Min Loads Added. The Load Shed priority that must be online before generator management will consider stopping a generator.
This is implemented so that generators aren’t stopped prematurely (before all the available load has been applied to the system).
All the generators in the system must have the same setting for Min Loads Added for the generator management to operate. If
this parameter is changed, it will be updated on all the generators which are connected to the PGEN network.
Note:
Min Loads Added should be set up to support the load control outputs which are connected to actual loads. There is no reason
to wait for a load control output to add if no load will be added to the system when it does. At the same time, it is important that
all load which the paralleling system will have to support be supplied by the system before generator management makes the
determination to stop a generator.
The load control outputs should be capable of shedding enough load that a single generator can support what remains (this
should be handled during commissioning, but is included for consideration as loads grow).
Load Control
Load Control drives 6 outputs (Load Priority 1 Shed through Load Priority 6 Shed) to remove loads from the paralleling bus when
the attached generators are unable to support them. See the Load Control Description section following for more information.
The outputs must be tied to programmable outputs in the configuration before they can be used, but they are controlled internally
regardless of output configuration or external connection status.
All generators on the PGEN network initiate load control at the same time and use the same measured values to determine the
Add and Shed timing (Bus % kW and Bus Frequency). If the load control settings are set identically, each load control priority
will add at the same time on all generators in the paralleling system. This allows Priorities 1 and 2 to be connected to one
generator, while Priorities 3 and 4 can be connected to another generator.
Note:
Load Control in a paralleling system operates identically to the load control on a single generator, except that it takes different
metered values into consideration.
Load Control Description
The purpose of Load Control is to permit a generator to support load which may occasionally exceed the rated capacity of the
generator. In paralleling systems, load shed permits the bus to stay at rated voltage and frequency while an additional generator
is synchronizing to it. In single-generator applications, load control may shed unimportant but highly demanding loads when the
generator is overloaded, preventing a power outage caused by the generator going offline.
The Load Control in the Decision-Maker
®
3500 controller supports 6 load control priorities. These priorities generate internal
notices for the shed condition. The internal notices are generated any time a load is shed, but they will only operate a load
control relay if they are configured to a digital output.
Only 4 load control priorities can be configured to the RDO outputs on the controller (2 in paralleling applications) but the optional
14 relay dry contact kit will permit all 6 load control priorities to be accessed and configured to disconnect 6 different loads (each
load priority can interrupt several devices).
In paralleling applications, the load shed priorities can be divided between all the generators. For instance, Generator #1 can
support Load Priorities 1 and 4, Generator #2 can support Priorities 2 and 5, and Generator #3 can support Priorities 3 and 6.
This configuration does not require the 14 relay dry contact kit and permits partial load shed functionality even if one controller
is powered down or fails (redundancy).
Load Priority 1 is shed last and added first, the priorities are added in increasing sequence and shed in decreasing sequence.
All Load Priorities are immediately shed when load control is initiated. Load control is initiated when the system receives a start
signal (a system start, a remote start, or a start by communication). In a paralleling application, the controller can receive a start
signal from any generator which is connected to the PGEN communication network. Pressing RUN on the controller will not
cause the loads to shed.
All loads are added immediately when Load Control is de-activated—this occurs when the start signal is removed.
Load Control adds loads based on the capacity of the system—loads will add more quickly if the available capacity is higher.
Load Control sheds loads based on the degree of overload of the system—loads will shed more quickly as the degree of the
system overload increases.
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