ABB RES670 Applications Manual page 127

1MRK 511 407-UEN C
Phasor measurement unit RES670 2.2 IEC
Application manual
oscillation would be found to be within the zone 1, only a very limited number
of pole-slips would be allowed, usually only one.
• StartAngle: 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 start 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 (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 12, 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.
Section 7
Impedance protection
121