The
ImpedanceZB
is the reverse impedance as show in figure
ZB
should be equal
to the generator transient reactance X'd. The impedance is given in % of the base
impedance, see equation
The
ImpedanceZC
is the forward impedance giving the borderline between zone 1 and
zone 2. ZC should be equal to the transformer reactance ZT. The impedance is given in
% of the base impedance, see equation
.
The angle of the impedance line ZB – ZA is given as
AnglePhi
in degrees. This angle
is normally close to 90°.
StartAngle
: An alarm is given when movement of the rotor is detected and the rotor
angle exceeds the angle set for
StartAngle
. The default value 110° is recommended. It
should be checked so that the points in the impedance plane, corresponding to the
chosen
StartAngle
does not interfere with apparent impedance at maximum generator
load.
TripAngle
: If a pole slip has been detected: change of rotor angle corresponding to slip
frequency 0.2 – 8 Hz, the slip line ZA – ZB is crossed and the direction of rotation is
the same as at start, a trip is given when the rotor angle gets below the set
TripAngle
.
The default value 90° is recommended.
N1Limit
: The setting
N1Limit
gives the number of pole slips that should occur before
trip, if the crossing of the slip line ZA – ZB is within zone 1, that is, the node of the
pole slip is within the generator transformer block. The default value 1 is
recommended to minimize the stress on the generator and turbine at out of step
conditions.
N2Limit
: The setting
N2Limit
gives the number of pole slips that should occur before
trip, if the crossing of the slip line ZA – ZB is within zone 2, that is, the node of the
pole slip is in the external network. The default value 3 is recommended give external
protections possibility to split the network and thus limit the system consequencies.
ResetTime
: The setting
ResetTime
gives the time for (PSPPPAM ,78) function to reset
after start when no pole slip been detected. The default value 5s is recommended.
8.16.3.1
Setting example for line application
SEMOD172162-25 v3
In case of out of step conditions this shall be detected and the line between substation 1
and 2 shall be tripped.
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
471
Application manual
Summary of Contents for RELION RET670
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