Earthing

Electrical Safety by Earthing

Authorised By SANTOSH BHARADWAJ REDDY Email: [email protected] Engineeringpapers.blogspot.com More Papers and Presentations available on above site

EARTHING BY EARTHING (OR GROUNDING), WE MEAN MAKING ELECTRICAL CONNECTION TO THE GENERAL MASS OF EARTH.

TYPES OF EARTHING  SYSTEM EARTHING  EQUIPMENT EARTHING  LIGHTNING PROTECTION EARTHING  STATIC EARTHING

SYSTEM EARTHING SYSTEM EARTHING IS THE EARTHING ASSOCIATED WITH THE CURRENT CARRYING CONDUCTOR (USUALLY THE NEUTRAL POINT OF THE TRANSFORMER OR GENERATOR) AND IS NORMALLY ESSENTIAL FOR THE SECURITY OF THE SYSTEM. (This is covered by IS 3043:1987 ± Code of   Prac Pr acti tice ce fo forr Ear arth thin ing) g)

EQUIPMENT EARTHING EQUIPMENT EARTHING IS THE EARTHING ASSOCIATED WITH NON CURRENT CARRYING METAL WORK & IS ESSENTIAL TO THE SAFETY OF HUMAN LIFE, ANIMALS & PROPERTY. (This is covered by IS 3043:1987 ± Code of Practice for Earthing)

STATIC EARTHING STATIC EARTHING IS THE EARTHING ASSOCIATED WITH METAL WORK MAINLY FOR  PROTECTION AGAINST UNDESIRABLE STATIC ELECTRICITY. (This is covered by IS 7689: 1989 ±  Guide for the control of undesirable static electricity)

LIGHTNING PROTECTION EARTHING LIGHTNING PROTECTION EARTHING IS CONCERNED WITH THE CONDUCTION TO EARTH OF CURRENT DISCHARGES IN ATMOSPHERE ORIGINATING IN CLOUD FORMATIONS AND IS ESSENTIAL FOR THE PROT PR OTE ECT CTIION OF BUI UILD LDIINGS GS,, TRA RANS NSMI MISS SSIO ION N LINE LI NES S AN AND D EL ELEC ECTR TRIC ICA AL EQ EQUI UIPM PMEN ENT T. (This is covered by IS 2309:1989 ± Protection of   buildings and allied structures against lightning ±  Code of Prac acttice)

ADVANTAGES OF EARTHED NEUTRAL SYSTEM

 EXPE EXPERI RIEN ENCE CE HA HAS S SH SHOW OWN N IN A   NUMBER OF SYSTEMS THAT GREATER SERVICE CONTINUITY MAY BE OBTAINED WITH GROUNDED NEUTRAL THAN WITH UNGROUNDED NEUTRAL.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM

 IN EA EART RTHE HED D NE NEUT UTRA RAL L SY SYST STEM EM A RETURN PATH FOR THE FAULT CURRENT IS MADE AVAILABLE WHICH CAN BE UTILIZED TO BRING ABOUT DISCRIMINATIVE OPERATION OF THE PROTECTION EQUIPMENT.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM

 BECA BECAUS USE E OF TH THE E AV AVAI AILA LABL BLE E RETURN PATH IN THE GROUNDED   NEUTRAL SYSTEM THE E/F CURRENT INITIATES TRIPPING OF CB THRU¶ E/F OR O/C RELAYS TO DEENERGISE FAULTY PART OF CIRCUIT WITHOUT INTERRUPTING SERVICE TO HEALTHY PARTS.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM

 THE THE FAU FAULT LT GE GETS TS LO LOCA CALIS LISED ED EA EASI SILY LY AND ISOLATED FROM THE HEALTHY PARTS OF THE SYSTEM.  SERV SERVIC ICE E RELI RELIAB ABILI ILITY TY IS HI HIGH GH WI WITH TH THE FAULTS LOCATED QUICKLY AND CORRECTED WITH EASE.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM EASIER LOCATION OF FAULTS  ON AN AN UNG UNGR ROU OUN NDE DED D SYS YSTE TEM M A GR GROU OUN ND FAULT DOES NOT CAUSE OPENING OF THE CIRCUIT, HENCE SOME MEANS OF DETECTING THE PRESENCE OF GROUND FAULT ON THE SYSTEM HAS TO BE INSTALLED.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM EASIER LOCATION OF FAULTS  GROU GROUND ND FAU AUL LT ON A GR GROU OUND NDE ED SYSTEM IS BOTH INDICATED AND IS AT LEAST PARTIALLY LOCATED BY AUTOMATIC INTERRUPTION OF THE ACCIDENTALLY GROUNDED CIRCUIT.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM GREATER SAFETY  PRO ROPE PER R GR GROU OUND NDIN ING G RE RESU SULT LTS S IN LE LESS SS LIKELIHOOD OF ACCIDENTS TO THE PERSONNEL.  IN UN UNGR GROU OUND NDED ED SYS YSTE TEM M AT TH THE E EVENT OF GROUND FAULT PERSON CONTACTING OTHER PHASE IS SUBJECTED TO  3 TIMES MORE VOLTAGE THAN IN A GROUNDED SYSTEM.

ADVANTAGES OF EARTHED NEUTRAL SYSTEM GREATER SAFETY

 IN UN UNGR GROU OUND NDED ED SY SYST STEM EM TH THE E GROUND FAULT CURRENT MAY  NOT BE HIGH ENOUGH TO CAUSE OPERATION OF O.C.P.D. CAUSING POTENTIAL FIRE AND SAFETY HAZARD TO EXIST FOR A LONGER  TIME.

GROUNDED Vs UNROUNDED SYSTEM GROUNDED

UNGROUNDED

 Gro Groun und d faul ultt ca caus uses es interruption of supply

 No interruption of supply

 Easy mean anss of faul ultt detection

Fault location is difficult

 Hi High gh va vallue of fau fault lt cu curr rren entt

Single ground fault value is very less.

 Neut Neutra rall mai aint ntai aine ned d at ne near  ar  to ground potential

 Neutral voltage during fault

 Chan Chance cess of mu mult ltip iple le fa faul ults ts are reduced

Susceptible to more multiple

can reach phase voltage faults

SYSTEM EARTHING METHODS  SOLID (EFFECTIVE) EARTHING  RESISTANCE EARTHING  INDUCTANCE EARTHING  GROUND FAULT NEUTRALIZER 

SOLID EARTHING  NEUT NEUTRA RAL L POI POINT NTS S OF OF TRA TRANS NSFO FORM RMER  ER  OR GENERATOR ARE CONNECTED DIRECTLY THROUGH AN ADEQUATE GROUND CONNECTION IN WHICH NO IMPEDANCE IMPEDANC E HAS BEEN INTENTIONALLY INSERTED. THE TERM EFFECTIVE GROUNDING IS ALSO USED FOR SOLID GROUNDING.

RESISTANCE EARTHING  THE NEU EUT TRAL POIN INT TS OF TRANSFORMER OR GENERATOR ARE GROUNDED THRU¶ IMPEDANCE THE PRINCIPAL ELEMENT OF WHICH IS RESISTANCE.  THIS THIS MET ETHO HOD D IS US USED ED WH WHEN EN EARTH FAULT CURRENT WOULD BE TOO LARGE IF NOT RESTRICTED

INDUCTANCE EARTHING  THE NEU EUT TRAL POIN INTS TS OF TRANSFORMER OR GENERATOR ARE GROUNDED THROUGH IMPEDANCE THE PRINCIPAL ELEMENT OF WHICH IS INDUCTANCE. IT IS ALSO KNOWN AS µREACTANCE EARTHING¶.

GROUND FAULT NEUTRALISER  ARC SUPPRESION COIL OR PETERSON COIL

 AN IN INDU DUCT CTOR OR CO CONN NNEC ECTE TED D BET BETWE WEEN EN THE NEUTRAL OF A SYSTEM AND GROUND AND HAVING SPECIALLY SELECTED RELATIVELY HIGH VALUE OF REACTANCE.  THE THE REA REACT CTAN ANCE CE VA VALU LUE E IS IS SO SEL SELEC ECTE TED D THAT IT ALMOST CANCELS OUT THE CAPACITIVE CURRENT & ELIMINATES DANGER OF ARCING GROUNDS.

System Earthing Provides Safety of Power System by:  Ensuring Ensuring pote potenti ntial al of each each condu conduct ctor or is rest restric ricted ted to such a value as is consistent with the level of  the insulation applied.  Ensuring Ensuring eff effici icient ent and fa fast st operat operation ion of prote protecti ctive ve gear in the case of earth-fault.  Ens nsur urin ing g at lea east st on onee con condu duct ctor or ± ne neut utra rall ± at ground potential (low voltage).

Syste Sys tem m Eart Earthi hing ng ± Bas Basic ic Rule Ruless  Ea Eart rth h at ea each ch vo volt ltag agee lev level el  Ea Eart rth h at so sour urce ce & not not at lo load ad  Earth Earth onl only y once once (at sou source rce)) & avo avoid id furt further  her  connections to earth  Eart Earth h by tw two o sep separ arat atee & di dist stin inct ct connections with earth i.e. minimum two earth pits

EQUIPMENT EARTHING WHY ? 1. FREEDOM FROM DANGEROUS ELECTRIC SHOC SH OCK K HA HAZ ZAR ARDS DS 2. REDUCTION IN FIRE HAZARDS 3. PRESERVATION PERFORMANCE

OF

SYSTEM

SHOCK HAZARDS  DIRECT CONTACT: Contact with an active

conductor (i.e.) which is alive with respect to eart ea rth h in no norm rmal al ci circ rcm mst stan ance ces. s.  INDIRECT

CONTACT: Contact with a conductive part of an apparatus, which is normally dead, but which has become alive due to an insulati tion on failure in the ap app par arat atu us.

EFFECTOF CURRENT ON HUMAN BODY CURRENT MAGNITUDE

1mA 1mA ± 10 mA

EFFECT EFF ECT

No sensation Let go curr current ent  No adverse advers e effect effect

10 mA ± 25 mA

Painful Pai nful,, can caus causee muscle contraction

25mA ± 50 mA

Ventricular Ventri cular fibr fibrillat illation ion

More than 50 mA

Can be fatal

DRY SKIN BODY RESISTANCE

350

kOhm

WET SKIN BODY RESISTANCE

1000Ohm

REDUCTION IN SHOCK HAZARDS CASE 1 : NO EQUIPMENT EARTHING EARTHING

LOAD

SOURCE

V

SYSTEM EARTHING

EQUIV EQUI VALENT CIRCU CIRCUIT IT

NORMAL CONDN.

R L

V

R i

CURRENT THRU¶ HUMAN BODY: V IL } R i + R H + R  N FAULT CONDN.

CURRENT THRU¶ HUMAN BODY: V IF } R H + R  N

R  N R H

EQUIVALENT CIRCUIT TYPICAL EXAMPLE SAY, V = 240 V R L = 60 ; R i = 1000000 ; R H = 1000 ; R  N = 1;

Iline R L

V

R i

CURREN T THRU¶ VARIOUS CURRENT VARIOUS PATHS: a) Before fault Iline } 4 A

R  N

IF R H

EQUIVALENT CIRCUIT Iline

CURREN T THRU¶ VARIOUS CURRENT VARIOUS PATHS:

R L

V

IF

R n R H

b) After fault Iline } 4.2 A & IF } 240 mA

REDUCTION IN SHOCK HAZARDS CASE 2 : EQUIPMENT EARTHING

EQUIV EQUI VALENT CIRCU CIRCUIT IT

NORMAL CONDN.

R L

V

R i

CURRENT THRU¶ HUMAN BODY: V IL } R i + R e+ R  N FAULT CONDN.

R n R e R H

CURRENT THRU¶ HUMAN BODY: V IF } R e + R  N

EQUIVALENT CIRCUIT TYPICAL EXAMPLE

Iline

SAY, V = 240 V R L = 60 ; R i = 1000000 ; R H = 1000 ; R  N = 1 ; Re = 1 ;

R L

V

IF

CURRENT CURREN T THRU¶ VARIOUS VARIOUS PATHS: a) Before fault Iline } 4 A

I body R n R e R H

b) After fault Iline & IF } 120 A Ibody } 120 mA

REDUCTION IN SHOCK HAZARDS CASE 3 : EQUIPMENT EARTHING WITH PE CONDUCTOR  CONDUC TOR 

LOAD

SOURCE

V

SYSTEM EARTHING

EQUIPMENT EARTHING

EQUIV EQUI VALENT CIRCU CIRCUIT IT TYPICAL EXAMPLE TYPICAL EXAMPLE

Iline R L

V

R i

SAY, V = 240 V SAY, V = 240 V R L = 60 ; R  = 60 ; R i =L 1000000 ; R  = 1000000 ; R H i= 1000 ; R  = 1000 ; R  N H= 1 ; R  = 1 ; Re N= 1 ; Re = 1 ; Rloop = 0.01 ; Rloop = 0.001 ;

CURREN T THRU¶ VARIOUS CURRENT VARIOUS CURRENT CURREN T THRU¶ VARIOUS VARIOUS PATHS: PATHS:

R n

I body

R e R H

a) Before fault a) Before fault Iline } 4 A Iline } 4 A b) After fault b) After fault Iline & IF } 240kA Iline & IF } 240kA Ibody } 60 mA Ibody } 60 mA

TN, TT & IT Systems In TN, Ud =

0.8 Uo RPE Rph1 + RPE Uo Re

In TT,

Ud =

In IT,

Ud