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Manual 26174
EGCP-2 Engine Generator Control Package
Woodward
141
Remember:
The new Master needs a reason to start. If the original Master was
started with a Run w/Load input and you switch the Master to another unit that
only has the AUTO input closed, the new Master will NOT start. This example
shows that the new Master will start due to a LOMs condition.
If all 3 units are in the AUTO mode, and a LOMs is detected. All 3 units will be
told to start by the Master. Once online the Master could sequence the slave
units off if the system load was low. Now if I switch Masters, the new Master will
start and synchronize on to the bus. The new Master will now follow its
sequencing values for starting and stopping the slaves.
The new master (Network Address 2) will start and parallel to the previous
master (Network Address 1). Load control will be isochronous load sharing
between the two units. See Figure 5-13. If the system load is greater than 25%,
then both units will remain on line. If the system load drops below 25%, then the
new master (Network Address 2) will sequence the slave (Network Address 1) off
line.
The new master has fully established itself on the network as the Master.
The above actions take place simply by changing the priority of any given unit so
that that unit is the New Master. As long as the unit is in auto mode, configured
for multiple unit operation and attached to the network, it will automatically
transfer itself to the Master Position.
Units operating in Auto with the Run with Load discrete input closed will
effectively transfer, or recognize the transfer of master units. However, being in
an auto and run with load mode, those particular units cannot be sequenced off
line by the master control.
If a unit is not in auto mode, or is configured for single unit operation, or is not
attached to the RS-485 network, then no transfer of master can occur.
Also, for a transfer of master to occur, the units have to be in an auto sequencing
mode of operation. This implies either a load sharing or process mode of load
control. Without being in these operating modes, a transfer of master cannot
occur because the New Master cannot sequence the Previous master off line.
The load control mode, which does not support master transition, is the Base
Load mode. In Base Load Mode, there is no sequencing between units, and
therefore a change of master cannot take place until the units are either taken
out of base load mode, or switched to an isochronous load sharing, or process
control mode.
Master Controls operating in the Process Control Mode must have a
4–20 mA or 1–5 Vdc transducer input to function properly.