Lauletta handout - paper 2

1. Laboratory Measurements for Power System
Condition Monitoring
Donald G. Kasten1, Stephen A. Sebo1 and John L. Lauletta2
1
The Ohio State University, Dept. of Electrical and Computer Engineering, Columbus, OH, U.S.A.
2
President and CEO, Exacter, Inc., Columbus, OH, U.S.A.
E-mails: kasten.1@osu.edu, sebo.1@osu.edu, jlauletta@exacterinc.com
Abstract – About 30 percent of all overhead power distribution Exacter, Inc., has developed a device it is marketing to
outages are caused by failing electrical equipment, e.g., surge detect and analyze the radiated EM noise from distribution
arresters, cutouts, insulators, wires, and grounding. Failing components that have a discharge. This Outage-Avoidance
equipment can be located and scheduled for removal prior to an System has been developed using a group of very sensitive
outage. Replacing failing equipment reduces all reliability index
figures. Equipment that was identified by the EXACTER®
high-frequency detectors, filters, an omni-directional
Outage-Avoidance System as an electromagnetic (EM) noise wideband antenna, a computer, GPS equipment, and data-
source was removed from service and tested in the High Voltage communication equipment that operate together to determine
Laboratory of The Ohio State University. The purpose of the the location of an arc source. The wide application of the
laboratory effort was to begin the process of identifying the EM system has shown that the system is practical and useful [1].
noise emission signatures of a failing component so that the The main objective is to use the Outage-Avoidance
effectiveness of the field measurement apparatus can be System to survey a particular distribution line, analyzing the
improved. In other words, ultimately develop a Failure Signature radiated EM noise from it, and to determine whether a
Library to identify what component failed and what type of discharge is producing some of that EM noise, and then to
failure occurred.
identify what component it is and where it is located. The next
Keywords – outage-avoidance system, laboratory measurements
step of the process is to bring the failed equipment into the
laboratory and under a controlled environment test the
“defective” components to extract as much information as
I. INTRODUCTION possible into the “what and why” of the failure. The common
assumption is that different equipment and different arcing
It is essential that the electric energy supply system scenarios associated with specific equipment may have
remain operational at all times to meet the electric energy different signatures of the radiated EM noise. Thus as an
needs of the industrial, commercial and residential sectors of ultimate objective, it would be desirable to determine a library
the system. Equipment failures do occur due to aging of the of failure signatures from the field and laboratory
equipment, installation shortcomings and lack of preventive measurements so as to make the field equipment “smarter”
maintenance. Many times low-level discharges are a precursor when identifying a component, and what type of failure that
to arcing followed by a more catastrophic failure later. This component experienced.
type of activity occurs on all parts of the electric energy Typical failure locations are all-metal hardware on a tower
supply system. If it can be detected early, then the system or pole, especially when there are contamination, oxidation, or
operator can choose when to remove the faulty component so bad contact points, and along insulators, splices, and clamps.
as not to jeopardize the integrity of the overall system. If the Mechanical damage and contamination of insulators can also
discharges and/or arcing were not detected and allowed to be disturbance sources. There are many problems associated
become worse and finally result in a complete failure, then the with surge arresters. They are typically related to the
operator no longer has a choice on when and how to remove insulation housing (porcelain or polymer), moisture
the faulty component and parts of the system may be out of penetration (ingress), contamination of gaps, poor contacts,
service for the repair interval. The key is to be able to detect ground lead disconnector (detonator), corrosion (e.g., at
the discharges and/or arcing early. grounding), and aging (material changes).
The effort described here intends to investigate the
spectrum of the EM noise from low-level discharges and
arcing and to identify it with the failure of a specific II. DESCRIPTION OF MEASUREMENT EQUIPMENT
AND PROCEDURES
component on the system. This effort will mainly be directed
towards the electric power distribution systems because there
are many, many more miles of distribution circuits compared Currently the laboratory effort is only associated with
with transmission lines. It should be emphasized that the components that have been identified from field measurements
principles applied for the distribution network can also be as emitting a radio frequency EM noise signal. When it can be
applied to the transmission system. coordinated with field personnel, after the identified
component is removed from service, it is salvaged and sent to

2. the laboratory for testing. The majority of the components applied to the component under test and the leakage current
tested were surge arresters. Some of the arresters were part of through the component to ground are monitored and the
a fuse-cutout and other arresters were separate. Also tested waveforms recorded using a digital oscilloscope. A precision
were disconnect switches, dead-end bell insulators, post current-viewing resistor is used to monitor the current.
insulators and pin insulators. The most recent tests (not yet The procedure was to test the component at its rated
completed at the writing of this paper) involved a string of voltage. For most cases, this meant the line-to-ground voltage
230-kV transmission line porcelain suspension insulators. of the component. Surge arresters were tested at the MCOV
(Maximum Continuous Operating Voltage) rating value. That
A. Field Effort value is defined by an IEEE standard as the “maximum
designated root-mean-square (rms) value of power frequency
The field measurements utilizing the Outage-Avoidance
voltage that may be applied continuously between the
System are fully described in a companion paper [1]. Basically
terminals of the arrester [2].”
they involve a survey-type process where the detection
The voltage applied to the component under test and the
equipment is driven within the system with multiple passes,
current through the component were monitored as the applied
and the measurements from all passes are correlated so as to
voltage was increased from zero to its rated value. In some
narrow down the location of the failed equipment. Various
cases where complete failure occurred, it was not possible to
other pieces of commercially available hand-held equipment,
reach the rated voltage. As indicated in Fig. 1, the applied
such as an ultrasonic detector and a portable EM noise
voltage was measured using a resistive voltage divider and the
detector, are used to further narrow the focus.
leakage current by measuring the voltage across a 50-ohm
current-viewing resistor. The instantaneous voltage and
B. Laboratory Effort
current waveforms displayed on a digital oscilloscope were
Tests were conducted in the High Voltage Laboratory of stored since the character of the waveforms changed as the
The Ohio State University (OSU). During all tests, each power failure mode of the component being tested changed.
system component identified earlier was energized at rated The EM noise signal emitted from the component under
voltage, or in some cases at an overvoltage. The specific goal test was monitored with the EXACTER equipment and with a
was to determine whether the components emitted any EM 1.5 GHz spectrum analyzer. Each device had its own antenna,
noise signal that could be detected and recorded. The test the same type for each. The EXACTER device monitors the
circuit used in the High Voltage Laboratory is shown in Fig. 1. EM noise signal, extracts information from that signal and
calculates, using a proprietary algorithm, a quantity referred to
as “maintenance merit.” When this value exceeds a certain
threshold, the equipment extracts from the EM noise signal a
spectrum of frequencies ranging from the fundamental up to
and including the 50th harmonic [60 Hz to 3 kHz]. This
spectrum is updated every second; these spectra are stored for
later recall and data analysis.
III. TEST RESULTS
Many laboratory measurements were conducted in order
to determine typical signatures of failing electrical equipment
used in the power distribution overhead network. The scope of
Figure 1: Schematic of test circuit used for laboratory measurements the measurements was to test electrical distribution system
components under controlled laboratory conditions. The
The laboratory effort is used to test the specific components were initially identified by the outage-avoidance
component that has been identified as failed or failing. These system. The laboratory measurements checked the
tests are only electrical in nature and cannot test the repeatability and consistency of emissions and signals from
component with the mechanical loading that it had component to component as well as a function of time.
experienced in the field. Furthermore, the laboratory tests are Most of the tests were conducted under ambient
voltage related as most components being testing are some laboratory conditions when the component tested was dry. A
form of insulation, so no electric current loading is associated few tests were conducted in a fog chamber within the High
with the high-voltage tests. Also, due to the building- Voltage Laboratory. The procedure was to monitor the applied
controlled environment of the laboratory, temperature and voltage and any leakage current with multi-meters as well as
weather changes cannot be simulated during the tests. observing the temporal characteristics of the waveforms on an
Two high-voltage sources are available. One is up to 50 oscilloscope. The EXACTER Outage-Avoidance System was
kV rms, 60 Hz, which was used for most of the components turned on so it could record the low-frequency spectrum. In
tested as most components are at the 15 kV level. If necessary, addition, the spectrum analyzer was monitoring the radio
a 250-kV rms, 60-Hz source is also available. The voltage frequency EM noise emission.

3. Fig. 2 shows photographs of two different components
tested. The two components are a 10 kV surge arrester, log
#30, and a 15 kV two-unit dead-end-bell, log #31. Their test
results will be presented here and are typical of those recorded
for all equipment tested.
Figure 2: Photographs of equipment tested and results presented
Fig. 3 shows test results of log #30, the 10 kV surge
arrester. The upper graph represents data recorded by the
EXACTER equipment over a period of time; this is the Figure 3: Surge arrester log #30 – EXACTER and spectrum analyzer
frequency spectrum from the fundamental 60 Hz up to 3 kHz measurements
extracted by EXACTER from the EM noise emission. The
graph gives the maximum, median, average and minimum Figs. 5 and 6 show a similar set of results for a dead-end
values of that spectrum for each frequency of the 798 recorded bell, log #31, which was shown in Fig. 2. The EXACTER-
data sets. The number of points indicates how long this determined low-frequency spectrum is shown as well as the
particular noise emission lasted; one data point is recorded full spectrum in Fig. 5. Fig. 6 gives the temporal variation in
every second. It should be noted that in many cases the EM the applied voltage and leakage current for the dead-end bell.
noise may be intermittent, so for a given period of
energization there could be several bursts of noise. The A total of 16 arresters were tested, with ratings of 9 kV,
EXACTER equipment does require that the EM noise be 10 kV and 27 kV. Other components tested included dead-end
above a particular level for a certain period of time before bells as shown in Fig. 2, cut-outs (with or without fuses),
starting data storage. Similarly, it stops data storage when the switches, suspension insulators, pin insulators and some post
EM noise ceases for a given period of time. insulators. Similar data was recorded for all components as
The photo shown in the lower section of Fig. 3 is that of illustrated in Figs. 3–6.
the spectrum analyzer that “looks” at the entire frequency
spectrum of the noise; for this particular photo the horizontal IV. SPECIAL TESTS
axis is 20 MHz/div.
Fig. 4 shows the time domain representations of the same Some special tests were also conducted. (a) A switch with
test results illustrated in Fig. 3. Both sections of Fig. 4 broken insulators was tested for EM noise emissions.
represent oscilloscope traces of the monitored applied voltage Conditions of the broken insulator were examined and
(top trace), measured leakage current through the current- correlated with the noise emission when the size of the gap
viewing resistor (middle trace), and the radiated noise as between the broken parts was changed. (b) Tree branches were
received by a simple monopole antenna (bottom trace). The brought to the laboratory and contact was established between
three traces of the upper section show about 3 cycles (approx. an energized conductor and a grounded tree branch in order to
50 ms) of these quantities, whereas the three traces of the simulate the failure conditions during a storm. (c) As
lower section have a time scale of 50 ns/div to more closely mentioned above, tests in a fog chamber were conducted. (d)
observe the fast temporal characteristics of the leakage current The changing phase shift between the leakage current and
(middle trace) as the arcing occurs. energizing voltage of surge arresters was monitored as the
voltage was raised.

4. Figure 4: Surge arrester log # 30 – scope waveforms at 15 kV; top trace: Figure 6: Dead-end bell insulator log # 31 – scope waveforms at 12.5 kV; top
applied voltage; middle trace: voltage across CVR; bottom trace: spectrum trace: applied voltage; middle trace: voltage across CVR; bottom trace:
analyzer input. Horizontal scale: upper: 5 ms/div; lower: 50 ns/div spectrum analyzer input. Horizontal scale: upper: 5 ms/div; lower: 100 ns/div
V. OBSERVATIONS AND CONCLUSIONS
The objective of the project described in this paper was to
characterize the electrical signatures of EM noise emission
sources. This noise radiates from those components of the
electric power systems that are in the process of partial or
complete failure. The ultimate goal is to develop a Failure
Signature Library so that the type of component and its failure
modes can be identified from the signals observed.
ACKNOWLEDGEMENTS
The OSU authors wish to acknowledge and thank
Exacter, Inc. for its financial support of this effort, and the
technical guidance of John Lauletta, President and CEO of
Exacter.
REFERENCES
[1] J.L. Lauletta, S.A. Sebo, “A novel sensing device for power system
equipment condition monitoring” (CMD 2010 paper).
[2] “IEEE Standard for Metal-Oxide Surge Arresters for AC Power Circuits
(> 1 kV),” IEEE Std. 66.22-2005.
Figure 5: Dead-end bell insulator log # 31 – EXACTER and spectrum
analyzer measurements