Basic Schemes - GE MiCOM P40 Agile Technical Manual

P543i/P545i
3

BASIC SCHEMES

Basic Scheme operation is always executed if distance elements are enabled. It is the process by which the
measured line impedance is compared against the Distance measuring zone configuration (reach settings and
timers). Instantaneous or time delayed tripping or blocking signals may be issued for a specific zone according to
its settings and the measured impedance values.
There are six basic scheme zones; Zone 1, Zone 2, Zone 3, Zone 4, Zone P and Zone Q.
The Basic Scheme settings include:
A mode setting, which is common to all zones
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Zone Tripping settings for each zone
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Zone phase delay settings for each zone
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Zone ground delay settings for each zone
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On a per-zone basis, phase and earth-fault elements may be set to have different time delays.
To supplement Basic Scheme operation, there are also standalone scheme designs (Non-Aided Distance Schemes)
that provide timely clearance for particular fault scenarios where carrier aided signalling is either not available, or
is unnecessary. These scenarios cover Trip on Closure (including Switch On to Fault, and Trip on Reclose), Loss of
Load, and Zone1 Extension.
The Basic Scheme is continually executed, regardless of any carrier-aided acceleration schemes which may be
enabled.
3.1 BASIC SCHEME MODES
The operation of distance zones according to their set time delays is called the basic scheme. The basic scheme
always runs, regardless of any channel-aided acceleration schemes which may be enabled.
The BasicScheme Mode setting defines how the timers associated with the different Distance zones in the Basic
Scheme are initiated by pick up (start) of zone elements.
In Standard mode, a zone timer starts only when the corresponding distance zone start occurs.
In Alternative mode, if a condition causes any of the enabled Distance elements to start, then the Any
Distance Start DDB signal is asserted. This starts the timers associated with all enabled zones (phase zone timers
and earth zone timers are started). The timers are reset if the Any Distance Start signal resets. If a Distance zone
measuring element is picked up when its associated zone timer times-out, a trip is issued for that zone element.
The Alternative mode is especially suitable for evolving faults, since all zone timers will be initiated at initial
fault inception, rather than waiting to start a timer as additional phases become faulted. This minimises the overall
fault clearance time as the fault develops.
The two modes are described by the following logic diagrams.
P54x1i-TM-EN-1
Chapter 9 - Non-Aided Schemes
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