Siemens SIPROTEC 4 7UT6 Series, Руководство пользователя

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User-defined Characteristics
When user-defined curves are utilised, the tripping curve may be defined point by point. Up to 20 pairs of
values (current, time) may be entered. The device then approximates the characteristics by linear interpola-
tion.
If required, the dropout characteristic can also be defined (see function description for “Dropout”. If no user-
configurable dropout characteristic is desired, dropout is initiated when approx. a 95 % of the pickup value is
undershot; when a new pickup is evoked, the timer starts again at zero.
Manual Close Command
When a circuit breaker is closed onto a faulted protective object, a high speed re-trip by the breaker is often
desired. The manual closing feature is designed to remove the delay from one of the time overcurrent stages
when the breaker is manually closed onto a fault. The time delay is then bypassed via an impulse from the
external control switch. This pulse is prolonged by at least 300 ms. To enable the device to react properly on
occurrence of a fault, address 3808A
IE MAN. CLOSE
have to be set accordingly.
Processing of the manual close command can be executed for each measuring location or side. Manual close
signal is also generated when an internal control command is given to a breaker which is assigned to the same
protection function as the time earth overcurrent protection, in the Power System Data 1 (see Section
2.1.4 Power System Data 1 ).
Strict attention must be paid that the manual close condition is derived from that circuit breaker which feeds
the object that is protected by the earth overcurrent protection!
Dynamic Cold Load Pickup
Dynamic changeover of pickup values is available also for time overcurrent protection for earth current as it is
for the time overcurrent protection for phase currents and zero sequence current. Processing of the dynamic
cold load pickup conditions is the same for all time overcurrent stages, and is explained in Section
2.6 Dynamic Cold Load Pickup for Time Overcurrent Protection .
The alternative values themselves are individually set for each of the stages.
Inrush Restraint
Earth current time overcurrent protection provides an integrated inrush restraint function which blocks the
overcurrent stages IE> or IEp.
If the second harmonic content of the earth current exceeds a selectable threshold, tripping is blocked.
The inrush stabilisation has an upper limit: If a certain (adjustable) current value is exceeded, it will not be
effective any more, since it must then be an internal current-intensive short-circuit. The lower limit is the oper-
ating limit of the harmonic filter (0.1
Ι
N
).
2.5.4
2.5.5
2.5.6
Functions
2.5 Time Overcurrent Protection for Earth Current
SIPROTEC 4, 7UT6x, Manual 165
C53000-G1176-C230-5, Edition 09.2016