ABB REC670 Applications Manual page 215

1MRK 511 401-UUS A
Bay control REC670 2.2 ANSI
Application manual
t2: Time delay of the back-up trip. The choice of this setting is made as short as
possible at the same time as unwanted operation must be avoided. Typical setting is 90
– 200ms (also dependent of re-trip timer).
The minimum time delay for the re-trip can be estimated as:
³ + +
t 2 t 1 t t
cbopen BFP reset _
EQUATION1430 V1 EN-US
where:
t is the maximum opening time for the circuit breaker
cbopen
t is the maximum time for breaker failure protection to detect correct breaker function (the
BFP_reset
current criteria reset)
t is a safety margin
margin
It is often required that the total fault clearance time shall be less than a given critical
time. This time is often dependent of the ability to maintain transient stability in case
of a fault close to a power plant.
Protection
operate time
Normal t
The fault Retrip delay t1
occurs
Trip and Pickup
CCRBRF
(50BF)
ANSI05000479 V3 EN-US
Figure 84: Time sequence
+
t
margin
cbopen
t after re-trip
cbopen
t
BFPreset
Minimum back-up trip delay t2
Critical fault clearance time for stability
Section 8
Current protection
(Equation 62)
Margin
Time
ANSI05000479_3_en.vsd
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