Basler Electric DGC-2020HD User Manual
Page 152
142
9469300990 Rev B
Figure 77. Inverse Overcurrent Table Curve
46 Curve
A 46 Curve is a special curve designed to emulate the I
2
t withstand ratings of generators using what is
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.
To use the 46 curve, the user should determine the K factor of the generator and the continuous (I2)
2
t
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
2
where 1 pu is the relay setting for nominal current.
Voltage Restraint Mode
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.
Source
A Source setting configures an overcurrent element to monitor the voltage at the generator sensing input
terminals or the bus sensing input terminals when voltage restraint is enabled.
Generator Protection
DGC-2020HD