Potentials - September/October 2017 - 10

Over their 100+ year history, power control
systems have become increasingly
complex and interconnected.

While power plants have these
general aspects in common, other
generation processes vary based on
the type of fuel being used. For example, nuclear and fossil-fuel units
balance steam production to meet
the electrical load and minimize the
cooling load. Hydroelectric units adjust the angle of the water admission
"wicket gates" to increase or decrease
the amount of power generated.
In the United States, regional transmission organizations (RTOs) are in
charge of their regional piece of the
power grid. RTOs match regional
power output to load, arrange the sale
and delivery of power across control

areas, and run an energy management system (EMS). The EMS takes
sensor data, computes power flows,
and performs contingency analyses
to ensure reliable transmission. Another aspect of many RTOs is the
conduct of a daily, day-ahead "auction" to determine the most economic
dispatch of the next day's generating units. These RTOs also manage
a real-time energy market that closely matches actual demand for energy
to load.
In addition to RTOs, there are
local transmission owner control
rooms that monitor and control power delivery throughout their piece of

Data from Devices

Commands to Devices

Power System Control Layers

Enterprise Level
Corporate Networks
Business Systems

Firewall

Regional Control Center Level
Energy Management System
Automatic Generation Control

Firewall

Local Control Center
Energy Management System
SCADA System

Firewall

Substation Level
Control Network
RTUs, PLCs, Master Relays

Device Level
Sensors, Actuators, Relays
Equipment Under Control

FIG2 Power system control layers.

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S e p t e m ber /O ctober 2017 IEEE POTENTIALS

Internet for
Data
to/from the
Enterprise
System and for
Commands to
Power Plants

Internet for
Data to
Enterprise
Systems and
for Remote
Vendor and
Employee
Access

the regional grid. This level of control room uses SCADA systems to
monitor and operate its field devices. Under the control of the SCADA
system, capacitor banks are used to
maintain voltage within 10% of nominal across the system, and circuit
breakers and switches, in coordination with field electricians, help create safe work zones for maintenance
and construction. Local-transmission cont rol rooms also operate
their own EMS.
Local-transmission control rooms
work in tandem with local-distribution control rooms that manage a
smaller portion of the grid. The distribution control operators work with
hands-on linemen, electricians, and
end-use customers. They receive customer feedback and service requests
and dispatch repair crews to restore
power delivery to those experiencing
outages. Many of these distribution
control centers also have SCADA for
system monitoring and remote control of equipment.
Over time, many utilities have
established connections from their
operat i ng tech nolog y (O T ), l i ke
SCADA systems, to their information technology (IT) through the
Internet. These connections facilitate easy access to data for utility
employees and vendors. They may
also allow utility engineers and
vendors to remotely troubleshoot
and reprogram field equipment.
These connections between utility
OT and IT over the publicly accessible Internet create "attack surfaces," potential holes in the OT
network's electronic perimeter. The
control-system layers and their typical connections to the Internet are
illustrated in Fig. 2.

Mandatory standards
in the power industry
In the wake of the Northeast blackout of August 2003, the U.S.-Canada
Power System Outage Task Force
was formed and conducted exhaustive investigations of the event. In
their final report, they discussed the
root causes of the massive outage.
The task force found that many who
worked directly with the power grid

Table of Contents for the Digital Edition of Potentials - September/October 2017