4-36
Protection and Control
BE1-951
Figure 4-19. Typical 81 Element
S<g>-32 Command
Purpose:
Read or set the directional over power pickup level, time delay, and forward/reverse
direction.
Syntax:
S<g>-32[=<pu>,<td>,<mode>]
Comments:
g = setting group 0 or 1. Use # as a wildcard to read or change all groups.
FREQUENCY PROTECTION
BE1-951 frequency protection consists of six independent elements
that can be programmed for underfrequency or overfrequency
protection. Each element has an adjustable frequency setpoint and
time delay. The 81 elements share a common undervoltage inhibit
setting. An over/underfrequency element is shown in Figure 4-19.
Power system frequency is measured on the A phase voltage input
for four-wire or single-phase connections, or the AB voltage input
when in three-wire mode. Power system frequency is measured on
the optional auxiliary voltage input as well. When the applied
voltage is greater than 10 volts, the BE1-951 measures the
frequency. The measured frequency is the average of two cycles of
measurement.
Frequency element designations are 81, 181, 281, 381, 481, and 581. Each of the six elements have
identical inputs, outputs, and setting provisions. Figure 4-16 illustrates the inputs and output of a frequency
element. A trip output (x81T) is provided on each element. The trip output becomes TRUE when the
monitored frequency decreases below (81U) or increases above (81O) the pickup setting and the element
timer times out.
The Block (BLK) input is used to disable protection. A BESTlogic expression is used to define how the BLK
input functions. When this expression is TRUE, the element is disabled by forcing the outputs to logic 0 and
resetting the timer. This feature functions in a similar way to the torque control contact of an
electromechanical relay.
An element is enabled or disabled by the Mode input. Three mode options are possible. Mode 0 disables
protection, mode 1 enable the element to monitor the frequency on VTP input mode x enables the element
to monitor the frequency on the VTX input. Security of your load shedding scheme can be enhanced by
monitoring two independent VT circuits. See section 8,
Application tips for more information. More
information about logic mode selections is provided in the following
BESTlogic Settings for Underfrequency
and Overfrequency Elements paragraphs.
Pickup settings define the frequency setpoint and time delay, and program the element for underfrequency
or overfrequency protection. The frequency setpoint defines the value of frequency that will initiate action
by an element. The time delay setting determines how long it takes for the trip output to become TRUE once
the measured frequency reaches the frequency setpoint. If three consecutive cycles of the measured
frequency have either decreased (81U) below or increased (81O) above the pickup threshold, and the timer
has timed out, then the 81T will trip. If the timer has not timed out and the frequency remains in the pickup
range for the remainder of the time delay, the 81T will trip. If the monitored voltage decreases below the
user-defined setpoint, frequency protection is inhibited.
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.
BESTlogic Settings for Under/Overfrequency Elements
Logic settings for the 81 functions are made using the SL-81 (settings logic–frequency) command. The
settings of this command enable the elements by connecting them to the VT circuits and provide blocking
Содержание BE1-951
Страница 157: ...BESTlogic Programmable Logic BE1 951 7 2 Figure 7 1 BESTlogic Function Blocks Courtesy of NationalSwitchgear com...
Страница 238: ...BE1 951 Human Machine Interface 10 5 Figure 10 5 Metering Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 239: ...10 6 Human Machine Interface BE1 951 Figure 10 6 Reports Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 270: ...12 2 Installation BE1 951 Figure 12 1 BE1 951 S1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 274: ...12 6 Installation BE1 951 Figure 12 5 BE1 951 H1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 283: ...BE1 951 Installation 12 15 Figure 12 16 Typical AC Connections Courtesy of NationalSwitchgear com...
Страница 394: ...A 18 Appendix BE1 951 Figure A 14 Time Characteristic Curve B Very Inverse 99 1376 Courtesy of NationalSwitchgear com...
Страница 396: ...A 20 Appendix BE1 951 Figure A 16 Time Characteristic Curve G Long Inverse 99 1622 Courtesy of NationalSwitchgear com...
Страница 397: ...BE1 951 Appendix A 21 Figure A 17 46 Time Characteristic Curve Courtesy of NationalSwitchgear com...