Lecture 8 SCADA systems

ZHU KUN 2012-4-17

Outline

• Course content -  Summary - Outlook

• SCADA -  SCADA system function -  SCADA architectures -  Non functional aspects

• Lab 2 –SCADA data engineering demonstration

Summary of study block 1

• Lecture 2 -  Power system apparatus

• Lecture 3 and 4

-  Power system protection basics -  Fault location analysis

• Lecture 5 ,6 and 7

-  Substation automations systems -  IEC 61850

Outlook for study block 2

• Lecture 8 -  SCADA -  Lab demonstration

• Lecture 9, 10 and 11 -  Communication network basics

• Guest lecture 1 -  SCADA security

• Guest lecture 2 -  SCADA and DMS

Course map

"IEEE Standard for SCADA and Automation Systems," IEEE Std C37.1-2007 (Revision of IEEE Std C37.1-1994) , vol., no., pp.1-143, May 8 2008 doi: 10.1109/IEEESTD.2008.4518930 URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4518930&isnumber=4518929

What is SCADA?

Supervisory Control And Data Acquistion -  Collect measurements and status data from the process -  Remotely interven the process -  Centralized system -  Distributed architecture

Applicable Processes - Oil or Gas prodcution facilities -  Piplelines for gas, oils, chemicals or water. -  Railway/Transportation Process -  Nuclear, Gas, Hyrdo generation plants

SCADA function

•  Data acquisition •  Analog and discrete values

•  Event and alarm processing •  Event and alarm

•  Control •  Tap changer •  Shut capacitor/reactor •  Switching devices •  Generator excitation (AGC)

•  Data storage, archiving and analysis

Data acquisition

• Points - Measured values

• Pseudo points -  Derived values

• Scan -  process by which data

acquisition system interrogates RTU/IED

• Scanning rate -  1 sample/2 seconds

• Time skew -  elapsed time between the

first measurement and the final measurement is taken

Event and alarm

•  Events •  Changing positions

–  Breaker/Disconnector opens or closes –  Value above/below a threshold

•  Equipment activated –  Reactor or capacitor engaged

•  Automatic changes –  tap changer changes its position

•  Alarms –  Criticality –  Sensitivity

Alarm management

What can be controlled

•  Tap changer •  Shut capacitor/reactor •  Switching devices •  Generator excitation (AGC) •  Sequential control

-  E.g. in the case of a set of sequential switching steps to restore power through predefined backup configuration.

Data archiving and analysis

• Data collected from the process is sometimes archived, this due to many reasons: •  Regulations •  Billing •  Future load planning •  Post Mortem Review, in case of disturbances or

interruptions in the process.

Squence of Event Recorder (SER)

• Local function implemented in IED that keeps a record of all events in the substation

• Not all events are sent to the SCADA system • SER logfiles can be uploaded to the SCADA

system to enable analysis

Remote Terminal Unit - RTU

• A remote terminal unit (RTU) is a microprocessors-controlled electronic device that interfaces objects in the physical world to a distributed control systems or SCADA by transmitting telemetry data to the system, and by using messages from the supervisory system to control connected objects.

RTU v.s IED

• Similarity -  Computation -  Communication

• IED focus on protection/automation function -  Build-in protection scheme -  Speed, the protection system operation is expected to be

completed within 20ms.

• RTU focus on communication -  Large number of I/Os -  ABB RTU560 PLC execution cycle is 100ms

Human Machine Interface - HMI

• Communication between operator and machine • Input

- Mouse, keyboard, touch screen • Output

-  Screen, audio, print-outs or mimic board • A weak link

-  Information overload/misinterpretation

Communication

• Wide Area Network -  Analog point to point and multi-point modem networks -  Frame relay/Cell relay type point to point and multi-point

networks - Wireless Radio/Satellite networks -  Fiber-optic based networks

• Protocols - Modbus -  Profibus -  IEC60870-5-101,104 -  DNP 3 -  IEC61850-90-2 -  IEC60870-6-ICCP (between control centers)

SCADA architecture I -classic

B

A

Static model

SCADA architecture II -modern

B

A

SCADA architecture III -modern

B

A

SCADA for “substation”

Three mile Island – Harrisburg 1979

video

Non functional requirements

Functional requirements specifies what is a system suppose to do and Non functional requirements specifies how a system suppose to be. • Availability

-  the ratio of uptime to the sum of downtime and uptime. • Maintainability

-  Repairing time for hardware and software • Scalability

-  How easy the system could be expand • Security

-  See SCADA security guest lecture • Interoperability/Openess

-  how easy can the system be integrated with systems from other vendors

Non functional requirements - Performance

• Desired response time should be designed for each SCADA function. These response time should be comply with power system control and operation procedure. -  Normal state, quansi-steady-state. Response time should

meet the requirements during normal state. -  Emergency state, when power system operation constraints

are violated. SCADA system are engineered to one specific emergency condition without degrading the performance.

Normal status

Emergency status

Restoration status

Non functional requirements - data quality

• Accuracy - Measurement transformer class -  ADC resolutions (bits) ….. - Measured/derived values

• Timeliness -  Scanning rate -  Communication delay

• Consistency -  Analog measurements and topology

Communication between control centers

• In a deregulated market -  Transmission is separated from generation -  Distribution is separated from sales -  Customers can purchase energy from any generating

facility -  Several transmission networks may be used for delivery

Communication between control centers