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3-80
Protection Functions
857-UM001A-EN-P – July 2009
Standard Inverse Delays IEC, IEEE, IEEE2, RI
The available standard inverse delays are divided in four categories
IEC, IEEE, IEEE2 and RI called delay curve families. Each category
of family contains a set of different delay types according to the
following table.
Inverse Time Setting Error Signal
The inverse time setting error signal will be activated, if the delay
category is changed and the old delay type doesn't exist in the new
category. See Table 3.50 for more details.
Limitations
The minimum definite time delay start latest, when the measured
value is twenty times the setting. However, there are limitations at
high setting values due to the measurement range. See Table 3.50 for
more details.
Table 3.50 – Available Standard Delay Families and Types
Delay type
DT
Definite time
NI1
Normal inverse
VI
Very inverse
EI
Extremely inverse
LTI
Long time inverse
LTEI
Long time extremely inverse
LTVI
Long time very inverse
MI
Moderately inverse
STI
Short time inverse
STEI
Short time extremely inverse
RI
Old ASEA type
RXIDG
Old ASEA type
IEC Inverse Time Operation
The operation time depends on the measured value and other
parameters according Equation 3.4. Actually this equation can only
be used to draw graphs or when the measured value I is constant
during the fault. A modified version is implemented in the relay for
real time usage.
Curve family
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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