Table 93: Application nominal current relation to the upper limit of linear
measurement range
Application nominal
current (I
n
)
Rated secondary value
with 80A / 0.150 V at 50
Hz (0.180 V at 60 Hz)
Upper limit of linear
measurement range
40...800 A 1.500...30.000 mV/Hz 60 × I
n
800...1250 A 30.000...46.875 mV/Hz 60...40 × I
n
1250...2500 A 46.875...93.750 mV/Hz 40...20 × I
n
2500...4000 A 93.750...150.000 mV/Hz 20...12.5 × I
n
Table 93
shows the upper limits of the linear measurement range based
on a certain range in application nominal current. The linear measurement
limit for a given application nominal current can be derived from the values
stated in the table with a simple proportion equation. For example, the
upper limit for linear measurement for 3000 A application nominal current
would be 17.5 xIn.
It can also be calculated from
Table 93
that with the stated sensor the relay
input can linearly measure up to 50 kA (RMS) short circuit currents.
Rogowski sensor and overcurrent protection setting evaluation example
A 20 kV utility substation with a single busbar switchgear rated up to 40
kA shortcircuit currents has one incomer and 20 outgoing feeder relays
using 80 A/0.150 V at 50 Hz Rogowski current sensors with rating plate
values similar to
Figure 56
. For the incomer panel, electrical system designer
has evaluated the application nominal current to be 1250 A. Customer
specification for these protection relays defines normal instantaneous and
time-delayed overcurrent and earth-fault protection functions. Overcurrent
protection requires functions to be settable up to 20 xIn.
The sensor setting
Primary current
is set to be the same as the evaluated
application nominal current 1250 A. According to the sensor’s technical data,
the application nominal current matches the sensor’s capability which is up
to 4000 A.
The setting
Rated secondary value
is calculated by using
Equation 1
.
(Equation 3)
From
Table 93
it is seen that with the 1250 A application nominal current
value, the maximum setting for overcurrent protection is 40 xIn. This covers
the customer specification requirements for overcurrent settings of up to 20
xIn.
Voltage sensor setting example
The voltage sensor is based on the resistive divider or capacitive divider
principle. Therefore, the voltage is linear throughout the whole measuring
range. The output signal is a voltage, directly proportional to the primary
1MRS759142 F
Basic functions
REX640
Technical Manual
159
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