Siemens 7SJ82, Manual

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(1) With down integration time
(2) With dropout delay
Measurand, Method of Measurement
The function calculates the peak voltage in a phase-segregated way from the fundamental component and
superimposed harmonics. Integration of the phase currents then yields the voltage. This approach captures
the higher harmonics considerably better since they are transferred better by current transformers than by
voltage transformers.
The peak voltage determined is then set with reference to the rated voltage of the capacitor. The resulting
measurand is Û/V
C-rated
(t). The threshold value for the stage is thus set as a referenced quantity.
The phase-selective peak overvoltages Û/V
C-rated
(t) are available as measured values for display or further
processing.
Pickup, Tripping and Dropout Behavior with the Inverse-Time Characteristic Curve
If the measurand Û/V
C-rated
(t) exceeds 1.045 times the set threshold value (for example, 1.045 × 1.1 ≈ 1.15),
pickup occurs and the inverse-time characteristic curve is then followed. For each input value that exceeds the
pickup value (1.045 × threshold value), the time value T
trip
is calculated. An integrator accumulates the value
1/ T
trip
. When the accumulated integral reaches the fixed value of 1, the stage trips.
If the measurand falls below 1.045 times the set threshold value (pickup value), processing of the character-
istic (accumulation of the time values) stops. In the hysteresis region between the pickup value and dropout
value (95 % of the pickup value, for example, 0.95 × 1.15 = 1.0925), the integral value remains unchanged.
The stage, however, remains in the picked-up state.
Use the parameter
Dropout principle
to select the method for the dropout of the stage:
•
Method with down integration time:
If the measurand falls below the dropout threshold, the pickup drops out immediately. If the value drops
below the pickup threshold, the internal integral value that depends on the selected
Down integra-
tion time
is slowly reduced. The
Down integration time
defines the duration in order to reduce
the internal integral value linear from 100 % to 0 %. The internal integral value is limited to 100 % and is
reached with the tripping function.
•
Method with dropout delay:
If the measurand falls below the dropout threshold, the pickup drops not out immediately. The pickup
remains for the duration of the set
Dropout principle
. The integral value remains frozen during
this time. If the pickup value is not exceeded again during this time, a dropout occurs and the integral
value is reset to 0. If the pickup value is exceeded during this time again, the integrator continues with
the integration of frozen values. The pickup remains active and the
Dropout principle
is reset.
Inverse-Time Characteristic Curve
The characteristic curve is defined by the Standards IEC 60871-1:2005 and IEEE Std 1036-2010, see
Figure 7-32 .
The points on the characteristic curve defined in the standards result from a threshold setting of 1.1.
Threshold values differing from this value shift the characteristic as shown in
Figure 7-32 .
Straight-line segments are implemented between the defined points on semi-logarithmic coordinates.
Capacitor Bank Protection
7.6 Peak Overvoltage Protection for Capacitors
1022 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017