Siemens SIPROTEC 7SS523 V3.2 Manual page 18

Introduction
1.1 Overall Operation
Bay units
Central unit
2
The SIPROTEC 7SS52 V4 distributed busbar and breaker failure protection consists
of compact bay units which are connected to the central unit by fiber-optic cables. Fig-
ure 1-1, page 3 shows the basic structure of the protection system.
All tasks from acquisition of the measured values up to the commands to the circuit
breakers are exclusively processed in a digital manner.
In the bay units the feeder or coupler currents are measured time-synchronized, digi-
talized, preprocessed and transmitted to the central unit via the fast serial port. The
input nominal current can be 1 or 5 A depending on the main current transformer de-
sign. A full galvanic and low-capacitive isolation of the measuring inputs is provided
by transducers. Suppression of disturbances is achieved by filters which are optimized
for the measured value processing with regard to bandwidth and processing speed.
The bay units can be parameterized and operated either directly or from the central
unit. Chapter 6.1, page 204 summarizes the operator options during operation.
The bay units capture the isolator positions and bay-related binary signals, process
functions of the breaker failure protection and fulfil auto diagnosis tasks.
Heavy-duty command relays take the protection system's trip commands directly to
the circuit breakers. Marshallable alarm relays and indicators (LEDs, LC display,
DIGSI communication software) allow event indication. In addition operational meas-
ured values are displayed.
For the marshalling of isolator positions, command relays, alarm relays and allocata-
ble binary inputs the DIGSI communication software is used.
Optionally, the bay units can be equipped with a backup protection function (definite-
time, inverse-time) including breaker failure protection.
The central unit reads in time-synchronized measured currents from the connected
bay units and processes them together with binary information from the protection
functions (differential protection, breaker failure protection). The central unit transmits
the results of the calculations cyclically to the bay units, which perform logical combi-
nations of the results.
Freely marshallable alarm relays and LED displays are provided for signalling. They
are marshalled with the DIGSI communication software.
The central unit manages all configuration and setting data for the busbar and breaker
failure protection functions. Communication is possible via the serial port by means of
a PC utilizing a current version of the DIGSI communication software. With DIGSI V4.6
the central unit - but not the bay unit - can also be operated via IEC 61850 with the
optional EN100 module. Indications, parameters and measured values are visualized
in the display or in DIGSI. In addition the program can read out fault data from the pro-
tection device and analyze it.
The central unit and bay units contain power supply modules for a reliable power sup-
ply on different voltage ranges.
7SS52 V4 Manual
C53000-G1176-C182-1