Comparing Grid Automation to Process Automation

Keywords: Process Control, Grid Automation, Safety Systems, MES, Data Historians, Optimization, ISA Levels of Control, Digital Transformation

Overview

ARC provides market research for the automation used in the process and utility industries. The automation for these two industries evolved separately but today they share considerable digital technologies. Often, the same companies that provide automation for process industries also provide grid automation for electric utilities. While process automation deals with managing solids, liquids, and gases, electric grids manage the flow of electrons. With such fundamental differences, why are there so many automation similarities?

The process industries focus on the manufacturing process for making products and delivering those products with distribution systems that may include pipelines, rail, or trucks. The utility industry is focused on providing reliable electric power to a geographically dispersed customer base distributed over wires. Both industries must focus on the real-time management of complex and hazardous processes. This requires measuring the current state of the process, acting quickly to respond to conditions that may present a hazard, while monitoring and controlling the variables that keep the process operating efficiently. The electric grid equipment at level 0 and level 1 may be measuring voltage, amperage, and AC waveforms to drive relays and switchgear; the process industry is more likely measuring temperature, level, pressure and flow and using on-off or modulating control valves, but in both cases this real-time information must quickly and reliably flow into the level 1 and level 2 control devices for safety protection and process control. Both industries need to have alarm management, graphic displays, and data historians and this software is very similar. Electric grids may have single diagram displays and GIS (Geographical Information Systems) for substations where process control may have P&ID type graphic displays that mimic process equipment piping.

Processes have MES (manufacturing execution systems), and grids have what you might call OES or operational execution systems. Both grids and processes have real-time closed loop control functions, optimization, asset management and ERP (Enterprise Resource Planning) that perform similar functions. ISA 95 standards describe the levels of control for process industries. The utility industry may have a different process, but they have similar levels of control. 

Grid Automation Has Unique Safety Concerns and Control Issues Compared to Process Automation 

While both grids and processes have regulatory and safety related controls, they use different systems. Safety systems for grid protection must protect power lines and equipment from failing but there is a high priority to keep power flowing. Protection systems for grids typically involve monitoring parameters like voltage and current that can detect various faults like short circuits (phase to ground or phase to phase), equipment overloads/failures, open circuits, and will operate switching relays or reclosers. Measurements are typically directly collected by the protective switch or recloser so there is near zero delay. If a tree falls on a power line, devices like reclosers will tolerate the high current load for a certain time before disconnecting power to prevent overheating wires or transformers and may re-energize the line a few times to see if the short circuit has cleared. Disconnecting power from homes and businesses creates an additional hazard for customers so burning the tree off the wires is often preferrable to losing power. The trip logic is typically configured in the switching device itself and redundancy can be implemented by aligning protection devices in series.

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