ABB Relion 670 Series Applications Manual page 121

1MRK 511 407-UUS Rev. J
particular with islanding. But for the two machine model as in Table 12, the most probable
scenario is that only one line is in service after the fault on one power line has been cleared by
line protections. The settings
reactance and resistance of only one power line.
• All the reactances and resistances must be referred to the voltage level where the Out-of-step
relay is installed; for the example case shown in Table 12, this is the generator nominal voltage
VBase = 13.8 kV. This affects all the forward reactances and resistances in Table 12.
• All reactances and resistances must be finally expressed in percent of ZBase, where ZBase is
for the example shown in Table
Observe that the power transformer's base impedance is different, ZBase = 0.6348 Ω.
Observe that this latter power transformer ZBase = 0.6348 Ω must be used when the power
transformer reactance and resistance are transformed.
• For the synchronous machines as the generator in Table 12, the transient reactance Xd' shall
be used. This due to the relatively slow electromechanical oscillations under out-of-step
conditions.
• Sometimes the equivalent resistance of the generator is difficult to get. A good estimate is 1
percent of transient reactance Xd'. No great error is done if this resistance is set to zero (0).
• Inclination of the Z-line, connecting points SE and RE, against the real (R) axis can be
calculated as arctan ((
Table
Other settings:
ReachZ1 : Determines the reach of the zone 1 in the forward direction. Determines the position
•
of the X-line which delimits zone 1 from zone 2. Set in % of
Table 12, where the reactance of the step-up power transformer is 11.32 % of the total
ForwardX , the setting ReachZ1 should be set to ReachZ1 = 12 %. This means that the
generator – step-up transformer unit would be in the zone 1. In other words, if the centre of
oscillation would be found to be within the zone 1, only a very limited number of pole-slips
would be allowed, usually only one.
pick up Angle : Angle between the two equivalent rotors induced voltages (that is, the angle
•
between the two internal induced voltages E1 and E2 in an equivalent simplified two-machine
system) to get the pickup signal, in degrees. The width of the lens characteristic is
determined by the value of this setting. Whenever the complex impedance Z(R, X) enters the
lens, this is a sign of instability. The angle recommended is 110 or 120 degrees, because it is at
this rotor angle where problems with dynamic stability usually begin. Power angle 120 degrees
is sometimes called "the angle of no return" because if this angle is reached under generator
swings, the generator is most likely to lose synchronism. When the complex impedance Z(R, X)
enters the lens the start output signal (PICKUP) is set to 1 (TRUE).
TripAngle : The setting TripAngle specifies the value of the rotor angle where the trip
•
command is sent to the circuit breaker in order to minimize the stress to which the breaker is
exposed when breaking the currents. The range of this value is from 15° to 90°, with higher
values suitable for longer breaker opening times. If a breaker opening is initiated at for
example 60°, then the circuit breaker opens its contacts closer to 0°, where the currents are
smaller. If the breaker opening time
precisely when opening must be initiated in order to open the circuit breaker contacts as
close as possible to 0°, where the currents are smallest. If the breaker opening time
is specified (that is, higher than the default 0.0 s, where 0.0 s means that
unknown), then this alternative way to determine the moment when a command to open the
breaker is sent, is automatically chosen instead of the more approximate method, based on
the
tReset : Interval of time since the last pole-slip detected, when the Out-of-step protection is
•
reset. If there is no more pole slips detected under the time interval specified by
the previous one, the function is reset. All outputs are set to 0 (FALSE). If no pole slip at all is
detected under interval of time specified by
Phasor measurement unit RES670
Application manual
ReverseX + ForwardX ) / ( ReverseR + ForwardR )), and is for the case in
12 equal to 84.55 degrees, which is a typical value.
TripAngle .
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ForwardX , ForwardR must therefore take into account the
12 the base impedance of the generator, ZBase = 0.9522 Ω.
tBreaker is known, then it is possible to calculate more
tReset since the pickup signal has been set (for
Impedance protection
ForwardX . In the case shown in
tBreaker is
tReset since
Section 7
tBreaker
115