Transcript Supervisory Systems

Supervisory Systems
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Supervisory Systems: Introduction
Purpose:
• To provide the user with the capability to
exercise control over a specific device.
• To confirm its performance in accordance
with the directed action.
• The commonly used name is SCADA.
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Supervisory Systems in Power Systems
Objective:
• To provide system operators with efficient
information and control capabilities.
• To operate the power system in a safe,
secure and economic manner.
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Typical Supervisory System
Analog
Input
Master
Station
M
o
d
e
m
M
o
d
e
m
Remote
Terminal
Units
Communications
User
Interface
Analog
Output
Digital
Input
User
Interface
Intelligent
Electronic
Devices
Digital
Output
Fig.1 Typical Supervisory System
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Types of Supervisory Systems
1. SCADA (Supervisor Control and Data
Acquisition)
2. SCADA/AGC
3. EMS (Energy Management System)
4. DMS (Distribution Management System)
5. Load Management System (LMS)
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1. SCADA
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A SCADA system, strictly speaking, is
limited to performance of traditional
function such as the gathering of data
and performance of control functions.
•
A small amount of record keeping and
other data reporting functions are usually
included.
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2. SCADA / AGC
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A SCADA and automatic generation control
(AGC) system is similar to a simple a SCADA
system except some limited generation control
capabilities are included.
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These capabilities include the ability to
calculate area control error, monitor frequency
and tie lines and perform a limited economic
dispatch of a few generating units.
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3. EMS (Energy Management System)
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The energy management system (EMS) incorporates
all the features of SCADA systems in terms of
gathering data and performing control.
It typically will include a fair amount of computing
power and probably extensive online data storage.
The user interface (UI) may be very complex, including
the use of full graphic CRT’s, dynamic map boards and
many recording charts.
Software frequently includes compute-intensive
programs for contingency analysis, security functions,
scheduling, load flows and optimal power flows.
Because the EMS is often considered the heart of the
utility’s main control center, it probably includes
extensive capabilities for record keeping and data
exchange.
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4. DMS (Distribution Management
System)
The distribution management system (DMS) is the next
logical step after a utility has implemented an EMS.
Initially it was viewed as a means to monitor
distribution feeder loads and to control the distribution
portion of the substation.
Technology has lowered the cost of control and
supervision of devices located throughout the feeder
lines to the point where it is now becoming routine.
The DMS frequently includes topology analysis and load
flow programs that allow rapid identification of
problems and restoration of service.
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5. Load Management System (LMS)
1.
The intent of a load management (LM) system is to
control peak demand and provide other economic
benefits without major inconvenience to the customer.
2.
An LM system can be stand-alone or it can be
integrated into an EMS or DMS.
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Network Application in EMS
Typical Applications
[1] State Estimation
[2] Security Analysis
[3] Power/Load Flow
[4] Optimal Power Flow
Unlike other EMS applications, they depend on
power system network models. They may
execute in EMS real-time and study
environments
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Real Time and Study Environment
In the real time environment network applications
execute periodically with virtually no operator
interaction.
They draw attention to actual or potential problems
and provide operating data enabling a
corresponding course of action.
In the study environment they execute on
demand to facilitate operator analysis of
different operating scenarios associated with
past, present or future power system
conditions.
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A. Real Time Environment
Security
Analysis
Reactive
Control
Optimal Power
Flow
SCADA
Power
System
Active
Control
State
Estimation
Fig. 2 Real Time Environment
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Real Time Environment
(Contd.)
State Estimation, Security Analysis and
Optimal Power Flow applications
provide the real time means of
developing controls for operating power
systems securely.
To achieve this objective, they execute
sequentially, validating the condition of
the power system.
Fig.2 illustrates the real time environment.
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Real Time Environment
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(Contd.)
Execution of the network applications may be initiated
several ways.
Commonly they execute continually at periodic rates
that range from 5 to 20 minutes.
Operators can set the optimum rates within limits
governed by EMS computing power.
State estimation is the first application to execute.
State Estimation uses telemetered, scheduled and
manually entered data to determine the network
topology and state of the power system.
Network topology refers to the connectivity of the
power system components and is determined from
status information collected by SCADA.
Once the state of the power system is calculated
security analysis may be execute, followed by optimal
power flow.
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Real Time Environment
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(Contd.)
Security Analysis determines the potential
impact of contingencies.
OPF recommends the control that may be
used to correct actual violations and/or prevent
or correct contingency violations.
In Fig.2 it is assumed that the controls
recommended by OPF are implemented
automatically in closed loop fashion via active
control, reactive control and SCADA.
SCADA sends EMS commands controlling
circuit breakers, transformers, phase shifters
and generators via remote terminal units.
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Real Time Environment
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(Contd.)
Typically active control includes automatic generation
control and economic dispatch.
Acting through SCADA, AGC/ED performs generation
control for very few seconds to meet load and
interchange schedules economically.
OPF, however, passes generating unit limits at the
slower periodicity of the network applications.
Reactive control provides an OPF interface that serves
the potential need for coordinating reactive power
controls such as generator voltage schedules;
transformer taps and shunts capacitor/reactor banks.
Though the controls may pass from OPF to SCADA
directly reactive control also allows for more frequent
power system feedback to be taken into account.
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B. Study Environment
Save case
Changes
Save case
Study
case
Optimal
power flow
Security
Analysis
Apply
Contingency
Fig.3 Study Environment
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Study Environment
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The network applications commonly used for studies
are Power flow, OPF and security analysis.
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Fig.3 illustrates the study environment where OPF
includes the Power flow applications.
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Execution of each study application is controlled by the
operator in an environment that is separate from the
real time environment.
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Typically, the study environment allows several
operators to make concurrent studies on a
noninterference basis and is supported by the ability to
store and retrieve input/output results through a library
of save cases.
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Study Environment
(Contd.)
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Once satisfied that the study case is correct the
operator normally execute power flow or OPF and
reviews the results.
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The operator can save the results and execute
Security Analysis to determine the potential impact of
contingencies.
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After reviewing the output from security analysis, the
operator may choose to apply a particular contingency
such as the one that has the severest impact to the
study case.
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Network Topology Processing
1
3
G
K(1)
S(1)
1
2
K(2)
S(2)
4
L(1)
SUB X
2
S(3)
SUB Y
Topological Classification
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Computer Control of Power Systems
National control
operator
National control
computer
area equivalent
circuit; effective
costs
desired boundary
line flows
security
cost, spare
Grid control
area computer
Control
desk
Area control
computer
desired boundary flows,
machine sync times
restrictions
in performance
T min & 30 min
instructions
generator
outputs
30 min instructions
Station
operator
Machine
controller
plant limits
plant
conditions
control of
auxiliaries
governor
set point
power output
Experimental automatic area control
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No
Function
Description
1
Automatic Generation
Control (AGC)
The function of the AGC is to allocate the generation among the system
generator units in real-time to meet the system load.
2
Economic Dispatch
Calculation (EDC)
This program allocates generation among the available units so as to
minimize the cost of supplying the system load.
3
Unit Commitment.
The Unit Commitment function is to establish the minimal cost
operating policy over a specified time period, (usually a day to one
week) within a set of specified constraints.
4
System Load Forecast
To forecast then system load, usually for the next one day to one week,
taking account of historical as well as weather load models.
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State Estimator
The State Estimator is a mathematical procedure for producing the best
estimate of the status of a network, from a set of measurements. The
result of the State estimation provides the base from which the
Contingency Analysis program is run.
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Power Flow
The Power Flow Program provides the capability for operators and
operation planners to study the effects on the power network under
postulated conditions.
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Short Circuit Analysis
This application program performs the calculation of three phase and/or
single phase to ground short circuit currents and the associated voltage
profile.
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Bus Load forecast
Provides short term forecasting of the loads on feeders and stations.
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Transient Stability
Simulates and analyses the dynamic response of an interconnected
system for several seconds following a disturbance.
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Contingency Analysis
This application program automatically assesses the impact of selected
outages on the real-time power system and alerts the user to rating
violations on affected pieces of equipment.
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Dispatcher Training
Simulator
This equipment provides the engineers with familiarization with the
operations in a power control system.
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