IS : 3043 -1987 CODE OF PRACTICE FOR EARTHING(REACTANCE GROUNDING)

BASIC DESIGN OF REACTANCE EARTHING

1. IS : 3043 -1987 CODE OF
PRACTICE FOR
EARTHING
Compiled by :
MayankS. Velani
EE2-160973109095

2. PANEL FOR THE REVISION OF IS
:3043,ETDC 20 : P38
Convener: Representing:
N. BALASOBBAMANIAN Larsen & Toubro ( Construction Group ), Madras
Members
PROF G. RAVEENDBAN NAIR Chief Electrical Inspector to the Government of
Kerala, Trivandrum
V. SATHTANATHAN TamilNaduElectricity Board, Madras
G. S. THAKUR Chief Electrical Inspector, Government of Madhya Pradesh, Bhopai
R. SATHIYABAL Tariff Advisory Committee, Madras
K. P. R. PILLAI Fact Engineering and Design Organization, Udyogamandal

3. REVIEW
This Indian Standard ( First Revision ) was adopted by the Bureau
of Indian Standards on August 1987, after the draft finalized by the
Electrical Installations Sectional Committee, had been approved by
the Electro technical Division Council. Under the Chairmen Shree
M.L.DONGRE in M-3 Satyam, 88 SionCircle, Bombay

4. FOR CONVENIENCE OF IDENTIFYING AREAS OF INTEREST
BY ANY SPECIFIC USERS OF THE CODE, THE INFOR-
MATION CONTAINED IN THIS STANDARD IS DIVIDED INTO
DIFFERENT SECTIONS AS FOLLOWS: Section 1 General guidelines
Section 2 Connections to earth
Section 3 Earth-fault protection in consumer's premises
Section 4 Power stations, substations and overhead lines
Section 5 Industrial premises
Section 6 Standby and other private generating plant
Section 7 Medical establishments
Section 8 Static and lightning protection grounding
Section 9 Miscellaneous installations and considerations
Section 10 Measurements and calculations
Section 1 1 Data processing installations

5. SECTION 1
GENERAL GUIDELINES
2.1 Arc-Suppression Coil ( Peterson Coil) —An earthingreactor so designed
that its reactance is such that the reactive currents to earth under fault
conditions balances the capacitance current to earth flowing from the lines so
that the earth current at the fault is limited to practically zero.

6. REACTANCE GROUNDING
Inthissystem,areactanceisinsertedbetweentheneutralandground.
Thepurposeofreactanceistolimittheearthfaultcurrent.Bychangingtheearthing
reactance,theearthfaultcurrentcanbechangedtoobtaintheconditionssimilarto
thatofsolidgrounding.
Thegroundfaultcurrentshouldbeatleast55%of3phasefaultcurrenttoprevent
transientovervoltages.
Thismethodisalsousedwhensystemneutralisnotavailablee.g.deltaconnected
system.Inthiscasethereactorisusedastransformergroundingtoobtainneutral.

7. ARC SUPPRESSION COIL
GROUNDING (OR RESONANT
GROUNDING)
Wehaveseenthatcapacitivecurrentsareresponsibleforproducingarcing
grounds.Thesecapacitivecurrentsflowbecausecapacitanceexistsbetween
eachlineandearth.
IfinductanceLofappropriatevalueisconnectedinparallelwiththe
capacitanceofthesystem,thefaultcurrentIFflowingthroughLwillbein
phaseoppositiontothecapacitivecurrentICofthesystem.IfLissoadjusted
thatIL=IC,thenresultantcurrentinthefaultwillbezero.Thisconditionis
knownasresonantgrounding.

8. WhenthevalueofLofarcsuppressioncoilissuchthatthefaultcurrentIF
exactlybalancesthecapacitivecurrentIC,itiscalledresonantgrounding.
Anarcsuppressioncoil(alsocalledPetersoncoil)isaniron-coredcoil
connectedbetweentheneutralandearth.
Thereactorisprovidedwithtapping'stochangetheinductanceofthecoil.
Byadjustingthetapping'sonthecoil,thecoilcanbetunedwiththe
capacitanceofthesystemi.e.resonantgroundingcanbeachieved.

9. Figure –Basic principle of the arc-suppression reactor Figure –Vector relationships between voltages and current

10. InthisexamplethepotentialinrelationtoearthonthesoundphasesSandTisassumedto
beequaltothenormalsystemvoltageU(line-to-line)
The capacitive currents to earth from phase S and T, I
csand I
ct, are leading 90°in relation to
U
sand U
trespectively. The capacitive current in the earth fault I
eis the Victoria sum of I
csand
I
ct.
I
cs= I
ct= U×ω×C
e
I
e= 2×U×ω×C
e×cos30°
=√3×ω×C
e
DependingonC
e,whichisproportionaltototallengthoflinesandcablesinthesystem,I
e
maybecomequitehighandmaysustainanarcatthefailurespot.

11. Figure –Connectingarc-suppression reactor (L)

12. When connecting an arc-suppression reactor L between the neutral of the transformer
winding and earth, an inductive current flows through L to earth where it finds its return
path through the earth fault.
The inductive current through the earth fault has the opposite direction of the capacitive
current provided by phases S and T.
Figure shows the I
Lvector added to the previous vector diagram in Figure before the
presence of the arc-suppression reactor
Δu is the voltage that drives the current I
Lthrough the reactor, and I
Lis naturally lagging 90°
in relation to Δu.
By adjusting the reactance of the reactor I
Lcan be given the same numerical value as I
eand
because l
eand I
Lhave opposite directions, the resulting current through the fault will become
zero or close to zero

13. HOW TO DETERMINE REACTOR DATA?
The current through the reactor shall equalize the capacitive current determined by
the capacitance to earth of the system where the reactor is to be installed.Then it is
necessary to know C
e.
C
ecan be found by direct measurement in the power system. However, the system
might rarely be at disposal for such measurements, so C
emust then be estimated on
the basis of calculations.
The contribution to C
efrom the overhead lines might not be just as easily to determine
with the same accuracy as for cables

14. C
EFOR OVERHEAD LINES IS DETERMINED BY SEVERAL
PARAMETERS SUCH AS:
The height of the conductors above the earth
The geometric configuration of the three phase conductors
The number of parallel conductors per phase
The number of earth wires, if any, and their distance to the phase conductors and to
the earth
The dimensions of the conductors
The extent of vegetation below the line
Seasonal variations due to ice and snow.

15. Figure –Typical charging currents (earth fault currents) in an
overhead line system

16. Figure –Conductor-to-earth capacitance C
eof single-core

17. DESIGN OF REACTOR
Arc-suppression reactors are single phase. They have a core consisting of steel sheets, just like
transformer cores. In most cases the core has a center limb, which is enclosed by the winding,
and two unwound side limbs and the upper and lower yokes close the magnetic path.
The winding is similar to transformer windings. It may have tapping's for tuning the reactance
to the capacitance to earth of the system.
The reactance can be varied within a certain range. The relation between the highest and the
lowest reactance is for practical reasons limited to 2,5:1. For lower system voltages (22 kV
and lower) the relation can be 3:1. If larger a range is required, 10-12:1can be achieved by
regulating the gaps in the core
Arc-suppression reactors are oil-immersed in most cases. Arc-suppression reactors are normally
equipped with a secondary winding for indication and measurement of the voltage across the
reactor

18. References
Transformer handbook by ABB
Distribution Automation Handbook –Elements of power distribution systems by ABB
Arc SupressionCoils bySwedish Neutral AB
https://electrical-engineering-portal.com/arc-suppression-reactors
BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002 September 1988