COMBITEST422
EN - 107
12.10. VERIFY OF PROTECTION COORDINATION L-L, L-N AND L-PE
Purpose of the test
Testing the coordination of protective devices (typically MCB or fuse) present in a single-
phase or three-phase installation as a function of the limit time of fault extinction by the
protection set by the user and the calculated value of the short-circuit current.
Parts of the system to be checked
The test must be performed at the point in which the minimum short-circuit current is
possible, normally at the end of the line controlled by the protection device in the normal
condition of the line. The test must performed between Phase-Phase in three-phase
installations and between Phase-PE or Phase-PE in single-phase installations.
Allowable values
The instrument performs the comparison between the calculated value of short-circuit
current and the
Ia
= tripping current of the protection device within the specified time,
according to the following expressions:
a
Min
L
L
S C
I
I
−
2
_
Three-phase system
→
Loop L-L impedance
a
Min
N
L
S C
I
I
−
_
Single-phase system
→
Loop L-N impedance
a
Min
PE
L
S C
I
I
−
_
Single-phase system
→
Loop L-PE impedance
where:
Isc L-L_Min2F
= Prospective short-circuit current minimum double phase L-L
Isc L-N_Min
= Prospective short-circuit current minimum L-N
Isc L-PE_Min
= Prospective short-circuit current minimum L-PE
The calculation of prospective short-circuit current is performed by the instrument based
on the fault loop impedance measurement in compliance with the following relationships:
L
L
NO M
L
L
MI N
Min
L
L
S C
Z
U
C
I
−
−
−
=
2
_
N
L
NO M
N
L
MI N
Min
N
L
S C
Z
U
C
I
−
−
−
=
_
PE
L
NO M
PE
L
MI N
Min
PE
S C
Z
U
C
I
−
−
−
=
_
L
Phase
– Phase
Phase
– Neutral
Phase
– PE
Measured voltage
U
NOM
C
MIN
230V-10% < Vmeasured < 230V+ 10%
230V
0,95
230V+10% < Vmeasured < 400V- 10%
Vmeasured
1,00
400V-10% < Vmeasured < 400V+ 10%
400V
0,95
where:
U L-L
= Nominal Phase-Phase voltage
U L-N
= Nominal Phase-Neutral voltage
U L-PE = Nominal Phase-PE voltage
Z L-L
= Measured Phase-Phase Impedance
Z L-N
= Measured Phase-Neutral Impedance
Z L-PE
= Measured Phase-PE Impedance
