Protections
87
7 DEAD BUS SYNCHRONISING (AUTO MODE)
Generator set specifications often contain the requirement for the set to be on load within 15 seconds of a mains
supply failure. This is easily achievable in single set applications. However in the current era of fuel conservation,
multiple sets are often used to provide the backup power solution for many applications. This gives challenges in
starting and synchronising the required sets before they can be used to power the load.
The solution to this is a longstanding one, having being used for many decades. However modern digital
communications such as the DSE MSC link has vastly improved the control and hence safety of the system
operation. The solution is called “Dead Bus Synchronising”
7.1.1 OPERATION
Before the generator sets are started, the load switches are closed. This requires DC controlled breakers. Next, the
alternator excitation field is disconnected from the AVRs and the engines are started.
Once running satisfactorily, the AVR is reconnected to the excitation field and load sharing begins. The MSC link
is used to ensure all sets excite the alternator at exactly the same time. Any sets not up to speed before the end of
the “Excitation Delay” timer are instructed to open their breakers. A short time later, these sets synchronise to the
bus in the traditional manner.
DEAD BUS SYNCHRONISING
During Dead bus synchronising a Start is issued from Mains control panel
Status
Excitation Delay 00:03
L-N V A
L-L V
kW
50 Hz
Pf
Status
Start Delay 00:00 s
Status
Fuel
Status
Crank Attempt
The Breaker will close onto a Dead Bus .
The generator voltage and frequency.
The Generator Breaker is closed ,
Excitation is switched off, start delay if
configured.
Fuel Output Activated
Engine Cranked
Excitation delay before excitation output
is activated. Generators run up to speed
if any on the MSC are out of limits they
are instructed to open their breaker and
synchronise in the normal manner.
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