Ampcontrol OCS - CURRENT RELATED PROTECTION FUNCTIONS; 8.1 Inverse Time Protection

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OCS USER MANUAL
MAG-182 Version 5 – FEB/2020
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8 CURRENT RELATED PROTECTION FUNCTIONS
Three current transformers within the Cassette are used to measure the three line currents. The
measured currents are used to implement the following protection functions:
 Inverse time protection - Over-Current or Motor Overload
 Short circuit
 Under current
 Phase current balance
The ‘Full Load Current Range’ setting determines the base current for all of the phase current related
functions: the measured currents are normalized based on the selected value. The range is selectable
from 5.125A to 640A.
8.1 Inverse Time Protection
The ‘Over Current Curve’ setting is used to select one of three Inverse Time-Current characteristics:
 Very Inverse Over Current
 Extremely Inverse Over Current
 Motor Overload
NOTE
When the Motor Overload parameter is set, the Short Circuit
functionality is also modified to better suit motor starting transients. See
the Short Circuit section (Section 8.2) for further information.
The Over Current Time Multiplier setting (TMS) scales the basic trip time for the basic over current
characteristics to the desired response time. Values are provided from 0.05 to 30; refer to Appendix A for
the full list of values. For cross reference, the nominal trip times are listed for each TMS value, for each
of the curve options at 10x FLC.
8.1.1 Over Current
Table 18: Protection Element – Over Current Trip Characteristics
Parameter
Action
Power Cycle
-
Reset
Requires a general reset (and all three measured phase currents must
be below the 100%).
Trip Actions
Open Main Contactor
Prevent Main Contactor from closing
Block restart if the thermal accumulator is not below the selected start
block level.
Active Period
When Over Current curve is set to Very Inverse or Extremely Inverse.
Logging
Always
Parameters
Time Multiplier
Full Load Current
Monitoring
Phase currents displayed as a percentage of selected full load current
Thermal Accumulator (TAC)