SMART GRID: MONITORING OF CABLE FAULT LOCATION

K. V. Suslov, N. N. Solonina and A. S. Smirnov

Irkutsk State Technical University, 83, Lermontov street, Irkutsk, Russia

Keywords: Smart Grid, Reliability, Rogowski Coil.

Abstract: Modern viewpoint suggests that Smart Grid is the network based on “smart technologies”; it is highly

reliable, self-controlled, and capable to receive energy from any source and transform it into a final product

without man’s participation. Changes that occur in the energy sector require higher speed of receiving and

processing the data on current state of power system. At the same time increasingly stricter requirements are

imposed on accuracy and validity of measurements of circuit parameters. The paper is devoted to solving

the problem of promptly determining the coordinates of short circuit location on transmission line, which

can be done by digital processing of information about currents in transmission lines and use of Rogowski

coil as a primary transducer.

1 INTRODUCTION

Nowadays there are different ways of providing the

required reliability of power system operation.

However, despite high reliability of power

equipment and control systems there can be failures

in operation, for example short circuits in supply and

distribution networks which can be caused by

unforeseen circumstances. Reduction of time for

search of the short circuit location on lines is a direct

way of improving the reliability of power systems.

There is a great variety of methods for detecting

location of overhead and cable line faults. We will

enumerate them in brief.

The pulse method is based on measuring time

intervals between the moment of transmitting a

probe pulse of alternating current and the moment of

receiving a reflected pulse from the fault location.

To make measurements by the method of oscillation

discharge the voltage supplied to the faulted cable

conductor is gradually raised to the voltage of cable

fault. The loop method is based on measuring

resistances by the direct current bridge. The

capacitance method is suggests measuring

capacitance of a broken conductor by measuring

bridges. The acoustic method supposes creation of a

spark discharge at the fault location and listening to

sound vibrations that occur above the fault point.

There is also the induction method and others. The

main flaw of these methods from the viewpoint of

promptness is the fact that their application requires

preparatory work and a lot of time.

2 MAJOR PRINCIPLES OF THE

APPROACH

The method suggested by the authors allows one to

timely detect the place of transmission line fault on-

line. The main idea of the method lies in the fact that

knowing circuit configuration and line parameters

we can obtain an equivalent circuit for calculation of

short-circuit currents at different points of

transmission line. Depending on the required

accuracy we choose a certain interval between the

calculated points. The points calculated theoretically

are then compared with measured short- circuit

currents.

Let us first consider the simplest case where the

short-circuit current is created by one source. Figure

1 shows a scheme of determining the location of

short circuit on transmission line for the considered

case.

There are primary current transducers at the

beginning of the line in all phases. Their

instantaneous values are processed and effective

current values are calculated. At the time of short

circuit this effective value will correspond to the

initial effective value of the short-circuit current.

Based on the relationship between phase currents the

logical circuit determines the type of short circuit.

129

V. Suslov K., N. Solonina N. and S. Smirnov A..

SMART GRID: MONITORING OF CABLE FAULT LOCATION.

DOI: 10.5220/0003947401290132

In Proceedings of the 1st International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2012), pages 129-132

ISBN: 978-989-8565-09-9

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

This makes it possible to compare real short-circuit

currents with those previously calculated and thus

determine the coordinate of l , i.e. the beginning of

section on which the short circuit occurred.

Figure 1: The scheme of detecting the cable fault point. L

– cable length, l – distance from the beginning of the line

to the point of short circuit, E

– system EMF, Z

–

internal resistance of the system, Z(l)- resistance of the

line section from its beginning to the short circuit location.

Simultaneous accurate measurement of voltage

at the point of connection allows the result to be

adjusted considering the difference between the real

voltage and calculated one. If to continuously

measure currents and voltages (updating memory)

the said values can be fixed at the moment of short

circuit. This, in particular will make it possible to

determine the point of self-clearing fault. This is

important since similar short circuit can occur in the

future. The identified location should be examined

and the reason for a potential short circuit -

eliminated.

Let us consider a general case where a short-

circuit current on the line is considerably affected by

several sources.

The number of sources depends on network

configuration. Therefore, the calculations should be

made for different possible network configurations.

From calculation made for each circuit configuration

at a rated value of voltage we obtain a matrix of

current values for different types of short circuit at

specified values of l. An example of the matrix is

given in Table 1.

It is supposed that there are primary transducers

of current and voltage at the beginning of the line

and effective values of current and voltage are

continuously measured. The indicated values are

stored in the data concentrator and constantly

updated. The location of line fault is detected in two

stages: preliminary and final.

The algorithm for preliminary detection of

coordinates of the short-circuit current location is as

follows: knowing the short-circuit currents of

different phases we determine the type of short

circuit, namely: if currents of three phases are almost

equal, this is a three-phase symmetrical short circuit;

if two currents are equal and considerably exceed

the third current, this is a two-phase asymmetrical

short circuit; if current of one of the phases

considerably exceeds the currents of other phases,

this is a one-phase short circuit. Knowing the value

of voltage at point “a” at the time instant preceding

short circuit, we adjust the data of matrix, supposing

that the calculated currents are linearly related to the

voltage. Knowing the type of short circuit we find an

interval from the matrix, within which the measured

initial effective value of short-circuit current lies.

Table 1: An example of data matrix for the first stage of

fault location detection.

lil

⋅

(

)

()

(

)

I kA

()

(

)

(

)

()

(

)

… … … … …

i-1

(

)

lil

⋅

−

()

−i

()

−i

(

)

−i

lil

⋅

()

(

)

i+1

(

)

lil

⋅

(

)

1+i

(

)

1+i

(

)

1+i

… … … … …

lnl

⋅

()

(

)

(

)

where i – number of calculated point of a possible

short circuit on the interval Δl;

l – distance from the beginning of line to the

fault location; n – the total number of points to be

calculated; Δl –sampling step (in meters);

Let it be established that the short circuit is a

three-phase one. Determine an interval that meets

the following inequality:

()

(

)

(

)

()

*33

1 −+

isc

III

(1)

where

()

(

)

1+isc

I ,

()

(

)

1−isc

I – calculated values of short-

circuit current at calculated points

()

1+i and

(

)

−

i ,

respectively;

(

)

– value of short-circuit current obtained

from measurement.

We suppose that

(

)()

3*3

iscsc

II ≈ and determine an

interval from

(

)

−

i to

(

)

1+i , i.e.

ll = , within

which the short circuit occurred. To define more

exactly the point of a short circuit the sampling step

is decreased on the found interval and the exact

SMARTGREENS2012-1stInternationalConferenceonSmartGridsandGreenITSystems

130

coordinates of short circuit location are determined.

For the limited number of intervals

(

)

ΔΔ

the

calculation Table is filled (Table 2).

And finally the short circuit point is determined:

()

() ()

()

*33

1 −+

jsc

III

(2)

Hence,

(

)

(

)

3*3

jscsc

II ≈ and the precise coordinates

of the short circuit location are determined

iji

lll

, where

is an interval from point

()

1−j

()

1+j

Table 2: An example of data matrix for the second stage of

fault location detection.

()

ljl

ΔΔΔ

()

I kA

(

)

(

)

(

)

(

)

… … …

j-1

()

()()

ljl

ΔΔΔ

−=

−

(

)

(

)

−

(

)

ljl

(

)

j+1

()

()()

ljl

ΔΔΔ

(

)

(

)

… … …

(

)

lml

(

)

where j – number of the possible short circuit

point on the subinterval of

()

lΔ

; m – total number

of points for subinterval calculation;

(

)

–

sampling step (in centimeters);

()

I – measured

value of short-circuit current;

The obtained Tables underlie formation of the

structural scheme of the considered network

fragment to determine coordinates of the short

circuit point on-line (Fig. 2) based on measurements

of currents, voltages and frequency.

Figure 2: Structural scheme of on-line determination of the

short circuit point on the transmission line.

Block 1 is intended for measuring the current

effective values of linear voltages at the connection

point of transmission line and the current network

frequency of the fundamental harmonic. These data

come from primary transducers and are adjusted

continuously. Their values obtained directly before

the short circuit are stored. Block 2 serves for

measurement of initial effective values of short-

circuit currents during the first period after the short

circuit. Currents of all three phases are measured.

Block 3 aims to determine the short circuit type:

one-, two- or three-phase. Block 4 is a logic device

to determine network configuration that is changed

by circuit breakers. Hence, the state of network

configuration at the given moment can be

determined by the state of circuit breakers.

Information on their state arrives to Block 4 through

telemechanic channels. The network configuration

can also be specified directly by dispatcher. Block 5

represents a matrix of the rated currents of

transmission line for the concrete configuration.

Block 6 is a logic device of the first stage of

determining the section, on which the short circuit

happened. Block 7 is a logic device of the second

stage of determining the short circuit point and

includes a matrix of the rated currents for the second

stage of determining the short circuit point. Block 8

precisely determines coordinates of the short circuit

point.

The method supposes a precise measurement of

currents and voltages. Current and voltage

transformers with the iron core do not provide

specified accuracy. Particularly it concerns current

transformers, since at short-circuit currents to be

measured their magnetic conductors operate almost

in saturation mode, which leads to unforeseeable

errors. It is of no consequences for relay protection,

however, it is inadmissible for solving this

measuring problem. The linear dependence can be

provided by using Rogowski coil instead of current

transformers. In essence the former is a current-to-

voltage transducer. This is convenient for further

conversion of information from the analog form into

the digital one. High accuracy of current

measurement is due to absence of the magnetic core

in it. Since there is no ferromagnetic coil in

Rogowski coil, the output signal (voltage) will

linearly depend on the input value (current).

The magnetic field strength (

h) excited by the

measured current and the measured current (i) are

known to be related by Ampere’s circuital law:

ihdl

∫

(3)

SMARTGRID:MONITORINGOFCABLEFAULTLOCATION

131

where L — integration loop that practically

coincides with the midline of the measuring (ring)

winding.

Multiplying both sides of equality (3) by S

obtain:

SihSdl

μμ

∫

(4)

Application of the known relations

;

(5)

;

hSbS

(6)

Ldl

∫

(7)

where b, Ф – magnetic induction and magnetic

flux through the winding, respectively,

Differentiate both sides of equation (6) and after

some transformations the following relation is

obtained

()

(7)

where

()

te — instantaneous value of the emf of

a winding turn of Rogowski coil.

In general, vectors h and dl are parallel to each

other at all points of integration loop L and then

eWtE =)(

(8)

here E(t) — instantaneous value of the emf of

the whole measuring winding of Rogowski coil

containing W turns.

Assuming the initial phase of measured current

to be zero and after differentiation the following

expression is obtained

)90sin()(

−= tICtE

ωω

(9)

where

⎟

⎠

⎞

⎜

⎝

⎛

ωμ

— design factor of the

transducer.

A phase shifter is used to alter the emf phase by

+90 degrees and obtain voltage

, proportional to

load current

tCIu

sin

(10)

For this purpose E{t) is divided by

and a

positive phase shift by 90° is performed.

In order to determine voltage proportional to the

measured load voltage it is necessary first to obtain

current proportional to load voltage with the help of

resistive transducer. The obtained current comes to

Rogowski coil, at whose outlet the voltage will be

proportional to load voltage

)sin(

tUu

(11)

It should be noted in addition that division of

E(t) by

eliminates one more error source, i.e.

dependence of the result on feed current frequency.

Thus, as distinct from the known methods

application of information technologies and

Rogowski coil makes it possible to determine

precise coordinates of the short circuit location on-

line with the required accuracy.

3 CONCLUSIONS

1. The authors offer the method for on-line

determination of a fault point on the transmission

line. It is based on preliminary theoretical

calculation of short-circuit currents at different line

cross-sections and determination of initial effective

values of short-circuit currents. Here the use is made

of the matrices of theoretical calculations of short-

circuit currents. The measured values of short-circuit

currents are compared with the calculated ones. The

accuracy of determining coordinates of the short

circuit point can be improved at two stages:

approximate and precise.

2. Rogowski coil is suggested for use as primary

transducers to improve the accuracy of

measurements of the current values of short-circuit

currents.

ACKNOWLEDGEMENTS

This research was financially supported by the

decree No. 220, «Measures to Attract Leading

Scientists to Russian Educational Institutions»

(Grant NO. № 11.G34.31.0044.)

REFERENCES

K. V. Suslov, N. N. Solonina, A. S. Smirnov, 2011. Smart

meters for distributed filtering of high harmonics in

Smart Grid // III International Conference on Power

Engineering, Energy and Electrical Drives, Powereng

2011, Spain, Malaga

K. V. Suslov, N. N. Solonina, A. S. Smirnov, 2011. Smart

Grid: A new way of receiving primary information on

electric power system state// IEEE PES Innovative

Smart Grid Technologies Europe 2011, Manchester,

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