ABB RELION REF615R, Technical Manual

Page: 139 / 664

Phase selection logic
If the fault criteria are fulfilled in the level detector, the phase selection logic detects the
phase or phases in which the measured current exceeds the setting. If the phase
information matches the
Num of pickup phases setting, the phase selection logic activates
the timer module.
Timer
Once activated, the timer activates the
PICKUP
output. Depending on the value of the
Operating curve type setting, the time characteristics are according to DT or IDMT. When
the operation timer has reached the value of Trip delay time in the DT mode or the
maximum value defined by the inverse time curve, the
TRIP
output is activated.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the
BLOCK
input and the global setting " Configuration/System/Blocking
mode " which selects the blocking mode. The
BLOCK
input can be controlled by a binary
input, a horizontal communication input or an internal signal of the protection relay's
program. The influence of the
BLOCK
signal activation is preselected with the global
setting Blocking mode .
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
trip timer is frozen to the prevailing value. In the "Block all" mode, the whole function is
blocked and the timers are reset. In the "Block TRIP output" mode, the function operates
normally but the
TRIP
output is not activated.
4.1.2.5 Timer characteristics
51LT supports both DT and IDMT characteristics. The user can select the timer
characteristics with the
Operating curve type and Type of reset curve settings. When the
DT characteristic is selected, it is only affected by the Trip delay time and Reset delay time
settings.
The relay provides 9 IDMT characteristics curves, of which eight comply with the IEEE
C37.112 and one with the IEC 60255-3 standard. In addition to this, a user programmable
curve can be used if none of the standard curves are applicable. The user can choose the
DT characteristic by selecting the
Operating curve type value "Long Definite Time".
Table 87: Timer characteristics supported
Operating curve type 51LT
(1) Long Time Extremely Inverse x
(2) Long Time Very Inverse x
(3) Long Time Inverse x
Table continues on next page
1MRS240050-IB C
Section 4
Protection functions
REF615R 133
Technical Manual