5-402
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS
CHAPTER 5: SETTINGS
5
The dead time for the initial reclose operation is determined by the
AR 1-P DEAD TIME
,
AR 3-P DEAD TIME 1
, or
AR 3-P DEAD
TIME 2
setting, depending on the fault type and the mode selected. After the dead time interval the scheme asserts the
AR
CLOSE BKR 1
or
AR CLOSE BKR 2
operands, as determined by the sequence selected. These operands are latched until the
breaker closes or the scheme goes to Reset or Lockout.
There are three initiate programs: single pole initiate, three pole initiate, and three pole time delay initiate. Any of these
reclose initiate signals start the reclose cycle and set the reclose-in-progress (
AR RIP
) operand. The reclose-in-progress
operand is sealed-in until the Lockout or Reset signal appears.
The three-pole initiate and three-pole time delay initiate signals are latched until the
AR CLOSE BKR1
,
AR CLOSE BKR2
, Lockout,
or Reset signal appears.
Autoreclose pause
The pause input offers the possibility of freezing the autoreclose cycle until the pause signal disappears. This can be done
when a trip occurs and simultaneously or previously, some conditions are detected such as out-of step or loss of guard
frequency, or a remote transfer trip signal is received. The pause signal freezes all four dead timers. When the ‘pause’
signal disappears the autoreclose cycle is resumed by continuing the shot timer it was left at when paused.
This feature can be also used when a transformer is tapped from the protected line and a reclose is not wanted until the
transformer is removed from the line. In this case, the reclose scheme is "paused" until the transformer is disconnected.
The
AR PAUSE
input forces a three-pole trip through the
3-P DEADTIME 2
path.
Evolving faults
1.25 cycles after the single pole dead time has been initiated, the
AR FORCE 3P TRIP
operand is set and later resets only when
the scheme is reset or goes to Lockout. This approach ensures that when a fault on one phase evolves to include another
phase during the single pole dead time of the auto-recloser the scheme forces a three-pole trip and reclose.
Reclosing scheme operation for one breaker
•
Permanent Fault
— Consider Mode 1, which calls for 1-Pole or 3-Pole Time Delay 1 for the first reclosure and 3-Pole
Time Delay 2 for the second reclosure, and assume a permanent fault on the line. Also assume the scheme is in the
Reset state. For the first single-phase fault the
AR 1-P DEAD TIME
timer is started, while for the first multi-phase fault
the
AR 3-P DEAD TIME 1
timer is started. If the
AR 3P TD INIT
signal is high, the
AR 3-P DEAD TIME 2
starts for the first shot.
If
AR MAX NO OF SHOTS
is set to “1”, upon the first reclose the shot counter is set to 1. Upon reclosing, the fault is again
detected by protection and reclose is initiated. The breaker is tripped three-pole through the
AR SHOT COUNT >0
operand
that sets the
AR FORCE 3P
operand. Because the shot counter has reached the maximum number of shots permitted,
the scheme is sent to the Lockout state.
If
AR MAX NO OF SHOTS
is set to “2”, upon the first reclose the shot counter is set to 1. Upon reclosing, the fault is again
detected by protection and reclose is initiated. The breaker is tripped three-pole through the
AR SHOT COUNT >0
operand
that sets the
AR FORCE 3P
operand. After the second reclose, the shot counter is set to 2. Upon reclosing, the fault is
again detected by protection, the breaker is tripped three-pole, and reclose is initiated again. Because the shot
counter has reached the maximum number of shots permitted, the scheme is sent to the lockout state.
•
Transient Fault
— When a reclose output signal is sent to close the breaker, the reset timer is started. If the reclosure
sequence is successful (there is no initiating signal and the breaker is closed), the reset timer times out, returning the
scheme to the reset state with the shot counter set to "0" and making it ready for a new reclose cycle.
Reclosing scheme operation for two breakers
•
Permanent Fault
— The general method of operation is the same as that outlined for the one breaker applications
except for the following description, which assumes
AR BKR SEQUENCE
is “1-2” (reclose Breaker 1 before Breaker 2). The
signal output from the dead time timers passes through the breaker selection logic to initiate reclosing of Breaker 1.
The Close Breaker 1 signal initiates the Transfer Timer. After the reclose of the first breaker, the fault is again detected
by the protection, the breaker is tripped three pole and the autoreclose scheme is initiated. The Initiate signal then
stops the transfer timer. After the 3-P dead time times out, the Close Breaker 1 signal closes the first breaker again
and starts the transfer timer. Since the fault is permanent, the protection trips again initiating the autoreclose scheme
that is sent to Lockout by the SHOT COUNT = MAX signal.
