EARTHING
Date: 03.12.2018
Presentation by :
SOURABH TIWARI
DY.MGR (E3)- ELECTRICAL
BHEL-PEM, NOIDA
Classification based on PEM Packages
Below ground earthing Materials
Above ground earthing Materials
Lightning Protection Materials
Applicable Standards:
IS 3043 : Code of practice for earthing.
CBIP 302 : Manual on Earthing of AC Power Systems
IEEE Std. 80/2013 : IEEE Guide for safety in AC power plant Grounding
IEEE 142 : Grounding of Industrial and Commercial Power Systems.
IER : Indian Electricity Rules 1956
Definitions and Terms
• Earth Electrode: Metal rod or pipe driven into earth for
collecting or dissipating earth current into ground/earth.
• Earth conductor or Earth Lead: Conductor providing
conductive part between system neutral or installation or in
equipment and earth electrode or Earth mat
• Earth Mat or Grid: System of interconnected bare horizontal
conductors together with or without vertical bare conductors
embedded into earth
Statutory Provision for Earthing
• As per IS 3043
• All medium voltage equipment shall be earthed by two separate
and distinct connections with earth.
• Incase of High and extra High voltages, the neutral points shall
be earthed by not less than two separate and distinct
connections with earth each having its own electrode at
generating station and may be earthed at any other point
provided no interference is caused by such earthing. If necessary
neutral may be earthed through a suitable impedance.
Types of Grounding System
• TT SYSTEM: has one or more points
of the source of energy directly
earthed and the exposed and
extraneous conductive parts of the
installation are connected to a local
earth electrode or electrodes are
electrically independent of the
source earth(s).
• Different Types of Earthing Systems - Methods of Earthing (1) (1).mp4
• IT SYSTEM: has the source either
unearthed or earthed through a
high impedance and the exposed
conductive parts of the installation
are connected to electrically
independent earth electrodes.
• Generally provided in substation or
Power distribution area
• TN SYSTEM: has one or more points of the source of energy directly
earthed, and the exposed and extraneous conductive parts of the
installation are connected by means of protective conductors to the
earthed point(s) of the source, that is, there is a metallic path for
earth fault currents to flow from the installation to the earthed
point(s) of the source.
• TN systems are further sub-divided into TN-S, TN-C and TN-C-S
systems.
• TN-S System: Neutral of Power
supply with connection of earth
only at one point to the source
• Consumer’s earthing terminal is
connected to metallic armour of
the distributer’s cable
• TN-C-S System: Supply neutral
conductor of distribution main
connected with earth at source as
protective multiple earthing.
• Supply neutral is also used to
return earth fault currents from
consumer installation back to
source
• TN-C System: It
combined neutral
conductor fulfils the
functions of both
Protective Earthing and
Neutral Conductor
• Neutral conductor is the
sheath of the cable and
therefore is concentric
with phase conductor.
Philosophy of Earthing based on
installations
• Earth Fault Protections on Consumer’s premises (i.e Household Earthing,
House hold appliances earthing
) and Industrial premises
• Earth Fault Protections in Power Stations and Substations
Household Grounding System
Design Philosophy in Power Plants
• Dedicated earth pit shall be provided for system earthing at
locations where Generator and Transformers including FGD
transformer, NGRs of UT & ST (Standby Transformer), Service
transformer neutrals, Lightning Arrestor, LA VT Cubicle which
shall be connected by two separate earthing leads.
• These Earth Pits can be Treated and Non Treated which in turn
shall be connected to Main Earth mat.1 Earth Pit.pdf
• A Continuous Flat (of suitable size) earthing conductor shall run
along each route of cable tray along the structure of overhead
cable trays/cable shafts.
• This Earthing conductor shall be attached to each section of
Cable Tray.2 Cable Tray Earthing.pdf
• All above ground equipments shall be connected to this
runaway conductor via two connections
• This runaway conductor inturn shall be connected to below
grade grounding system through building column within plant
buildings and through risers for overhead cable tray/ cable shaft.
• Runaway conductor running in cable trays inside the cable
tranches shall be connected with riser from grounding mat.
• The steel columns, metallic stair case, hand rails, fencing of
transformer yard, storage tank, steel pipe rack etc. are
connected to the below ground earthing system through nearby
risers. All joints shall be bonded to provide electric continuity.
• Street lighting pole, flood lighting pole and the respective
junction boxes are connected at two points to an individual
earth rod.3 Equipment Earthing.pdf
• Railway tracks within plant area shall be connected to grounding
grid at different locations. The point where rail track leaves plant
area, the rail section is provided with insulated joint at both
ends. 5 Rail Earthing.pdf
• Flexible braided copper conductor is used for grounding of
metallic fence gates (e.g. in transformer yard fencing, etc) to
permit movement. 4 Fence Earthing.pdf
• Metallic sheaths, cable screens and armour of cables shall be
earthed at one either switchgear/ MCC/ DB or equipment ends.
• In case of HT Cable with Core Balance CT, the amour of the cable
shall be earthed either before entering through CT or once
entered armour to be brought back in CT then earthed.
Above Ground earthing materials
HT Motor Earthing
CABLE BOX
EARTHING
CT BOX
EARTHING
BODY
EARTHING
RING
ALONG
MOTOR
Motorised operated valve
8 SWG WIRE
CONNECTED
TO EARTH
FLAT FOR
ACTUATOR
EARTHING
EARTH FLAT
RUNNING
ALONG
CABLE TRAY
CONNECTED
TO 8 SWG
WIRE FOR
ACTUATOR
EARTHING
Oil Filled Service Transformer
RING CONNECTED
TO RISERS
TRANSFORMER
BODY CONNECTED
TO RING
RING ALONG
TRANSFORMER
TRANSFORMER
MARSHLLING BOX
CONNECTED TO
RING
Power Transformer
EARTHING FLATS
OF COOLING FANS
CONNECTED WITH
RING
Dry Type Transformers
BUSDUCT
EARTHING
NEUTRAL
EARTHING
CABLE BOX
EARTHING
MARSHALLING BOX
EARTHING
THANK YOU