BE1-951
Protection and Control
4-13
Each instantaneous overcurrent function has a pickup and time delay setting. When the measured current
increases above the pickup threshold, the pickup output (PU) becomes TRUE and the timer starts. If the
current stays above pickup for the duration of the time delay setting, the trip output (T) becomes TRUE. If
the current decreases below the dropout ratio, which is 95 percent, the timer is reset to zero.
The phase overcurrent protective functions include three independent comparators and timers, one for each
phase. If the current increases above the pickup setting for any one phase, the pickup output asserts. If the
trip condition is TRUE for any one phase, the trip logic output asserts.
If the target is enabled for the element, the target reporting function will record a target for the appropriate
phase when the protective function trip output is TRUE and the fault recording function trip logic expression
is TRUE. See Section 6,
Reporting and Alarm Functions, Fault Reporting for more information about target
reporting. The overcurrent elements have adaptable targets. If one is set for directional control, it will report
a 67 target (67A, B, C, N or G). If one is set for non-directional control it will report a 50 target.
BESTlogic Settings for Instantaneous Overcurrent Elements
Logic settings for the 50T functions are made using the SL-50T (Settings Logic-50T) command. The settings
of this command enable the 50T functions by connecting them to the CT input circuits and provide blocking
control as determined by the logic expression assigned to the BLK input. The SL-50T command is also used
to define the way the 50TN elements obtain neutral or ground current values. SL-50T command settings are
summarized in Table 4-5.
Table 4-5. SL-50T Command Settings
Function
Range/Purpose
Default
mode
0 = Disabled
1 = Enabled (x50TP and x50TQ)
1 = 3-phase Input Neutral (x50TN only)
G = Ground Input (x50TN only)
1
BLK logic
Logic expression that disables function
when TRUE.
0
SL-50T Command
Purpose:
Read or set logic for instantaneous overcurrent elements.
Syntax:
SL-<x>50T<p>[=<mode>,<BLK logic>]
Comments: x = 1 for 150 or no entry for 50
p = P for Phase or N for Neutral
SL-50T Command Examples.
1.
Read all 50T element settings.
>SL-50TP
SL-50TP=1,0; SL-50TN=1,0; SL-50TQ=1,0
These settings indicate that the 50T phase, neutral, and negative sequence elements are enabled (1)
and have no blocking (0).
2.
Change the 50TN logic so that a ground CT is selected. Block the 50TN function when input 1 is
closed (TRUE).
>SL-50TN=G,IN1
NOTE
If the BE1-951 has 5 ampere phase inputs and a 1 ampere independent ground input,
the valid pickup setting range of the neutral overcurrent functions will depend on the logic
mode setting which designates whether the three-phase residual or the independent
ground input is to be monitored. If changing logic schemes or settings causes a neutral
overcurrent setting to be OUT OF RANGE, the out of range setting will be forced in-
range by multiplying or dividing the current setting by 5.
