Siemens siprotec 7SA522 User Manual

2 Functions
294
7SA522 Manual
C53000-G1176-C155-3
2.17 Fault locator
The measurement of the distance to a fault is an important supplement to the protec-
tion functions. Availability of the line for power transmission within the system can be
increased when the fault is located and cleared faster.
2.17.1 Functional Description
Initiation Condi-
tions
The fault location function in the 7SA522 distance protection is a function which is in-
dependent of the distance measurement. It has a separate measured value memory
and dedicated filter algorithms. The short-circuit protection merely has to provide a
start command to allow the selection of the valid measuring loop and the best suited
time interval for the storage of the measured signals.
The fault location function can be triggered by the trip command of the short-circuit
protection, or also by each fault detection. In the latter case, a fault location calculation
is also possible if a different protection device clears the fault. For a fault outside the
protected line, the fault location information is not always correct, as the measured
values can be distorted by e.g. intermediate infeeds.
Determination of
the Fault Location
The measured value pairs of fault currents and fault voltages (in intervals of 1/20
period) are stored in a cyclic buffer and frozen shortly after the trip command is issued
before any distortion of the measured values occurs due to the opening of the circuit
breaker even with very fast circuit breakers. Filtering of the measured values and the
number of impedance calculations are automatically adapted to the number of stabi-
lized measured value pairs in the determined data window. If a sufficient data window
with stabilized values could not be determined, the alarm ´)OW/RFLQYDOLGµ is
issued.
The evaluation of the measured values in the short-circuit loops is carried out after the
short-circuit has been cleared. Short-circuit loops are those which caused the trip. In
the event of tripping by the earth fault protection, the three phase–earth loops are eval-
uated.
At least three result pairs of R and X are calculated from the stored and filtered mea-
sured quantities in accordance with the line equations. Average and standard devia-
tions are calculated from the result pairs. After elimination of “deviants”, which are rec-
ognized by their large deviation from the standard deviation, a new average is
calculated. This average for X is the fault reactance which is proportional to the dis-
tance to fault. If several loops were evaluated, the loop with the smallest reactance is
valid. In this manner, the fault on the protected feeder is in any event determined
during multiple faults or in the event of tripping by only the earth fault protection.
Output of the Fault
Location
The fault location function issues the following results:
• the short-circuit loop which was used to determine the fault reactance,
• the reactance X per phase in Ω primary and Ω secondary,
• the resistance R per phase in Ω primary and Ω secondary,
• the distance to fault d in kilometres or miles of the line proportional to the reactance,
converted on the basis of the set line reactance per unit line length,
• the distance to fault d in % of the line length, calculated on the basis of the set re-
actance per unit length and the set line length.

Siemens siprotec 7SA522 Specifications

General

Brand	Siemens
Model	siprotec 7SA522
Category	Protection Device
Language	English