Emerson Site Supervisor, User Manual

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Site Supervisor Controller User Guide 2.0 026-1800 Rev 3 02-AUG-2016
The demand setpoint is determined based on the
current season - Summer or Winter. For each season, there
are two setpoints available. The active setpoint is chosen
based on the state of a setpoint switch input. In this way,
different demand setpoints may be selected depending on
the time of day or some other signal.
5.8.3 Shed Outputs
There are up to 60 shed requests for a system. These
shed requests are placed into three categories.
During the configuration of the various control
applications, a user assigns a particular shed request to any
of the following control loop:
•
First Shed
- Loads assigned to First Shed Requests
are shed first when the demand goes above setpoint
and are the last loads to be restored. They are shed
sequentially in assigned order.
•
Rotational Shed
- Loads assigned to Rotational
Shed Requests are shed in a rotational scheme after
the First Shed loads are shed. On each new demand
condition the next rotational load in the sequence is
shed first. This is done so that the DLC burden is
shared equally.
•
Last Shed
- Loads assigned to Last Shed Requests
are only shed once the First Shed and all available
Rotational loads are shed. They are shed
sequentially in assigned order. These loads are the
first loads to be restored.
When a level is shed, the shed timer is started and the
staging interval timer (minimum time to wait before
shedding the next load) is set to the value programmed for
this shed level.
The shed sequence depends on the type of loads that
are available to be shed. Loads assigned as first shed are
always the first shed in the user assigned sequence. Once
all the first shed loads are shed, the rotational loads are
shed. Assigning a load to be a rotational scheme is done to
balance the burden of demand shedding among all the
loads. This means that the application will not shed the
same load until all other rotational loads are shed. After all
available rotational loads are shed, the last shed loads are
shed in the user assigned sequence.
The loads are restored based on the following rules:
• Last shed loads are restored first in a last shed first
restore order.
• Rotational loads are restored based on which one
are shed the longest.
• First shed loads are restored in a last shed first
restore order.
• After a load is restored, the staging interval timer is
set (set to the same value used when this load is
shed). Once the staging interval expires the next
load is restored if the power level is still below the
setpoint minus the deadband.
• If a load is restored due to maximum shed time-out
that counts for the restored load for that application
update interval.
There are several factors that affect the order of how the
loads are shed and restored:
•
Minimum shed time
- the minimum time that a
shed load must stay in shed
•
Minimum restore time
- the minimum time that a
shed load must stay in restore (not shed)
•
Maximum shed time
- the maximum time that a
shed load may remain actively shed
Another load is not shed to replace a load that is
restored due to the maximum shed time expiring unless the
power level is still above setpoint.
If a shed level is in restore mode but its minimum
restore time is not met, levels in the next higher category
will not be shed. For instance, if all the first sheds are shed
and one of the first sheds times out due to max shed time,
rotate and last shed loads will not continue to shed until all
first shed loads are shed again.
Multiple loads can be assigned to each shed level, but a
user should assign the same KW to each shed level. The
KW assigned to a shed level is used by the application in
determining how many shed requests should be shed at
one time. However, since the application doesn't know the
On/Off status of the loads assigned to a shed level and
since the total KW that can be shed is usually only a
portion of the total electrical power used, the application
cannot accurately predict the actual results of a shed
request. To compensate for this, the application assumes
only 75% of the reported load being On. Additionally, the
application is always taking immediate action when the
power level is exceeding the KW Demand setpoint and it
can bring the power level under control without a new
demand level being recorded by the power company.
5.8.4 Application Alarms
The Demand Control an application provides applica-
tion alarm to signal a high demand. The demand alarm
limit and alarm delay should be configurable.
5.8.5 KW Load Specification
The application allows the user to specify the KW
rating for each load connected to the Demand Control
application. The application uses this information to help
determine how many loads to shed at one time to prevent
exceeding the demand setpoint.