2 PHASE FAULT OVERCURRENT PROTECTION
Phase fault overcurrent protection is provided as a form of back-up protection that could be:
● P
ermanently disabled
● Permanently enabled
● Enabled only in case of VT fuse/MCB failure
● Enabled only in case of protection communication channel failure
● Enabled if VT fuse/MCB or protection communication channel fail
● Enabled if VT fuse/MCB and protection communication channel fail
In addition, each stage may be disabled by a DDB signal.
It should be noted that phase overcurrent protection is phase segregated, but the operation of any phase is
mapped to 3 phase tripping in the default PSL.
The VTS element of the IED can be selected to either block the directional element or simply remove the directional
control.
2.1 POC IMPLEMENTATION
Phase Overcurrent Protection is configured in the OVERCURRENT column of the relevant settings group.
The pr
oduct provides four stages of three-phase overcurrent protection, each with independent time delay
characteristics. The settings are independent for each stage, but for each stage, the settings apply to all phases.
Stages 1 and 2 provide a choice of operate and reset characteristics, where you can select between:
● A range of IDMT (Inverse Definite Minimum Time) curves based on IEC and IEEE standards
● A range of programmable user-defined curves
● DT (Definite Time) characteristic
This is achieved using the cells:
● I>(n) Function for the overcurrent operate characteristic
● I>(n) Reset Char for the overcurrent reset characteristic
● I>(n) Usr Rst Char for the reset characteristic for user-defined curves
where (n) is the number of the stage.
The IDMT-equipped stages, (1 and 2) also provide a Timer Hold facility. This is configured using the cells I>(n)
tReset, where (n) is the number of the stage. This does not apply to IEEE curves.
Stages 3 and 4 have definite time characteristics only.
2.2 DIRECTIONAL ELEMENT
If fault current can flow in both directions through a protected location, you will need to use a directional
ov
ercurrent element to determine the direction of the fault. Once the direction has been determined the device
can decide whether to allow tripping or to block tripping. To determine the direction of a phase overcurrent fault,
the device must compare the phase angle of the fault current with that of a known reference quantity. The phase
angle of this known reference quantity must be independent of the faulted phase. Typically this will be the line
voltage between the other two phases.
The phase fault elements of the IEDs are internally polarized by the quadrature phase-phase voltages, as shown in
the table below:
Phase of protection Operate current Polarizing voltage
A Phase IA VBC
Chapter 9 - Current Protection Functions P54A/B/C/E
196 P54xMED-TM-EN-1
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