Advanced Electrical Safety

8/3/2019 Advanced Electrical Safety

1/123

Two Day National Course forExecutives

4/29/2012 Prashant Srivastava 1


2/123

Hazards of electricity Shock

Burns

Arc FlashArc Blast

Hazards from static charge

Secondary Hazards

All of above may cause injury and death.

4/29/2012 2Prashant Srivastava


3/123

ShockFactors which determine severity of shock

Level and type of Voltage

Current Path through body

Duration of shock

Even a voltage as low as 50 Volts andcurrent as low as 10 mA can be fatal.



4/123

VoltageAC or DC

Level

Frequency



5/123



6/123

Current Low current < 3mA Tingling

Slightly higher current 10mA Cause paralysis, Can not releaselive part due to temporary muscular paralysis causingincreased duration of shock

Still Higher, 30mA Respiratory Paralysis

Still higher> 75mA May affect electrical activity ofheart like fibrillation

>4A Tissue burning



7/123

Path Through Body Through skin only- Less dangerous

Through Heart can cause heart failure

Through Respiratory system Cause breathingparalysis.



8/123

Duration Long duration can cause burning of tissues

But even small duration of current passing through

vital organs can cause its failure leading to death orpermanent damage.



9/123

Shock ProtectionStrategies that are used

Reduce shock voltage to very low level by earthing

Reduce Shock current by increasing resistancebetween man and touched part and between man andearth.

Sense leakage to earth and trip supply



10/123

Shock protection by rubber gloves

and matsClass of rubber gloves and mats

Class 00 ((Only gloves) For use up to 500 VAC

phase to phase Class 0 For use up to 1000 VAC phase to phase

Class 1 For use up to 7500 VAC phase to phase



Class4 For use up to 36000 VAC phase to phase



11/123

Arc FlashArc flash is caused by one of the several reasons

Dielectric breakdown causes short circuit and limiting

impedance is low.When air becomes superheated and metal vaporizes

When high current is broken



12/123

Conditions conducive to Arc Flash High voltage

High current

Overheating of conductors Large inductance in the circuit



13/123

Dangers of Arc flashArc Flash can cause many of the following injuries

Shock

Burns Blindness

Deafness

Can burn almost any type of clothes increasing danger

of secondary burns.Arc Flash can cause second degree burns

at very large distance.



14/123

Arc Blast In confined space Arcing heats up air rapidly

Air Expands rapidly

Can blow out panel doors, shatter insulators and evenknock down walls

Throw molten metal over large distance

Can puncture ear drum

Normal panel doors are not designed

to withstand Arc Blast pressure.Specially designed panel doors are needed.



15/123

BurnsElectric shock causes local burns but Arc Flash can cause

extensive burns in face, Chest, Back and limbs.

First degree Burn- Superficial burns on the skin,Painful but no permanent damage.

Second degree burn- Skin and growth tissues areburnt. Growth of skin is slow. Usually leaves scar.

Third degree burn- Skin and growth glands are alsoburnt. Skin can not grow without grafting. Leaves scarand some permanent damage.



16/123

Hazards from Static Charge Static charge accumulates on human body specially

during winter by rubbing against clothes

It may also be passed through touching chargedsurface

Rapid transfer of electric charge to and from humanbody can give severe electric shock

Electric charge develops when liquid passes throughpipe lines both on liquid as well as in pipe line

Specially hazardous when transferring petroleum orother easily ignitable liquids.



17/123

Hazards from Static ChargeStatic charge accumulates during

Agitation or mixing of liquid or solid material.

Transfer of material Running on belt conveyor

Pneumatic conveying



18/123

Hazards of static electricityFilling inflammable liquid



19/123

Secondary Hazard Shock can cause person to fall down from height and

cause fractures or death

Person may fall on the live conductor and continuereceiving shock till help is available

Person may drop tools etc. on live parts causing arcflash

Short circuits can cause fires leading to large scaledeaths and injuries.

Arc Flash can start secondary fires.



20/123

Reasons for Electrical Accidents Ignorance

Misuse

Overload Switch in neutral instead of phase in 1 f circuits

Sparking due to loose contacts

Not proper grounding

Inappropriate design or workmanship

Bad maintenance

Use of earth in place of neutral



21/123

Reasons for Electrical AccidentsWrong instruments or instruments in bad condition

Improper PPE

Unnecessary risk by working on live parts Un insulated tools

Bypassing protection

Improper display of hazard

Improper of missing fence in hazardous areas

Not testing residual voltage before starting work

Ignoring visual or available information about status



22/123



23/123

Incidence of Arc FlashAn arc flash can occur while;

Doing work on live system e.g. bus bars, switches etc.

Racking in breaker Touching any live part by a tool

Spontaneously when air and metal parts becomeoverheated in closed space like panel boards



24/123

Properties of Arc FlashArc is a very heavy current passing through air under

certain conditions.

The current further heats up air through which itpasses and creates state of Plasma or ionized air.

This plasma is conductive and supports f low ofcurrent.

This current creates strong thermo-magnetic force.

This force moves plasma through space

Temperature at the core of arc can be > 20,000 o K



25/123

Properties of Arc Flash Large part of heat is radiated to large distance

It can inflict second degree burns at a distance of even12 feet

All type of clothing can be set on fire by arc flash

Molten metal flies at large distances

In oil immersed devices like transformers, arc flash on

bushings can set fire to oil and destroy entiretransformer and even may set establishment on fire



26/123

Flash Energy Light- Intense light is emitted which can cause loss of

sight temporarily

Heat is intense in the form of radiation andconduction to the person in touch.

Mechanical- In form of blast

Heat energy intensity is measured as cal/cm2



27/123

Incident Flash EnergyDefined as Arc Flash energy experienced by a person

Depends upon

Bolted short circuit current System Voltage

Distance from arcing electrode

Duration of fault

Absorbent coefficient of the victim

Box effect



28/123

Factors affecting injury by Arc Flash



29/123



30/123

Flash Protection boundaries Restricted Approach Boundary-A shock protectionboundary to be crossed by only qualified persons. Whencrossed, shock protection techniques and equipment isrequired.

Prohibited Approach boundary-A shock protectionboundary to be crossed by only qualified persons. Whencrossed, same protection is to be used as with live contact.

Flash Protection boundary- Distance at which incident

energy levels equals 1.2 cal/cm2

for fault clearing time of 0.1sec or more. For fault clearing time less than 0.1 sec, thiscan be considered a distance at which incident energy levelis 1.5 cal/cm2.



31/123



32/123

Class of Arc Flash HazardThe NFPA 70E 2004 standard provides 5 Arc Rating

levels

Class 0 for incident energy up to 1.2 cal/cm2

Class 1 for incident energy up to 4 cal/cm2






33/123

Arc Flash Hazard AnalysisReasons for arc flash Hazard Analysis

To know hazard level at each location

To know safe boundaries for approach To determine suitable clothing for approaching near

live area

To know suitable PPE for workers to work on live parts



34/123

Arc Flash Hazard AnalysisNecessary information for doing Arc Flash hazard

analysis;

Bolted fault current at each location

Clearing time for the source side protective device

Working distance for energized work

ATPV (Arc Thermal Performance Value) for PPE

combinations use at site Site specific issues e.g. ingress, egress, working space,

illumination etc.



35/123

Steps required to do Arc Flash

Hazard Analysis Site assessment and data gathering

Short circuit analysis

Protective device coordination Use of software for detailed analysis.

IEEE standard 1584-2002 comes with software

Other free wares are available on the net

Checkwww.cadickcorp.com andwww.oberoncompany.com

http://www.cadickcorp.com/http://www.oberoncompany.com/http://www.oberoncompany.com/http://www.cadickcorp.com/


36/123

Arc Flash Labeling Depending upon Arc Flash analysis Various locations

will have different classes of Arc Flash Hazard

Labels clearly describing hazard class, Flash hazardboundary, Limited approach, Restricted approach,Prohibited approach, Incident Energy level,Recommended clothing etc. is prominently put atlocations in a way that it can not be missed byworkmen.



37/123



38/123

PPE for Arc FlashMaterial for Arc flash resistant clothing should; Be in two part; One overall or long jacket and other

face shield

Be made from Flame Resistant (FR) material Gloves are also of same material. Additionally, rubber

gloves are put on over this glove for electricalinsulation

Typically heavier grade NOMEX or PBI is usedATPV should be 40cal/cm2



39/123



40/123



41/123

TrainingWorkers who are required to do hot work on live parts

are to be trained for this type of work.

Training in safety

Precautions to be taken

Tools permitted to be used

Instruments permitted to be used

PPE training



42/123

Mitigation of Arc Flash HazardStrategies

Reduction of bolted fault current

Reduction in response time of Protection system Increase of working distance

Reduced relay settings during hot work

Arc Detection devices



43/123


44/123

Reduction of Bolted current; Use

Current limiting Fuse


Fuse should clear fault within half cycle

Reduces voltage sag duration

Reduces transients and thus improves power quality


45/123

Reduction of fault currentCurrent; Actual andProspective

Voltage: Source and fuse



46/123

Reduction in response time By protective relay coordination, correct the response

time

Use of lower operating time relays

Bus differential protection

Use of lower settings reducing operating time



47/123



48/123

Increase working distance Incident energy is inversely proportional to square of

distance.

Hence increasing working distance can increase safetyimmensely

Distance can be increased by;

Using remote operated racking, remote operated

breaker closing and opening and using extension toolsand hot sticks.



49/123



50/123

Reduced relay settings during hot

work Temporarily reduce relay settings during hot work.

(Instantaneous settings just above peak demand)

Least expensive solution

Numerical relays can have two programs ; one fornormal operation and another for Hot Work

SCADA control can also implement this program.



51/123



52/123

Arc Detection devices Principle

Arc results in very bright light flash whose intensity ismuch higher than sun light or any other illumination

used. Optical sensors, based upon sudden increase in

intensity of light, sense beginning of arc flash and givesignal to trip coil of breaker.

To protect a zone optical fiber cable without outersheath is run throughout the protected zone.

Optical sensor can send signal within 2.5 msec. of startof the flash.



53/123

Optical Fiber Cable Routing



54/123

Arc Detection and Relay block

diagram



55/123

Tripping time comparison



56/123

Incident energy reduction



57/123

Arc Detection relay covering a zone



58/123

A Zero Potential surface



59/123

Reasons for earthing To create a reference voltage

To create a safe zero potential surface.

To create a return path for neutral currents

To reduce transients

To reduce harmonics



60/123

Earthing Pit Earth surface has high resistance and therefore we

have to create a pit which maintains low resistancebonding with earth and brings out a low resistance

connection which can be distributed. Neutral has to be earthed either directly or through

grounding resistors to create reference voltage otherwise lines can assume very high voltages which can be

a serious safety threat.



61/123



62/123

Requirements from earthing For substations and industrial users, Earthing resistanceshould be between 0.1 ~ 1.0 ohms

If resistance is higher, saline water should be added to the

pit. Many pits should be connected together to create a low

resistance path for large short circuit current withoutcreating large voltage drop

Every motor, panel and switchgears body should be

earthed at two places. Neutral of generators and Transformers should be

connected to two earthing pit which are independent ofbody earthing pits.



63/123

Some important notesWater pipes should not be used for earthing

Lead sheathing and armor of cables should be earthed.

Wherever RCC poles are used as in substations, Fourpoles can be tied with earthing strip and thenconnected to earthing pit.

Earthing electrode should not get corroded. GI or

tinned copper is preferred. Aluminum can be usedabove ground connections



64/123

Substation EarthingCriteria Low earthing resistance

Low step potential

Low touch potential



65/123

Earthing resistance requirements EHV AC Installations 33 kV


66/123

Step potential hazard



67/123

Touch Potential Hazard



68/123

Earthing mesh



69/123

Transmission Line earthing


EHT Lines 110 kV One aerial earthing wire 220 kV lines Two aerial earthing wires to be run through

towers At least at 4 towers every mile, aerial earthing wire is to be

earthed. HT Lines Earthing rods are driven in ground at each tower if

resistance is less than 15 ohms. For higher resistance two rods are driven in ground whose

distance should not exceed 200ft. Even then resistanceshould not exceed 25 ohms.


70/123

If it can not be done safely, it neednot be done



71/123

Basic six steps to safety1. Think Be Aware2. Understand Procedures

3. Follow Procedures

4. Use Appropriate safety equipment

5. If not sure, ask; do not assume

6. Do not answer if you do not know



72/123

Pre Job Briefing, SHEPP Special Precautions to be taken

Hazard Associated with the job

Energy control Procedures

Procedures and policies

Personal Protective Equipment



73/123

When?At the beginning of new shift

At the beginning of new job

Any time job conditions change

Any time when new personnel are introduced in anongoing job



74/123

Energized or De-energized?As much as possible de-energize before start of work

If job requires energized work, assess the hazard anduse proper tools, equipment and PPE

If control circuit is to be tested, shut power to powercircuit.

Production loss should not be the sole reason for

doing energized work Only qualified and trained workers to do energized

work



75/123

Energized work Excessive restart time in continuous process plant

High product loss in un scheduled stoppage

Testing electrical circuit

Trouble shooting controls

Infrared scan



76/123

Safe conditions for De-Energized work Only qualified people who know about system should

switch it off.

As far as possible switches and breakers should be

remotely operated. No load isolating switches should not be used for load

interruption.

All energy control devices feeding the area should beopened.

Locks and tags should be placed on energy controldevices.



77/123

Safe conditions for De-Energized work

Locks and Tags



78/123

Safe conditions for De-Energized workAll previously energized parts e.g. bus bars should be

discharged and grounded.

Voltage measurement to ensure all live parts are dead

and at zero potential. The work areas must be inspected by qualified person

to ensure no parts are still energized. This step is oftenmissed by many.

Remove all conducing material on body

e.g. rings, watches, ornaments, metal buttons etc.



79/123

Proximity Tester



80/123

Contact Voltage tester



81/123

Voltage measurement



82/123

Voltage measurement



83/123

Racking in and out metal clad breakers Many Arc Flash accidents happen while racking in and out

of breakers

Safe way to do so is to do this by remotely operated gear.Even a handle with long operating rod is better thanmanually operating from near the breaker.

Keep face and eyes away from breaker. Stand at an anglerather than face full square on.

Do not forget to put on PPE. Depending upon class of

hazard, if required, Arc Flash suit should be put on. Always have two people operating the breaker. One to do

the physical work and other to monitor from a distance andcall for help if necessary.



84/123

Racking in and out metal clad breakers Racked out breakers springs or pneumatic operating

energy should be discharged if not done so already.

Similarly make sure operating spring or other operatingdevice is off before racking in the breaker. Usually breakershave mechanical and electrical interlocks to take care ofthis but making sure is a good practice.

External safety grounding should be doneby using proper grounding connections with tested earth

bus. All previously live parts should be looped and a singleground connection should be made firmly to the earth busby suitable clamps.



85/123

Remote racking of Breakers



86/123

Safety groundingEarthing Clamps



87/123

GroundingSwitchgear Grounding Metal Tower Grounding



88/123

Operation of Gang Operated Switch Gang operated switches are usually used on overhead

lines.

A zero potential surface should be created below the

pole on which operator should stand. Using rubber gloves and glasses with side shields and

standing upon zero potential plate operate the switch.



89/123



90/123

Re-energizing equipment Before re-energizing inspect thoroughly to ensure that the

work which was to be done is completed satisfactorily.

Ensure re-insulation and other closing work has been doneproperly. Remove temporary ground connection.

Ensure that no tools are left where they should not be.

Inform all concerned people to move away.

Remove locks and tags

Recheck that breaker spring is de- energized.

Rack in the breaker Close doors

Close switch and energize



91/123

Energized working Pre Job briefing , SHEPP Inspect all energized working tools and PPE

Only qualified personnel to be near place of work

Work only with special tools and measuringinstruments.

Reduce protective relay setting , if required

At least two persons should work in teams with at leastone person monitoring the process.



92/123

Hot sticks and Insulated Tools



93/123

Safety Electrical One Line DiagramAn updated single Line diagram which is made for the

purpose of safety.

It should be Accurate and should be updated from

time to time Concise- Too much information clutters up the

drawing and many important information goes hidingSEOLD should clearly show sources of power,

disconnect switches, interconnections.

Legibility- If the drawing has become old and notlegible, new drawings should be made.



94/123



95/123

One minute safety Audit Notify responsible person of your presence in the area.

Listen for any abnormal sound and sniff for unusualodor.

Locate emergency exits.

Locate fire alarms and telephones.

Inspect all transformers liquid levels, temp. and

pressure gauges to ensure the readings are inacceptable range.

Locate Single line Safety Diagram. It should be legible.



96/123

One minute safety AuditArea should be neat and tidy. Panels should not be

used as almirah for storage of material and equipment.

All safety equipment should be within easy reach.

Check to see that all protective relay flags are reset.



97/123

Accidents dont just happen.

They can be prevented.



98/123

By PlanningPlan after making detailed studies

Arc Flash Hazard Studies

Load flow studies

About Voltage , Amp., Active and Reactive power. Used forsizing equipment.

Stability StudiesTransient and steady state stability of Power system. These

studies inform about stability during slow and fast changes

Motor starting analysis It is a computer generated model of a large motor under

starting condition, how it affects power system



99/123

By Planning Harmonic Analysis

Harmonics and other power quality problems which cancause equipment malfunction , failures and safety hazards

Switching Transient analysisCertain loads create switching transients. Switch

malfunctions also creates transients. Study shows magnitudeof transients and allows to develop solutions

Reliability Analysis It is a study of frequency of interruptions an number of

interruptions in a year. A reliability study will help evolvestrategies to operate system safely during interruption.



100/123

By Planning Cable Amp analysisThis study recommends proper size of cable for each

application depending upon capacity, type of cable, route andenvironment.

Ground Mat analysisStudy of earth resistance, touch and step voltages

Fault currents magnitude and duration

Geometry of grounding system

Soil resistivityProbability of contact

Human body resistance and assumptions on conditions ofindividual



101/123

By Planning Short Circuit study and Protective device CoordinationStudy about short circuit and earth fault currents

magnitude at various locations.

Study also shows protective Zones relay coordinationand selectivity

Time curves and coordination

Study of collateral damage to cables and other currentcarrying devices during short circuits

This study is one of the most important from safetypoint of view and should be repeated every five years inan operating plant.



102/123

By Design Select Switch gear, cables etc. with extra capacity keeping

in mind safety factor, over and above, plans for expansion Select arc flash protected switchgear Select switches for remote operation Select only good brand products with relevant safety

certification Make good layout with adequate space for ingress and

egress. Plan for adequate number of disconnect switches for

isolation for maintenance Plan for motor disconnect switch near a motor for

operation during maintenance



103/123

By Design Specify transformer with Pressure relief valve and drain pipe

instead of explosion vent

Design sufficient and strategically located safety fences to keepout un authorized entry by man and animals.

Plan proper routing for cables with proper ventilation and access. Plan for proper measuring and testing instruments

Specify flame proof switchgear and motors in locations wherethey are needed.

Plan for static earthing plates earthing tankers of Petroleumproducts loading and unloading.

Use low voltage for controls.

Purchase adequate number and type of PPE



104/123

By installation Select only Certified contractor Insist upon contractor providing proper uniform and safety kit to

their worker as part of contract. Insist upon contractors workersusing them. Take adequate managerial steps to ensurecompliance.

Make quality plan for each work, discuss with contractor andinspect its implementation.

Put safety inspectors on the job of monitoring hot work likewelding, cutting by gas with adequate arrangement for firefighting.

Provide training in specific jobs to contractors workers. Inspect contractors tools and machines for safety. Machines e.g.

welding machine, hand tools, power tools etc. Maintain overall discipline at work site



105/123

By Operation

Provide training to workers Provide safety kits and PPE

Provide suitable tools and measuring instruments

Provide competent supervision

Make detailed plan for maintenance Use of Predictive maintenance tools

Provide good quality spares

Make safety teams including workers and actively

participate in their meetingPlan for a rapid response team to provide rescue andmedical aid in case accidents still do happen.



106/123

Grounding of power systems for

safety



107/123

What & why of System Grounding It is connecting one of the supply conductors to the

earth.

Grounded systems provide sufficiently high short

circuit and earth fault currents to operate protectiveequipment.

They are less prone to transient over voltages

They are generally more protected from lightening

Solidly grounded systems are less prone to resonanceand to insulation failure.



108/123

System Grounding In DC supply, either + ve or ve can be grounded.

In single phase supply neutral is grounded

In star connected three phase system, star point is

grounded and used as neutral for single phase supply.

In three wire delta connected supply, earthingtransformer is used for grounding.



109/123

Solid grounding



110/123

Solid grounding


Used mostly for LT where earth fault current is low.

Also used for voltages above 33kV where line capacitivecurrents and inductive earth fault current neutralize

each other to such an extent that effective neutralcurrent is not very high during earth fault.


111/123

Neutral Grounding Resistance



112/123

Neutral Grounding Resistance Used mostly in 3.3 kV to 33 kV systems.

At these voltages line capacitive currents are not highenough and earth fault current is large enough.

Is so chosen that it does not affect neutral voltagemuch in normal operation.

In earth fault conditions, it limits earth fault current atthe cost of raising neutral voltage but makes thesystem safer.


G di d d 3 i l


113/123

Grounding ungrounded 3 wire supply



114/123

For sustained growth and safe

operation



115/123

Necessity of safety management Legal requirement

Employees health and safety

Money involved in accidents and down time

Industrial Relations

Social Obligation



116/123

Legal Requirement There are certain mandatory requirements which must

be fulfilled.

Some of these requirements start from design of

system and continue in purchase, installation andcommissioning of equipment and continue inOperation and maintenance.

An alert management knows about these requirementsand complies.

In case any changes are required to be done, thenagain legal requirements need to be studied andimplemented.



117/123

Employee Health and safety Every employer has responsibilities towards safety and

health of his employees.

With out proper planning and implementing safe and

healthy practices health and safety of employees cannot be ensured.



118/123

Financial loss Man hour loss

Production loss

Bad reputation

Market share loss



119/123

Industrial RelationsAccidents lead to bad IR

Loss of man hours and production



120/123

Electrical Safety Program Structure


Company Electrical Safety Team


121/123

p y y

CEST Consists of a senior electrical person as chair person

And many more qualified electrical persons

Management provides representative as advisor to

advise company policiesA SHE member who has ultimate responsibility to run

safety program.

A legal advisor to inform and clarify legal obligations



122/123

Responsibilities of CEST To develop, implement, evaluate and modify company

safety procedures.

Degree of authority to this team should be high

CEST should have a member at management level todevelop company safety policy



123/123

Companys commitment To safe work practices

To comply with legal requirement

In any electrical work safety is prime consideration

All employees are required to follow safety procedures If a job can not be done safely, it need not be done.

Each employee is responsible for his own safety

The commitment and cooperation of all employees is

required to sustain safety program

To ensure regular safety team meeting

Advanced Electrical Safety

Documents

Transcript of Advanced Electrical Safety