Technical description
2 Protection functions
2.6 Current unbalance stage I2>
(46)
VM59.EN001
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55
2.6.
Current unbalance stage I
2
> (46)
The purpose of the unbalance stage is to detect unbalanced load
conditions, for example a broken conductor of a heavy loaded
overhead line in case there is no earth fault.
The operation of the unbalanced load function is based on the
negative phase sequence component I
2
related to the positive
phase sequence component I
1
. This is calculated from the phase
currents using the method of symmetrical components. The
function requires that the measuring inputs are connected
correctly so that the rotation direction of the phase currents are
as in chapter 8.8. The unbalance protection has definite time
operation characteristic.
1
2
2
I
I
K
, where
I1 = I
L1
+ aI
L2
+ a
2
I
L3
I2 = I
L1
+ a
2
I
L2
+ aI
L3
2
3
2
1
120
1
j
a
, a phasor rotating constant
Setting parameters of the current unbalanced stageI
2
> (46)
in feeder mode:
Parameter Value
Unit
Default
Description
I2/I1>
2 … 70
%
20
Setting value, I2/I1
t>
1.0 … 600.0
s
10.0
Definite operating time
Type
DT
INV
-
DT
The selection of time
characteristics
S_On
Enabled;
Disabled
-
Enabled Start on event
S_Off
Enabled;
Disabled
-
Enabled Start off event
T_On
Enabled;
Disabled
-
Enabled Trip on event
T_Off
Enabled;
Disabled
-
Enabled Trip off event
Measured and recorded values of of the current unbalanced
stageI
2
> (46) in feeder mode:
Parameter Value Unit
Description
Measured
value
I2/I1
%
Relative negative sequence
component
Recorded
values
SCntr
Cumulative start counter
TCntr
Cumulative start counter
Flt
%
Maximum I
2
/I
1
fault component
EDly
%
Elapsed time as compared to
the set operating time, 100% =
tripping