ABB RELION RET670, Applications Manual

Page: 493 / 1016

• 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 pickup signal has been set (for example a stable case with
synchronism retained), the function is as well reset, which includes the pickup
output signal (
PICKUP
), 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
36 , 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 Enabled , Disabled . If OperationZ1 = Disabled , all
pole-slips with centre of the electromagnetic oscillation within zone 1 are ignored.
Default setting =
Enabled . 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).
• OperationZ2 : Operation zone 2 Enabled , Disabled . If OperationZ1 = Disabled , all
pole-slips with centre of the electromagnetic oscillation within zone 2 are ignored.
Default setting =
Enabled .
• tBreaker : Circuit breaker opening time. Use the default value tBreaker = 0.000 s if
unknown. If the value is known, then a value higher than 0.000 is specified, for
example
tBreaker = 0.040 s : the out-of-step function gives a trip command
approximately 0.040 seconds before the currents reach their minimum value. This
in order to decrease the stress imposed to the circuit breaker.
• VBase : This is the voltage at the point where the Out-of-step protection is
installed. If the protection is installed on the generator output terminals, then
VBase is the nominal (rated) phase to phase voltage of the protected generator. All
the resistances and reactances are measured and displayed referred to voltage
VBase . Observe that ReverseX , ForwardX , ReverseR , and ForwardR must be
given referred to VBase.IBase is the protected generator nominal (rated) current, if
the Out-of-step protection belongs to a generator protection scheme.
• InvertCTCurr : If the currents fed to the Out-of-step protection are measured on the
protected generator neutral side (LV-side) then inversion is not necessary
(
InvertCTCurr = Disabled ), provided that the CT’s orientation complies with ABB
recommendations, as shown in Table 36 . If the currents fed to the Out-of-step
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 487
Application manual