Basler BE1-11m, Instruction Manual, Page: 88 / 610

14-4 9424200996
Inverse Overcurrent (51) Protection BE1-11 m
elements to annunciate the condition, control other elements in logic, and start the fault recorder (logic
element FAULTTRIG).
Assertion of the Pickup output initiates a timer that begins timing to a trip. The duration of the timer is
established by the Time Dial and Curve settings. A Time Dial setting of zero (0) makes the 51 element
instantaneous with no intentional time delay.
If the pickup condition subsides before the calculated inverse time expires, the timer and Pickup outputs
are reset, no corrective action is taken, and the element is rearmed for any other occurrences of
overcurrent.
Trip
The Trip output becomes true if an overcurrent pickup condition persists for the duration of the calculated
inverse time. In BESTlogic
Plus
, the Trip output can be connected to other logic elements and to a
physical relay output to annunciate the condition and to initiate corrective action. If a target is enabled for
the element, the BE1-11 m will record a target when the Trip output becomes true. See the Fault
Reporting
chapter for more information about target reporting.
Voltage Restraint Mode (51/27R)
When a 51 element is set for 3 Phase, IA, IB, or IC mode, the 51 element can be set for voltage control or
voltage restraint mode of operation. This feature is used to allow increased phase overcurrent sensitivity
while providing security from operation due to load current.
A Voltage Restraint threshold of zero (0) disables voltage restraint/control and allows the 51 element to
operate normally.
Note
BE1-11 m protection systems enabled for IEC-61850 communication
(style Mxxxx5xxxxxxxx) do not allow voltage controlled or restrained
overcurrent elements. Blocking a 51 with an Undervoltage (27)
element may allow control pending application requirements.
Control Mode
When set for Control mode of operation, the 51 element is disabled until the measured voltage drops
below the Voltage Restraint threshold. Thus, as long as the voltage on the appropriate phase is above the
Voltage Restraint threshold, the 51 element will be blocked. When set for this mode of operation, the 51
Pickup setting is typically set near or below load current levels.
Restraint Mode
When set for Restraint mode of operation, the pickup of the 51 element is adjusted based upon the
magnitude of the measured voltage. Figure 14-2 shows how the 51 Pickup setting is adjusted in response
to the measured voltage level. Equation 14-3 determines the pickup level for the 51 element when the
measured voltage is between 25% and 100% of the Voltage Restraint threshold. Below 25%, the pickup
level stays at 25%. Above 100%, the pickup level stays at 100%. For example, if the Voltage Restraint
threshold is set for 120 V and the measured voltage on the appropriate phase is 100 V (83% of the
Voltage Restraint threshold), the phase overcurrent pickup level will be reduced to 83% of its setting.
When set for this mode of operation, the 51 element Pickup setting is typically set above worst case, load
current levels.