User manual

33
VDE 0100-compliant demonstration case
5.3 Loop impedance
5.3.1 Loop impedance and short-circuit current in the TN system
Starting conditions:
  &RQQHFWWKHPDLQVSOXJDQGVZLWFKRQWKH5&'
  DOOIDXOWVZLWFKHVLQ2.SRVLWLRQ
  EULGJH7177$8;LQ71SRVLWLRQ
Switch position at the BENNING IT 110 / IT 120:
  =
S
/
,N/3(
, hypofunction: Z
s rcd
ZLWKRXWWULSRIWKH5&'
  7\SHQRPLQDOFXUUHQWDQGWULSSLQJWLPHRIWKHRYHUFXUUHQWSURWHFWLRQGHYLFHKDYHWREHVHW
e.g. line safety switch type C, nominal current 10 A, tripping time 0.4 s
Notes on measurement:
The effect of measuring the loop impedance Z
s
LVWKDWDQH[LVWLQJ5&'LVWULSSHGLIWKHWHVWLQJFXUUHQW
is as high as or higher than the nominal current of the RCD.
7KHORRSLPSHGDQFHKDVWREHGHWHUPLQHGEHWZHHQWKHH[WHUQDOFRQGXFWRU/DQGWKH3(RU3(1
FRQGXFWRU,QFDVHRIDVKRUWFLUFXLWEHWZHHQWKHH[WHUQDOFRQGXFWRU/DQGWKHSURWHFWLYHFRQGXFWRU
3( WKH VKRUWFLUFXLW FXUUHQW ,
k
must be so high that it trips the overcurrent protection device
connected in series within the admissible time t
a
V9

  LQILQDOFLUFXLWVV9V9V9ZLWKVRFNHWVRUILUPO\FRQQHFWHG
equipment of protection class I
  VLQDOORWKHUHOHFWULFDOFLUFXLWVULVHUVODPSFLUFXLWVRXWVLGHWKHFRQWDFWDUHD
The short-circuit current I
k
must be higher than the absolute value of the tripping current I
a
of the
overcurrent protection device. I
k
> I
a
I
k
= U
o
/ Z
s
U
o
: nominal voltage to earthed conductors
Limiting values:VHH',19'(3DUWWDEOH1$71V\VWHPV
HJOLQHVDIHW\VZLWFKW\SH&,
a
 ,
n
,
n
= 10 A, t
a
= 0.4 s: Z
s
ȍ,
a
= 100 A
Measuring point Measured value
mains socket
Z
s
= Z
[
ȍ
e.g. Z
s
§ȍ,
k
§$
Error: =
LINE
VZLWFKLQ)DXOWSRVLWLRQ
mains socket
Z
s
= Z
[
ȍ
e.g. Z
s
§ȍ,
k
§$
Z
[
: loop impedance at the input of the supplying mains socket
Measuring current: for Z
s
$PVIRU=
s rcd
$ȝV

The current that trips an overcurrent protection device within a certain time t
a
can be taken from
its switch-off characteristic.