IEEE Electrification Magazine - December 2015 - 26

Corporate
Network
SCADA
Network
Firewall

SCC

RCC

HMI: Human-Machine Interface
RTU: Remote Terminal Unit
SDR: Station Data Repository

Transformer
Transformer
Monitoring and Control
Station PC
(SDR)

Harmonics
Relay

Yard

Hall-Effect
Transducer

RJ232→Fiber
Converter
Fiber→RJ232
Converter

HMI

Control
House

Oscillography

GIC
Relay

Fiber

Figure 4. GHM system-substation level.

can be used to meet NERC CIP requirements. A GPS receiver
is housed in the GIC relay cabinet to provide time-stamps for
GIC data and event recording.
Depending on a transformer's design, age, loading, and
health condition, the same level of GIC flow may have different impacts (saturation, heating, etc.) on different transformers. The programmable logic in the GIC relay can set up multiple alarms to alert system operators to take appropriate
actions when the detected GIC current reaches a trigger
threshold for a sustained period of time, for example, 30 s.
Because of the lack of detailed transformer assessment, the
alarm thresholds are to be set with considerable margin
based on historical GIC observations and inputs from transformer subject matter experts and vendors. However, caution
should be taken to avoid generating too many unnecessary
alarms to compete for the operator's attention, and the alarm
settings should be evaluated and refined once we gain more
insight on the transformer GIC response. It is desirable to
have multiple levels of GIC alarms, for instance, with a Level I
alarm (a lower-level GIC threshold) to alert the operator for
elevated GMD activities at the monitoring site; a Level II alarm
(signaling significant risk to the equipment or system operation if not responded to accordingly) to trigger necessary
operator's actions prescribed in GMD operating procedures;
and a Level III alarm to direct operators to take immediate
actions to protect a transformer from potential damage.

GIc monitor Installation
It is not easy to get a transformer outage for GIC monitoring
device installation, especially for an EHV transformer.

26

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

Fortunately, temporary safety grounds can be placed on the
transformer grounding structure for GIC installation without
taking the transformer out of service. The structure will be at
ground potential at all times, but neutral current will be circulating on the neutral bus. The construction crew should be
aware of this during the installation.
Depending on the individual utility's practice, transformer ground leads may be replaced with appropriate
insulated size cables (e.g., 4/0 cable) that will enter the dc
transducer cabinet through a weatherhead, pass through
the dc transducer, and pass through conduit to the ground
grid. The new grounds should be checked to solidly connect the grounding structure and the ground grid. Once
the new grounds are verified, the existing grounds can be
removed. The other option is to install a split-core-design
transducer on existing grounding neutral to avoid a transformer outage request.
For a typical GIC monitor installation (shown in
Figure 5), a dc transducer cabinet and a GIC relay cabinet
will be added to existing transformer neutral structure.
Multimode fiber in interduct must be run with ac and dc
cables to the GIC relay cabinet through existing cable trench
and new conduit connecting the GIC relay to an RTU and/or
a local substation computer in the control house.

Harmonics Monitoring
The transformer half-cycle saturation due to GIC flow
can generate harmonics into the power grid, increase
transformer reactive power losses, and overheat a transformer if significantly high GIC presents for a sufficiently



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

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