Ampcontrol OCS - 8.2 Short Circuit

Ampcontrol Pty Ltd – ABN 28 000 915 542
OCS USER MANUAL
MAG-182 Version 5 – FEB/2020
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 44 of 72
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– NOT TO BE REPRODUCED IN PART
8.2 Short Circuit
Table 20: Protection Element – Short Circuit Trip Characteristics
Parameter
Action
Power Cycle
Trip Status maintained
Reset
Specific short circuit reset
Trip Actions
Open selected output – circuit breaker or main contactor
Prevent Main Contactor from closing
Active Period
Always
Logging
When a fault occurs
Parameters
Short Circuit Output Relay
Short Circuit Trip Level
Short Circuit Trip Time
Monitoring
Phase currents displayed as a percentage of selected full load current.
The short circuit function has a definite time characteristic. If the current exceeds the selected level for
the pre-set time then a trip occurs.
The short circuit trip level is adjustable from 1.5 to 12.5 times (full load current) in 0.25 increments. Note
however that there is also an upper limit in the current measuring system of 6kA (RMS). This limit will
effectively over ride selections where the combination of the selected full load current and the selected
short circuit level exceeds 6kA. For example, if 640A is selected, the short circuit will trip at 9.4PU
(940%) even if the short circuit level is set to 9.5x or above. The per unit current at which the 6kA limit
takes effect is listed as ‘SC max’ along with the full range current values in APPENDIX A: PROTECTION
ELEMENT LOAD CURRENT TABLES.
The trip time is selectable from 40 to 200ms.
If the Over Current function is set to Motor Overload, the short circuit functionality is modified as follows:
1. The primary ‘instantaneous’ short circuit trip level is double the selected value: therefore, so it
covers a range of 3.0 to 25 times full load current.
2. A second ‘time delayed’ short circuit element becomes active. This element operates at the
selected Short Circuit Trip Level, but the trip time is the selected (primary) trip time plus 60ms.
There is a separate ‘SC-LT’ trip bit (LT for ‘long time’) & event log to differentiate each of the short circuit
elements.
This modified functionality allows the short circuit protection to be set just above the locked rotor current
level without risking spurious trips due to initial transient offsets (which can effectively double the initial
inrush peak current).
The Short Circuit Output Relay setting is used to control which trip action a short circuit trip: the trip can
be directed to either the CBR (preferred) or the MCR.
WARNING!
The circuit interrupting device tripped by the selected output relay for
the Short Circuit function MUST be rated to interrupt the full
prospective system short circuit current.