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Protective Elements
I>> - IOC Function
The instantaneous overcurrent function (IOC) or 50P is intended to protect in the event of a high-current fault.
The example IOC setting used in the Motor Protection Curve (see the Motor Protection Curve Examples in the
Ultimate Trip Current Section) is 12 times (1,200%) of FLA. In general, the instantaneous IOC should be at least
1.5 times LRC (Locked Rotor Current), well above the locked rotor current normally seen at the moment of a
start.
IOC should trip fast and therefore no run or pickup delay is provided. A start delay is set at a minimum of 0.03
sec. or more if needed to block IOC tripping on magnetizing inrush when the motor is first energized. An
additional IOC tripping delay setting is set at a default of zero seconds.
IOC Trip
L
evel
The IOC sets the instantaneous overcurrent trip limit in percentage of »
Ib«
(FLA) above at which the relay trips.
This trip type can be set to Inactive to deactivate this protective device element. For currents clearly above the
setting, the IOC function picks up in 1.5 power cycles or less (at 50 Hz).
IOC Start Delay (IOCSD)
This setting sets the number of power cycles after a start is recognized until the IOC trip and alarm functions are
enabled. Use this delay to inhibit IOC tripping on a current peak caused by magnetic inrush when the motor is
first energized (usually two to three cycles).
I - Overcurrent [50, 51]
Available elements:
I[1] ,I[2] ,I[3] ,I[4] ,I[5] ,I[6]
If you are using inrush blockings, the tripping delay of the current
protection functions must be at least 30ms or more in order to prevent
faulty trippings.
All overcurrent protective elements are identically structured.
This module offers Adaptive Parameter Sets.
Parameters can be modified within parameter sets dynamically by means of
Adaptive Parameter Sets.
Please refer to chapter Parameter / Adaptive Parameter Sets.
The following table shows the application options of the Overcurrent Protection element
Applications of the I-Protection Module
Setting in
Option
ANSI 50 – Overcurrent protection, non-
directional
Device Planning menu
Measuring Mode:
Fundamental/TrueRMS/negative
phase sequence current (I2)
Page 288
EN MRM4 01/11
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