13
13
Ip (log)
U
out
U
p
uout =
M
di
p
dt
1000
100
10
1
0,1
0,01
0,01
1
0,1
1000
100
10
Current sensors
without ferro-
magnetic nucleus
Current transformers
with ferromagnetic
nucleus
Saturation
se
co
nd
ar
y
cu
rr
en
t
primary current
General diagram of the Rogowski coil (current sensor).
Extent of error “
ε
”made by the current sensors and by traditional current
transformers.
Combined current voltage sensor applied to the circuit-breaker poles.
5.3.6. Current and voltage sensors
– Rogowski sensors: only for current measurement in the
versions of eVD4 where voltage measurement is not
required.
– Combisensor sensors: allow current and voltage
measurement. Together with the Rogowski coil they
integrate a capacitive divider for measuring the voltage
applied to each pole.
This new generation of sensors is characterised by limited
dimensions, better performance compared to traditional
current and voltage transformers and a higher degree of
standardization.
5.3.6.1 Rogowski coils
A uniform winding on a closed circular support with a
constant cross section and without the ferromagnetic core.
The voltage induced in the winding is directly proportional to
the let-through current variation.
There are many advantages provided by using the Rogowski
coil, among which are:
– absolute linearity of the output signal according to the one
measured
– no saturation
– no currents magnetizing the metal nucleus, which is
important at low values for the current transformers
– no hysteresis phenomena.
These characteristics allowed the eVD4 circuit-breaker to be
designed with just three sensor sizes able to cover all rated
current values from 50 to 2500 A, and to protect against
short-circuits up to 40 kA.
Response characteristic of the Rogowski coil compared with that of a cur-
rent transformer.
Precision limit
Current
sensor
Rated
current
Current
transformer
Summary of Contents for eVD4
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