partial disconnected cable fault detection using...

Partial Disconnected Cable Fault Detection Using

Improved SSTDR

Ga-Ram Han1, Jeong-Chay Jeon1, Jae-Jin Kim1 and Myeong-Il Choi1

1Korea Electrical Safety Corporation

#12 Ogong-ro, Iseo-myeon, Wanju-gun, Jeollabuk-do, 55365,

Rep. of Korea

Abstract. To prevent electric shock accidents caused by electric leakage, it is

important to detect cable insulation faults in advance. This paper shows the

results that an improved SSTDR is more effective in detecting partial

disconnected cable fault than the conventional method. The existing SSTDR

has difficulties to determine accurate partial fault location due to signal

attenuation. The improved SSTDR was validated through comparison with

existing methods in partial cable fault.

Keywords: Cable fault location, Partial disconnection, SSTDR, Fault detection

1 Introduction

Power cables are susceptible to many faults such as insulation damage, open fault, or

short circuit due to inappropriate installation and other various physical, electrical, or

environmental factors, which could lead to electrical fires. According to the electrical

accident statistics published by the Korea Electrical Safety Corporation, 20% of

electric facility accidents are caused by cables, and most electrical fires are related to

cables [1].

Many methods have been proposed to diagnose cable faults and detect their

locations such as partial discharge measurement. Among them, reflectometry has

been most commonly used for fault detection, in which a specific pulse such as radar

is injected into a cable, thereby measuring a reflected signal produced due to the

mismatch of characteristic impedance from fault location. (TDR, TFDR, STDR,

SSTDR, etc.)

SSTDR (Spread Spectrum Time Domain Reflectometry) have been studied to

minimize measurement error and facilitate easy fault detection [2]. But, in the case of

partial disconnection, fault detection is more difficult to find correct location than

open- and short-circuit fault due to small change of characteristic impedance.

This paper demonstrates an improved SSTDR for Partial Disconnection

Fault(PDF) detection. Improved SSTDR proposed in [3] is consisted of two steps:

peak value of the correlation coefficient of the reference signal is detected using time-

frequency correlation analysis, and then a peak value of the correlation coefficient of

Advanced Science and Technology Letters Vol.141 (GST 2016), pp.113-117

http://dx.doi.org/10.14257/astl.2016.141.23

ISSN: 2287-1233 ASTL Copyright © 2016 SERSC

the reflected signal is detected after removing the reference signal to solve the

problem of the inaccurate PDF detection due to signal attenuation.

2 The PDF Detection Using Improved SSTDR

The existing SSTDR analyzes signals in the time correlation function and it has

difficulties to determine the accurate PDF location due to side lobe and reflected

signal attenuation. The improved method analyzes signals in the time-frequency

correlation to solve the problem. That’s why it has enhanced performance in

determine the PDF point with main lobe despite signal attenuation. The time-

frequency correlation analysis in the SSTDR improved employs the Wigner Ville

Distribution (WVD) to analyze the reference and reflected signals in the time-

frequency domain [4].

Also, PDF detecting error increases when the reflected signal overlapped with the

injected signal or the reflected signal is too small to be analyzed in contrast to the

injected. In order to solve such weaknesses, it is possible to make the reflected signal

stand out by removing the influence of the reference signal from the measured signal.

According to the reference [3], the improved method searches the maximum value

location 1 of the reference signal from the time-frequency correlation function )(srC

of reference and the reflected signals to find a )(ts location as shown in Fig. 1. Then,

the reference signal )(ts is removed from the measured signal )(tr to make

)()()( 1 tstrte , and the peak value 2 of the correlation function of the reflected

signal is found via the second time-frequency correlation function )(seC of )(te and

)(ts . Finally, a time difference 21 d between the peak values is calculated to

obtain the distance to the PDF location.

Fig. 1. Diagram of the improved SSTDR

Advanced Science and Technology Letters Vol.141 (GST 2016)

114 Copyright © 2016 SERSC

3 Experimental Results

To validate the performance of the improved SSTDR, an experiment was conducted

as shown in Fig. 2. An F-CV2C6SQ cable was used for the experimental target cable

because it has been most widely used in low-voltage power systems. The SSTDR

experimental setup in Fig. 2 consists of a control unit, an arbitrary waveform

generator, a digital oscilloscope and “T” connector. To automatically control the

Arbitrary Waveform Generator (NI PXI 5422, 16bits, 200 MS/s) that generates a

signal injected into a cable and digital oscilloscope (NI PXIe-5162, 10bits, 5 GS/s, 1.5

GHz) that acquires a signal reflected from the PDF point, the NI LabVIEW program

was developed and MATLAB was used to analyze correlations between reference and

measured signals. In the experiment, the reference and measurement signals were

injected and measured through the T connector and RG58 cables.

Fig. 2. Experimental setup for the improved SSTDR

In this experiment, in order to simulate the PDF at 70m, 130m on a 200m cable,

one of 2 cores was cut step by step (a core consists 7line).

The PDF location D using a time difference and VOP (Velocity Of Propagation)

which is a variable that represents the propagation velocity of the electromagnetic

wave in a corresponding cable is given by

(1)

Where rt is detection time of reflection signal, and st is start time of reference

signal.( VOP of 1.905×108m/s)

As shown in Fig. 3., the existing SSTDR using the time correlation cannot

determine the PDF location because of the weak reflected signal due to attenuation.


Copyright © 2016 SERSC 115

Fig. 3. Measurement for PDF with the conventional SSTDR

The improved SSTDR has correlation value that can detect the PDF location more

effectively than the conventional method through time-frequency correlation analysis

as shown in Fig. 4(a). However, in some cases a larger correlation value was occured

in the reference signal portion and the detecting error occurs in which the PDF

location is measured at 38.1m. In oder to solve this problem, it is possible to

accurately detect the PDF as 128.7m as shown Fig. 4(b) by removing the reference

signal(error in 1%).

(a)

(b)

Fig. 4. Measurement for PDF with the improved SSTDR

4 Conclusions

Even if the PDF (due to various physical or electrical factors) is occurred, the

traditional methods of detection is difficult to find fault points because of small

changes of the impedance.


116 Copyright © 2016 SERSC

The performance of the improved SSTDR, which used time-frequency correlation

analysis and remove the reference signal, was evaluated through the PDF detection

experiments using 200m (PDF at 70m, 130m) low-voltage power cables. Against the

existing SSTDR, the ability to detect the cable fault and the accuracy of finding the

PDF point are increase.

The improved SSTDR is expected to apply for resolving the difficulties of the PDF

detection due to various noises and signal attenuation.

Acknowledgments. This study was supported by "2013 Dual Use Technology

Program".

References

1. Korea Electrical Safety Corporation: A Statistical Analysis on the Electrical Accident

(2013)

2. Chirag R. Sharma, Cynthia Furse and Reid R. Harrison: Low-Power STDR CMOS Sensor

for Location Faults in Aging Aricraft Wiring: IEEE Sensors Journal, Vol. 7, No. 1, pp.

43—50 (2007)

3. Jeong-Chay Jeon, Jae-Jin Kim, Myeong-Il Choi: Detection and Location of Cable Fault

Using Improved SSTDR: KIEE The Transactions of the Korean Institute of Electrical

Engineers, Vol. 65, No. 9, pp. 1583—1589, (2016)

4. Y. J. Shin, E. J. Powers, T. S. Choe, C. Y. Hong, E. S. Song, J. G. Yook and J. B. Park:

Application of Time -Frequency Domain Reflectometry for Detection and Localization of

a Fault on a Coaxial Cable: IEEE Trans. on Instrumentation and Measurement, Vol. 54,

No. 6, pp. 2493--2500(2005)


Copyright © 2016 SERSC 117

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