COMBITEST422
EN - 101
Measurement of tripping current for protection differential switches
➢
This test aims at checking the real tripping current of general differential switches (
it
does not apply to selective differential switches
).
➢
In the presence of differential switches with selectable tripping current, it is useful to
perform this test in order to check the real tripping current of the differential switch. For
differential switches with fixed differential current, this test may be performed in order to
detect possible leakages of the users connected to the system.
➢
Should an earth system not be available, perform the test by connecting the instrument
to a terminal on a conductor downstream of the differential device and a terminal on the
other conductor upstream of the device.
➢
Tripping current must be between ½Idn and Idn
12.5. VERIFICATION OF THE BREAKING CAPACITY OF PROTECTION DEVICES
Purpose of the test
Checking that the breaking capacity of the protection device is higher than the maximum
fault current possible in the system.
Parts of the system to be checked
The test must be performed at the point in which the maximum short-circuit current is
possible, normally immediately downstream of the protection device to be checked.
The test must be performed between phase and phase (Z
pp
) in three-phase systems and
between phase and neutral (Z
pn
) in single-phase systems.
Allowable values
The instrument performs the comparison between the measured value and the value
calculated according to the following relationships:
2
3
3
L
L
NO M
L
L
MAX
MAX
Z
U
C
I
BC
−
−
=
N
L
NO M
N
L
MAX
N
L
MAX
Z
U
C
I
BC
−
−
−
=
Three-phase systems
Single-phase systems
where:
BC
=
breaking capacity of protection device
Z
LL
=
Impedance measured between phase and phase
Z
LN
=
Impedance measured between phase and neutral
Measured voltage
U
NOM
C
MAX
230V-10% < Vmeasured < 230V+ 10%
230V
1.05
230V+10% < Vmeasured < 400V- 10%
Vmeasured
1.10
400V-10% < Vmeasured < 400V+ 10%
400V
1.05
