IEEE Electrification Magazine - December 2015 - 24

GMD. GMD appeared to have less impact on AEP than on
utilities closer to the Earth's poles, and the GIC monitors
were removed after the cycle peak for the past two cycles.

Gmd monitoring

layer networks within the GMD monitoring system: the
corporate level and the substation level.

GIC/harmonics
monitoring can
provide insightful
assessment on
the GMD impacts
on substation
equipment and
system operations.

To mitigate the risks of severe solar
storms and operate its grid through
such events, AEP is implementing a
permanent GMD monitoring system
to detect and evaluate GMD impacts
on its system and critical transformers, as well as to provide assistance
to transmission operators to protect
transformers and to prevent a system blackout.

Architecture of the GMD
Monitoring System

The GMD monitoring system at the
corporate level comprises a system
control center (SCC), a few regional
control centers (RCCs), and a number of GIC/harmonics monitoring
(GHM) systems located at key substations. Figure 3 provides a company-wide overview of the configuration of the GMD monitoring system.
The number of RCCs depends on a
utility's geographical service territories, practice, etc. The GMD database
(DB) can be located at the SCC and
connected to the backup server of
the SCC to minimize interventions
to other key functions of the SCC, such as real-time system monitoring and control functions. The GMD DB may
be accessed by authorized users from the corporate-wide
area network.

To provide wide-area situational
awareness during a GMD event, an
effective and reliable GMD monitoring system, comprising GIC monitoring and harmonics monitoring, has
been implemented. The functional diagram of the
GMD monitoring system is shown in Figure 2. Transmission operators monitor the GIC and harmonics
information from multiple sites via an existing supervisory control and data acquisition (SCADA) system.
The monitoring sites were selected based on a set of
criteria including network configuration, asset criticality, historical GIC observations, ground resistivity, GIC
sensitivity, and grid coverage. The GMD K-indices from
the U.S. National Oceanic and Atmospheric Administration's (NOAA's) multiple geomagnetic observatories
are also monitored, and AEP Transmission is currently
receiving K alerts and warnings of level five or higher
from NOAA's Space Weather Prediction Center and
PJM. Based on the monitored GIC/harmonics information and GMD alerts, AEP Transmission coordinates its
operating actions with generator operators, nuclear
plant operators, and PJM.
The GMD monitoring system is a substation-based
corporate-wide area monitoring network. There are two

GIC/Harmonics
Monitoring

GHm System-Substation Level
As shown in Figure 4, a typical GHM configuration at a substation comprises two parts: 1) GIC detection in the yard
and 2) GIC data collection and harmonics monitoring in the
control house. It is recommended to use fiber to connect
the GIC relay in the yard and the remote terminal unit
(RTU) in the control house to minimize electric field interference to GIC measurements. If a substation network is
identified as a critical cyber asset per NERC critical infrastructure protection (CIP) standards, serial-to-fiber converters such as RMC20s can be used in the GIC cabinet and
at the RTU/station data repository panel to provide serial
connection over fiber.

GIC Monitoring

NOAA

D

The GIC detection includes 1) a Hall-effect dc transducer
installed on transformer neutral to measure three-phase
total GIC current and 2) a GIC relay to
filter out ac components. Typically,
pole-mounted cabinets close to a
monitored transformer or common
grounding structure for three singleRTO
phase transformers are used to house
the Hall-effect dc transducer, the GIC
relay and global positioning system
(GPS) receiver, and fiber splicing.

ast

GM

SCADA

rec

Fo

Station Data
Repository

Operator

Figure 2. A functional diagram of a GMD monitoring system. RTO: regional transmission organization.

24

I E E E E l e c t r i f i cati o n M agaz ine / december 2015

Gmd monitoring
System-corporate Level

Hall-effect dc Transducer
The dc transducer uses a Hall-effect
sensor capable of measuring both ac
and dc. The integrated output amplifier



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