ABB Relion 670 Series Applications Manual page 177

1MRK 511 358-UUS A
faults in these systems it is necessary to measure the residual current separately. Also in
effectively grounded systems the setting of the ground-fault current protection can be chosen to
relatively low current level. The
in accordance to the setting of the sensitive ground-fault protection. The setting can be given
within the range 2 – 200 % of
t1 : Time delay of the re-trip. The setting can be given within the range 0 – 60s in steps of 0.001 s.
Typical setting is 0 – 50ms.
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
EQUATION1430 V1 EN-US
where:
t
cbopen
t
BFP_reset
t
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.
Application manual
BuTripMode is set 1 out of 4 . The current setting should be chosen
IBase .
+ +
t t t
cbopen BFP reset _ margin
is the maximum opening time for the circuit breaker
is the maximum time for breaker failure protection to detect correct breaker function
(the current criteria reset)
is a safety margin
Section 7
Current protection
(Equation 62)
171