IEEE Electrification Magazine - December 2015 - 32

procedure to 1) ensure the AEP SCC and Transmission Dispatch Center are aware of GMD forecast information, 2) provide guidance on how to respond to the potential GMD event,
3) include voltage monitoring as an indicator of any reactive
power support issue, and 4) provide options to reduce the
risk of damage to transformers due to N-GIC current. For
instance, if the transformer N-GIC exceeds a threshold
value that could jeopardize the transformer, the GMD procedure prescribes actions to mitigate the risk to the transformer. Some of the operator actions specified in the GMD
procedure following a GMD event are
xx
log the event and any observed system anomalies (K ≥ 6)
xx
notify plant operators, transmission operators/dispatchers, and
the reliability coordinators (K ≥ 6)
xx
maintain a heightened awareness
for the known symptoms and problems associated with GMD (K ≥ 6)
xx
monitor PI charts for unusual voltage fluctuations and associated
transformer Mvar losses where
available (K ≥ 7)
xx
review existing and planned outages on the EHV system (K ≥ 7)
xx
be extra diligent in following AEP
voltage and reactive guide (K ≥ 7).
Similar procedures have also been
developed based on observed transformer GIC currents from monitoring
sites. Three GIC level alarms (30, 90, and 250 A) are monitored by the transmission operator, and corresponding
actions including potential emergency switching after

consulting the regional reliability coordinator are defined
for each GIC level.

GMD Monitoring System Expansion
In addition to monitoring the GIC currents, harmonics, and
transformer reactive power losses, three magnetometers for
measuring geomagnetic field were installed in AEP East: one
is in northern Indiana, one in central Ohio, and the third one
in southern Virginia. These installations are strategically
located apart to have full coverage of the AEP PJM footprint.
The geomagnetic-field measurements can be correlated
with the monitored GIC currents/harmonics/Mvar losses for
model validation, and they can also be
used to support GIC flow simulations
based on nonuniform E-fields.

The AEP asset
renewal program
frees up more EHV
transformers, with
the best of the
retired transformers
retained as
emergency spares.

Through the past decade, AEP has
strengthened its GIC-related requirements in transformer specifications.
The latest EHV transformer specifications for AEP's transmission system
include design and performance
requirements for single-phase transformers (e.g., 765 kV and 500 kV) to withstand six cycles of 5 min on and 5 min
off of 120 A dc in the common and series
windings without exceeding the dissolved-gas values listed in AEP EHV
Transformer Specification, and six cycles of 5 min on and
5 min off of 300 A dc (or 100 A dc per phase) for 345-kV threephase transformers. No restriction is placed on core configuration.

% MVA Rating Versus GIC/Phase
100

90

90
% MVA Rating

% MVA Rating

% MVA Rating Versus GIC/Phase
100

80
70
60
50
40
270

Equipment Hardening

80
70
60
50

275

280

285

290

295

300

GIC/Phase (A)
Winding Hot-Spot Temperature = 140 °C for 30 min
(a)

40
150

155

160

165

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

175

Tie-Plate Hot-Spot Temperature = 160 °C for 30 min
(b)

Figure 11. Calculated GIC capability of a 765-kV transformer for 30-min continuous GIC: (a) winding and (b) tie plate.

32

170

GIC/Phase (Av)



Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2015

IEEE Electrification Magazine - December 2015 - Cover1
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IEEE Electrification Magazine - December 2015 - 1
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