A New Technique for Detection of High Impedance Faults by zib42419

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     A New Technique for Detection of High Impedance Faults in Power Distribution
                    System Based on Current Harmonic Analysis

                                       M. Jannati and L. Eslami
                      Electrical Engineering Department in University of Kurdistan
                        mohsen.jannati@uok.ac.ir and Laleheslami@yahoo.com)


         Keywords : High Impedance Fault, Fault Detection, Distribution Systems and EMTPWorks



     Abstract :                                            proposed. Most of these approaches are
     In every distribution system, physical contact        complicated or difficult in implementation. In
     between conductors of a phase and substances          this paper, a novel approach for detecting
     around them like trees, walls of the buildings        high impedance faults based on harmonic
     and surfaces below them, always is possible.          analysis of current in distribution systems has
     These conditions, known as High Impedance             been presented. Various simulations in
     Faults (HIFs), can lead to death due to               EMTPWorks environment have validated that
     electricity congestion, burning or ignition via       proposed      approach       is    simple    in
     arc or heat of the substances. On the other           implementation and has great accuracy.
     hand, the whole energy produced by the
     power company doesn’t achieve by the                  NTRODUCTION
     arbitrary loads and a part of them is lost that       HIGH Impedance Fault (HIF) is defined as an
     this loss is harmful for the power supply             electric connection between an energized
     companies. Current relaying in distribution           conductor and an external dielectric substance
     systems is only capable of detecting short            [1-2]. Dielectric substances, regarding their
     circuit conditions leads to flowing significant       nature, have a great resistance against the
     amount of generated electric power to the             current and only a limited value of current can
     earth without achieving by the load. It is very       cross from them. So such a fault is not
     difficult to detect HIFs by protection                considered as an unusual situation for
     equipments. Because occurrence of them just           protection equipments. A current with low
     leads to slight increase in the amount of load        amplitude flows from the energized conductor
     current. So it can be considered as a usual           to the earth, ignoring how the connection has
     increase in the value of load current                 been established. This current flows to the
     incorrectly. However, various solutions for           earth via the connected substances which have
     detecting high impedance faults have been

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        A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                                24th International Power System Conference


high potential now. This high potential can                  Most of the proposed approaches don’t have
leads to human damages [3-6].                                enough accuracy or their implementation is
Usual types of HIF occur when the                            very complicated. In this paper a new
conductors of the distribution system impact                 approachhas been represented to detect HIF
with the foliage, concrete walls and earth                   based on harmonic analysis of current in
surface. These cases subjected to undesirable                distribution systems. Various simulations in
                                                             EMTPWorks environment validate that this
                                                             approach has a great accuracy for HIF
                                                             detecting in addition of its simplicity and
                                                             simple implementation

                                                              Dynamic Model of Hif Arc
                                                             The HIF arc used in this paper is based on a
                                                             general model used in [23]. In this model that
                                                             is based on the thermal equations, following
                                                             equation is used to determine the variable
                                                             conductance of the arc:

                                                             dg 1                                                (1)
                                                                (G  g )
  Fig. 1 Possibility for connection between conductors       dt 
                   and branches of a tree
                                                             Where g is the time varying arc conductance,
connections are usually around the conductors                G  i / Varc is arc stationary conductance, i is
of distribution system lines. Such a                         the absolute arc current, Varc is constant value
distribution system that its conductors are                  of the arc voltage and  is arc time constant.
prone to connect with branches of trees has                  The parameters of the above equation are
been shown in Fig. 1.                                        determined so that their results are validated
 As the main property of HIF is its difficult                by experimental results. The characteristic in
detection, unlike the other faults that leads to             [23] has been used for calculating these
current with very high amplitude, the fault                  parameters. The following equation is used
current in HIF is very low. So the usual                     for calculating the  value:
protection systems like the over current
protection cannot detect this type of fault. If                Ae Bg                                           (2)
HIF detection is Unsuccessful, it can incur
human damages or leads to firing [7-10].                     Where A and B are constants that have
In recent years, many researchers represented                different values in two positive and negative
various techniques in HIF detection. These                   half cycle of fault voltage and current and are
techniques generally consist of: low                         computable by the experimental results.
frequency components of energy method [11],                  Calculated values of positive half cycle in
neural network method [12-13], kalman
                                                             [23]       are: Varc  2520V , A  6.6 E  5 , B  41977
filtering method [14], low order harmonics
ratio of current method [15-16], fault current               and values of negative half cycle as:
                                                             Varc  2100V , A  2.0E  5 , B  85970.30 .
flicker and half-cycle asymmetry method [17]
and fractal analysis techniques [18]. In most                The dynamic model of HIF arc has been
above approaches signals generated by arc                    shown as a general block diagram in Fig. 2.
have been used to HIF detection. Also
Discrete Wavelet Transform (DWT) method                      Under Study Distribution System
has been used in [19-22] that is an appropriate              Fig. 3 is a single line diagram of a 20 kV
tool in analysis of transient phenomenons.                   unearthed distribution system simulated in
                                                             EMTPWorks. The line frequency dependent

                                                         2
        A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                                24th International Power System Conference


model in EMTPWorks is intentionally                                                                                                                            L1 (40 km)
                                                                                                                                                                                            DYg_1
                                                                                                                                                                                            1          2
                                                                                                                                                                                                                            1.5MW
selected to account for unsymmetrical faults.                                                                                                         +           CP
                                                                                                                                                                                                           20/0.4
                                                                                                                                                                                                                            0
                                                                                                                                                                                                                    P     Q Load5
When the system and the fault modeling are                                                                                                                     L2 (34 km)
                                                                                                                                                                                            DYg_2
                                                                                                                                                                                            1          2
                                                                                                                                                                                                                           1.5MW
combined in one arrangement, the network                                                                                                              +           CP

                                                                                                                                                                                            DYg_3          20/0.4   P
                                                                                                                                                                                                                           0
                                                                                                                                                                                                                          Q Load4

behavior during this fault can be investigated.                                                                                 DY_1
                                                                                                                                                      +
                                                                                                                                                               L3 (29 km)
                                                                                                                                                                  CP
                                                                                                                                                                                            1          2
                                                                                                                                                                                                                            1.5MW
                                                                                                                                                                                                                            0
In this study, the neutral of the main transformer                                                                             1    2

                                                                                                                                                                                            DYg_4
                                                                                                                                                                                                           20/0.4   P     Q Load3


is isolated consistent with an unearthed system.                                                                                66/20                          L4 (36 km)                   1          2
                                                                                                                                                                                                                           1.5MW
                                                                                                                      66kVRMS /_0                +               CP                                                        0
Although this system is not intentionally                                                                                                                                                                  20/0.4




                                                                                                              +
                                                                                                                                                                                                                    P     Q Load2
                                                                                                                       AC2                Measuring
connected to the earth, it is grounded by the                                                                                              point


natural phase to ground capacitances.                                                                                    Fig. 3 Distribution system used in EMTPWorks
Therefore, the fault phase current is very low
allowing a high continuity of service.                                 It should be noted that available voltage and
                                                                       current are the voltage and current detected by
Proposed Approach for Hif Detection                                    the measurement devices at the beginning of
A HIF has been created in the middle of line                           the line, not the same voltage and current of
L4 in Fig. 3. The measurement devices have                             the fault location typically. Hence voltage and
been set at the beginning of the line and HIF                          current waveforms at the beginning of the L4
starts at t = 50 ms. The voltage and current                           when the HIF is occurred in the middle of line
waveforms in the fault location have been                              L4 at t = 50 ms have been showed in Fig. 5.
showed in Fig. 4.                                                      It’s evident from these waveforms that none
                                                                       of them have any significant change before
                                        i       Fault Current
                                                                       and after the fault. Therefore, these
                                                                       waveforms are not suitable for detecting this
                                            i                          type of faults.
                                                                       As the voltage waveform in HIF doesn’t have
                                                            Varc       any significant change, the current waveform
                                        i / Varc                       should be used in HIF detection.
                                                                                                                         4
                                                                                                                  x 10
                                                                                                              3

                                      1                                                                                                         Voltage (V)
            Ae Bg                     (G  g )
                                                                                                                                                                         Current
                                                                                                                                                                        (*10E-5 A)
                                                                                                             2
                                                                                Fault V oltage and Current




                                                                                                              1



                                                                                                              0
        Control Signals                     
                                                                                                             -1



                                                                                                             -2



                                                                                                             -3
                                            1                                                                     0          0.01       0.02   0.03       0.04       0.05          0.06         0.07        0.08        0.09    0.1
                                                                                                                                                                  Time (Sec)
                                            g
                                                                                                             Fig. 4 The voltage and current waveforms in the fault
                                                                                                                                    location
                      Return to the
                                                R                                                                       4
                         Netork                                                                              3
                                                                                                                  x 10

                                                                                                                                                                       Current (*10E-2)
                                                                                                                                                 Voltage (V)
          Fig. 2 Dynamic model of HIF arc                                                                    2
                                                                       Fault Voltage and Current




                                                                                                             1


This figure illustrates the HIF characteristic.                                                              0

Voltage waveform doesn’t have any                                                                            -1

significant change. But the current                                                                          -2

waveform is a periodic waveform as seen and                                                                  -3

it’s like a sinusoidal waveform, but in every                                                                     0          0.01       0.02   0.03       0.04       0.05
                                                                                                                                                                  Time (Sec)
                                                                                                                                                                                     0.06       0.07        0.08        0.09    0.1




zero crossing, arc is extinguished and starts                                                                           Fig. 5 The voltage and current waveforms at the
                                                                                                                                    beginning of the line L4
again.

                                                                   3
                                   A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                                                           24th International Power System Conference


So, the waveform of the current in is used                                                                               8

                                                                                                                         7

ignoring in which phase the fault is occurred:                                                                           6

                                                                                                                         5                              Threshold

in  ia  ib  ic                                                                                                        4


                                                                                                         (3)




                                                                                                                    DF
                                                                                                                         3

                                                                                                                         2



where in is residual current and ia , ib and ic                                                                          1

                                                                                                                         0


are the phase currents at beginning of the line.                                                                         -1

                                                                                                                         -2


The waveform of in in the case that HIF is
                                                                                                                              0   0.01    0.02   0.03       0.04       0.05      0.06     0.07   0.08   0.09   0.1
                                                                                                                                                                    Time (Sec)


                                                                                                                         Fig. 7 DF criteria Corresponding to the waveform of
occurred in the middle of L4 has been shown
                                                                                                                                        current in in the Fig. 6
in Fig. 6. It is evident from Fig. 6 that in this
case, in has the same behavior as HIF current
                                                                                                                          
in the fault location.                                                                                                                     Distribution Systems 
Although different approaches based on
harmonic analysis of the current for HIF
detection have been proposed, but most of                                                                                                           Sensors

them have used only even or odd harmonics.
In this paper a new criterion based on joint
using of even and odd harmonics has been                                                                                          Calculate in  within data window 

proposed:
                                  H1  H 3
DF 
                                  H2  H4                                                                (4)                         Extracting the Harmonics of in  


Where H 1 ، H 2 ، H 3 and H 4 are the first,
second, third and forth harmonics of in                                                                                                                                                 No 
                                                                                                                                                  DF  2  
respectively and DF is the Detection Factor.
Fig. 7 shows DF Corresponding to the
                                                                                                                                          Yes 
waveform of current in in the Fig. 6. As
specified on the Fig. 7, if the DF exceeds of
                                                                                                                                         High Impedance Fault 
value 2, it demonstrates that HIF has been
occurred. This threshold is achieved by
various simulations.                                                                                               Fig. 8 Flowchart of proposed approach for HIF detection


Hif Detection Algorithm                                                                                            Then, residual current ( in ) is calculated. In
In proposed algorithm for HIF detection, the                                                                       next step, harmonics of current in is extracted
current of each three phases is detected at the                                                                    by FFT technique or other methods. Then,
beginning of under study line.                                                                                     index DF is calculated and if DF exceeds of
                                                                                                                   threshold 2, it illustrates that HIF is occurred.
                       0.2                                                                                         The flowchart of proposed approach has been
                      0.15
                                                                       in                                          shown in Fig. 8.
                       0.1



                                                                                                                   Simulation Results
  Fault Current (A)




                      0.05


                         0
                                                                                                                   In this section several different cases has been
                      -0.05


                       -0.1
                                                                                                                   considered to realize whether the new
                      -0.15
                                                                                                                   approach has the ability to detect HIF from
                       -0.2
                              0    0.01   0.02   0.03   0.04       0.05      0.06   0.07   0.08   0.09   0.1
                                                                                                                   similar situations or not. For this reason, 6
                                                                Time (Sec)
                                                                                                                   different situations are considered as below:
      Fig .6 The waveform of                                   in at beginning of the line L4                      a) Capacitor switching (out)
                                                                                                                   b) Capacitor switching (in)
                                                                                                               4
       A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                               24th International Power System Conference


c) Load switching (HV)                                          Transmission & Distribution Conference
d) No load line switching                                       and Exposition: Latin America,pp. 1-6,
e) Full load trans. switching                                   2006.
f) High impedance fault                                   [3]   N. Ramezani, M. Sarlak, S. M. Shahrtash
Each of these situations has been assumed at                    and D. A. Khabori “Design and
the end of line L4. The waveform of HIF                         implementation of an adaptive High
current with the DF index for these 6 different                 Impedance        Fault   relay”      Power
situations has been shown in Fig. 9                             Engineering Conference, IPEC 2007, pp.
According to the Fig. 9, DF exceeds of given                    1131-1136, 2007.
threshold, just when the HIF is occurred and it           [4]    E. S. T. Eldin, D. K. Ibrahim, E. M.
means that this index has an acceptable                         Aboul-Zahab and S. M. Saleh “High
behavior in comparison with the other similar                   Impedance Faults Detection in EHV
situations. This approach has a special                         Transmission Lines Using the Wavelet
simplicity in addition of high accuracy that                    Transforms” Power Systems Conference
simplifies its implementation and hence it can                  and Exposition, PES '09. IEEE/PES, pp.
be under the attention of distribution system                   1-10, 2009.
operators.                                                [5]   T. Cui, Xin Dong, Z. Bo and S. Richards
                                                                “Integrated scheme for high impedance
Conclusion                                                      fault detection in MV distribution system”
As the main property of HIF is its difficult                    Transmission and Distribution Conference
detection, unlike the other faults that leads to                and      Exposition:    Latin     America,
current with very high amplitude, the fault                     IEEE/PES, pp. 1-6, 2008.
current in HIF is very low. So the usual                  [6]    E. S. T. Eldin, D. K. Ibrahim, E. M.
protection systems like the over current                        Aboul-Zahab and S. M. Saleh “High
protection cannot detect this type of fault. If                 impedance fault detection in mutually
HIF detection is Unsuccessful, it can incur                     coupled double-ended transmission lines
human damages or leads to firing. In this                       using high frequency disturbances” Power
paper a new approach has been represented to                    System Conference, MEPCON 2008. 12th
detect HIF based on harmonic analysis of                        International Middle-East, pp. 412-419,
current in distribution systems. Various                        2008.
simulations in EMTPWorks environment                      [7]   C. J. Kim and B. D. Russell “A learning
validate that this approach has a great                         method for use in intelligent computer
accuracy for HIF detecting in addition of its                   relays for high impedance faults” IEEE
simplicity and simple implementation. Hence,                    Transactions on Power Delivery, Vol. 6,
using proposed approach can lead to detecting                   pp. 109-115, 1991.
this type of faults faster and more accurately            [8]   S. R. Samantaray, B. K. Panigrahi and P.
with increasing in system reliability.                          K. Dash “High impedance fault detection
                                                                in power distribution networks using time-
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       A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                               24th International Power System Conference


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A New Technique for Detection of High Impedance Faults in Power Distribution System Based on …
                        24th International Power System Conference




            Fig. 9 The waveform of HIF current with the DF index for 6 different situations:
 (a) Capacitor switching (out) (b) Capacitor switching (in) (c) Load switching (d) No load line switching
                         (e) Full load trans. Switching (f) High impedance fault




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