Basler BE1-11g Instruction Manual page 120

108 9424200994 Rev U
46 Curve
The 46 curve is a special curve designed to emulate the I t withstand ratings of generators using what is
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frequently referred to as the generator's K factor. Do not confuse the 46 curve with the I2 mode. The 46
curve was designed for use with the I2 mode. However, in actuality, the 46 curve can be selected for use
with any mode of the inverse overcurrent element as well.
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To use the 46 curve, the user should determine the K factor of the generator and the continuous (I ) t
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rating of the generator (supplied by the manufacturer) and use this to set the time dial and pickup for the
46 curve by the process described in the Time Curve Characteristics chapter. The K factor is the time the
generator can withstand 1 per unit I where 1 pu is the BE1-11g setting for nominal current.
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Pickup and Trip
The Pickup output occurs first, followed by the Trip output.
Pickup
The Pickup output becomes true when the measured current increases above the current threshold
established by the Pickup setting. In BESTlogicPlus, the Pickup output can be connected to other logic
elements to annunciate the condition, control other elements in logic, or 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 BESTlogicPlus, the Trip output can be connected to other logic elements and to a
physical relay output to annunciate the condition and initiate corrective action. If a target is enabled for the
element, the BE1-11g 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. This feature is also often used for generator
backup protection to ensure delayed tripping during a short-circuit where the fault current contribution
from the generator falls to a value close to the full-load rating of the generator.
A Voltage Restraint threshold of zero (0) disables voltage restraint/control and allows the 51 element to
operate normally.
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 67 shows how the 51 Pickup setting is adjusted in response
to the measured voltage level. Equation 16 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
Inverse Overcurrent (51) Protection BE1-11g