High Voltage Safety Course Handout CD 1

8/18/2019 High Voltage Safety Course Handout CD 1

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HIGH VOLTAGE SAFETY PROGRAMPlease Fill in The Registration Forms

SAFETY HAS PRIORITY OVER SERVICECONTINUITY AND ECONOMICS

IEEE - IECPROVE DEAD THE PLACE OF WORK

WELCOME TO IMTC


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High Voltage System Safety RequirementHigh Voltage system training is now part of STCW code

2010 ( Manila Amendment ) as mentioned on sectionB- III /2

The convention is in force till - 2013The convention covers the responsibility for operating

and maintaining the High Voltage ( above 1000 volts)electrical power plants on board ships and processplate forms


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MODULE STRUCTURE

THE ROUTINE / TIMINGS

PRE & POST COURSE ASSESSMENT

LAYOUT AND GENERAL SAFETY IN THE PREMISES AND THE highvoltage ELECTRICAL LAB

DURATION OF THE COURSE

ATTENDANCE

BRIEF ABOUT IMTC

IMTC COMPLIMANTRY BUS


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SAFETY IS MORE ABOUT ATTITUDE THANAPPTITUDE

GENERAL ACTIVITIES ONBOARD• Inspection• Operation• Maintenance

• Repair• Replacement

BEFORE CARRYING OUT ANY ONE OF THE ABOVEACTIVITIES MAKE SURE: -

1. What is to be done. If required make notes2. Where. Location. Environment. Elements3. How. Procedures. Caution. Warning. Risk assessment (Permits)4. When. Precedent5. Why.


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MODULE : 1

SCOPE:-

The program is intended for:-• Electrical Personnel maintaining, operatingand repairing Electrical apparatus

• Non Electrical Personnel operating electricalequipment

• Engineers• Watch keepers• Those responsible for safe control and

management of high voltage power systemsin a marine environment


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This training includes:• The functional operational and safety requirement for a Marine

High Voltage system• Maintain and repair of High Voltage switch gear• Taking appropriate action when dealing with faults in a High

Voltage system• Switching strategies for isolating components of High Voltage

system• Using suitable apparatus for isolation and testing of High Voltage

equipment• Switching and isolation procedures on a Marine High Voltage

system• Understanding safety documents for High Voltage systems• Testing of Insulation Resistance (IR) and Polarization Index (P/I)

on High Voltage equipment


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General Personal safety includes

1 Follow Safety policies: Every company has its own safety policy as per the rules ofSOLAS (ISM code). Understand and follow these points but also put them in practice

2 Situational Awareness: Know your surroundings and working environment and the riskinvolved and tackle the problems

3 Knowhow and Training: Correct operating knowledge of different equipment tools andsystems on board, including safety procedures and emergency plans through proper training

4 Use of PPE: Every person on board ships must know what PPE is to be used and when anddonning and checking. Maintain your PPE so as it is fit for use all the time as and when required

5 Help Yourself First: When you and your colleagues are trapped in dangerous situation,help your self first to get out of the situation and then help others

6 Know Your Ship Inside - Out: On joining a ship be familiar and know every nook andcorner of the ship including location of fire fighting appliances, life saving appliances, alarms ,

escape routes, life boats and every thing needed in an emergency7 Know Your Emergency Duties: Every crew member should know his emergency

duties

8 Avoid Panic Attacks: It is human to get tensed or nervous in case of an accident. Try tocontrol emotions to maintain mental peace and to act in a quick and smart manner under thepressure of an emergency situation


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High Voltage Safety

Isolation and access for Maintenance

DIEDisconnect – Isolate – Earth

PROCEDURES• No Electrical conductors should be regarded as being safe unless it has been

isolated earthed, secured and proved dead• Precautions should be taken to ensure that isolated equipment can not be re

energized. Lock out …. Tag out. Put up Warning and Caution notices• Voltage indicators should always to be tested before and after use• When not attended the barriers should be placed around live conductors• If isolation is done by other than competent person then it should be

demonstrated to the competent person


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Electricity can kill

• More than 3000 non fatal electric shock accidentsare reported every year in USA,1000 in UK• About 1000 people die every year from electrocution

and surprisingly voltage was < 600 volts• Be careful about Ice berg syndrome in case of

Electrical injuries / burns


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SAFETY PRECAUTIONS


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INTRODUCTION -

The management of Marine High Voltage Power Plant

• High voltage safety rules and procedures• Electrical hazardous and precautionsa ) Electric shock (touch potential)b) Arcs/sparks and blastc) Earthingd) Operation and safety features

• Legislative background1. International Health and safety legislation2. Flag state health and safety legislation

3. ESR (Electrical Safety Rules). Company specific4. Code of Safe Working Practices (CSWP)5. Health and Safety Executive (HSE)


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MODULE :- 2Brief revision of Power system on board


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ELECTRICAL POWER SYSTEM

The generator ( Alternator ) - Source of power. (Converts mechanicalenergy into Electrical energy by Electro Magnetic Induction)Brief on power and power factor

Advantages of high voltage over low voltage

AC / DC SERIES OR PARALLEL


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POWER AND POWER FACTOR

ACTIVE POWER = V x I x Cos. phai = KW

REACTIVE POWER = V x I x sine phai = KVAR

APPARENT POWER = V x I = KVA

POWER FACTOR = KW / KVA


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• Impedance ( Z ) of the load decides thePower demand

• Resistive component of the impedance

decides Active power. kW ( Governor )?• Inductive component of the impedancedecides the Reactive power. kVAR (AVR )?


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INTRODUCTION

The Management of Health and Safety atWork, regulation :

Risk Assessment .Every employer (Senior personnel, Manager, Superintendent) shall

make a suitable and sufficient assessment of :-1. Risk to the health and safety of his employees (subordinates)

to which they are exposed whilst they are at work: and2. In making or reviewing the assessment the employer shalltake particular account of ; -

a) The experience, lack of awareness of risk and immaturity ofNew joiners, Trainees and Apprentices

b) The fitting – out and lay out of the work placec) The nature, degree and duration of exposure to physical

biological, chemical agents and radiation ( very high Voltage)d) The form, range and the use of the work equipment and the

way it is handled


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Contd.e) The organization of process and activitiesf) The extent of health and safety training provided to young and new

employees (Operators, Maintainers and Trainees)Capabilities of training:-1. Every employer (Senior authorized/ Authorized person ) shall, in

entrusting tasks to his employee ( Competent person) take intoaccount their capabilities as regards health and safety

2. Every employer shall ensure that his employees are provided withadequate health and safety training:-

a) On their being recruited into the undertaking and on their beingexposed to new or increased risk because of :-(Transfer, introduction of new work equipment, introduction of newtechnology and introduction of new system of work, modificationetc.)


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• THE TRAINING REFERED ABOVE SHALL :-

a) Be repeated periodically where applicable

b) Be adapted to take account of any new orchanged risk to the health and safety of theemployees concerned

c) Take place during working hours


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General Safety Principles and Prevention

1. Avoiding risk2. Evaluate the risk which can not be avoided3. Combating the risk at source4. Adapting to technical progress5. Replacing dangerous by non dangerous or by less

dangerous

6. Developing a coherent overall prevention policy whichcovers technology, organization of work , workingconditions, social relationships and influence of factorsrelating to the working environment

7. Giving collective protection measure priority over individual

protective measures8. Giving appropriate instructions to employees (subordinates)


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Management of high voltage on boardships / platforms

• Arrangement of high voltage switch roomsSwitch rooms EquipmentSwitch BoardsTransformers

Protection Relays• Tripping and auxiliary supplies (110 / 220 dc source)• Earthing• Key safe / trapped key system

• Fault levels• Application of protection system• Prove dead the place of work. Switching schedule• Documentation


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ENERGY TRANSMISSION

Energy can be transmitted by various means:Mechanically

HydraulicallyElectricallyBy Radiation and other means

Electricity is the most common “energy transmission” mean

ADVANTAGES OF ELECTRICAL MEANS:Most efficientPollution freeFlexible

Instant availability over any distanceComparatively less maintenanceLow weight to high power ratio for a given capacity


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VOLTAGE AND VOLTAGE LEVELS

VOLTAGE & LEVELS

Low Voltage : Up to 1000 volts

Medium Voltage : 1000 to 6600 voltsHigh Voltage : 6600 to 11000 voltsExtra High Voltage Above 11000 voltsNOTE : ON BOARD ANY VOLTAGE ABOVE 1000 VOLTS IS BETREATED AS HIGH VOLTAGE

• Above voltage figures are in RMS

• The peak value of the voltages would be above figures divided by 0.707

• Illustration:• 1000 volts RMS = 1414 volts peak &

• 6600 volts RMS = 9335 volts peak

• 9000 volts RMS = ? volts peak


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MODULE :- 3SAFETY BOOK / MANUAL

AN OVERVIEW

THE SAFETY MANUAL / BOOK & IT’S PURPOSE


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THE SAFETY MANUAL / BOOK & IT’S PURPOSE

Safety has priority over service continuity, equipment damageor economics (IEEE )

Provide safety principles to be used for protecting individuals frompotential injuries and even death caused by electrical hazards.

The basic safety program is for supervisors, managers, electricians,engineers and the designers / specifiers of equipment used in electricalsystems

The purpose of the safety book is to increase the safety awarenessissues faced by the individuals who work on or near electricalequipment as well the system operators and equipment designers /specifiers

Safety guide lines are recommended by various international and nationalsafety organizations like:OSHA : Occupational Safety and Health Administration(USA)

IEC : International Electro technical Commission (UNO)

ANSI : American National Standards Institute (USA) EAW : Electricity At Work (United Kingdom ) (Regulation 1989)

ELECTRICAL SAFETY RULES – AN OVERVIEW


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ELECTRICAL SAFETY RULES – AN OVERVIEW

See:1) ESR 12 ESR 3

Competenceassessmenttraining

Competence5

See:1) ESR 1( company

specific)2) Safety Management

System (SMS)3) Hazardous Area Guide

Electricaldistribution,operating positions,permits, planning,risk assessment,preparation,completion, testing

Work4

See:

1) ESR 1 (Companyspecific rules)

Rooms, locks,

duties

Access3

See:1) ESR 1(companyspecific)

Modifications,adjustments,approvals, records,maintenance

Integrity2

See:

1) ESR 1(companyspecific)2) Code of safe working

practice for merchantSeamen

Rules, scope,responsibilities,authorities,familiarization,objections

Responsibilities and

Authorization1

HIGH VOLTAGE SAFETY RULES


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HIGH VOLTAGE SAFETY RULES

OBJECTIVES- Govern all works undertaken on highvoltage system include;

• Duties• Variations / amendments• Issue

• Approval / sanctionsDEFNITIONS-• Approved- Of type and method sanctioned in writing• Live /dead – Electrically charged• Isolated – Disconnected from all sources of power• High voltage – Any voltage in access of 1000 volts


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• High voltage apparatus• Electrical engineer• Senior authorized person

• Authorized person• Competent person• Permit to work

• Sanction to test• Limitation of access• Caution/Danger notice

• Circuit main Earth• Additional Earth/Earthed• Key safe• Safety lock


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ARRANGEMENTS FOR SAFE WORKING

Personal protective equipment (PPE)

Guarding (when working in the proximity of live

electrical equipment)

Use of safety locks, key exchange and lock out boxes

Risk assessment “ Matrix” HSE.( HEALTH AND

SAFETY EXECUTIVE)

Documentation ( permits should be ” in writing “ and

not verbal, on telephones or walkie talkies)


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EMERGENCY CONDITIONS ’

When does an emergency condition arise?How would you define an emergency condition?Fire, flood, gas leak, trapped person, etc.• First preference should be the safety of personnel• Immediate steps to be taken to remove the danger and inform

the people/person• Do not enter an area which is prohibited to you

• Switch off the power supply .This may not be possible in certain circumstances

NOTE; THINK AND BE AWARE OF THE EFFECTSCAUSED BY ANY ACTION TAKEN


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MODULE - 4

• Advantages of High voltagesystem

• Risks and hazards associatedwith high voltage


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ADVANTAGES OFHIGH VOLTAGE (3.3/ 4.4 / 6.6 / 11K.v. etc.

• TRANSMISSION OF POWER TO LONG DISTANCES

• FOR A GIVEN ENERGY LEVEL THE ARC INTENSITY IS

LOW (The current is low hence I x I x t is low)

• LOW WEIGHT / POWER RATIO. ( COMPACT SYSTEM )

• LOW / NO MAINTENANCE ON METAL ENCLOSED

SWITCH GEAR


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RISKS / HAZARDS ASSOCIATED WITH HIGH VOLTAGE

Note :- PROPERLY USED ELECTRICITY IS NOTDANGEROUS

• FOLLOW THE RULES AND REGULATIONS FOR SAFEWORKING (WARNING AND CAUTION)

• OUT OF CONTROL ELECTRICITY CAN CAUSE HARM TOHUMANS, THE EQUIPMENT AND THE ENVIORNMENT

• HEATING EFFECTS ( ARCS AND SPARKS )CAN ALSOCAUSE FIRES AND BURNS EVEN WITHOUT CONTACT

RISKS / HAZARDS ASSOCIATED WITH HIGH


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RISKS / HAZARDS ASSOCIATED WITH HIGHVOLTAGE

Hazards can include :

a) Poor work conditions, equipment and practices

b) Careless and inadvertent actions on the part of theindividuals

Common electrical hazards that can cause injury and evendeathElectric shock with touch potential (current is the boss)

Arc-flash burns ( from contact, short circuits ) and radiant's(Tissue damage ).Temperatures reaching up to 37,000*C

Arc blast impact from expanding air and vaporized material(vaporized copper expands 67,000 times in volume )Obnoxious / toxic gases

Formation of HCl from burning PVC insulation on the cables


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A high voltage electric shock will almost certainly lead tosevere injury or fatality

Factors that could increase the risk of receiving anelectric shock;

• High Voltage work carried out close to a person who is not familiar withHigh Voltage hazards

• High Voltage insulation testing• Equipment using water as part of High Voltage plant• Using test instruments when taking High Voltage measurements• High Voltage equipment stores energy even after disconnection

• If the High Voltage circuit main earth is removed while carrying out anymaintenance


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Ensure that necessary precautions / safetystandards are being followed up duringoperations & maintenance.

1)Ensure proper electrical connection before chargingany switchgear

2)Ensure that we are not leaving any tool within panel,electrical equipment

3) HT breakers – Do not charge without wearing 33KVhand gloves & without closing breaker panel

4) Do not touch pf capacitor terminals withoutdischarging them

5) Ensure all electrical safety standards whilehanding any electrical equipment


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EFFECTS OF ELECTRIC CURRENT( )


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ON HUMAN BODY(TOUCH POTENTIAL )

The severity of an Electric shock, can have dramatic effects and,depends upon the following key factors :

Current intensity and type- ac/dcContact duration

Tension (Voltage)

Body resistance. (Approx. 1500 Ohms)Current ”path ways” through the body

“FREQUENCY” (Hz) of the shock currentPsychological condition of the recipient

Sex, age and general health of the recipient

Environment

Attire etc. (PPE)


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EFFECTS OFELECTRIC CURRENT ON HUMAN BODYCurrent just perceptible0.9 – 1.2 mA


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Death can occur at relatively low currents, but time is importantAT LOW

The recipient can be thrown off and may survive but with severe burnsAT HIGHVOLTAGES

VENTRICULAR- FIBRILLATION. HEART MUSCLES UNABLE TO RELAX thuspumping stops leading to death

50 – 100 mA

Serious and very painful contractions of the muscles, breathing stops, but

normally resumes if current is interrupted within 5 seconds

20 – 40 mA

REALEASE IMPOSSIBLE CAN NOT BE TOLERATED15 – 20 mA

MEN CAN JUST BREAK THIS CONTACT9.0 mAWOMEN CAN JUST BREAK THIS CONTACT (LET GO)6.0 mA

Slight cramp in the upper arm ( unpleasant )5.0 – 7.0 mA

Cramp in the lower arm4.5 – 5.0 mA

Feeling of cramps and slight trembling in the hands4.0 – 5.0 mA

Considerable stiffening of the hand, the lower arm growing tired3.4 – 4.5 mA

Slight stiffening of the hand2.8 – 3.5 mA

Same sensation perceptible in the wrist also2.2 – 2.8 mA

Sensation that the hand has gone to sleep1.6 – 2.2 mA

Tickling sensation in the hand as from ants1.2 – 1.6 mA


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Importance of Earthing


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A rough relationship between the shock currentmeasured in milliamps and time measured inmilliseconds, that can be tolerated by a normalhealthy person

CURRENT = 116 / root TIME

Roughly, thus a 50 mA current for 4 seconds would notbe very dangerous.

Calculate the approx. current that would flow through ahuman body with 1500 Ohm,s resistance from atouch potential of 230 volts

MODULE 5


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MODULE – 5

High Voltage systemsGeneral Lay out of High Voltage Switch Board

Comparison between 440volts and 6600 volts

TABLE OF COMPARISON BETWEEN 6.6 kV AND 440V


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NO NEEDMECHANICAL INTERLOCKSYSTEM

MSB DOORS

NO EARTHING SWITCHWITH EARTHING SWITCHEARTHING DEVICE

NO SAFETY SHUTTERSWITH AUTOMATIC SAFETYSHUTTERS

CIRCUIT BREAKER CONNECTOR

NO PRESSURE RELIEF FLAPSPRESSURE RELIEF FLAPSAND REINFORCED DOORSPROTECTION AGAINST SHORTCIRCUIT

NO EXPLOSIONEXPLOSIONUNDER SHORT CIRCUIT

WITHOUT COMPARTMENTSSEGREGATEDCOMPARTMENTS

MSB PROTECTION

NARROWWIDERBUS BAR DISTANCE

LARGESMALLBUS BAR

DC 24 VDC 110VCONTROL CIRCUIT VOLTAGE

INCLUDED INSIDE ACBSEPARATE PROTECTIONSAFETY DEVICE LOCATION

VISUAL CHECKVACUUM CHECKER/GAPACB/VCB MAINTENANCE

ACBVCB,SF6,OIL,Air BlastTYPE OF CIRCUIT BREAKER

HIGHLOWCURRENT(FOR A GIVEN CAPACITY)440 volts6.6 k V high voltage


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Diesel Generator Panel


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MODULE - 6


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High voltage switch gear


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STANDARDS AND GUIDE LINESRELATED TO SAFETY


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Key organizations , agencies and commissions throughout the world associated withthe safety are:

IEEE Institute of Electrical and Electronics Engineers (USA)

NFPA National Fire Protection Agency (USA)

OSHA Occupational Safety & Health Organization (USA)

BIS Bureau Of Indian Standards ( INDIA)

IEC International Electro-technical Commission (Standards - UNO)

CENELEC European Committee For Electro-technical Standards (EU)

IEEE 1584 guide for flash/ arc” hazard calculations”:

Incident energy < 1.5 calories / cm 2 will cause a burn just curable

The guide lines from NFPA- 70 provide guidance on appropriate level ofPersonal Protective Equipment (PPE) as follows

ARCS / SPARKS / BLASTS


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Arcs can also take place due to breakdown of air gaps

Due to a high voltage across the gap a flash over between phases orphase to earth causing a very large fault currents. (CORONA)

Partial Discharge ( P D ). Premature failure of insulationThe arc temperature can be as high as 20,000* C. This may cause severeburns, loss / temporary loss of vision. The effects may be dramatic

A” blast” may follow the power arc and lead to vaporization of the material

involved ( contacts , bus bars and steel panels etc.)In case of copper the metal expands 67,000 times in volume when

vaporized, leading to an explosion

An explosion is a very fast expansion of surrounding air and objects can

be knocked out from fixtures and fittings and hurled about with very highforce

Since the fault energy is calculated as ( i 2t,), limiting the current will limitthe amount of the fault energy by use of proper/certified protective devices

TYPICAL INCIDENT ENERGY LEVELSAND RISK CATEGORIES


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The table is based on the calculations to IEEE 1584 for a typical LNGcarrier with two 2.5 MW turbine and two 1.25 MW Diesel generator setsconnected to an insulated distribution system at 440 volts 60 hz.

The distances are measured to the arc source and the figures shown onthe table refer to the open doors and covers

Table clearly shows that the arc flash energy is much higher close to thesource of the power generation

Long length of cables, right capacity fuses / fast acting MCCBs helpreduce the risk when working on panels and starters remote from themain switch board

PPE ( gloves, goggles / glasses and full sleeve boiler suits should beused for all the live work. Face shields with hood should be used wherethe incident energy is 5 cal/cm 2 and above

TYPICAL INCIDENT ENERGY LEVELS AND RISK CATEGORIES


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01.26 cal / cm 2457 mm0.2 sec8 kA63 kW motor ( supplied via 30m of3 core 25mm 2 )

25.15 cal / cm 21186 mm0.2 sec.10 kAMachinery space vent fan starter.One Diesel Generator connectedto Main Switch board

39.6 cal / cm 21811 mm0.2 SEC.20 kAMachinery Space vent fan starter.Two turbine Generatorsconnected to Main Switch board

13.1 cal / cm 2850 mm0.2 sec5.8 kACargo switchboard.*Two Turbineand one Diesel Generatorconnected to Main Switch Board

424 cal / cm 23375 mm0.5 sec20 kAMain Switchboard* One TurbineGenerator connected

RiskCategory

IncidenceEnergy at455 mm

Arc SafeDistance

FaultClearing

Time

Faultcurrent

Scenario

STANDARDS NFPA 70 E (TABLE FROM NFPA 70) (PPE)Wearing PPE increases the level of incident energy that can be endured without injury


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PPE basically is to provide a barrier between the arc and the naked skin .Note: From a practical viewpoint , over reliance on PPE is counterproductivePPE is restricting and may not permit the wearer to work effectively

Specially rated flash suit and hood< 45 cal / cm 24

As above + FR jacket and hood< 20 cal / cm 23

Cotton underwear + FR pants, shirts or coverall< 8 cal / cm 22

Fire resistance shirt, pants or coverall. Face shield< 5 cal / cm 21

Non melting flammable material e.g. Cotton, Rayon,Wool


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Personal Protective Equipment• PPE must be used when risk can not be avoided or

reduced to an acceptable level by safe workingpractices

• PPE does not reduce the hazard, and can only

protect the person wearing it and leaves othersvulnerable

• It should be noted that the use of PPE may in itselfcause a hazard- for example, reduced field of vision,loss of agility etc.


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Personal Protective Equipment• PPE should be provided by the ship, free of cost

where it is needed and suitable for the job to beperformed

• Fit the worker correctly (comfortable as far aspossible)

• Take account of ergonomic requirements and theworkers health

• Be compatible with any other equipment the workerhas to use same time


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Personal Protective Equipment• There has to a mechanism in place to check and maintain the PPE• The wearer should check the PPE before using• PPE should fit the wearer and be comfortable• The wearer should know the correct use of the PPE• PPE should be made available free of charge on board

NOTE ; More PPE related details are available with MCA on request for aparticular plant and activity.


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HIGH / MEDIUM VOLTAGE SWITCH GEAR


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Salient features of H.V./ M.V. switch gear :Basic switch gear operation is not different from low voltage system butspecial safety features are added to high voltage switch gear against :

• Arcs & Sparks that take place when the contacts are making andbreaking with normal load currents• Under fault currents

‘ARC’ depends on the following factors:

The nature and pressure of the medium of arcThe external ionizing and de-ionizing agents presentThe voltage across the electrodes and variation of timeThe material and configuration of the electrodes

The nature and configuration of the arcing chamber

NON INTERNAL“ARC PROTECTED” SWITCHGEAR


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Non-Internal Arc protected switch gear :A thorough analysis of arc protection system is to be performed. It is anITERATIVE process. It can not be performed by ship’s staff however it is doneand recorded by the designer / specifies / installers of the switch gear

IEE 1584 A has advised the following steps :1) Acquire the short circuit data for “normal operating conditions” (at sea) - (in

port-cargo discharging/ loading ) from the original short circuit study or bynew calculations.

2) Determine the arc fault current and duration3) Determine the arc fault energy at the working distance at 100% and 85% of the

arc fault current4) Determine the flash protection boundary. Risk category and required PPE

Note :OTS / 332 will provide the relevant data where ever it does not exist on old ships and tothe new buildings obviously in case of new buildings the flash protection and RISKcategory should be determined and included in the short circuit calculations. (Soft wareprograms are available from ETAP and CYNCAL for these procedures)

I t l “A t t d” it h

INTERNAL “ARC PROTECTED” SWITCH GEAR


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Internal “Arc protected” switch gear :In this case what the arc flash analysis will do is - quantify the flash hazardbut will not quantify the physical hazard that switch gear presents duringand after the fault .Unless the physical construction is robust enough there is a danger ofdoors, covers being open and even getting detached.Internal parts may be severely damaged, and safety interlockscompromised,i.e: Earthing connections may be detached.It is difficult to verify the exact mechanical strength by calculation.Testing will verify to a sufficient degree that the switch gear is robust toarcing faults. This is internal arc protected switch gearMV switch gear is almost exclusively internal arc protected

Note:The MV switch gear is generally internal arc protected therefore the operation andmaintenance of the switch gear is to be performed as per the manufacturer'sinstructions. An arc fault analysis is not strictly necessary, but it is recommendedfor the recordsMV voltage equipment should be classified (IAC) in accordance with IEC 67221-200

or any other acknowledged commission etc.

ARC PROTECTED” SWITCH GEAR


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It is recommended that the specification include thefollowing when generating the arc flash warning labels:

Short circuit calculations must include determination of incident energyfor 3 phase arcing faults as per IEEE 1584

Arc flash warning labels based on the normal electrical installationsoperating conditions should be created and available for installation on

switch boards, MCC,s, panels and GSP,s. These operating conditionsshould be clearly indicated on the level

The maximum arcing time for the arc flash calculation should be nogreater than 5sec.

A motor contribution for at least seven cycles should be included

The objective should be to design the electrical installation so that onlystandard PPE is necessary. If not possible then FLASH warning labels

should be posted on the panels etc .

REDUCING THE ARC FLASH HAZARDS ON NEW SHIPS


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The energy that a worker might be exposed to can

be reduced by :

Decreasing the prospective short circuit current

Decreasing the time taken to cut off the current

Increasing the working distance

Install current limiting reactorIncorporate current limiting fuses inprotection scheme

Reduce theProspective Fault

Design

Non PreferredMethods

Preferred MethodsTechniques to reducethe Arc fault hazard


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Increase transformerimpedance

Provide the dedicated test supplies

Select arc tested equipment

Ensure withdrawal parts are movedfrom/to the service position withonly with panel doors closed

Use arc fault detection and trippingdevices

Use arc eliminators ( divertingthe arc to a metallic shortcircuit by means of fast actingand rapid closing devices)

Provide protection elements forpower transformers secondarycircuits as well as primary circuitsto reduce operating time

Use interlocked zone trippingscheme to provide rapidoperation of upstreamprotection elements

Use instantaneous protectionelements, e,g, bus tie circuitbreakers, transformers, differentialprotection elements

Use “arc flash reduction”maintenance switches on low

voltage circuit breakers to override breaker timings settingsduring maintenance activities

Ensure that time/currentcharacteristics having the minimum

practicable margins, are selected

Limit the Duration ofthe Fault Current

protection schemeProspective FaultCurrent Level

Non PreferredMethods

Preferred MethodsTechniques to reducethe Arc fault hazard


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Have the minimum number ofon –line sets generators

Reduce thecapacity ofpower supplysource

Provide warning levelsindicating the level of arcflash hazard and the

appropriate level of PPE foroperating, faulting findingand maintenance.

Increase the length oftools used forwithdrawing functionaldevices, e.g.circuit

breaker racking handle

Operate the switch gear froma remote position. Use localelectrical control desks awayfrom switch gear

Increase theworkingdistance forpersonnel

Operation

MODULE 6 ( )


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MODULE 6 (a)Safety and use of portable tools


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All tools, leads, plugs and extension should be FIT and suitable for the purpose. Toolsincluding instruments are to be maintained / inspected / checked after and before the use

SELECTION OF ELECTRICAL TOOLS


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including instruments are to be maintained / inspected / checked after and before the usewhich should include the mechanical wear, leads, plugs

There are three categories of equipment protection against electric shock :

Class I : The apparatus is provided with basic insulation and the metal work is suitablyearthed. Most of the domestic and heavy duty tools are class I. In case of insulationfailure the earthed metal will reduce the hazardous voltage LEVEL

Class II : Is sub divided into two sub groups: - IIA and IIB

Class IIA : All insulated . The apparatus has two layers of insulation eg. Drill chucks andfixing screws

Class IIB : Double insulated. All exposed metal work separated from the conductors bytwo layers of insulation so that the metal work can not become live. There is no earth

connection hence the safety of the user depends on the integrity of the insulation. (Hairdryers, Small hand tools)

Class III : Apparatus operates on Separated Extra Low Voltages (SELV). The voltage notexceeding 50 V AC or DC between conductors or to earth. The apparatus has basicinsulation and no earthing is required


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Recommended Frequency and Scope of Test and Inspection

Recommended Frequency and scope of Test and Inspection


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Type of Equipment User/Informal checks Inspection & Testing CommentBattery-operated power tools,


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MODULE - 7

Energy Levels

ENERGY


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Energy in electrical system is measuredin;-

Kilo Watts – Generally in 440 voltssystem or so called low voltage system

Mega Watts – Generally in High/Medium voltage system

ARC ENERGYWhen a fault occurs, the Energy at the fault = Current


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, gysquired. x time

FAULT LEVELS AT DIFFERENT VOLTAGES:

Fault level @ 11,000 volts = 1.732. x k V. x Fault currentTherefore Fault current = Fault level (MVA ) / 1.732. x

Voltage (Kv)Typical Fault level in HV (11,000 /6600 v) system ismeasured in MVA. Standard 250 MVA

Calculate the fault current for the above fault at 11,000and 6600 volts


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Fault level at 440 volts is measured at 31MVACalculate the fault current.

HIGH VOLTAGE EARTHINGCONDUCTOR


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HIGH VOLTAGE EARTHINGCONDUCTOR

The cross sectional area of the earthling conductor forCopper and AluminumThere are tables ( IEE ) and regulations:Cross sectional area – S = Root ( I square x time ) % kI = fault currentt = time duration of the fault currentK = properties of earthling conductor (resistivity, temp.

coefficient etc. )

Earthing conductor:


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Earthing conductor:-For a copper conductor with PVC insulation

(thermoplastic) and a temperature rangefrom 30 C – 160 C, k = 143 and

For a aluminum conductor k = 95Typical Copper Earthing conductor used =

70mm2It can withstand a fault current of 10,010 A for 1

secAluminum conductor of 120 mm2 will handle a

fault current of the same magnitude

In maritime high voltage installation the


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In maritime high voltage installation theminimum size of Earthing conductors

required is = 30 mm2 . As per Norwegianregulations


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SAFETY AND PROTECTION SYSTEM


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The safeties incorporated in any powersystem include protection against

• Normal over loads but, with time and %• Short circuit between phases• Short circuit between phases and earth

Faults cause Heavy sparks and Arcs


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ARC- ENERGY AND CURRENT

B id l / i i hi i h hi h i


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Besides normal / routine switching operations the arc energy which isgenerated by faults is a serious concern in designing the high voltagesystems

Fault generated by arc energy= (I 2arc x t ). Magnitude of the faultcurrent (The current in the Arc) and the duration in seconds

Fault magnitudes fault level in HIGH VOLTAGE systems are expressedin “ MVA“ This is the “ fault level”

Fault currents are expressed in kilo amperes ( k.A.)

MODULE 8


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MODULE 8MEDIUM VOLTAGE SWITCH GEAR

There occurs a fault

Then the current should haltOtherwise the fault current would increase


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Otherwise the fault current would increaseAnd the service continuity decrease

But the relay acts quickAnd the circuit breaker trips

The faulty circuit is disconnected

And the power system is protectedThank you Mr. Switch gearBecause of you there is no fears


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MEDIUM VOLTAGE SWITCH GEARCONSTRUCTION AND “SALIENT “ SAFETY

FEATURES

SWITCH BOARDS/ SWITCH ROOMS

h h ll d f h


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On ships with installed capacity in access of 3MW theswitch boards are segregated.

Links / interconnecting breakers are installed tointerconnect the switch boards

1. Marine switch rooms containing switch gear andcontrol gear2. Transformers3. Protection relays

4. Tripping and auxiliary supplies (Batteries)5. Earthling

• PROTECTION;Current transformers and associated relays placed as

close as possible with special featuresSECURITY;


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• SECURITY;Unauthorized entry to switch rooms is restricted

Special “key safe / trapped key” system isincorporated. Doors are “secured’

• ACCESS AND LIGHTING;Switch boards should have an unobstructed well litpassage not less than one Meter widthAnti slip certified insulated coverings are required

NOTE; NEVER USE SWITCH ROOMS AS WORKSHOPSOR STORAGE SPACES

SWITCH GEARCLASSIFICATION OF CIRCUIT BREAKERS:


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CLASSIFICATION OF CIRCUIT BREAKERS:• Based on Voltage

Low – Less than 1kVMedium – 1kV to 52 kVHigh/extra high – 66kV to 765 kVUltra high – above 765 kV

• Based on locationIn doorOut door

SWITCH GEAR

B d i t ti M di


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• Based on interrupting Media

Air breakAir blastBulk oilMinimum OilSF6 Gas Insulated

Vacuum

SWITCHGEAR AND SAFETY FEATURES

3300 / 6600 volt switch gear is metal enclosed


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• ISOLATORS - DISCONNECTORS

a) Where isolation is required for other thanelectrical purposesb) On duplicate bus bar system to facilitatethe change over without interruptionc) All withdraw able circuit breakers,contactors

SAFETY FEATURES:- Most isolators are OFFLOAD devices

SWITCH GEAR

• SWITCHES : Load break- fault make devices.


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Not capable of handling the fault currents• EARTHING SWITCHES: Normally not designed

to break fault currentFeatures;a) Independent manual operation. May have

stored energyb) Inter lock is provided when connected to

circuit main earth

c) Some switches are fitted with anti - flexhandles

SWITCH GEAR

CONTACTORS ; Mechanical switching devices operated other than by


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CONTACTORS ; Mechanical switching devices operated other than byhand. Not capable of breaking the fault current hence fitted withfuses

Features ;a) Frequent operations with vacuum interrupterb) Are “dependent power operated”c) Withdrawal not possible with contactor “ON”d) Can not be closed until the isolating contacts are fully engaged

e) Automatic shutters cover the exposed live contacts whenwithdrawnf) The contactor opens on failure of a single fuse to prevent the single

phasingg) In some cases the earthing switch automatically closes on

withdrawal

SWITCH GEAR

C C S h i l i hi d i


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CIRCUIT BREAKERS; Mechanical switching devices

Features;

a) Capable of making, carrying and breaking currentsunder normal circuit conditions and also makingcarrying for a specified time and breaking currents

under specific abnormal conditionsb) Arc quenching medium may be SF6, vacuum, oiletc.

c) Operations may be independent manual

CIRCUIT BREAKERS


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SAFETY FEATURES ;

a) Can not be isolated whilst in closed positionb) Automatic shutters are in all withdrawal able unitsc) Oil circuit breakers have a pressure relief valved) Gas circuit breakers are fitted with alarms for low

gas pressure and subsequent lock oute) Locking facilities are provided

INTERNAL ARC PROTECTED SWITH GEAR

Metal enclosed Switchgear


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gear

» The switch Ready to installassemblies requiring high voltage andlow voltage cable connections

» assemblies have earthed metallicenclosures

» These switch gears have generally

three high voltage compartmentsseparated by partitions

DESIGN AND CONSTRUCTION

• The design is such that the normal operation,


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g p ,inspection and servicing can be carried outsafely

• Removable parts and fixed parts shouldwithstand the insulation level of the switchgear

• Interlocks between different components are

provided to ensure the safety and the desiredsequence of operation (Trapped key system)

Metal enclosed Switch Gear with removableparts


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parts• The withdrawal or engagement of the Circuit

Breaker should be impossible unless it is in openposition• The operation of the circuit breaker should be

impossible unless:

1- It is in the service

2- Disconnected, removed, test position

• It should be impossible to close the circuit breakerin the service position unless it is connected to theauxiliary circuit

Metal enclosed Switch Gear withoutremovable parts with disconnector

• The operation of the disconnector


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The operation of the disconnectorshould be impossible unless theassociated circuit breaker is in openposition

• The operation of the circuit breakershould be impossible unless theassociated disconnector is in theclosed, open or earth position


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SF6 CIRCUIT BREAKER

SULPHUR HEXAFLUORIDE :


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• Contacts close and open in a chamber filledwith SF6 Gas

• SF6 gas IS A GREEN HOUSE GAS

• The gas has very good dielectric properties

• Well suited to high and very high voltages


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Vacuum Circuit Breaker


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VACUUM TECHNOLOGY

Another media used in metal enclosed


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switch gear is vacuum for dielectricbetween contacts and cooling thearcing chamber

NOTE :-Vacuum switch gear is the most

commonly used switch gear in systemsup to 65 kV .

VACCUM ARC

General characteristics :


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The vacuum arc is really a metal vapor discharge

The vacuum arc is different from general low or highpressure arcs since the arc forming particles are the

electrons, ions and neutral atoms , derived from theelectrodes itself. ( Contact material )

The base gas pressure here is very low ( vacuum).Therefore conduction process role is not significant

VACUUM CIRCUIT BREAKERS

GENERAL CONSTRUCTION :• Arc interruption takes place in vacuum• Arcing contacts are placed in the metal chamber


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Arcing contacts are placed in the metal chamber• Moving contacts are attached to metal bellows• The interrupter is finally enclosed in a metallic body• Proved to be most suitable for medium voltage

• The material of the contacts plays very

important role in overall performance ofthe breaker [ Cu Bi, Cu Cr, Cu Ag ].• Cu Cr is most common material used• Contact geometry ( VERY IMPORTANT)

Vacuum InterrupterDesign aspects;• Interrupter length ( 8-20 mm) depending upon voltage• Contact travel (contact gap) 6 – 10 mm for 6 6 k V


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Contact travel (contact gap) 6 10 mm for 6.6 k.V.• Contact shape• Contact size• Time of travel

0.5 to 0.8 mm/ms

0.5 mm/ms

Contact speed

OpeningClosing

8 to 12 mmContact Gap


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Construction of Vacuum Interrupter

Parts 0f the interrupter;• Enclosure made of impermeable insulating material


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p g• Enclosure retains a vacuum of 10/10x11 Torr• End flanges. Made of non magnetic material• Contacts are “disc shaped” with symmetrical

grooves, segmented (misaligned fixed and moving)

• Contacts (Sintered) Copper Bismuth• Vapour condensing shield. Metallic tube around the

contacts• Metallic bellows welded to metallic flange• Seals. Metal glass or ceramics

Interrupter


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Vacuum interrupter

• Vacuum testing


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Vacuum testing

Checking VACUUM.1. Check the pull on moving contact

2. Connect the power to the OPEN terminals of theinterrupter from a dedicated vacuum checkeravailable on board/plant ( usually 15 kV – 50kV )

Merits and Demerits of VCB and VCT

1. Self contained unit. No gas or oil required2. Pollution free


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3. Modest or no maintenance4. Compact unit .Easy installation5. Non Explosive6. Silent operation7. Large nos. of operations. Well suited for repeated

operation of almost all types of loads (30,000)8. Sealed unit keeps the elements out, maintains the

contact resistance

Demerits• The vacuum interrupter is more expensive


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• The vacuum interrupter is more expensive• Restriction on rated voltage• High technology involved in designing the

interrupter• Loss of vacuum will render the switch gear

useless

• Surge suppresser are required for certainswitching operations

Vacuum Contactor

• Capable of millions of operations on loadand overload


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and overload

• Short circuit interruption capability is limited• Back up fuses give the short circuit

protection• Strikers are provided to take care of single

phasing and short circuits• Sustaining power is required ( 110 volt DC on

board )

OPERATING MECHANISM

• SPRING MECHANISM


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• PNEUMATIC MECHANISM

• HYDRAULIC MECHANISM

• SF6 DYNANAMIC MECHANISM

• MOTOR DRIVEN MECHANISM

SYSTEM REQUIREMENTS OFCIRCUIT BREAKERS

The main function of the circuit breaker is to interrupt shortcircuit currents and protect their loads against the effects ofsuch faults.


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suc au ts.

This function must be carried out with a high degree of safetyand reliability

• Terminal faults

• Short line faults• Transformer magnetizing and reactor

currents• Switching of unloaded capacitor banks• Out of phase switching

TESTING SWITCH GEAR

ROUTINE TESTS1. Di electric test on the main circuit2 Di electric test on the auxiliary and control


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2. Di electric test on the auxiliary and controlcircuits

3. Measurement of the resistance of the maincircuit

4. Tightness test5. Design and visual checks.( name platedetails and values )

6. Mechanical operation tests.( minimum/maximum operating test. Atleast five closing opening time andpressure where applicable)

• TYPE TESTS: All type tests should becarried out by using the number of


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carried out by using the number ofsamples specified in IEC 60694

MODULE 9

REMEDIAL ACTION SCHEME


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FAULTS AND PROTECTIONSYSTEM

FAULTS AND PROTECTION SYSTEMElectrical safety regulations clearly


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specify:-EFFICIENT MEANS, SUITABLY LOCATED, SHALLPROVIDE PROTECTION ;

• FROM EXCESS OF CURRENT IN EVERY PARTOF A SYSTEM AS MAY BE NECESSARY• TO PREVENT DANGER TO PERSONNEL AND THE

EQUIPMENT

WHAT IS A FAULT?

WHAT IS FAULT LEVEL?


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FAULT ENERGY?

FAULT ENERGY IS MEASURED AS ( I x I x t )

Consequently, the FAULT ENERGY is to bekept to a minimum level to limit the damage

to plant and more importantly, toprevent injury to personnel

FAULT LEVELS

In high voltage system the faults are measured in MVA


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g g y

Fault = 1.732 multiplied by voltage multiplied by current= 1.732 x Voltage x Current

= 1.732 x V x I

TABLE FOR FAULT CURRENT

5035000400

FAULT CURRENT (kA)FAULT LEVEL( MVA )SYSTEM VOLTAGE (kV )


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43.031.4158.8503.3

13.11506.6

26.25001126.215003321.8250066327500132

31.415000275


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FAULTS CONTD.

• SOLID FAULTS :- These faults occur dueto suddenly the complete break down of


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y pinsulation due to external damageresulting in very high fault currents and anexplosion. Such faults also must becleared as rapidly as possible otherwise itwill result in any of the following

consequences;

FAULTS CONTD .

• Increased damage at location of the faultsince fault energy = (current)2 x time

• Danger to personnel ( arcs and flashes)


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• Danger to personnel ( arcs and flashes)• Enhanced probability of earth faults

spreading to healthy phases

• Higher mechanical and thermal stressingin all items of the plant carrying the faultcurrent, particularly in transformers

• Sustained voltage dips

FAULTS CONTD .

The incipient faults :- The small faults developing into catastrophicfailure

Passive Faults :- Not really direct faults but may result into


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y y

active faults if not attended to:-

a) Over loading- leading over heating and insulation deterioration.

b) Over voltage which stresses the insulation

c) Under frequency

d) Power swing:- Generators running in parallel can go out ofsynchronism

e) In adequate cooling

f ) Bearing failure

FAULTS CONTD .

• TRANSIENT AND PERMANENTFAULTS :- These faults occur mostly


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yon out door equipment

• PERMANENT FAULTS:- Faults with

permanent damage to insulation

• SYMMETRICAL AND ASYMMETRICALFAULTS:- Faults related to power factor

PROTECTION SYSTEM

Protection system provides protection


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to the complete electrical system;• From source to the consumers• Maintainer and the operator.The system also activates alarms andindicates the cause of the faults andabnormalities

PROTECTION SYSTEM SHOULD:


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• DETECT THE FAULT AS EARLY ASPOSSIBLE

• DISCRIMINATE

• DISCONNECT ONLY THE FAULTY CIRCUIT

THE ROLE AND PURPOSE OF PROTECTIION SYSTEM

Protection system, however sophisticated, can not


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prevent a fault• A good number of faults are caused by human error• Condition monitoring has its limitationsSo the role of the protective system is to detect a fault

at the lowest possible level consistent with theability to supply full load to the plant. That is;;

TO MINIMISE BUT NOT PREVENT DAMAGE TO THEAFFECTED PLANT

TO DETERMINE THE AREA OF THE FAULT ANDDISCONNECT THE AFFECTED AREA

PROTECTION SCHEME

5-S principles ;-1.SECURITY : The system should be reliable so that security of supply

is ensured


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2.SENSITIVITY : The system should be able to sense minimum valueof the fault current, thereby reducing the consequent damage

3.SPEED: Protective system should be able to isolate the fault in theshortest possible time

4.SELECTIVITY : Protective system should be able to select and triponly the nearest circuit breaker

5.STABILITY: Protective system should not operate for external faults

PROTECTION SYSTEM

Protection System includes the :-• Generator Protection


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• Switch Board Protection• Feeder Protection

• Transformer Protection• Motor protection

COMPONENTS OF SAFETY ANDPROTECTION SYSTEM

PROTECTION SYSTEM INCORPORATES :-


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•The relays;Electro mechanical relaysStatic relaysNumerical relays

•Transformers;Required for the measurements of currents and

voltagesCurrent transformersPotential transformers (voltage transformers)Instrument transformers

The above transformers are classified as instrument (measuring) andprotection transformers

THEORY OF CURRENT TRANSFORMERThe ideal CT-


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• Primary and Secondary AT (Ampere Turns)should be exactly equal IN MAGNITUDE• The AT should also should be in perfect

phase oppositionTwo basic factors can effect the performanceof a CT

1. The phase error2. The current error ( the Ratio Error)

The CT performance can be improved by-

• Using a core of very high permeability and lowhysteresis loss


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• Maintaining the rated burden (load)• Ensuring a minimum length of flux path• Lowering the internal secondary burden• Use of wound type primary• Keeping the secondary burden to minimum

possible value

PARAMETERS OF INSTRUMENTTRANSFORMERS

• CURRENT RATING

• RATED BURDEN


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• ACCUEACY CLASS FOR PROTECTION CT,s ( 5P,10P,15P.)

• INSTRUMENT SECURITY FACTOR (In case of short circuit)

• KNEE POINT VOLTAGE

Knee point; The point on the magnetization curve at which 10%increase in flux density causes a 50% increase in excitingampere turns

CURRENT TRANSFORMERS (CT,s)

• Most current transformers are supplied in the ratio of


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100/1, 200/5, 400/5, 800/1, 1600/5, 2000/1 etc.

• Metering CT,s are linear to a value of 20%

• Protection CT,s are linear during a large fault current

• Typical burden on CT,s is 2.5 – 15 VA

• Summing CT,s are used to add different currents

Sequence Components:1. Positive sequence, caused by locked rotor


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2. Negative sequence, caused by current imbalance3. Zero sequence, caused by earth faults

Zero – phase sequence systems1. Placing a CT around earthed neutral


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2. Using a core balance CT3. Current balance system


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APPLICATION OF INSTRUMENT TRANSFORMERS

• DIFFERENTIAL PROTECTION;Used for the protection of generators, transformers,transmission lines and large motors etc. (Vector differencesbetween two or more electrical quantities)


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• RESTRICTED EARTH FAULT PROTECTION;Generally incorporated in generators with earthed neutral. Inthis arrangement usually up to 15% or less earths are notincluded

• CORE BALANCE CT;A core balance CT is used in sensitive earth fault protectionsystem. The CT is put around all the three phase cables todetect the zero sequence current. These CT,s are very sensitive

and can detect the leakages of 500mA• SUMMATION CT,s

• CURRENT BALANCE CT,s

NON RELAY OPERATEDP ROTECTION


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• SURGE PROTECTION

• FUSES


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Fig. 2

Shows “ I squire t” rating of some different

i f HRC F

EXAMLES 0F HRC FUSE SELECTION


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sizes of HRC Fuses.

It should be noted that the “ I squire t” parameter is given on a logarithmic scale

Fig. 3

Shows the time / current characteristic of thefuses given in fig 2



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fuses given in fig. 2

Fig. 4 (a)Shows simple distribution system with fusediscrimination using the “2 to 1” rule.

The discrimination is achieved by doubling the



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The discrimination is achieved by doubling therating of the fuse at each ascending stage of thedistribution system

Fig. 4 (b)Shows the corresponding system with

discrimination achieved by using the ‘ I squire t ;method based on the “ I squire t” characteristicsshown in fig 5.


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Fig. 6 (Continued)MOTOR :- 30 kW 4 pole DOL starting current( 7 x FLC ) for 10 seconds would require a fuse towith stand a starting current of 378 amperes for 10

PRACTICAL EXAMPLE OF HRC FUSESELECTION AND DISCRIMINATION


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with stand a starting current of 378 amperes for 10seconds

Therefore a 100 Amps fuse will be required towithstand the motor starting current of 378 Amps for10 seconds as per fig 7

Fig. 7

Shows time current characteristics of some ofthe fuses Therefore fuse “A” in figure 6 will



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Shows time current characteristics of some ofthe fuses. Therefore fuse “A” in figure 6 willhave to withstand the following loadconditions

1. STEADY STATE – current = 28 + 42 + 54 =124 Amps continuously

2. TRANSIENT - current = 28 + 42 + 378 = 448Amps for 10 seconds

Fig. 8Shows the “ I s quire t “discriminationcharacteristics associated with the fusetime/current character shown in fig 7 125 A



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time/current character shown in fig. 7, 125 Afuse will withstand 448 amps for 10 seconds.However on checking fig. 8 “ I squire t “

characteristics it can be seen that the prearcing time of a 125 A mps fuse is LESS thanthe total operating time

(ie. Pre arcing time + arcing time) of 100Ampere fuse in the motor circuit and thereforeWILL NOT BE SUITABLE

Fig. 8 (Continued)

Consequently Fuse A will need to be rated at



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Consequently Fuse A will need to be rated at160 Amperes

NOTE :-160 A FUSE PRE ARCING TIME IS GREATERTHAN THE TOTAL OPERATING TIME OF 100 Ampsfuse

Fig. 1 depict a diagram showing two squirrel cageinduction motors connected to a 415 volts distributionsystem and their starters

Motor 1 (M 1) is 37 kW 4pole, (In = 67.5 A) with DOLstarting current = 7 x In for 10 seconds (67 5 x 7 =



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( ) p , ( )starting current = 7 x In for 10 seconds (67.5 x 7 =472.5 A)

Motor 2 (M2) is 110 kW 4pole, (In = 189A) withESS (Electronic Soft Starter) starting current = 3.5 x Infor 40 seconds (189 x 3.5 = 661.5 A)

Refer the time /current and I squire t characteristics,determine the required HRC fuse rating for fuses F1,F2 and F3.

SURGE PROTECTION

SURGE; A transient over voltage steeply risingfollowed by slowly decaying voltage wave


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• EXTERNAL SURGE;- On transmission lines due to lightning and ittravels in both the direction. This results in an increase, of voltageseveral time, of the rated voltage and subsequently gets attenuated.Protection is normally provided by lightning arresters

• INTERNAL SURGE / SWITCHING SURGES ;- These surges arecaused due to switching action of certain types of circuit

breakers, connected to inductive loads in particular. SF6 andVacuum circuit breakers

SURGE PROTECTION

TYPES OF SURGE PROTECTION CONNECTED TO ANY SYSTEMDEPENDS UPON THE VOLTAGE AND THE INSULATION OFTHE SYSTEM

• OIL INSULATED SYSTEM; - This type generally doesn’t require


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OIL INSULATED SYSTEM; This type generally doesn t requireprotection due to inherent properties of the oil used.

• DRY INSULATED SYSTEM; - Rotating machines, dry coretransformers can not withstand large switching surges. Thistype of apparatus requires surge protection

NOTE- SURGE ARRESTER/SUPPRESSORS ARE CONNECTED ONTHE ON LOAD SIDE ,FROM ALL THE THREE PHASES TOGROUND

SURGE PROTECTION

OUT SIDESUBSTATION

LIGHTNING ARRESTERLIGHTNINGEXTERNAL

MOUNTINGPROTECTIONDEVICETYPE OFSURGES0URCE OFSURGE


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LOAD SIDE OF THEBREAKERS

SURGE ARRESTERSSUPRESSORS

SWITCHINGINTERNAL

SURGE PROTECTION

DEVICES USED FOR SURGE PROTECTION;-

1. Metal oxide type surge arrester-2 C it R i t surge suppressor


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2. Capacitance Resistance surge suppressor-

Metal Oxide type surge arrester

The metal used is Zinc Oxide(90-95%) and 5-10%additives such as Alumina, Antimony Trioxide and

Bismuth Oxide etc.Principal Ratings


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Principal Ratings• Rated Voltage and continuous operating voltage• Basic Insulation level expressed to withstand

lightening impulse and frequencies• Thermal rating. Discharge capability and current

rating

• Impedance


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C - R VALUES FOR MEDIUM VOLTAGE

C – 0.04 mF to 0.3mF

h h


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R – 20 Ohms to 1000 Ohms

For Medium Voltage motor control thevalues are

C- 0.1 mFR – 100 Ohms

FUSESSimple construction and consistency

Last resort against faults if the protection

system failsSelecting a right fuse will meet the discrimination


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ySelecting a right fuse will meet the discrimination

requirement

Excursions of currents can affect the safety factor of afuse

Check the time / current curve of the fuses

TYPES OF FUSES

• Semi enclosed or rewire able type

• Totally enclosed cartridge


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• Drop out fuse

• HRC fuse ( Used on Medium Voltage )

• Striker Fuse ( used with High Voltage contactors)

SPECIFICATION OF A FUSE LINK• Voltage rating ( To be specified by the manufacturer)• Frequency• Current rating ( Continuous RMS Value)• Minimum Fusing current


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• Fusing factor (Ratio between maximum fusing currentto current rating ( This factor is more than 1 )

• Prospective peak current• Breaking capacity. Highest prospective current• Operation of fuse link ( Process of pre arcing )

• Cut Off ( melting of fuse element before the currentreaches the prospective current)

OPERATION OF A FUSEThere are two distinct periods in blowing of a fuse

1. Pre-arcing time . Time during which the fuseelement is melting. (depends on current)


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2. Arcing time. This is the period during whicharcing exists. (depends on voltage)

3. Total arcing time .


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Characteristics and classification of aFuse ;• Check the characteristic curves

• Duty of category – AC1 – AC5 etc.Classification


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Classification1. Class P fusing factor less than 1.25

2. Class Q fusing factor less than1.753. Class K fusing factor more than 1.75

FUSING FACTOR = Minimum fusing factor/Rated current


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RELAYS

MODULE -10

D t t


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• Detect

• Discriminate• Disconnect

PROTECTION RELAYS

The most vital component in power safetysystem is the PROTECTION RELAY . Sensesthe current and voltage

A protective relay is an electrically operateddevice designed to :


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Sense the identified circuit parameters and

To initiate the disconnection with or without awarning signal, of the intended part of anelectrical section in case of any abnormal

condition in the installation


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TYPES OF PROTECTIVE RELAYING

• Directional- comparison Relaying

• Directional – comparison Blocking


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• Phase comparison Relaying

• Differential Relaying

• Loss of field

• Field grounding

TYPES OF RELAYS

Electromechanical Relays1 Attracted Armature2 Moving Coil

d


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3 Induction

4 Thermal5 Motor operated

6 Mechanical


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Current setting

• For a given current setting as the currentincreases the operating time decreases.

• British and most of the other standardsrequire that the relay does not operate belowthe 110% setting


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the 110% setting

• For electromechanical over current relays of1A, the typical settings range as-0.5A (50%) to 2A (200%)

NUMERICAL RELAYS- Features available

1. Thermal protection2. Unbalance protection3. Under-current protection

4. Over-current and earth faultprotection and temperature protection


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p p p(RTD)

5. Number of starts6. Hour run meter7. Ampere meter


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APPLICATION OF NUMERICALPROGRAMMABLE RELAYS –

Functions available• Remote computer/HMI capability• Sequence quantity (positive, negative, zero)

• Power ( active, reactive, power factor)• Average, RMS, Peak values


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• Harmonic quantities• Frequency• Temperature (RTD)• Motor start/stop

Numerical Relay for Motor Protection-Feature:-

• Self check feature – Ability to detectand correct a failure before theprotection system operate


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protection system operate

• Data Acquisition System• Memory Testing• Set Point Testing• Watch Dog Timer

HI - MAP RELAYS

Hyundai- Intelligent Measurement andProtection Relays


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HIMAP RELAYS PTOTECTION FUNCTIONS

Phase sequence voltage47

Reverse phase46Loss of excitation40Q

Under current relay37

Over voltage relay32

Bus under voltage definite time27B

Under Voltage, instantaneous, Definite time27

Automatic Synchronizing25/A

Over Excitation protection24

PROTECTION FUNCTIONANSI No.


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Start inhibit66

Ground over voltage64

Residual over voltage59N

BUS over voltage relay59B

Over voltage relay59

Locked rotor51LR

Current earth fault50GNBreaker failure50BF

Thermal overload49

HIMAP RELAY PROTECTION FUNCTIONS(Hyundai Intelligent Measurement and Protection)

Bus frequency supervision81 B

Frequency supervision81

Auto Reclosing79

Out of step tripping78 S

Vector surge supervision78

AC directional earth faults definite time67GS/GD

AC directional over current67

Protection functionANSI No


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Fuse failure- FF

Inrush blocking95 i

Trip current supervision94

Restrict earth fault relay87N

Line differential87LD

Generator differential87G

Transformer differential87T

Motor differential87M

Lock out86


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Other Advantages-Remote communication is very cost

effective

• Change of Settings• Change of Group setting• Control of Breaker (closing and


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• Control of Breaker (closing andopening)

• Instrumentation viewing• Event Recorder down loading

Any three general categories of protective relaystechnology is used :-

1. Electromechanical: Uses magnetic flux to create torque fromvoltage and current

2. Solid state relay: Uses low voltage analog signals sensed from


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y g g gcurrent and voltage. Uses discrete electronic and logic circuitsand may contain a basic microprocessor for logic andmathematical operations

3. Numeric relays: A multifunction, programmable logic relay ;digitized sensed current and voltage, then calculates an RMS or

phasor equivalent value. Also uses high end microprocessor


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TRANSFORMERS

INSULATIONOil, Fluorogas, Nitrogen,On ships, dry type resin encased transformers are

common

COOLINGMarine transformers are air cooled and placed in

separate well ventilated rooms ( In some cases in


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separate well ventilated rooms ( In some cases in

A/C rooms. ( Avoid moisture ingress)Special protection against surges is integral part ofsafety system associated with transformers

Precautions are also taken against shock and vibrationdue to heavy seas

TRANSFORMER PROTECTION

• High set Over Current :- HSOC [50/51] – I >>or inst.-To provideoperation for high levels of fault current associated with primaryside phase /phase faults. Set to be stable for phase to phase faultson the secondary side. – Trip primary and inter trip the secondarycircuit breaker

• IDMTL OVER CURRENT:- To provide non directional IDMTLprotection for over current discrimination external to thetransformer as a back up


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• IDMTL DIRECTIONAL OVER CURRENT:- DOC [67] I > To providedirectional discrimination protection for over current external tothe transformer in the opposite direction to the normal currentflow.

• INTER TRIP:- INT. [94] – To inter trip another circuit breaker whichcould possibly feed into the fault

• DIFFERENTIAL RELAYING (87) – Measured difference between theinput and output current initiates the tripping of the breaker

OTHER PROTECTIONS INCLUDE :

• In rush detection and trip blocking• Energizing inrush• Recovery inrush – This occurs at clearing an

external fault as a result of sudden increase ofvoltage

• Sympathetic Inrush


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Sympathetic Inrush

• Over excitation due to over voltage or underfrequency

• Ground fault sensing

• Turn to turn fault ( differential relay )


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MOTOR PROTECTION

Sequence Components and supply unbalanceThree sequence Components

1. Positive Sequence Component (locked rotor effect)

2. Negative sequence Component (caused by supply


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unbalance)

3. Zero Sequence Component ( earth fault)

MOTOR PROTECTION

Although environment and load may affect the life and integrity of the motor byand large all motors are liable to the same types of failure, namely:-Primary cause of motor failure is the “ EXCESSIVE HEATING “

• Negative sequence Protection : -CAUSES : -

a) Voltage unbalance in the feeder supplyb) Phase reversalc) SINGLE PHASING

• Some kind of mechanical over load resulting in an electrical over load


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• Stalling due to mechanical failure

• Phase failure

• Insulation failure

Motor protection

• Short circuit protection is provided by fuses• The fuses are large in size in comparison with low voltage• Access to fuses is available only after isolation• Fuses are firmly bolted on the contactor and are part of the contactor

• When working on Medium voltage, level 3 or 4 safety is required as perNFPA 70E

• All modern motor protection relays have computer interface such asRS – 232 or RS – 485 communications that allows the user to ;a) Set the parameter


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a) Set the parameterb) Look at real time running datac) observe vectors of currents and voltagesd) Event recordinge) Start inhibit for number of starts etc.

MOTOR PROTECTION. Contd.

• MOTOR PROTECTION :- MP - Generally consists ofnumber of elements incorporated into the same relayThermal – [46] [49] :- Over current due tomechanical loading, out of balance due to singlephasing and failure of power factor correctingcomponents/capacitor

• Earth fault:- cable breaking down to earth


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• HSO/C: [50/51] :- Instantaneous operation for motor /cable phase to phase fault ( only with circuitbreakers ). Contactors are fitted with fuses

• UNDER VOLTAGE ( Fitted with circuit breaker fed

motors ) UV – [27] < V


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Documents

High Voltage Safety Course Handout CD 1