ABB REL300 Instruction Manual page 53

VALUE MEANING
OUT No CIFT or SBP selected
CF Standard CIFT, without timer; No SBP
CFT Modified CIFT, with timer; No SBP
STUB SBP logic; No CIFT
SCF SBP plus standard CIFT
SCFT SBP plus modified CIFT
The CIFT logic employs low voltage sensing functions LVA, LVB, and LVC, which deliver a log-
ic one when the particular phase-ground voltage is below the LV setting, adjustable from 40 to
60 volts in one volt increments. Current sensors are also employed, IAL, IBL, and ICL, which
deliver a logic one if the particular phase current is above the IL setting. Additional current sens-
ing of 3I0 greater than the IOM setting is also employed. In the standard logic, for 180 msec
after the breaker is closed (52b opens), simultaneous low voltage and current sensing for 16
msec, implying a closure into a fault, produces a CIF trip via OR-22B and OR-3, and reclose
blocking (RB). A CIF target will appear on the relay fault record and display.
Stub-Bus protection employs the 89b switch from an open line disconnect, in conjunction with
the CIFT current sensing functions, to high-speed trip on overcurrent only, for faults on the stub
between the current transformers and open disconnect. This is to compensate for the lack of
the potential source, connected on the line side of the disconnect. Operation is independent of
the operation of the breaker(s) and the line voltage condition. Tripping, reclose blocking and
targeting are the same as for CIFT.
The modified CIFT logic is employed for the special application shown in Figure 3-15b. Two
relays, looking in opposite directions, control a single breaker and share a common 52b input
and a common set of voltage transformers, located on one side of the breaker. Each relay trips
the main breaker and the load breaker on the power transformer secondary, for faults on the
line section being protected. The standard CIFT logic was found to produce false tripping of
one of the load breakers upon reclosing after a successful initial trip, if the fault still persisted.
This was due to "arming" of the CIFT logic by the common 52b, in the relay which did not trip
for the initial fault.
The 200/0 msec timer delays the sensing of low voltage and momentarily disables the CIFT
function during the reclose situation. this timer was selected to be greater than the 180 msec
reset time of the 52b, but less than the minimum reclose dead time. For this logic to work prop-
erly, the following application rules apply:
1) For the relay with bus-side potential , that is cts and vts on the same side of the breaker (Re-
lay 1) , set CIF to OUT. With bus-side potential, CIF logic is not needed and may misoperate
for some situations if enabled.
2) For the relay with line-side potential , that is cts and vts on opposite sides of the breaker
(Relay 2) , set CIF to CFT . Also be sure that the minimum reclose dead time is greater than
I.L. 40-385.7
3-9