Permissive overreaching scheme
In a permissive overreaching scheme there is an overreaching zone that issues the send
signal. At the remote end the received signal together with the start of an overreaching
zone will give an instantaneous trip. The scheme can be used for all line lengths.
In permissive overreaching schemes, the communication channel plays an essential roll to
obtain fast tripping at both ends. Failure of the communication channel may affect the
selectivity and delay the tripping at one end at least, for faults anywhere along the
protected circuit.
Teleprotection, operating in permissive overreaching scheme, must consider besides the
general requirement of fast and secure operation also consider requirement on the
dependability. Inadequate security can cause unwanted tripping for external faults.
Inadequate speed or dependability can cause delayed tripping for internal faults or even
unwanted operations.
This scheme may use virtually any communication media that is not adversely affected by
electrical interference from fault generated noise or by electrical phenomena, such as
lightning. Communication media that uses metallic paths are particularly subjected to this
type of interference, therefore they must be properly shielded or otherwise designed to
provide an adequate communication signal during power system faults.
The send signal (CS) might be issued in parallel both from an overreaching zone and an
underreaching, independent tripping zone. The CS signal from the overreaching zone
must not be prolonged while the CS signal from zone 1 can be prolonged.
To secure correct operations of current reversal logic in case of parallel lines the send
signal CS shall not be prolonged. Set the tSendMin to zero in this case.
There is no need to delay the trip at receipt of the signal, so set the timer tCoord to zero.
Section 16 1MRK 506 369-UUS -
Scheme communication
752 Line distance protection REL670 2.2 ANSI
Application manual
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