SCADA system for Dummies

SCADA system (Supervisory Control and Data Acquisition) which consists of number of Remote Terminal Units (RTU) which serves to collect data and send it to the Master Station via a communication system. Master Station function to display the data obtained and enables the operator to control remotely.We can put the sensors and control at each critical point in the process. Along with the SCADA system technology is getting better, we can put more sensors in many places so that more things that can be monitored, the more detailed operation can be seen, and everything works in real-time.

Common system components of SCADA are
  •  Human Machine Interface (HMI) :  is the apparatus or device which presents process data to a human operator, and through this, the human operator monitors and controls the process.
  • supervisory system,  acquiring data on the process and sending commands (control) to the process.
  • Remote terminal units (RTUs) connect  to the sensors in the process, converting sensor signals to digital data and sends digital data to supervising system.
  • Programmable logic controller (PLCs) used as field devices.
  • Various process and analytical instrumentation.
Process:Acquisition of the data begins at the RTU or PLC level, includes meter readings, equipment status reports and are communicated to SCADA.
Data is then compiled and formatted in such a way that a control room operator using the HMI can make supervisory decisions to adjust or override normal RTU (PLC) controls.
Data may also be fed to a Historian, often built on a commodity Database Management System , to allow trending and other analytical auditing.
 1) Human Machine Interface (HMI):A human–machine interface or HMI is the apparatus which presents process data to a human operator, and through which the human operator controls the process.HMI is usually linked to the SCADA system's databases and software programs, to provide trending, diagnostic data, and management information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides.The HMI system usually presents the information to the operating personnel graphically.

2)Supervisory System : The term supervisory system refers to the servers and software responsible for communicating with the field equipment (RTUs, PLCs, etc.), and then to the HMI software running on workstations in the control room, or elsewhere.

3)Remote terminal units (RTUs) :
The remote terminal unit(RTU) connects to physical equipment. Typically, an RTU converts the electrical signals from the equipment to digital values such as the open/closed status from a switch or a valve, or measurements such as pressure, flow, voltage or current. By converting and sending these electrical signals out to equipment the RTU can control the equipment.

DSCADA in power generation systems:

Distribution feeder Supervisory Control and Data Acquisition (DSCADA) is a set of technologies for providing remote monitoring and control of equipment located in distribution substations and out on the distribution feeders themselves. Distribution SCADA (DSCADA) is a basic building block upon which Smart Distribution is based. DSCADA provides the ability to monitor the distribution system components in real-time or near real time. Smart distribution applications use the monitoring and control capabilities provided by DSCADA to determine steps needed to optimize the performance of the distribution system.Main Functions Of DSCADA:

The main purpose of the DSCADA system is to continuously monitor the loading, status, and performance of equipment located on distribution feeders. Under normal conditions, the system periodically acquires real-time values of current and voltage at various strategic measurement points and the open/closed status of all monitored switches.
Typical sources of DSCADA measurement information and equipment status indications include:

 Intelligent Electronic Devices (IEDs) associated with distribution system power apparatus. IEDs include protective relays, device controllers (voltage regulators, capacitor bank controllers, etc.), and Remote Terminal Units (RTUs)

 Standalone sensors, such as faulted circuit indicators (FCIs) and line monitoring devices.

 External systems, such as Advanced Metering Infrastructure
This information is typically displayed to an operator and stored in a database for future reference and analysis. When an abnormal condition occurs (such as recloser operation due to a line fault), alarm information is reported to alert the operator to the event.
The DSCADA system also enables operators to remotely control devices located on the feeders. Controllable devices include reclosers, capacitor bank switches, voltage regulators, and any other electrically operable device.
DSCADA is also being used to monitor and (in some cases) control the growing number of Distributed Energy Resources (DERs) being connected to the distribution system. DERs include distributed generating units (including renewables) and energy storage units.
However, there are relatively few examples of use of SCADA system. Monitoring and control of the electric distribution feeders has been a manual process for the most part. Two main reasons for the lack of DSCADA installations are:
• High implementation cost. 
 Lack of customer demand for improved distribution feeder performance and reliability.
But the situation is changing. Technological advancements, especially in wide area communications, and the evolution of industry standard products have driven down the cost of DSCADA implementation, while an increasingly computerized customer base has driven up the demand for improved power quality and service reliability. As a result, there has been a growing interest in deploying DSCADA capabilities.

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