Inverse Time Curves Characteristics - GE F650 Instruction Manual

5 SETTINGS
Inverse time curves available in time overcurrent elements are as follows:
IEEE extremely/very/moderately inverse
IEC Curve A/B/C/Long-Time Inverse/ Short-Time Inverse
IAC extremely/very/normally/moderately inverse
ANSI extremely/very/normally/moderately inverse
I2t
Definite time curves
Rectifier time curves
User Curve - FlexCurve A/B/C/D
Recloser Curves
The saturation level for the user curve is 20 times the pickup value, for the rest of time overcurrent elements the
saturation level is 48 times the pickup.
All these curves follow the standards defined for each of them, allowing an efficient coordination with other devices located
downstream. A dial or curve setting allows selection of a tripping time X times the set time in the selected curve. Fixing this
value to 0 would produce an instantaneous response for any selected curve.
Tripping time calculations are performed on the base of an internal variable called "energy". This energy represents the
system dissipation capability, that is, when 100% of energy is reached, this means that the tripping time associated to the
curve for a certain current value has expired.
Therefore, once the current value has exceeded the pickup value, the relay starts increasing the energy variable value. If it
reaches 100%, a trip is produced. When the current value falls below 97% of the pickup value, the element is reset. There
are two reset types: Instantaneous and Timed (IEEE) or Linear.
The instantaneous mode provides that, when the current value falls below the reset level, energy is immediately reset to 0.
This mode is used for coordinating with static devices, which behave in a similar way. In the Linear mode, energy is
reduced at a speed associated to the reset times curve (showed in the curve tables), trying to simulate the behavior of
electromechanical relays.
5.4.2.1 IEEE CURVES
This family of curves follows the standard IEEE C37.112-1996 for extremely inverse, very inverse, and inverse curves. The
following formulas define this type of curve:
Where:
t = Operation time in seconds
Dial = multiplier setting
I = Input current
Itap = Current pickup value
A, B, p = constants defined by the standard
T = reset time in seconds
RESET
t = characteristic constant.
r
GEK-106310AB

5.4.2 INVERSE TIME CURVES CHARACTERISTICS

F650 Digital Bay Controller
5.4 PROTECTION ELEMENTS
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