Control Systems Terminology


Thread Starter

J.R. Leith

Hi There:

I am starting to help in the preparations of specifications for the automation of a large substation in South America. At this time, my comments are in basic terminology.

SCADA (Supervisory Control and Data Acquisition) appears to be what I am looking for in this substation automation. Thus, the pursued DCS solution consist in precisely supervisory control and data acquisition. However, the
term appears to have gained a specific meaning different to what is normally provided in a substation automation. I am noticing that the SCADA products seem to be applicable for controlling other processes so I tend to stay away
from them.

I need to understand and use the terms properly. What is preciselly SCADA nowadays?

Best regards,

J.R. Leith
IIS Engineering

Darold Woodward

While I work for a producer of protective relays, my main focus is integration and automation in substations and other power handling/generation facilities. My experience is similar to yours in that the power delivery industry has a different meaning than that used in the process control industry. More properly, I think that both definitions are just shades of the generic
definition you mentioned below.

In the power industry SCADA is usually used only for a supervisory system based on a master station at a central location and many remote terminal units (RTUs) in the field. The term has been used in the process control industry to refer
to Human Machine Interface (HMI) software independent of the devices used to collect the data.

In the power industry the original purpose and hardware used to implement RTUs has also changed significantly as RTUs have taken on the duty of protocol conversion, I/O (input/output) monitoring, automated decision making, and local
database operations.

I would be happy to discuss additional project specific details with you as someone who doesn't sell SCADA, but works on interfaces with SCADA systems on a regular basis. I can also recommend that our distributor in Pretoria, IST Energy ( who deals with substation automation/integration projects and SCADA systems as a possible resource.

Darold Woodward PE
SEL Inc.
[email protected]

SCADA is precisely what you said. "Supervisory Control and Data Acquisition". It is my opinion that "SCADA" can be molded to do whatever you
want it to do. I personally have created SCADA applications to control Lights and signs on a bridge, as well as used it to create an application to control medium voltage switchgear (28.8Kv Circuit Breakers). I've seen SCADA used to control prison doors and security, as well as Airport lighting, and not to forget Train Control. I see SCADA as a combined package of HMI,
Control, and Status. With the right tools, you can make a SCADA system for just about anything you desire. Maybe you feel SCADA is for certain
applications due to the "Template" feel of some packages? I've found pumps, valves, gauges, (and general Factory Floor devices) and the like are widely used as "Templates" in most Development packages. I have yet to use a Single "Template" for developing a system. I think the real issue here is do you want to control your substation from a PC, as well as gather information about the substation and bring it to the P.C. in a real time environment? If the answer is yes, then I would say that you DO want a SCADA solution. The
route you take from there has many forks. the hard part will be determining what you want the system as a whole to do, then find the right development software to fit your needs. Frankly I don't think even that is going to be too difficult.

Stated as an opinion,

J. R.,

The usual application of SCADA entails allowing the process to be controlled "locally" meaning instrumentation, I/O, etc. directly monitoring and
adjusting to the individual aspects of the process being controlled. The "SC" part of SCADA then entails that there is a blanket system that the "local" controlling and monitoring devices feeds info to which allows the "supervisor" part of the system to either alert personnel to alarm
conditions or signal other devices in the total control scheme to take an action. This sometimes means that the "local" control will have the ability to have parameters downloaded to them as well. This then gets you into the recipe type control that allows for different setpoints and actions on data from the same instrumentation, etc. The "DA" part of SCADA entails just that, Data Acquisition. Purposes of collecting that data vary due to whomever it is collecting it for whatever reason but typically it is to analyze it for making adjustments to the process to produce a more desired end product, or for historical tracking that can be tied back to the product
in case a problem arises in the future and a look at the process conditions that were prevalent when that product was produced could be helpful. Rather a broad swipe at it but I hope that this helps.

Sid Roberts

[email protected]