GE D90 Plus - Page 310

300 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
Events
Range: Enabled, Disabled
Default: Enabled
This setting enables and disables the logging of permissive over-reaching transfer trip
(POTT) scheme events in the sequence of events recorder.
The figure shows the POTT scheme logic.
Figure 257: POTT logic
Hybrid permissive over-reaching transfer trip
The hybrid permissive over-reaching transfer trip (hybrid POTT) scheme uses an
overreaching zone 2 distance element to compare the direction to a fault at all terminals
of the line. Ground directional overcurrent functions available in the D90
Plus
can be used in
conjunction with the zone 2 distance element to key the scheme and initiate operation.
This increases the coverage for high resistance faults.
The scheme is intended for three-terminal applications and for weak-infeed conditions. As
a long reach of the overreaching distance element can be required for three-terminal
applications, transient blocking logic is provided for both distance and ground directional
overcurrent elements. An echo feature is available to cope with weak-infeed conditions.
By default, the hybrid POTT scheme uses the reverse-looking zone 4 distance element to
identify reverse faults. Additionally, reverse-looking ground directional overcurrent
functions can be used in conjunction with zone 4.
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