SCADA:


What is SCADA?

  1. SCADA means Supervisory Control and Data Acquisition.
  2. A Scada system is one which facilitates an operator to control a remote system and acquire real time information from a remote location.
  3. Control and data acquisition can be from a single point or from multiple points.

Where SCADA is used?

  1. Power Generation, Transmission and Distribution.
  2. Defence.
  3. Avionics.
  4. Meteorological stations.
  5. Civic bodies – viz Control of street lights.

Benefits of SCADA:





Scada for Power Transmission:

  • The Load dispatch center is the hub for load dispatch and control.
  • LDC requires data with respect to available generation and load to be attended as such,
    • Real time Data is required from all Generating stations
    • Real time Data is required from Receiving stations
    • Real time Data is required from Interface points (Feeders) from where power is delivered to Distribution companies or Consumers.
  • LDC has to exercise control over the receiving stations, and consumers and if necessary the Generators also as such,
    • Supervisory control is required to shed loads by opening a breaker.
    • Supervisory control is required switch off or switch on a consumer.
    • Supervisory control is required to control the generation as and when control is extended.


Scada Components:



What is a transducer ?

  • A transducer is a device, usually electrical, electronic, or electro-mechanical, that converts one type of energy to another for the purpose of measurement or information transfer. In a broader sense, a transducer is sometimes defined as any device that senses or converts a signal from one form to another.

  • An Electrical transducer in our case, is one, which is used to change an electrical quantity such as voltage, current, power or frequency into a proportional dc output.
    • AC voltage and/or Current--------> Transducer-------->DC current.

  • AC Transducer inputs

    • Current,Voltage,Power (watts, Vars, VA),Frequency,Power Factor.

  • AC Transducer outputs

    • Industry standards:4-20mA,0-10mA.Others available: 0-1mA, 0-10V, ...
  • Transducer outputs are load independent
  • Advantages,
    • Simplified transmitting of data over long distances.
    • Several indicating instruments can be connected to the same transducer without any adjustments.
    • Adjustment of instrument wire resistance is not required.
    • Use of thin wires makes wiring simple and inexpensive.
    • Instruments can be easily connected or disconnected without affecting the measuring value of other instruments in the circuit.
    • The transducer can be open-circuited or short-circuited without causing any problems.

What is a RTU ?

  • The SCADA RTU is
    • small ruggedized computer
    • provides intelligence in the field,
    • allows the central SCADA master to communicate with the field instruments.
    • stand alone data acquisition and control unit.
  • Its function are
    • to control process equipment at the remote site.
    • acquire data from the equipment.
    • transfer the data back to the central SCADA system.

Software functionality in an RTU:

  • Real time operating system.
    • scanning the inputs,
    • monitoring the communications ports.
    • Driver for the communications system.
    • Device drivers for the I/O system (field devices).
  • SCADA application
    • scanning of inputs
    • processing and storing of data
    • responding to requests from the SCADA master

RTU – Basic operation:

  • The RTU will operate scanning its inputs normally at a fairly fast rate
  • Responds to Master when polled
  • Some processing changes such as,
    • Change of state
    • Time stamping of changes
    • Storage of data awaiting polling from Scada master
    • Reporting to Scada Master
    • Alarm processing





SCADA Components in Energy Sector:

  • RTUs at stations, Generating stations and control centers
  • Communication media by VSAT
  • SCADA Master control system at LDC

Utilization of SCADA functions:

  • REAL TIME DATA ACQUISITION FROM ALL RTUs
  • PROCESSING OF ACQUIRED DATA.
  • DATA EXCHANGE BETWEEN CONSTITUENTS
  • LIMIT / STATUS MONITORING & ALARMING.
  • SEQUENCE OF EVENT RECORDING.
  • INFORMATION STORAGE & RETRIEVAL.
  • DATA RETRIEVAL FOR ABT FUNCTIONS.
  • DATA RETRIEVAL FOR RMMI FUNCTIONS.
  • SUPERVISORY CONTROL.
  • VIDEO TRENDS
    • Dynamic trends of key analog data against time are set for LDC
  • DISTURBANCE DATA COLLECTION
  • REPORT GENERATION
    • Reports are generated from stored data
  • CONTINUOUS RECORDING DATABASE
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