Page 4 of 4
Tel. (+45) 9614 9614
•
Fax:(+45) 9614 9615 E-mail: [email protected]
Normally the settings of the RMC-142D are selected to ensure optimum protection of
the voltage source (generator, transformer, line), however without causing unwanted
disconnections.
Unwanted disconnections may occur in installations based on 3 or 4 CTs with the
secondary windings coupled in parallel. In connection with a short circuit between 2
phases, the short circuit current arising thereby may get so high that a differential
signal occurs because of the different saturation characteristics of the applied CTs.
In order to avoid this, the disconnection limit must be selected with due consideration
of the characteristics of the applied CTs. Alternatively a cable transformer must be
applied instead of 3 (4) current transformers.
RMC-142D is provided with a special filter suppressing the harmonic currents. This
filter suppresses the 3rd harmonic 18db (8 times), so that the latter does not influence
the measurings. However, in certain cases the 3rd harmonic is so high that the
disconnection limit must be set accordingly.
If shortest possible time delay is selected (50 ms), unwanted disconnection may occur
during synchronisation caused by a pulse signal which may be transmitted in
connection with the switching on of the voltage source and unbalance of the applied
CTs (saturation).
In order to avoid this, connection of the auxiliary voltage to the relay in connection with
the switching on of the voltage source is recommended.
The built-in power-up circuit (200 ms) will then ensure that the relay is not activated
until 200 ms after switching on the voltage source.
6. Technical specifications
Frequency range: 40…50/60…70Hz
Max. input current: 4 x I
n
, continuously,
20
x
I
n
for 10 s (max. 75A)
80
x
I
n
for 1 s (max. 300A)
Load: Max.
0.3VA per phase
Relay contact:
2 changeover switches
Contact rating:
250V-8A-2000A (AC), 24V-8A-200W (DC)
Response time:
<50 ms
Galv. separation: Between input, output and aux. supply: 3250V-50Hz-1 min.
Consumption: (Aux.
supply) 3.5VA/2W
