2.10 Unbalanced Load (Negative Sequence) Protection (ANSI 46)
73
7UM61 Manual
C53000-G1176-C127-3
Pickup Threshold /
Warning Stage
The value for I2> is set at Address 1702. It is at the same time the pickup value for a
current warning stage whose delay time T WARN is set at address 1703.
Example:
Negative Sequence
Factor K
If the machine manufacturer has indicated the loadability duration due to an unbal-
anced load by means of the constant K = (I
2
/I
N
)
2
· t, it is set directly at address1704
FACTOR K. The constant K is proportional to the admissible energy loss.
Conversion to Sec-
ondary Values
The factor K can be derived from the unbalanced load characteristic according to the
following figure by reading the time at point I
2
/I
N
= 1, corresponding to FACTOR K .
Example:
t
adm
= 20 s for I
2
/I
N
= 1
The constant K
primary
= 20 s determined in this way is valid for the machine side (pri-
mary side).
The factor K
primary
can be converted to the secondary side by means of the following
formula:
The calculated asymmetry factor K
sec
is set as FACTOR K at address 1704.
Example:
I
N Mach
= 483 A
I
N CT prim
= 500 A
Factor K
primary
= 20 s
Setting value at address 1704:
Machine I
N Mach
= 483 A
I
2 perm prim
/ I
N Mach
= 11 % permanent (salient-pole machine,
see Figure 2-18)
Current transform-
er
I
N CT prim
= 500 A
Setting value I
2 adm.
= 11 % · (483 A/500 A) = 10.6 %
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