Introduction
1
1 Introduction
1.1
Product Overview
The Sentron™ Systems Breaker Energy Communicating Trip Unit
(SB Energy-Comm) is a microprocessor controlled protection and
metering device for application with Siemens’ state-of-the-art fam-
ily of SB Encased Systems Breakers. In addition to the basic over-
current protection functions, SB Energy-Comm trip units have a
full complement of standard and optional features. Included in
these features are serial communications, energy monitoring, and
additional protective relaying functions. This full-featured capabil-
ity, together with programmable flexibility, allows for easy adapta-
tion to new and changing protection requirements. The SB
Energy-Comm trip unit, shown in
Figure 1.1,
is a high perfor-
mance device, integrating metering and ACCESS communication
capabilities with overcurrent protective functions.
Figure 1.1
SB Energy-Comm Trip Unit
Four models of the SB Energy-Comm are available. They are:
SBxxTP01
Basic protection and power measurement
SBxxTP01G
Basic plus ground fault protection
SBxxTP02
Advanced protection, power measurement
and harmonics
SBxxTP02G
Advanced plus ground fault protection
The “xx” in the model number denotes the breaker’s current trans-
former rating (MAX rating).
Table 1.4
on page 6 describes the
functions included with each model.
The programmability of the SB Energy-Comm trip unit allows the
user to easily accommodate load changes and other protective
requirements while still ensuring optimum coordination. In addi-
tion to the programmable protective functions, the trip unit is
designed to use field interchangeable rating plugs. These rating
plugs allow the ampere rating of the circuit breaker to be changed
to meet specific applications.
For ease of installation and interchangeability in the field, the trip
unit has been designed as a plug-in unit to mount directly into an
SB circuit breaker frame.
Current transformers within the SB circuit breaker provide signal
currents and operating power for the circuit protection function of
the trip unit. When the circuit breaker is closed and current is flow-
ing, the trip unit requires no external connections or control power
to perform its circuit protection functions. External control power is
required for metering, communications, and protective relaying
functions, as well as setting adjustments and viewing the display.
A standard feature on all Siemens trip units is RMS current sens-
ing. As opposed to peak-current sensing, RMS sensing measures
the true heating potential of the current waveform. This allows for
more accurate overcurrent protection and eliminates nuisance
tripping due to harmonic distortion of the current waveform.
1.2
Principles of Operation
The SB Energy-Comm trip unit uses a microprocessor to execute
the numerous logic functions and calculations programmed in the
device. The keypad and display on the trip unit’s front panel allow
the user to select what numerical values are to be used by the
microprocessor in performing its functions. These settings allow
the trip unit to be tailored to a customer’s application. The overall
functional diagram is shown in
Figure 1.2
on page 2.
Current data is derived from current transformers (CTs) mounted
in the Siemens SB circuit breaker. As passive devices, they pro-
vide high reliability with minimum signal error, while also providing
power for the trip unit’s circuit protection functions. The current
signals from the CTs are converted to digital values in the trip unit.
These values are then stored in memory and are used by the
microprocessor to detect and process overcurrent conditions. This
operation is illustrated in
Figure 1.3
on page 3.
The microprocessor reads the stored current values and com-
pares these with the set of values that correspond to the user-
selected settings. When it detects an overcurrent condition, the
microprocessor’s software begins to process the appropriate pro-
tection function. During this processing, the microprocessor con-
tinues to monitor the incoming current level data. If the overcurrent
MAX Rating
2000 A
System
Status
System
Check
Tripped
Protective
Alarm
Meter
Rating Plug
I
n
= 1600 A
ESC
Serial Port
Test Connector
Display
(LCD)
Status
Indicators
(LEDs)
Key Pad
Communications
Connector
to Test Set
Port for PC
