Distance Protection; Earth Fault Recognition; Method Of Operation - Siemens siprotec 7SA6 User Manual

Distance protection

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Distance Protection

Earth Current 3·I

Distance protection is the main function of the device. It is characterized by high

measuring accuracy and the ability to adapt to the given system conditions. It is

supplemented by a number of additional functions.

Recognition of an earth fault is an important element in identifying the type of fault, as

the determination of the valid loops for measurement of the fault distance and the

shape of the distance zone characteristics substantially depend on whether the fault

at hand is an earth fault or not. The 7SA6 has a stabilised earth current measurement,

a zero sequence current/negative sequence current comparison as well as a

displacement voltage measurement. Furthermore, special measures are taken to

avoid a pickup for low-current earth faults in an isolated or resonant-earthed system.

For earth current measurement, the fundamental sum of the numerically filtered phase

is monitored to detect if it exceeds the set value (parameter ,!

currents 3·I

7KUHVKROG, address ). It is stabilized against over-operation resulting from

unsymmetrical operating currents and error currents in the secondary circuits of the

current transformers due to different degrees of current transformer saturation during

short-circuits without earth: the actual pick-up threshold automatically increases as the

phase current increases (Figure 6-15). The reset value is approximately 95 % relative

to the pick-up value.

Earth current stage: pick-up characteristic — example

C53000-G1176-C133-1

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