Allen-Bradley Rockwell Automation 857 User Manual page 43

The rated CT secondary may also be less than the rated input but
the measurement accuracy near zero current will decrease.
DEVICE SETUP
•
Bit rate for the command line interface in ports X4 and the front
panel. The front panel is always using this setting. If SPABUS
is selected for the rear panel local port X4, the bit rate is
according SPABUS settings.
•
Access level [Acc]
LANGUAGE
•
List of available languages in the relay
CURRENT SCALING
•
Rated phase CT primary current (Inom)
•
Rated phase CT secondary current (Isec)
•
Rated input of the relay [Iinput]. 5 A or 1 A.
•
Rated value of I CT primary current (Ionom)
01
•
Rated value of I CT secondary current (Iosec)
01
•
Rated I input of the relay [Ioinp]. 5 A or 1 A.
01
•
Rated value of I CT primary current (Io2nom)
02
•
Rated value of I CT secondary current (Io2sec)
02
•
Rated I input of the relay [Io2inp]. 5A, 1 A or 0.2 A.
02
The rated input values are usually equal to the rated secondary
value of the CT.
The rated CT secondary may be greater than the rated input but
the continuous current must be less than four times the rated
input. In compensated, high impedance earthed and isolated
networks using cable transformer to measure residual current I
it is quite usual to use a relay with 1A input although the CT is
5A or 1A. This increases the measurement accuracy.
The rated CT secondary may also be less than the rated input but
the measurement accuracy near zero current will decrease.
Local Panel User Interface
857-UM001A-EN-P – July 2009
2-27
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