18
b) Block type current transformers (Figure 36).
The resin-insulated current transformers are used for
supplying measurement instruments and protections.
These transformers have a wound core with one or
more cores.
Their performances and accuracy classes comply with
the functional requirements of the apparatus. They
comply with IEC 61869-1, IEC 61869-2 which have
fully replaced previous standard IEC 60044-1. Their
dimensions are in accordance with DIN 42600
Standards for Narrow Type Medium and Long Size
versions. The current transformers can also be
equipped with a capacitive socket for connection to
voltage presence indicating system.
c) Ring core current transformers (Figure 37).
The ring core current transformers are air or resin-
insulated and are used for supplying measurement
instruments and protections. These transformers can
have a ring or a split core.
Their performances and accuracy classes comply with
the apparatus requirements. They are suitable both for
measuring phase currents and for determining earth
fault currents. They comply with IEC 61869-1, IEC
61869-2 which have fully replaced previous standard
IEC 60044-1.
Figure 37: Ring core current transformer.
4.4.4. Current and voltage sensors
Indoor current sensors
Current measurement in KECA sensors is based on
the Rogowski coil principle.
KECA 250 B1
For dynamic current measurement (protection
purposes) the ABB sensors KECA 250 B1, fulfill
requirements of protection class 5P up to an
impressive value reaching the rated short-time thermal
current Ith (31.5 kA).
With KECA 250 B1 sensors, measuring class 0.5 is
reached for continuous current measurement in the
extended accuracy range from 5 % of the rated
primary current Ipr not only up to 120 % of Ipr (as
being common for conventional current transformers),
but even up to the rated continuous thermal current
Icth (2 000 A).
That provides the possibility to designate the
corresponding accuracy class as 5P125, proving
excellent linearity and accuracy measurements.
Technical parameters
Continuous thermal current 2 000 A
Rated primary current 250 A / 150 mV @ 50 Hz
Rated primary current 250 A / 180 mV @ 60 Hz
Accuracy class 0.5 / 5P125
Figure 38: Current sensor KECA 250 B1
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