Overview
Load Management Executive performs load management functions for electric utility
companies. It implements those functions as dictated by the utility
industry, using resources provided by the NTMC
core components.
LMEX organizes its data as follows: LMEX maintains global management
parameters and a list of user defined metering
points. Load management can be done globally, or on metering point level. In
the latter case one can have multiple load management systems running in
parallel, using different management strategies.
Each metering point maintains a list of user defined demand
points. These are I/O points
used by LMEX for importing demand data. Each point can be programmed to
add to the metering point demand total, to subtract from it, or to not affect it
at all.
Each metering point also maintains a list of user defined load
points. These are I/O points
used by LMEX for control of relays on the power grid. Each load point is
assigned a power rating so LMEX knows how many loads to control at any time.
LMEX also maintains a list of user defined schedules.
These are collections of load point parameters shared between load points.
Multiple load points can be assigned the same schedule. All those points share
all parameters in that schedule.
Database
Each of the above items must be defined by the operator. This is a one time
process, most of which is done at the time of system installation. Subsequently
definitions usually get added or modified only when new devices are added to the
system, or when system changes are taken into account, such as changes in remote
unit model being used (new switch model, larger RTU, etc). Definition of each
item comes in several steps.
- First, a new database entry is made. This creates a record corresponding
to the item to be managed. For example, to import new demand numbers one
must define a new demand point database entry. At that time, the
item is said to be off-line.
- In case of demand points and load points, a mapping onto appropriate I/O points
in RUEX needs to be made. A load point must be mapped onto an
appropriate control point in RUEX so the latter knows how to operate it when
requested to do so by LMEX. Similarly, each demand point must be mapped onto
an appropriate analog point in RUEX, so LMEX knows where to find new demand
figures when they come in.
- Next, the new item has to be 'put on-line'. LMEX does not 'know' about the
new item until this step is performed. At that time LMEX verifies the type,
location, and integrity of the database entry. If all tests are passed LMEX
creates a manager of appropriate type. (For those familiar with modern
software engineering jargon, LMEX creates an object of appropriate class.)
From that time on LMEX 'knows' about that item and maintains it by calling
functions exposed by the manager. At that point the item said to be on-line.
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Data Processing
Data processing is done by both, RUEX and LMEX. The former does data
acquisition and calculations resulting in analog point values. Analog point
managers impose limits on acceptable value ranges. When numbers fall out of
those operator defined ranges, LMEX ignores the values and works with last
good known numbers. This is to prevent unwanted system oscillations caused by
occasional bad numbers which can come in because of hardware and / or software
problems. LMEX loads these analog point values into its demand points, then
adds them up, as configured by the operator, into metering point totals, and
overall system total. Subsequent load management cycle is done based on the
new numbers and other system settings.
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Data Recording
LMEX records the following demand values: system total, all metering point
totals, and all individual demand point numbers. The latter can be programmed
in RUEX as well, but this would only be duplication of data and is
unnecessary.
LMEX records load point states by generating appropriate event log entries.
In addition, RUEX makes control point event log entries in its event log file.
Control point states are also recorded in standard data recording files by
RUEX. In addition to control point states, other information, such as manual /
auto, and which component issued control commands is recorded.
Load management cycle logs can be generated on the global (system) level,
and / or metering point level.
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Data Archiving
All data recording files and event logs fill up after a while, and must be
archived to a separate location, either on the same computer, or elsewhere on
the LAN. This is done manually by
the operator who executes archiving commands. Two kinds of information get
archived: data recorded from remote units, and event logs. LMEX does not
back up archived data recording files stored elsewhere on the computer (for
example, on a ZIP disk), or the LAN.
It is the user's responsibility to back those files up after each archiving
operation.
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Billing Periods
Two billing periods can be defined, Peak billing period, and Off-peak
billing period. All data recorded as described above gets stamped with an
attribute specifying if billing period is peak or off-peak at the time. MCDA
filters provide for filtering out either of the two periods when analyzing
data.
Peak billing period start and end times of day are defined by the operator.
In addition, whenever there is a management waiver in effect, off-peak billing
period is in effect.
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One-Way Load Management
This section describes how to implement load peak shaving using one-way
load management. Several things need to be defined: Times and days when
management is to be performed, peak shaving parameters, and load groupings which
further define when to use which load points to accomplish load management
goals.
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Two-Way Load Management
This section describes how to implement load peak shaving using two-way
load management. Several things need to be defined: all the parameters
relevant to one-way load management, as well as parameters enabling two-way load
management functionality.
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Strategy Based Load Management
Strategy load management, as opposed to peak shaving, is done by switching
load management strategies as
pre-defined by the operator. Each strategy is a collection of load management schedules.
Each load point is assigned three distinct schedules, one for each strategy.
Load management strategy in effect can be switched manually by the operator,
or automatically based on the time of day, or system load.
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Load Rotation
Load rotation is reconnecting disconnected customers after some elapsed
time while disconnecting others. This mode of operation may be opted when load
control duration is exceedingly long, when loads are such that long disconnects
simply can not be tolerated by the customers (air conditioners in the summer,
for example), etc.
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Load State Reinserting
Sometimes it is necessary to reinsert load states, i.e. re-transmit control
codes to all load points in order to make certain that their states agree with
what is in NTMC database. Such reinserting cycles may be issued after initial
load shed is complete, after all loads have been released, etc. LSR manager
simply transmits an OFF code to a load if it thinks that the load is supposed
to be OFF, and an ON code if the load is supposed to be ON at the time.
LSR can also be programmed to reinsert only loads which where operated on
the day of LSR manager execution. This means LSR manager sends no reinsertion
codes to loads which were not previously operated that same day.
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Load Pre-polling
To further shorten duration of initial load sheds one can pre-poll all
loads to see which loads are actually running at the time. This is possible
when load control remote units are sufficiently sophisticated to be able to
report load activity. For example, a simple RTU with one relay, and one pulse
counter can do the job. After pre-polling LMEX sorts the loads by shed
priority where active loads are placed higher in the priority list. When it is
time to shed system load, active loads receive control codes first
thereby eliminating time wasted when sending control codes to loads which are
inactive to begin with.
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Load Point Operation Modes
Load points can be operated manually or automatically. To resolve conflicts
between the two modes, load points can be put in one of available operations
modes: AUTO, MANUAL, FROZEN. Below is the table explaining the respective
functionalities.
Please note: Administrative accounts have all privileges and can
operate loads in any mode, at any time, from any location.
Please note: Non-administrative accounts have privileges defined by
security attributes. The table below shows operation permissions via control
room or Remote Client assuming those accounts are permitted to operate
loads. The table below shows operation permissions via the web - those
permissions are irrespective of account permissions.
The following abbreviations are used: C = Control Room, R = Remote Client,
W = web browser.
| |
Auto Mode Peak Period |
Manual Mode Peak Period |
Frozen Mode Peak Period |
Auto Mode Off-Peak P. |
Manual Mode Off-Peak P. |
Frozen Mode Off-Peak P. |
| Manual OFF from C or R |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
| Manual OFF from W |
Yes, also switches to Frozen mode |
No |
Yes |
Yes, also switches to Frozen mode |
No |
Yes |
| Manual ON from C or R |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
| Manual ON from W |
No |
No |
No, just switches to Auto mode |
Yes |
No |
Yes, also switches to Auto mode |
| Auto OFF |
Yes |
No |
No |
No |
No |
No |
| Auto ON |
Yes |
No |
No |
Yes |
No |
No |
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Management Waivers
LMEX can be programmed to waive load management part of a day, or all day.
This feature can be configured locally by the operator, or remotely via an
external command sent over via an external communications channel of choice.
The waiver automatically expires the following midnight so normal operations
can resume the next day.
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Secondary Load Points
Sometimes it is desirable to send out notification message(s) to various
devices when certain primary loads are operated (turned OFF or ON). In
LMEX terminology, such devices are called secondary loads. Primary load
can be any load with non-zero power consumption rating. Secondary loads are
usually messaging devices with zero assigned power rating. For example, a
farmer might want to be notified via his pager (secondary load, not
controlling any power) when his irrigation sprinkler (primary load, power
user) gets re-connected to the power grid. Secondary loads operate after load
management cycle is complete.
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Twin Load Points
Sometimes it is desirable to send out notification message(s) to various
devices as soon as certain primary loads are operated (turned OFF or ON). In
LMEX terminology, such devices are called twin loads. Each primary load
can have only one twin load. Every twin load is a secondary load, while every
secondary load is not a twin load. While secondary loads operate in a group
after load management cycle is complete, twin loads operate during load
management cycle, right after their respective primary loads.
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