2electrical safety-20 04 18 · • transformer kept in on-load condition for a day and periodic...

Electrical Safety

Presented ByPresented ByPresented ByPresented By----

C S Chakraverty

Head- E&I Operation

L&T Construction ( MMH )

Objective of the session

• Create an awareness about importance of electrical safety in

our day today activities , in industrial applications and in our day today activities , in industrial applications and in

construction Industries .

Topics Coverd

• Competence

• Electrical Hazard

• Earthing System

• Documentation

• Guidelines for Maintenance & Testing• Guidelines for Maintenance & Testing

• Portable Equipment

• Using PPE

• Cable selection Criterion and precautions

• Statutory Norms

CompetenceCompetence

Purpose of competence

• Deployment of right workmen for a particular job to enhance productivity

complying safety.

• Development of supervisors and workmen skill by various means .• Development of supervisors and workmen skill by various means .

• Development of a robust process which enhances the skill set of the people .

• Inculcate a culture for safety.

Competence

Technical Statuatory

Competence Development

On Field Training Class Room Training Training by OEM

Workmen

Development through

CSR activities

Electrical Licence for

WorkmenSupervisory Licence

Classification of Licence for supervision and execution

• LT licence up to 415 V

• H.T Licence up to 33 KV

• EHT licence beyond 33 KV

• Licence for HT jointer• Licence for HT jointer

• Licence From Director General of Mines

& Safety

Licence can be obtained

• At state level

• At national level

ElectricalHazard

MINIMUM SAFE CLEARANCE VALUES

Minimum Safe

clearance (Metre)

6.6 kV 2.57

>6.6 kV <= 11 kV 2.59

Voltage KV Ph. to Ph.

rms

>11 kV <= 22 kV 2.64

>22 kV <= 33 kV 2.75

>33 kV <= 66 kV 3.00

>66 kV <= 132 kV 3.43

>132 kV <= 220 kV 4.57

>220 kV <= 400 kV 5.48

Shock Protection Measures

• Isolation

• Current limitation

• Low voltage

• Double insulation

• Earthing• Earthing

• Over Current Protection Devices

• Residual/Leakage Current Protection Devices

15

Isolation Transformer

• Power can be tapped from isolation transformer

• Avoids shock between earth and phase

SINGLE PHASE

TRANSFORMER

16

Low Voltage

• 24V hand lamps.

• By earthing the mid point of a single phase transformer, the line to earth

voltages are reduced to 115V while the full supply(230) is available to the

apparatus.

17

CENTRE TAPPED

TRANSFORMER

230V

115V

Relays are the devices which sense the abnormal conditions

from the power system and take trip decisions.

Overcurrent protection devices

Power Syste

Bus

CT

Relay

System CB

VT

Other devices

StationBattery

T

EQUIPMENT

RCCB WORKING PRINCIPLENo fault Condition I1 = I2

Fault Condition I1 > I2 (I1 = I2 + IP)

Tripping Condition IP > 30 mA

N

L

CORE BALANCE

CURRENT

TRANSFORMER

I2

I1

Ip

Application of RCCB

• Domestic & Industrial Lighting

• Welding Machine

• Refrigerator

• Hand Tools

ELR WORKING PRINCIPLE

• Normal E/F protection = Ir+

Iy+ Ib+ In=0.

• During E/F , the residual

current flows through neutral

and in-built E/F release in CB

operates .

EarthingEarthing

23

Purpose of earthing

• Prevention of electrical shock.

• Allowing passage to electrical fault current through least resistive path.

• Sensitive Earth fault protection

• Safety of the electrical system and equipment's.

Industrial Guidelines for earthling

• The combined Electrical earthing value of electrical system to be less than 1 Ohm

• Electronic earthing for PLC /DCS should be different from electrical earthing

• The value of the electronic earthing should be less than 1 ohm• The value of the electronic earthing should be less than 1 ohm

• Neutral of transformers should be separately earthed and should be able to isolated.

• For residential applications the voltage between neutral and earthing not to exceed 5V.

• All the equipment's to be earthed at two points

Methods of earthing

• Deep bore earthing for soils having more resistivity

• Use of good earth

• Use of chemical earthing in rocky soils.

• Earthing grid formation by MS rod or G.I flats

Sub-station Grounding

Step Potential

Step potential is the step voltage

between the feet of a person standing

near an energized grounded object. near an energized grounded object.

Touch Potential

Touch potential is the touch voltage

between the energized object and the

feet of a person in contact with the

object. It is equal to the difference in

voltage between the object and a point

some distance away.

How to limit step and touch potential

• Providing low resistance path to ground

• Proper insulation between body and ground- By providing resistive

surface layers

• Proper design and installation of earthing conductors • Proper design and installation of earthing conductors

• Use of current limiting reactors

• Use of highly insulated shoes

Typical Earthing Scheme for Construction Power Facilities

MAIN DB

EARTH ELECTRODE

50 X 6 G.I. FLAT

CLIENTS

INTERCONNECTION WITH

EARTH ELECTRODE

MAIN DB

SUB - DBPIPE EARTH PIPE EARTH

DRG NO. STD/CONP/002

FDBPIPE EARTH PIPE EARTH

EARTH CONTINUITY CONDUCTOR(SEPARATE OR AS THIRD / FOURTH CORE

25 X 3 G.I. FLAT

NO. 8 SWG G.I. WIRE

INTERCONNECTION WITHCLIENTS EARTH GRID

Documentation

Purpose/Importance of documentation

• Adopt a systematic approach by following a robust safety systems during

maintenance /operation.

• Leads towards zero accident .

• Minimises disruption in work

• Boost up confidence of the working professionals .

• Statutory Compliance – OHSAS 18001

Documents

• Release work permit routed through concerned departments

• Strictly adhere to the Lock Out Tag Out (LOTO) concept

• Raising and mitigation of NCR ( non-compliance report) on regular basis

• On line monitoring of NCR’s

• Compliance of Check list prior to installation and safe energisation .

PERMIT TO WORK (PTW)Typical Permit to work on Plant, Machinery & other Power Driven EquipmentName of the equipment :Area / Location :Clearance required for : (Time) ______ to ______ on ______ (Date)Nature of the job to be done:

Requested by: Approved by:Name: Name:Designation: Designation:Date & Time: Date & Time:_______________Equipment de-energised at __________ (Time) ____________ (Date)Fuses removed Yes / NoCircuit Breaker Lowered / Removed Yes / NoDanger Tag provided Yes / NoDanger Tag provided Yes / NoEarthing Lead No Provided Yes / No

Authorised Signature: Name: Designation: Date & Time:_____________________________________________________________________________We have completed job on the above equipment & we certify that •The equipment is clear of all the men doing the job; All tools and tackles have been removed; Whole of the area has been cleared; The equipment can be energised

Authorised Signature: Name: Designation: Date & Time:_______________________________________________________________________________Equipment Energised at __________ (Time) _________ (Date)Earthing Lead No. Provided Yes / No

Authorised Signature: Name: Designation: Date & Time:

• To ensure safety

Lock out/Tag out - LOTO

Maintenance & Testing

• Need for the Testing and Maintenance

• Safety features to be adopted during Testing and

maintenance .

Contents-

maintenance .

• Charging of power/Distribution transformer

• Do’s and Don'ts in Testing & Maintenance ( T & M ) of

electrical equipment's

Need for Testing and Periodic Manitenance

• check the installation completeness.

• check the healthiness of the individual equipment.

• ensure the required integrated electrical power system.

• ensure the protection system is in order to protect the

electrical equipment.electrical equipment.

• verify proper functioning

• verify that the performance of the installed equipment

/systems meet with the specified design.

• record performance data of the whole installation as the

baseline for future operation and maintenance.

Safety features

• Ensure the testing equipment and test kits are connected to

Earthing system.

• Check that the testing power supply taken through proper

fuse or RCCB.

• Ensure that the manufacturer catalogue, system Single Line

Diagram available with Testing Engineer.

Relay testing – Safety Features

• Ensure the Earthing of relay casing and test kit

• Protection for Auxiliary supply and test kit power

• confirm information about terminal connections of the following.• confirm information about terminal connections of the following.

• Auxiliary supply

• Current terminal

• Potential terminal

• Out put contact

23rd July 2008

Charging of the Power/Distribution Transformer

Before “ Switch ON” or Charging of the following points to be checked-

• Visual Inspection.

• Oil Level in the Transformer Conservator tank.

• Bucholtz Relay Input / Out put Opened.

• Oil in Transformer Breather Pot.•

• Stopper installation of Transformer Wheel.

• Transformer Tap position.

• Tightness of the Primary & Secondary Cable connection.

• Neutral Grounding Resistor kept “ON” Position.

• Setting of Oil Temperature Alarm & Trip.

• Setting of Winding Temperature Alarm & Trip.

Charging of the Power/Distribution Transformers

• Field Isolator Position “ON”.

• IR & PI and other routine test done of equipment along with Cable.

• Transformer Secondary side Breaker kept in “TEST” Position, for safety reason.

If all checks found “OK or ACCEPTABLE” then transformer Primary side breaker can be closed.be closed.

After Charging of the transformer

• A humming sound from transformer.

• Secondary side voltage check

• Transformer kept in ON-LOAD condition for a day and periodic noting of oil & winding temperature ..

Testing & Maintenance

• Understand the basics on the equipment's and the systems.

• Basics about the equipment to be tested, instruments and meters used for the testing and commissioning.

Do’s

• Procedures to be adopted during testing and maintenance .

• Formats to be used testing and maintenance .

• Fair Ideas on test results, standards to be followed and reference value.

• Purpose of testing, test results to compare.

Don’t

• Do not forget the safety norms.

• Do not start the testing of any equipment with out understanding and knowing

the expected test results

Testing & Maintenance

the expected test results

• Do not switch on the equipment with out protection

• Do not leave the secondary terminal of CT under open condition.

• Do not leave the secondary terminal of PT in short circuit condition.

Portable EquipmentPortable Equipment

Procedures for using portable electrical equipment

• Proper handling of cords

– don’t raise or lower equipment by its cord

– don’t unplug the equipment by pulling on its cord

don’t staple or fasten the cord so as to damage outer jacket– don’t staple or fasten the cord so as to damage outer jacket


• Equipment inspection

– visually check for:

• loose parts

• deformed or missing parts• deformed or missing parts

• damaged jackets or insulation

7b



– inspect for internal defects, as indicated by pinched or

crushed outer jackets

– perform inspections prior to beginning each shift– perform inspections prior to beginning each shift

7c



– remove defective equipment from service

– check the plug and receptacle mating configuration before connecting

7d


• Flexible cords

– flexible cords with grounding-type of equipment must

have an equipment grounding conductorhave an equipment grounding conductor

– never remove or alter the cord’s grounding pin

– never use an adapter with a missing grounding pin

7e


• Plugging/unplugging cord and cord-connected equipment and flexible cords

– ensure hands are dry

– never pull the plug out by the cord– never pull the plug out by the cord

7g


• Plugging/unplugging cord and cord-connected equipment and flexible cords

– handle cords and equipment with insulating protective

equipment when the cord connector is wetequipment when the cord connector is wet

– secure locking-type connectors after making connection

7h


• Circuit breakers and circuits

– never use the following to open and close electrical circuits

• fuses• fuses

• terminal lugs

• cable connectors

• cable splice

connections

7i


Circuit breakers and circuits

– don’t manually re-energize a circuit without first

determining if the equipment and circuit can be safely determining if the equipment and circuit can be safely

energized

7j


• Circuit breakers and circuits

– repeatedly closing a circuit breaker or replacing a fuse is

not allowed

– keep flammables and combustibles away from electrical

equipment

7k

Protective equipmentProtective equipment

Guidelines-

• Use appropriate protective equipment in damp or wet environments

• Inspect protective equipment to ensure reliability

• Guard normally enclosed live parts during maintenance

Safeguards for personnel protection

• When working near exposed energized conductors or circuit parts,

each employee shall use insulated tools or handling equipment if

the tools or handling equipment might make contact with such

conductors or parts

Special PPE’s

• Cool Coat

• 11KV, 6.6KV Hand gloves

Special Tools-Fuse Puller

Special Tools-

Discharge Rod

Fuse Puller

Power Tester

Discharge Rod

Cable Design/Selection /Precaution

Cable Routing

• All electrical cables should be run either on trenches , trays or underground

• Cable routing layout map to be prepared so that it does not cause tripping hazards

or accidents

• Welding and power cables not to be overlapped.

61

Design criterion of cable sizing

• Proper consideration of de-rating factor

• Current carrying capacity

• Voltage drop and short circuit calculation

• Type of grounding : solidly earthed or NGR earthed.

• Cable route

Precautions

• All cable should have tags at regular intervals .

• Underground cables to be laid with route markers.

• Minimum depth to be maintained for under ground cables

• Duct bank to be made while crossing roads/railway lines.• Duct bank to be made while crossing roads/railway lines.

• Minimum Bending radius to be maintained

• All electrical cables should be run either on trenches , trays or underground

• Cable routing layout map to be prepared

• Welding and power cables not to be overlapped.63

Duct Bank

Temporary Installation

Check in General for Temporary DBs

• Neutral earthing (In case of DG)

• Protective shed

• Body earthing

• Earth pit for body earthing

65

• Earth pit for body earthing

• Earth resistance

• Fuses

• Loose connection of cable

• Housekeeping

• Fire extinguisher and sand buckets

Typical Earthing Scheme for Construction Power Facilities

MAIN DB

EARTH ELECTRODE

50 X 6 G.I. FLAT

CLIENTS

INTERCONNECTION WITH

EARTH ELECTRODEDRG NO. STD/GRD/021

MAIN DB

SUB - DBPIPE EARTH PIPE EARTH

DRG NO. STD/CONP/002

FDBPIPE EARTH PIPE EARTH

EARTH CONTINUITY CONDUCTOR(SEPARATE OR AS THIRD / FOURTH CORE

25 X 3 G.I. FLAT

NO. 8 SWG G.I. WIRE

INTERCONNECTION WITHCLIENTS EARTH GRID

ELCB

Typical Sub Distribution Board

67

ELCB

63 A

30 mA

PLUG TOPS

• Plug tops should be used to avoid shock danger.

• Three point plug in case of metallic body hand tools and

two point plug in case of double insulated hand tools.

68

HAND TOOL

METALLIC BODY

Statutory Requirements

• Electricity acts 2003- Guides for the public safety arising out of generation

,transmission and distribution as well as plant maintenance .

• Building and other construction workers act 2003- Guide line for safety and health • Building and other construction workers act 2003- Guide line for safety and health

measures for construction workers .

• Factory act 1948- Guide line for health and safety of workmen in factory premises .

Thank You

Safety is something you learn from the start,

Being accident free is doing your part

Thank You