I2MTC 2008 – IEEE International Instrumentation and
Measurement Technology Conference
British Columbia, Canada, May 12-15, 2008
Diagnostics and Prognostics of Electric Cables in Ship Power Systems
via Joint Time-Frequency Domain Reflectometry
Jingjiang Wang, Philip Crapse, Yong-June Shin, and Roger Dougal
Department of Electrical Engineering,
The University of South Carolina,
301 South Main St., Columbia, SC 29208, USA
Abstract – The integrity of the wiring in the electric power system of
a ship is vital to its safe operation. To ensure the wiring integrity,
it must be tested to determine if any incipient defects exist. Due to
this problem, a non-destructive, non-intrusive condition assessment
technique is highly desirable. Joint time-frequency domain reflec-
tometry (JTFDR) is proposed and the theory behind JTFDR is also
discussed. The experimental results demonstrate and verify the abil-
ity of JTFDR to be effective for polytetrafluoroethylene (PTFE) coax-
ial cable, which has been widely adopted for military applications in
ship power systems. It is shown that JTFDR has the ability to detect
and locate incipient defects with high accuracy and monitor the aging
process of the cables to predict both future defects and the remaining
service life of the cables.
Keywords – Joint Time-Frequency Domain Reflectometry (JTFDR),
Diagnostics, Prognostics, PTFE
The safe operation of the ship power system depends
largely on the integrity of the wiring system.
electric ship power system contains miles of wiring. Some of
which is difficult to reach and most of which is exposed to
constant vibration, routine maintenance operations, heat and
other age-related disturbances .
technique is needed which can detect and locate these defects
accurately before they lead to any kind of damage. However,
the ideal scenario is for these incipient defects to be detected
before they evolve into hard defects. In order to both prevent
hard defects and save cost on periodically changing cables,
a non-destructive,non-intrusive prognostic technique is
required, which can monitor the status of the cable and predict
the remaining life of the cable ,.
The current state-of-the-art technology for wiring diagnos-
tics can be largely categorized as time-domain analysis or
frequency-domain analysis. Time-domain analysis typically
employs time-domain reflectometry (TDR); frequency-domain
analysis commonly involves either frequency-domain reflec-
tometry (FDR) or standing-wave reflectometry (SWR) .
These reflectometry techniques are based on the analysis of a
reference signal and any signal(s) reflected by imperfections
on the wire being tested. However, these classical techniques
are limited by the fact that they analyze the reference and
Therefore, a diagnostic
reflected signals in either the time domain or the frequency
Thus far, all available techniques are destructive, need
to be performed in a laboratory setting, or cannot provide
information about the remaining useful life of the cables
. Ideally, a technique would exist that could eliminate
the disadvantages and undesired effects of these techniques
for diagnostics, while also providing prognostic information.
However, presently there is no single, feasible technical
solution that can achieve both diagnostics and prognostics
for all the types of cables and environments in ship power
systems. JTFDR is proposed as a comprehensive solution.
In this paper, JTFDR is first applied to a M17/95-RG180
military grade cable protected by PTFE insulation with
incipient defects to verify the efficacy and configurability of
this technique. The theory of JTFDR is discussed in Section
II. The experimental setup of JTFDR is described in Section
III. In Section IV, we will discuss the experimental results of
JTFDR, how JTFDR can achieve scientific prognosis of an
aging cable, and how JTFDR can monitor a cable for signs of
insulation degradation. Conclusions are provided in Section V.
II. JOINT TIME-FREQUENCY DOMAIN
In this paper, a new signal processing-based reflectom-
etry technique, joint time-frequency domain reflectometry
(JTFDR) is proposed. This innovative technique captures the
advantages of both TDR and FDR while avoiding some of
their limitations by using advanced digital signal processing.
JTFDR utilizes a reference signal that is localized in both the
time and frequency domains simultaneously. This reference
signal is composed of a Gaussian envelope applied to a linear
chirp signal as below:
s(t) = (α/π)1/4e−α(t−t0)2/2+jβ(t−t0)2/2+jω0(t−t0)
where coefficient α determines the time duration of the refer-
ence signal; coefficients α and β determine the bandwidth of
the reference signal; and ω0is the center frequency.
erence signal is created in MATLAB and displayed in Fig. 1.
The real-world reference signal used in the experiment can be