5.3.5
Parameters
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Table 71: Inverse time overcurrent function - parameters
Signal
Description
ParSet4..1
Parameter for determining in which set of parameters a particular function is
active.
c-Setting
Setting for the exponential factor determining the operating characteristic
according to BS 142 or for selecting the RXIDG characteristic.
k
1
-Setting
Constant determining the parallel shift of the characteristic (time grading).
IStart
Pick-up current at which the characteristic becomes effective.
t-min
Definite minimum tripping time.
NrOfPhases
Defines the number of phases measured.
CurrentInp
Defines the CT input channel.
All current I/P's may be selected.
IB-Setting
Base current for taking account of differences of rated current I
N
.
BlockInp
Defines the input for an external blocking signal.
•
F: not used
•
T: function always blocked
•
xx: all binary inputs (or outputs of protection functions).
Trip
Tripping signal.
Start
Pick-up signal.
5.3.6
Configuration
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The following parameters have to be set:
Base current
I
B
-Setting
Characteristic
enabling current
IStart
Type of
characteristic
c-Setting
Multiplier
k
1
-Setting
The Inverse time overcurrent function is used to protect transformers, feeders and loads of
the auxiliaries supply system against phase and earth faults. The function responds largely
only to the fundamental component of the fault current.
Base current I
B
-Setting
The function does not have a fixed current setting above which it operates and below which it
does not, as does a definite time-overcurrent relay. Instead, its operating characteristic is
selected such that it is always above the load current. To this end, the relay has a reference
current I
B
that is set the same as the load current of the protected unit I
B1
. The reference
current I
B
determines the relative position of the relay characteristic which is enabled when the
current exceeds the reference current by a given amount (IStart). By setting the reference
current I
B
to equal the load current of the protected unit I
B1
instead of its rated current, for
I
B1
< I
N
of the protected unit: the protection is more sensitive
Section 5
1MRK 505 406-UEN B
Bay protection functions
96
Bay protection functions REB500
Technical manual
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