Glossary
79
Protective menu
The available protection functions, including
Long Time, Short Time, Instantaneous, and Ground Fault.
PT
Potential Transformer. A transformer which generates a volt-
age in the secondary proportional to the voltage in the primary at
a specified ratio.
PT rating
The ratio between the potential transformer voltage
sensed, and voltage transmitted.
PU
Pickup (value).
R
RS-232 (EIA-232)
An industry standard (EIA-232) serial com-
munications interface through which data is sent one bit (binary
digit) at a time. The physical and electrical specifications that
apply to the transfer of data between Data Terminal Equipment
(DTE) and Data Communication Equipment (DCE), typically
between a personal computer and a peripheral device.
RS-485 (EIA-485)
Commonly used communications standard
(EIA-485) typically for communication among several field
devices.
remote operations
Opening or closing of the breaker by a sig-
nal from the communications port. This is distinguished from trips
caused by actual faults.
residual ground sensing scheme
The method of sensing
ground current based on the vectorial summation of currents in all
phases.
Reverse Power
Power flow from the load towards the source.
kW and kVAR supplied by the load.
RX
Receive signal (communications).
S
SB
Systems Breaker. The family of encased systems breakers
on which the trip unit operates.
SEAbus
The protocol used by the SB Energy-Comm trip unit
and other Siemens ACCESS field devices.
Security menu
The menu selection, available from the Main
menu, that allows the operator to choose the password and
enable security.
serial number
See
Breaker Serial Number
.
serial port
The data port on the front of the trip unit that allows
RS-232 communications to a personal computer.
short time
Overcurrent protection that is activated after a brief
delay. This is for higher levels of overcurrent activity than the long
time protective function.
ST
Short Time (protection).
supervisory device
A device that can remotely configure, read
back, check the configuration of, and poll real-time data from field
devices. Supervisory devices display the information and add the
capabilities of programming, monitoring alarms, and logging sys-
tem events.
System Check LEDs
The indicators on the front panel of the
trip unit that indicate the proper operation of the trip unit’s protec-
tive and metering functions.
System Configuration menu
The menu selection, available
from the Main menu, that allows the operator to view and config-
ure power system characteristics.
System Status LEDs
The two indicators on the front panel of
the trip unit that indicate the status of the breaker, whether it has
been sent a trip command and whether an alarm has occurred.
T
test set
See
Portable Test Set
.
total harmonic distortion (THD)
The ratio of the sum of the
parts of the system power waveform that resides in the harmon-
ics to the value of the power residing in the fundamental line fre-
quency.
trip
The opening of the circuit breaker or the command to open
the circuit breaker originating at the trip unit.
trip unit
The field device connected to a circuit breaker that
senses overcurrent conditions and sends a signal to open the
breaker. The SB Energy-Comm trip unit also includes metering,
protective relay, and communications capabilities.
trip log
The list of trips or breaker openings stored in memory of
the trip unit.
TS-31
See
Portable Test Set
.
TX
Transmit signal (communications).
U
unbalance
See
Phase Balance
.
under voltage alarm
The alarm signal that is output by the trip
unit when the control voltage drops below a user-specified set-
ting.
