:
  =
I
/ I
N/1/
  7\SHQRPLQDOFXUUHQWDQGWULSSLQJWLPHRIWKHRYHUFXUUHQWSURWHFWLRQGHYLFHKDYHWREHVHWHJ
line safety switch type C, nominal current 10 A, tripping time 0.4 s
Note:
Measuring the line impedance Z
I
PDLQVLQWHUQDOLPSHGDQFHRUWKHVKRUWFLUFXLWFXUUHQW,
k
/1LVQRW
required by the test standards.
Nevertheless, it is recommended to carry out this measurement additionally, if the short-circuit current
is possibly limited by longer line lengths. The line impedance has to be determined between the
H[WHUQDOFRQGXFWRU/DQGWKHQHXWUDOFRQGXFWRU1,QFDVHRIDVKRUWFLUFXLWEHWZHHQWKHH[WHUQDO
FRQGXFWRU/DQGWKHQHXWUDOFRQGXFWRU1WKHVKRUWFLUFXLWFXUUHQW,
k
must be so high that it trips
the overcurrent protection device connected in series within the admissible time.
The short-circuit current I
k
must be higher than the absolute value of the tripping current Ia of the
overcurrent protection device. I
k
> I
a
I
k
= U
o
/ Z
I
U
o
: nominal voltage to earthed conductors
Limiting values:VHH',19'(3DUWWDEOH1$71V\VWHPV
HJOLQHVDIHW\VZLWFKW\SH&,
a
 ,
n
,
n
= 10 A, t
a
= 0.4 s: Z
I
ȍ,
a
= 100 A
Measuring point Measured value
mains socket
Z
I
= Z
[
ȍ
e.g. Z
I
§ȍ,
k
§$
Error: =
LINE
VZLWFKLQ)DXOWSRVLWLRQ
mains socket
Z
I
= Z
[
ȍ
e.g. Z
I
§ȍ,
k
§$
Z
[
= line impedance at the input of the supplying mains socket
0HDVXULQJFXUUHQW $PV