Load-dependent start and stop
The load-dependent starts and stops are based on either power (P, in kW) or apparent power (S, in kVA). The load-dependent start
and stop parameters are independent of the asymmetric P load sharing parameters.
The load-dependent start and stop parameters determine how many gensets are connected. The asymmetric P load sharing
parameters determine the load distribution among the connected gensets.
Active power and reactive power load sharing
Asymmetric P load sharing only applies to active power (P). The controllers can share the reactive power (Q) using either
asymmetric Q load sharing, or equal Q load sharing.
If asymmetric P load sharing is enabled, but equal Q load sharing is enabled, then the generators each supply the same proportion
of the reactive power (Q). When one genset has a small asymmetric P load, there can be a big difference between the power factors
of the generators that supply the highest and lowest active power.
Power factor example for asymmetric P load sharing with equal Q load sharing
Three 100 kW gensets use asymmetric P load sharing to supply 165 kW. Genset A and Genset B each supply at 80 kW,
while Genset C supplies at 5 kW.
If the total system reactive power is 30 kvar, then, with equal Q load sharing, each genset supplies 10 kvar.
The power factor for Genset A and Genset B is around 0.99, while the power factor for Genset C is 0.45.
INFO
If you enabled asymmetric P load sharing, you can ensure that the power factor is the same for each genset by enabling
asymmetric Q load sharing with the same set points.
More information
See
Asymmetric Q load sharing
in this chapter for more information.
Example of asymmetric P load sharing
Load
[%]
G
G
G
P1
P2
P3
80
Maximum
Asymmetric
Equal
Minimum
0
Genset A
Genset C
Genset B
Set point
90
70
Stop
Start
Load-dependent
Asymmetric load-sharing
Equal
95
30
0
Load
[%]
The following examples are based on this configuration:
•
Gensets A, B and C: Nominal load = 100 kW
•
All the gensets are in the same section
•
Asymmetric P load sharing
◦
Enabled
for all gensets
◦
Set point
= 80 % for all three gensets
◦
Minimum
= 30 % for the section
◦
Maximum
= 95 % for the section
•
Genset A has the highest priority
•
Genset C has the lowest priority
•
Load-dependent start = 90 %
•
Load-dependent stop = 70 %
DESIGNER'S HANDBOOK 4189340911K UK
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