ABB SYNCHROTACT Synchronizing devices
Synchronizing devices are widely used in power stations or
industrial installations with their own power generating facilities,
where the generators need to be paralleled with an island line
or a public line, or in power distribution systems.
Power circuit breakers may only be closed if both voltages are
approximately synchronous (coincident). Otherwise, faults in
line operation, loading of the generators and, in extreme cases,
damage to the generators can result.
SYNCHROTACT® 5 performs these functions safely and reliably,
whether as a monitoring element for manual paralleling or as
an independent fully-automatic synchronizing device.
SYNCHROTACT® 5
Range of applications
1. Automatic synchronizing and paralleling of synchronous generators
with line.
2. Automatic paralleling for synchronous and asynchronous lines,
transmission lines and busbars.
3. Paralleling monitoring (synchrocheck) for the monitoring of
automatic or manual paralleling procedures including the
connection of voltage-free lines (dead bus).

SYNCHROTACT® 5
Principle of operation
The synchronizing and paralleling process can be divided
into the following blocks
Measuring
Voltage difference ΔU (amplitude), slip s (frequency diffe rence), and phase-angle α, are all required for paralleling.
These values are formed from the two measurement signals
U1 and U2 (see illustration, left).
Matching
Voltage and frequency matching functions reduce the voltage
difference ΔU, and slip s by sending adjusting pulses to the
voltage or turbine regulators.
Monitoring of paralleling conditions
This function compares the actual values with their set
maximum values and releases paralleling (CHK RELEASE) if
all conditions are fulfilled simultaneously.
Synchrocheck mode (paralleling monitoring)
In synchrocheck mode, only the measuring and monitoring
function blocks are active. The output relay is closed during
paralleling release.
Command generation
The command generation calculates the necessary lead angle
αv, by which the paralleling command must be advanced
due to closing time delay. The action ensures that the main
contacts close at precisely the right time. If α reaches αv at
the same time as paralleling release (CHK RELEASE), the
command is issued. Under synchronous conditions, ie,
permanent paralleling release during the adjustable monitoring
time, tsup, the CMD is also issued without taking the lead
angle into consideration.

From a synchronizing device, it is expected to close the
power circuit breaker at the correct time but also that, if
required, paralleling can take place whenever permissible.
Although the series connection of the output contacts of two
independently-functioning channels (dual-channel system),
which is usual in synchronizing systems, greatly increases
security against incorrect paralleling, it necessarily leads to a
reduction in availability.
Single or dual-channel?
Not every synchronizing system needs to be structured
according to the above pattern. The SYNCHROTACT® 5
single-channel synchronizing devices offer a high degree of
security and are often used in practice. However, security
can be significantly increased by means of dual-channel
systems. It is unlikely that the two channels - of which the
hardware and software are structured differently - will have
the same malfunction simultaneously. The extra cost of a
dual channel system can prove beneficial compared to the
damage arising from incorrect paralleling.
Second, redundant synchronizing system?
Often, two redundant synchronizing systems are installed
in a single plant so that, in the event of one system failing,
the other can be used, thereby increasing availability. The
second system is often designed for manual synchronizing
with or without synchrocheck.
In addition, with SYNCHROTACT® 5, ABB offers two automatic
dual-channel systems in a single casing, thus avoiding
manual synchronizing.
Advantages of such a solution:
– No engineering and wiring costs for the second system
– Further increased security since all four output contacts
are normally operated in series
– No problems with synchronizing where the
manual synchronizing system is seldom used.

Specific settings for synchronizing and paralleling are stored
in a parameter set. Devices with seven parameter sets have
seven times the same parameters, with the possibility of
individual setting. That way, seven paralleling points with
individual settings may be operated. Firstly, the parameter
set, or the circuit breaker to be synchronized has to be
selected. Then the synchronizing process can be started.
The software-driven link between parameter set and
paralleling point guarantees the correct assignment of the
setting values to the related plant components