ABB REG670 Applications Manual page 286

Section 8
Impedance protection
280
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 (START) 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
tBreaker is known, then it is possible to calculate more exactly 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 tBreaker is
specified (that is, higher than the default 0.0 s, where 0.0 s means that tBreaker is
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 TripAngle.
• 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 tReset since 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
tReset since the start signal has been set (for example a stable case with
synchronism retained), the function is as well reset, which includes the start
output signal (START), which is reset to 0 (FALSE) after tReset interval of time
has elapsed. However, the measurements of analogue quantities such as R, X, P,
Q, and so on continue without interruptions. Recommended setting of tReset is in
the range of 6 to 12 seconds.
• NoOfSlipsZ1: Maximum number of pole slips with centre of electromechanical
oscillation within zone 1 required for a trip. Usually, NoOfSlipsZ1= 1.
• NoOfSlipsZ2: Maximum number of pole slips with centre of electromechanical
oscillation within zone 2 required for a trip. The reason for the existence of two
zones of operation is selectivity, required particularly for successful islanding. If
there are several pole slip (out-of-step) relays in the power system, then
selectivity between relays is obtained by the relay reach (for example zone 1)
rather then by time grading. In a system, as in Table 29, the number of allowed
pole slips in zone 2 can be the same as in zone 1. Recommended value:
NoOfSlipsZ2 = 2 or 3.
• Operation: With the setting Operation OOSPPAM function can be set On/Off.
• OperationZ1: Operation zone 1 On, Off. If OperationZ1 = Off, all pole-slips with
centre of the electromechanical oscillation within zone 1 are ignored. Default
setting = On. More likely to be used is the option to extend zone 1 so that zone 1
even covers zone 2. This feature is activated by the input to extend the zone 1
(EXTZ1).
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
Application manual