VAMP Ltd
Feeder and motor manager
Technical description
VAMP 257
VM257.EN002
VAMP 24h support phone : +358 (0)20 753 3264
47
VAMP 255
IL1
IL2
IL3
I
01
I
01
L1
L2
L3
X
1
:
1
X
1
:
2
X
1
:3
X
1
:
4
X
1
:
5
X
1
:6
X
1
:7
X
1
:8
VA
M
P
25
7
T1
I
02
I
02
X
1
:9
X
1
:
10
b
an
k_v
amp25
7
Figure 2.3.13-1. Typical capacitor bank protection application with VAMP
257
Compensation method
The sophisticated method for unbalance protection is to
compensate the natural unbalance current. The compensation
is triggered manually when commissioning. The phasors of the
unbalance current and one phase current are recorded. This is
because one polarizing measurement is needed. When the
phasor of the unbalance current is always related to I
L1
, the
frequency changes or deviations have no effect on the
protection.
After recording the measured unbalance current corresponds
the zero-level and therefore, the setting of the stage can be very
sensitive.
Compensation and location
The most sophisticated method is to use the same compen-
sation method as mentioned above, but the add-on feature is to
locate the branch of each faulty element or to be more precise,
the broken fuse.
This feature is implemented to the stage I
02
>>, while the other
stage I
02
> can still function as normal unbalance protection
stage with compensation method. Normally, the I
02
>> could be
set as an alarming stage while stage I
02
> will trip the circuit-
breaker.
The stage I
02
>> should be set based on the calculated
unbalance current change of one faulty element. This can be
easily calculated. However, the setting must be, say 10%
smaller than the calculated value, since there are some