ABB RELION SMU615 Technical Manual page 60

Basic functions
the linear measurement range. Furthermore, the effect on protection
functions utilizing inverse time characteristics should be considered. The
upper limit of the linear measurement range depends on the selected
application nominal current and the type of the current sensor used.
34
shows the limits for an 80A/150mV 50Hz sensor.
Table 35: Application nominal current relation to the upper limit of linear
measurement range
Application nominal
current (In)
40...800 A
800...1250 A
1250...2500 A
2500...4000 A
Table 35
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
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
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
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
1250
80
From
value, the maximum setting for overcurrent protection is 40 xIn. This covers
60
shows the upper limits of the linear measurement range based
Figure 21
Primary current is set to be the same as the evaluated
Rated secondary value is calculated by using
A
150
mV
mV
A
= 46 875 .
50
Hz Hz
Table 35
it is seen that with the 1250 A application nominal current
Rated secondary value
with 80A / 0.150 V at 50
Hz (0.180 V at 60 Hz)
1.500...30.000 mV/Hz
30.000...46.875 mV/Hz
46.875...93.750 mV/Hz
93.750...150.000 mV/Hz
Table 35
that with the stated sensor the relay
. For the incomer panel, electrical system designer
1MRS758407 C
Table
Upper limit of linear
measurement range
60 × I
n
60...40 × I
n
40...20 × I
n
20...12.5 × I
n
Equation 2
.
(Equation 3)
Technical Manual
SMU615