Siemens siprotec 7SA6 User Manual page 259

Distance protection

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C53000-G1176-C133-1

corresponding protection function picked up. The transmitted signal may be prolonged

(settable in address 6HQG 3URORQJ), to compensate for possible

differences in the pick-up times at the two line ends. The distance protection is set in

such a way that the first zone reaches up to approximately 85 % of the line length. In

three-end lines Z1 is also set to approx. 85 % of the shorter line section, at least,

however, up to the T-point.

The overreach zone Z1B is not relevant for this signal transmission scheme, but it can

be controlled by the automatic reclosure (see also Subsection 6.12.1).

Operation scheme of the permissive underreach transfer trip method via pickup

Figure 6-43 shows the logic diagram of the permissive underreach transfer trip

scheme for one line end.

The permissive transfer trip should only trip for faults in the )RUZDUG direction.

Accordingly, the first zone Z1of the distance protection must definitely be set to

)RUZDUG in address 2S PRGH =, refer also to Subsection 6.2.4.2 under the

margin heading "Independent Zones Z1 up to Z5".

On two terminal lines, the signal transmission may be done phase segregated. On

three end lines, the transmit signal is sent to both opposite line ends. The receive

signals are then combined with an OR logic function. By means of the parameter /LQH

&RQILJ (address ) the device is informed whether it has one or two opposite

If at one line end there is weak or zero infeed, so that the distance protection does not

pick up, the circuit breaker can still be tripped. This "weak-infeed tripping" is referred

to in Section 6.7.

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