SCADA is an abbreviation for Supervisory Control And Data Acquisition.
There is always an argument that a SCADA system can perform all the functions of control, that is protection, indication, alarms, instrumentation, interlocks and control both manual and automatic.
This begs two questions, if the SCADA system breaks down or its communication network to a starter breaks down how is operational continuity maintained; second in general SCADA systems are programs that run on computers with Microsoft Windows operating systems the reliability of those operating systems is highly questionable as is their security. There is also the possibility that windows operating systems have back doors to allow ‘others’ to monitor activities or to remotely control or sabotage computers, it should be noted that such activities by the US federal organisations against US citizens is illegal in the United States however it is not illegal for US federal organisations to target non US citizens in any other country!
What was that statement in the declaration of independence (4th July 1776) “We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness.” The word hypocrisy comes to mind.
How often do Window’s operating systems update to correct errors and vulnerabilities and is that what the updates are really doing?
Therefore the SCADA system within this article forms part of the alarm, indication and control system, the key word is ‘part’, a failure or malicious attack on the SCADA system will not cause a total failure of operations, it may cause disruption but because of the hierarchical system of control described within this article the next lower level of control can take over fully from the SCADA system.
The SCADA system should also not play any part in the interlocking or process control systems, that should be left to either relays or programmable logic controllers with isolated inputs and outputs and that are totally stand alone, that is, not connected to the SCADA system or to the internet and do not have Microsoft operating systems.
Using various displays a motor may be controlled and monitored from the SCADA system the control element is dependant on the control being passed to the SCADA system. An engineer putting his key in a local control station and switching control to local will remove any control from the SCADA system; similarly switching a control panel to local will remove the control element from SCADA.
A sample of a MCC compartment; with ident 09/916054; SCADA display is included in the pdf version of this article. The display shows the instrumentation, mimic, metering, control, indication and alarm for the motor and displays for the associated plant status. The notes to the drawing give the various colour codes for the display, descriptions of the control functions and the addresses of the various inputs and outputs.
It is a separate file entitled SCADA screen display.pdf with an original paper size of A1 (841mm x 597mm) printing on to an A1 sheet will give a scale of 1:1, on an A2 sheet a scale of 0.707:1 and on an A3 sheet a scale of 0.5:1. To be able to read the drawing a recommended minimum paper size of A3 should be used, at the stated scaling the general text on the drawing has a minimum height of 1.125mm.