VAMP 59 - Page 97

Technical description
2 Protection functions
2.14 Inverse time operation
VM59.EN001
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97
Figure 2.14.1-9 ANSI/IEEE short time inverse
delay
Figure 2.14.1-10 ANSI/IEEE short time
extremely inverse delay
IEEE2 inverse time operation
Before the year 1996 and ANSI standard C37.112
microprocessor relays were using equations approximating the
behaviour of various induction disc type relays. A quite popular
approximation is Equation 2.14.1-3, which in VAMP relays is
called IEEE2. Another name could be IAC, because the old
General Electric IAC relays have been modeled using the same
equation.
There are four different delay types according
Table 2.14.1-4. The old electromechanical induction disc relays
have inverse delay for both trip and release operations.
However, in VAMP relays only the trip time is inverse the
release time being constant.
The operation delay depends on the measured value and other
parameters according Equation 2.14.1-3. 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.
Equation 2.14.1-3
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