ABB Relion SMU615, Technical Manual

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Current (Rogowski) sensor setting example
In this example, an 80 A/0.150 V at 50 Hz (0.180 V at 60 Hz) sensor, such as
the example shown in
Figure 21
, is used in a 50 Hz electrical network. The
application has a 150 A nominal current (In) corresponding to the protected
object’s nominal current. The application nominal current is set to Rogowski
sensor setting
Primary current. Taken from the sensor’s technical data, this
example sensor can be used with up to 4000 A application nominal current.
As the Rogowski sensor is linear and does not saturate, the 80 A/0.150 V at
50 Hz sensor also works as a 150 A/0.28125 V at 50 Hz sensor. When defining
another primary value for the sensor, also the nominal voltage has to be
redefined to maintain the same transformation ratio. However, the setting
in the protection relay (
Rated Secondary Value) is not in V but in mV/Hz,
which makes the same setting
Rated Secondary Value valid for both 50 and
60 Hz nominal frequency.
RSV
I
I
K
f
n
pr
r
n
=
×
(Equation 1)
RSV
Rated Secondary Value
in mV/Hz
I
n
Application nominal current
I
pr
Sensor-rated primary current
f
n
Network nominal frequency
K
r
Sensor-rated voltage at the rated current in mV
In this example, the value is as calculated using the equation.
150
80
150
50
5 625
A
A
mV
Hz
mV
Hz
×
=
.
(Equation 2)
With this information, the protection relay's current (Rogowski) sensor
settings can be set.
Table 34: Example setting values for current (Rogowski) sensor
Setting Value
Primary current 150 A
Rated secondary value 5.625 mV/Hz
When considering setting values for current sensor interfaces and for
protection functions utilizing these measurements, it should be noted
that the sensor measurement inputs in the relay have limits for linear
behavior. When this limit is exceeded, the input starts to saturate. The
saturation is reflected to the protection functions connected to the
sensor inputs. To ensure that the related protection functions operate
correctly, the start value setting for protection functions utilizing either
instantaneous or definite minimum time characteristics must not exceed
1MRS758407 C Basic functions
SMU615
Technical Manual
59