Load Add / Substract - Datakom D-500 MK2 User Manual

D-500 MK2 User Manual

34.2. LOAD ADD / SUBSTRACT

The load add/subtract output functions are designed to provide control signals for an external, multi-step
load adding/substracting system.
This external system will add either linearly or by small steps a dummy load that will prevent the genset
from running below the minimum required load level.
The same function may be used in order to supply loads of different priority levels following the available
genset capacity.
When the load is below the Load Shedding Low Limit, the controller will activate the Load Add output.
The external system will increase the load until it goes over the low limit, where the Load Add output will
become inactive.
When the load is above the Load Shedding High Limit, the controller will activate the Load Substract
output. The external system will decrease the load until it goes below the high limit, where the Load
Substract output will become inactive.
There are protection delays between two pulses. These timers help to stabilizing the decision algorithm
and preventing unwanted multiple operations.
The parameters used in Load Shedding feature are in the Electrical Parameters Group:
Load Shedding Low Limit: If the genset power goes below this limit then the load_add relay will be
active.
Load Shedding High Limit: If the genset power goes above this limit then the load_substract relay will
be active.
Load Add Delay: This is the minimum delay between 2 load_add pulses. This is also the minimum delay
between 2 load_substract pulses.
Load Subtract-Add Delay: This is the minimum delay between load_add and load_substract pulses.
t :
the load goes below the Load Shedding Low Limit, thus the Load Add output becomes active.
1
t :
the load goes above the Load Shedding Low Limit, thus the Load Add output becomes inactive.
2
t :
the load goes above the Load Shedding High Limit, thus the Load Substract output becomes active.
3
t :
the load goes below the Load Shedding High Limit, thus the Load Substract output becomes inactive.
4
t :
the load goes below the Load Shedding Low Limit, but the Load Substract-Add delay is not expired. The
5
controller waits until expiration of the timer.
t :
the timer is expired and the load is still below the Load Shedding Low Limit, the Load Add output
6
becomes active.
t :
the load goes above the Load Shedding Low Limit, thus the Load Add output becomes inactive.
7
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