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3-16
Protection Functions
Current unbalance
protection I
> (46)
2
857-UM001A-EN-P – July 2009
I
K =
2
, where
2
I
1
2
I1 = I
+ aI
+ a
I
L1
L2
L3
2
I2 = I
+ a
I
+ aI
L1
L2
L3
1
=
∠
°
=
−
+
a
1
120
2
Table 3.8 – Setting parameters of unbalanced load function: I
Parameter
Value
I2/I1>
2 ... 70
t>
1.0 ... 600.0
Type
DT
INV
S_On
Enabled;
Disabled
S_Off
Enabled;
Disabled
T_On
Enabled;
Disabled
T_Off
Enabled;
Disabled
Table 3.9 – Measured and recorded values of unbalanced load function: I
(46R)
Parameter
Measured
I2/I1
value
Recorded
SCntr
values
TCntr
Flt
EDly
Current unbalance in a motor causes double frequency currents in the
rotor. This warms up the surface of the rotor and the available thermal
capacity of the rotor is much less than the thermal capacity of the
whole motor. Thus an rms current based overload protection (see
"Thermal Overload Protection T> (49)") is not capable to protect a
motor against current unbalance.
The current unbalance protection is based on the negative sequence of
the base frequency phase currents. Both definite time and inverse time
characteristics are available.
3
j
, a phasor rotating constant
2
Unit
Default
%
20
Setting value, I2/I1
s
10.0
Definite operating time
-
DT
The selection of time
characteristics
-
Enabled
Start on event
-
Enabled
Start off event
-
Enabled
Trip on event
-
Enabled
Trip off event
Value
Unit
%
Relative negative sequence component
Cumulative start counter
Cumulative start counter
%
Maximum I
%
Elapsed time as compared to the set
operating time, 100% = tripping
/I
> (46R)
2
1
Description
/I
>
2
1
Description
/I
fault component
2
1
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