Efficient Plant March 2018 - 29

PdM partial-discharge testing
bushings
arresters
dry-type and liquid-filled transformers
air-insulated and gas-insulated circuit
breakers
potential, current, and control power
transformers
insulators of all types
motors and generators.
No matter the location, effectively detecting PD signals requires the right sensors.
Determining which sensor to use depends on
the type of signal created and its frequency,
something that can range from tens of kilohertz to a few gigahertz. The various types
include acoustic, ultrasonic, transient-earth
voltage (TEV), ultra-high frequency (UHF),
and high-frequency current transformer
(HFCT). While PD sometimes can be detected with just one or two types of sensors,
the best approach is to apply all applicable
sensors to a chosen asset and correlate the
information that's gathered.
Although there's no such thing as good PD
in an electrical-distribution system, some
equipment may have low levels of it with no
signs of damage. In these cases, it's not the
level of a PD signal that should cause concern, but, rather, any changes in it. An initial
PD investigation will establish a baseline that
can be compared with future testing results.

BOTTOM LINE
Annual or semiannual preventive maintenance and testing is recommended to
maximize system reliability and availability
of electrical systems. But, with so many sites
operating around the clock, maintenance
schedules can stretch beyond the comfort
level of plant managers. That's why online
predictive tools such as IR surveys and PD
testing are becoming increasingly important.
These techniques can uncover areas of overheating and insulation deterioration-two
of the leading causes of equipment failure-
sooner than later. Leveraging multiple sensor

MARCH 2018

technologies in these procedures helps
ensure accurate data for improved diagnostics. Accurate interpretation of test data will
provide operations with actionable information and, ultimately, lead to moreinformed risk-management decisions. EP
Steve Park is the manager of Technical
Services for Vertiv's (Columbus, OH, Vertivco.

com) Electrical Reliability Services business.
His 35+ years of experience with power systems includes 14 years with the U.S. Air Force,
during which he served as a high-voltage
lineman, electrical-power-distribution engineer, and instructor. He holds Bachelor's and
Master's degrees from Purdue Univ. and an
MBA from Indiana Wesleyan Univ. Contact
him directly at Steve.Park@Vertivco.com.

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