ABB REL 356, Instruction Booklet

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ABB REL 356 Current Differential Protection
3-7 Settings and Application
·
OUT No open breaker keying. Note that this will disable the Open Breaker function in the remote end as no
open breaker code will be received there.
Very Low Set Phase Current Unit (IE)
This unit is used with the open breaker keying logic (OPBR). It should be set sensitive enough to pick up when the local
breaker is closed.
Note that the minimum setting is 0.04 x In (0.2 A for a 5 A ct). The charging current of a very short line might be
insufficient to operate this element why open breaker condition would be given even when the breaker is closed. In that
case, the 52b contact should be used.
Note that there is
±
20% hysteresis associated with this setting. Open breaker keying will start when the current drops
below 0.8 x IE and will remain so until it increases above 1.2 x IE.
In case OPBK is set to 52B or OUT, this setting is ignored by the system.
Low Set Phase Unit (IPL)
The low set overcurrent units supervise differential trip when ILTS is set IN.
The low set units are also used for tripping during stub bus and open breaker conditions, if these functions are used. To
prevent trip from the stub bus logic during line energizing, the phase IPL unit should be set at 1.5 times the net line
charging current, but must be at least 0.5 A.
Net line charging current is defined as: the steady state net single end line charging phase current, as measured under
balanced conditions (all local poles closed and all remote poles open). Net line charging current indicates the distributed
capacitive current minus any line side shunt reactor current.
High Set Phase Overcurrent Unit (IPH)
This unit is provided in the REL356 system to supplement the current differential protection by providing a non-pilot
direct trip capability for high current faults. The IPH unit should be set above the maximum expected external fault
current with a security margin.
The IPH unit should be set for 1.25 times the maximum through current for an external three phase fault.
The high set overcurrent units can be made directional when FDOP, the phase directional unit, is set to IN, and three
phase voltage is applied to the relay. IPH is then supervised by FDOP.
Low Set Ground Unit (IGL)
The low set ground overcurrent unit supervises differential trip when ILTS is set IN. The low set units are also used for
tripping during stub bus and open breaker conditions, if these functions are used.
Since the effect of charging current is minimum for the ground subsystem, the setting should only allow for inherent
unbalance under normal operation. A minimum setting of 0.5 A is recommended.
High Set Ground Overcurrent Unit (IGH)
The high set ground unit should follow the same guidelines as the high set phase units.
The high set ground overcurrent unit can be made directional when FDOG, the ground directional unit, is set to IN, and
three phase voltage is applied to the relay. IGH is then supervised by FDOG.