4-18
Protection and Control
BE1-951
Actual Pickup Level
sensing voltage level
restraint pickup setting
X 51P pickup setting
=
Equation 4-1. Restraint Pickup Level
Note: For single sensing, the un-monitored phase is not restrained or controlled. These phases are marked
in the table by NA.
When single-phase voltage sensing is used, only the overcurrent element on the phase with voltage
magnitude information is affected by the 51/27R feature. Thus, in voltage control mode, the 51 elements on
the two unmonitored phases will always be disabled. In voltage restraint mode, the 51 elements on the two
unmonitored phases will not have their overcurrent pickup settings adjusted from 100%.
The VT fuse loss detection function (60FL) can also be set to supervise the 51/27R function. It is possible
to set the 60FL function to automatically prevent misoperation on loss of sensing voltage. When the 51/27R
function is set for control, and a 60FL condition is detected, the phase overcurrent elements will be disabled.
When the 51/27R function is set for restraint, and a 60FL condition is detected, the phase overcurrent
elements will remain enabled but the pickup will not be adjusted from 100% of its setting. See the paragraph
titled Voltage Transformer Fuse Loss Detection later in this section for more information.
Setting Voltage Restraint and Control for Phase Time Overcurrent Function
The operational settings for the voltage restraint/control are shown in Table 4-10. These settings are made
through the ASCII command interface using the S<g>-27R command. Settings can also be made through
the front panel HMI using screen 5.2.6.5.
Table 4-10. Voltage Restraint/Control Operating Settings
Setting
Range
Increment
Unit of
Measure
Default
Pickup
30 to 250, 0 = disable
0.1 for 30 to 99, 1.0 for 100 to 250
volts
0
Mode
C (control), R (restraint)
N/A
N/A
R
Control or restraint operation is determined by the S<g>-27R command.
S<g>-27R Command
Purpose:
Reads or sets the restraint/control pickup level and operating mode.
Syntax:
S<g>-27R[=<Pickup>,<Mode>]
Comments:
g = setting group 0, 1, 2, or 3. Command settings are described in the following
paragraphs. See Table 4-10 for S<g>-27R Settings Information.
Pickup Setting (pu). A setting of zero disables voltage restraint/control and allows the 51P time-overcurrent
function to operate normally. When voltage restraint or control is desired, the pickup value can be set over
a range of 30 to 250 volts.
Mode Setting (mode). Two mode settings are available: (R)Restraint and (C)Control.
Restraint (R). In restraint mode, the 51P pickup level is reduced linearly when the sensing voltage
decreases below the restraint pickup level. The 51P pickup level is determined by Equation 4-1.
Control (C). In Control Mode, pickup level is as selected by the 27R pickup setting.
Programmable Curves
Time-current characteristics for trip and reset programmable curves are defined by Equation 4-2 and
Equation 4-3 respectively. These equations comply with IEEE standard C37.112-1996. The curve specific
coefficients are defined for the standard curves as listed in Appendix A, Time-Current Characteristics. When
time current characteristic curve P is selected, the coefficients used in the equation are those defined by the
user. Definitions for these equations are provided in Table 4-11.
