Available power
The available power (also called
P avail.
) is the difference between the nominal power and the consumed power.
For PMS power, the available power calculation uses the
connected consumed power
, and NOT the PMS consumed power. The
PMS available power thus shows whether the PMS generators can meet the section's power needs. If a generator in SEMI mode or
under switchboard control is supplying the section, the PMS available power can be negative.
For connected power, the available power is the difference between the nominal power and the consumed power for the connected
sources.
Available power = Nominal power - Total consumed power
The section can use the available power immediately, without starting more gensets. The section should always have some
available power for sudden load increases.
Interaction between the power types
The following graph shows an example of how the nominal power, consumed power and available power could interact over time.
The example is a system with three gensets, with nominal powers of 1000 kW, 1200 kW and 1500 kW respectively.
0
500
1000
1500
2000
2500
3000
3500
Power
[kW]
time
1000 kW genset
1000 kW and
1200 kW genset
1000 kW and
1200 kW genset
1000 kW, 1200 kW and 1500 kW genset
Nominal
power
Consumed
power
Available
power
1
2
3
4
5
1. At the start of the period, the 1000 kW genset is running.
2. The load gradually increases, and so the power management system starts the 1200 kW genset. The available power jumps up
when the genset starts.
3. The load continues to increase, and so the power management system starts the 1500 kW genset.
4. The system runs, consuming power from all three gensets.
5. Towards the end of the period, the load decreases, so that the power management system stops the 1500 kW genset.
Available power delay
To avoid over-loading a connected genset when a new genset connects to the busbar, the power management system can
communicate the new available power after a delay. When you delay communicating the new available power, the system has time
to reduce the load on the genset that is already connected before the consumers increase the load on the busbar.
DESIGNER'S HANDBOOK 4189340911K UK
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