SCADA Systems
SCADA (Supervisory Control and Data Acquisition) systems are used to control dispersed assets where centralized data acquisition is as important as control . These systems are used in distribution systems such as water distribution and waste water collection systems, oil and natural gas pipelines, electrical utility transmission and distribution systems, and rail and other public transportation systems.
Supervisory Control and Data Acquisition systems integrate data acquisition systems with data transmission systems and Human-Machine Interface (HMI) software to provide a centralized monitoring and control system for numerous process inputs and outputs.
Supervisory Control and Data Acquisition (SCADA) systems are designed to collect field information, transfer it to a central computer facility, and display the information to the operator graphically or textually, thereby allowing the operator to monitor or control an entire system from a central location in real time. Based on the sophistication and setup of the individual system, control of any individual system, operation, or task can be automatic, or it can be performed by operator commands.
Supervisory Control and Data Acquisition (SCADA) systems consist of both hardware and software. Typical hardware includes an MTU (SCADA Server or Master Terminal Unit) placed at a control center, communications equipment (e.g., radio, telephone line, cable, or satellite), and one or more geographically distributed field sites consisting of either an Remote Terminal Unit (RTU) or a PLC (Programmable Logic Controllers), which controls actuators and/or monitors sensors.
The Master Terminal Unit (MTU) stores and processes the information from RTU (Remote Terminal Unit) inputs and outputs, while the Remote Terminal Unit or PLC (Programmable Logic Controllers) controls the local process. The communications hardware allows the transfer of information and data back and forth between the MTU and the RTUs or PLCs.
The software is programmed to tell the system what and when to monitor, what parameter ranges are acceptable, and what response to initiate when parameters change outside acceptable values.
An IED, such as a protective relay, may communicate directly to the SCADA Server, or a local Remote Terminal Unit (RTU) may poll the IEDs (Intelligent Electronic Devices) to collect the data and pass it to the SCADA Server. IEDs (Intelligent Electronic Devices) provide a direct interface to control and monitor equipment and sensors.
IEDs may be directly polled and controlled by the SCADA Server and in most cases have local programming that allows for the IED to act without direct instructions from the SCADA control center. SCADA systems are usually designed to be fault-tolerant systems with significant redundancy built into the system architecture.
The figure below shows the components and general configuration of a SCADA system. The control center houses a SCADA Server (SCADA Server or Master Terminal Unit (MTU)) and the communications routers.
Other control center components include the Human-Machine Interface (HMI), engineering workstations, and the data historian, which are all connected by a LAN (local area network) . The control center collects and logs information gathered by the field sites, displays information to the Human-Machine Interface (HMI), and may generate actions based upon detected events.
The control center is also responsible for centralized alarming, trend analyses, and reporting. The field site performs local control of actuators and monitors sensors. Field sites are often equipped with a remote access capability to allow field operators to perform remote diagnostics and repairs usually over a separate dial up modem or WAN (wide area network) connection.
Standard and proprietary communication protocols running over serial communications are used to transport information between the control center and field sites using telemetry techniques such as telephone line, cable, fiber, and radio frequency such as broadcast, microwave and satellite.
SCADA System General Layout
12 Responses to “SCADA Systems”
What are the functions of an IED ?
1) protection,
2) control
3) monitoring
4) metering
5) communications
What are the control functions of an IED ?
1) Local and remote control of up to twelve switching objects
2) Control sequencing
3) Bay level interlocking1 of the controlled devices
4) Status information2
5) Information of alarm channels2
6) HMI panel on device
What are the monitoring functions of an IED ?
1) Circuit-breaker condition monitoring, including operation time counter,
electric wear, breaker travel time, scheduled maintenance
2) Trip circuit supervision
3) Internal self-supervision
4) Gas density monitoring (for SF6 switchgear)
5) Event recording
6) Other monitoring functions, like auxiliary power, relay temperature,
What are the metering functions of an IED ?
1) Three-phase currents
2) Neutral current
3) Three-phase voltages
4) Residual voltage
5) Frequency
6) Active power
7) Reactive power
8) Power factor
9) Energy
10) Harmonics
11) Transient disturbance recorder (up to 16 analog channels)
12) Up to twelve analog channels
What are the SCADA system hierarchies ?
1) Field level instrumentation and control devices
2) Marshalling terminals and RTUs
3) Communications system
4) The master station(s)
5) The commercial data processing department computer system
Can you tell me some open software packages for SCADA ?
Citect and WonderWare
interesting post
a very good article about SCADA Systems