Electrical Safety. Presented By- C S Chakraverty. L&T Construction ( MMH ) Head- E&I Operation

Transcription

1 Electrical Safety Presented By- C S Chakraverty Head- E&I Operation L&T Construction ( MMH )

2 Objective of the session Create an awareness about importance of electrical safety in our day today activities, in industrial applications and in construction Industries.

3 Topics Coverd Competence Electrical Hazard Earthing System Documentation Guidelines for Maintenance & Testing Portable Equipment Using PPE Cable selection Criterion and precautions Statutory Norms

4 Competence

5 Purpose of competence Deployment of right workmen for a particular job to enhance productivity complying safety. Development of supervisors and workmen skill by various means. Development of a robust process which enhances the skill set of the people. Inculcate a culture for safety.

6 Competence Development Competence Technical Statuatory Training by OEM Class Room Training On Field Training Workmen Development through CSR activities Electrical Licence for Workmen Supervisory Licence

7 Classification of Licence for supervision and execution LT licence up to 415 V H.T Licence up to 33 KV EHT licence beyond 33 KV Licence for HT jointer Licence From Director General of Mines & Safety Licence can be obtained At state level At national level

8 ElectricalHazard

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14 MINIMUM SAFE CLEARANCE VALUES Voltage KV Ph. to Ph. rms Minimum Safe clearance (Metre) 6.6 kv 2.57 >6.6 kv <= 11 kv 2.59 >11 kv <= 22 kv 2.64 >22 kv <= 33 kv 2.75 >33 kv <= 66 kv 3.00 >66 kv <= 132 kv 3.43 >132 kv <= 220 kv 4.57 >220 kv <= 400 kv 5.48

15 Shock Protection Measures Isolation Current limitation Low voltage Double insulation Earthing Over Current Protection Devices Residual/Leakage Current Protection Devices 15

16 Isolation Transformer Power can be tapped from isolation transformer Avoids shock between earth and phase SINGLE PHASE TRANSFORMER 16

17 Low Voltage 24V hand lamps. By earthing the mid point of a single phase transformer, the line to earth voltages are reduced to 115V while the full supply(230) is available to the apparatus. CENTRE TAPPED TRANSFORMER 115V 230V 17

18 Overcurrent protection devices Relays are the devices which sense the abnormal conditions from the power system and take trip decisions. Bus Power Syste m CB CT VT Relay Other devices Station Battery

19 RCCB WORKING PRINCIPLE T No fault Condition I 1 = I 2 Fault Condition I 1 > I 2 (I 1 = I 2 + I P ) Tripping Condition I P > 30 ma EQUIPMENT L I1 N I2 Ip CORE BALANCE CURRENT TRANSFORMER

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21 Application of RCCB Domestic & Industrial Lighting Welding Machine Refrigerator Hand Tools

22 ELR WORKING PRINCIPLE Normal E/F protection = Ir+ Iy+ Ib+ In=0. During E/F, the residual current flows through neutral and in-built E/F release in CB operates.

23 Earthing 23

24 Purpose of earthing Prevention of electrical shock. Allowing passage to electrical fault current through least resistive path. Sensitive Earth fault protection Safety of the electrical system and equipment's.

25 Industrial Guidelines for earthling The combined Electrical earthing value of electrical system to be less than 1 Ohm Electronic earthing for PLC /DCS should be different from electrical earthing The value of the electronic earthingshould be less than 1 ohm Neutral of transformers should be separately earthed and should be able to isolated. For residential applications the voltage between neutral and earthing not to exceed 5V. All the equipment's to be earthed at two points

26 Methods of earthing Deep bore earthing for soils having more resistivity Use of good earth Use of chemical earthing in rocky soils. Earthinggrid formation by MS rod or G.I flats

27 Sub-station Grounding Step Potential Step potential is the step voltage between the feet of a person standing near an energized grounded object. Touch Potential Touch potential is the touch voltage between the energized object and the feet of a person in contact with the object. It is equal to the difference in voltage between the object and a point some distance away.

28 How to limit step and touch potential Providing low resistance path to ground Proper insulation between body and ground-by providing resistive surface layers Proper design and installation of earthingconductors Use of current limiting reactors Use of highly insulated shoes

29 Typical Earthing Scheme for Construction Power Facilities CLIENTS EARTH ELECTRODE 50 X 6 G.I. FLAT PIPE EARTH PIPE EARTH MAIN DB 25 X 3 G.I. FLAT SUB - DB NO. 8 SWG G.I. WIRE FDB EARTH ELECTRODE INTERCONNECTION WITH CLIENTS EARTH GRID PIPE EARTH DRG NO. STD/CONP/002 PIPE EARTH EARTH CONTINUITY CONDUCTOR (SEPARATE OR AS THIRD / FOURTH CORE

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31 Documentation

32 Purpose/Importance of documentation Adopt a systematic approach by following a robust safety systems during maintenance /operation. Leads towards zero accident. Minimises disruption in work Boost up confidence of the working professionals. Statutory Compliance OHSAS 18001

33 Documents Release work permit routed through concerned departments Strictly adhere to the Lock Out Tag Out (LOTO) concept Raising and mitigation of NCR ( non-compliance report) on regular basis On line monitoring of NCR s Compliance of Check list prior to installation and safe energisation.

34 PERMIT TO WORK (PTW) Typical Permit to work on Plant, Machinery & other Power Driven Equipment Name of the equipment : Area / Location : Clearance required for : (Time) to on (Date) Nature of the job to be done: Requested by: Approved by: Name: Name: Designation: Designation: Date & Time: Date & Time: Equipment de-energised at (Time) (Date) Fuses removed Yes / No Circuit Breaker Lowered / Removed Yes / No Danger Tag provided Yes / No Earthing Lead No Provided Yes / No Authorised Signature: Name: Designation: Date & Time: We have completed job on the above equipment & we certify that The equipment is clear of all the men doing the job; All tools and tackles have been removed; Whole of the area has been cleared; The equipment can be energised Authorised Signature: Name: Designation: Date & Time: Equipment Energised at (Time) (Date) Earthing Lead No. Provided Yes / No Authorised Signature: Name: Designation: Date & Time:

35 Lock out/tag out -LOTO To ensure safety

36 Maintenance & Testing

37 Contents- Need for the Testing and Maintenance Safety features to be adopted during Testing and maintenance. Charging of power/distribution transformer Do s and Don'ts in Testing & Maintenance ( T & M ) of electrical equipment's

38 Need for Testing and Periodic Manitenance check the installation completeness. check the healthiness of the individual equipment. ensure the required integrated electrical power system. ensure the protection system is in order to protect the electrical equipment. verify proper functioning verify that the performance of the installed equipment /systems meet with the specified design. record performance data of the whole installation as the baseline for future operation and maintenance.

39 Safety features Ensure the testing equipment and test kits are connected to Earthing system. Check that the testing power supply taken through proper fuse or RCCB. Ensure that the manufacturer catalogue, system Single Line Diagram available with Testing Engineer.

40 Relay testing Safety Features Ensure the Earthing of relay casing and test kit Protection for Auxiliary supply and test kit power confirm information about terminal connections of the following. Auxiliary supply Current terminal Potential terminal Out put contact 23 rd July 2008

41 Charging of the Power/Distribution Transformer Before Switch ON or Charging of the following points to be checked- Visual Inspection. Oil Level in the Transformer Conservator tank. Bucholtz Relay Input / Out put Opened. Oil in Transformer Breather Pot. Stopper installation of Transformer Wheel. Transformer Tap position. Tightness of the Primary & Secondary Cable connection. Neutral Grounding Resistor kept ON Position. Setting of Oil Temperature Alarm & Trip. Setting of Winding Temperature Alarm & Trip.

42 Charging of the Power/Distribution Transformers Field Isolator Position ON. IR & PI and other routine test done of equipment along with Cable. Transformer Secondary side Breaker kept in TEST Position, for safety reason. If all checks found OK or ACCEPTABLE then transformer Primary side breaker can be closed. AfterCharging of the transformer A humming sound from transformer. Secondary side voltage check Transformer kept in ON-LOAD condition for a day and periodic noting of oil & winding temperature..

43 Do s Testing & Maintenance Understand the basics on the equipment's and the systems. Basics about the equipment to be tested, instruments and meters used for the testing and commissioning. Procedures to be adopted during testing and maintenance. Formats to be used testing and maintenance. Fair Ideas on test results, standards to be followed and reference value. Purpose of testing, test results to compare.

44 Don t Testing & Maintenance Do not forget the safety norms. Do not start the testing of any equipment with out understandingand knowing the expected test results Do not switch on the equipment with out protection Do not leave the secondary terminal of CT under open condition. Do not leave the secondary terminal of PT in short circuit condition.

45 Portable Equipment

46 Procedures for using portable electrical equipment Proper handling of cords don t raise or lower equipment by its cord don t unplug the equipment by pulling on its cord don t staple or fasten the cord so as to damage outer jacket

47 Procedures for using portable electrical equipment Equipment inspection visually check for: loose parts deformed or missing parts damaged jackets or insulation 7b

48 Procedures for using portable electrical equipment Equipment inspection inspect for internal defects, as indicated by pinched or crushed outer jackets perform inspections prior to beginning each shift 7c

49 Procedures for using portable electrical equipment Equipment inspection remove defective equipment from service check the plug and receptacle mating configuration before connecting 7d

50 Procedures for using portable electrical equipment Flexible cords flexible cords with grounding-type of equipment must have an equipment grounding conductor never remove or alter the cord s grounding pin never use an adapter with a missing grounding pin 7e

51 Procedures for using portable electrical equipment Plugging/unplugging cord and cord-connected equipment and flexible cords ensure hands are dry never pull the plug out by the cord 7g

52 Procedures for using portable electrical equipment Plugging/unplugging cord and cord-connected equipment and flexible cords handle cords and equipment with insulating protective equipment when the cord connector is wet secure locking-type connectors after making connection 7h

53 Procedures for using portable electrical equipment Circuit breakers and circuits never use the following to open and close electrical circuits fuses terminal lugs cable connectors cable splice connections 7i

54 Procedures for using portable electrical equipment Circuit breakers and circuits don t manually re-energize a circuit without first determining if the equipment and circuit can be safely energized 7j

55 Procedures for using portable electrical equipment Circuit breakers and circuits repeatedly closing a circuit breaker or replacing a fuse is not allowed keep flammables and combustibles away from electrical equipment 7k

56 Protective equipment

57 Guidelines- Use appropriate protective equipment in damp or wet environments Inspect protective equipment to ensure reliability Guard normally enclosed live parts during maintenance

58 Safeguards for personnel protection When working near exposed energized conductors or circuit parts, each employee shall use insulated tools or handling equipment if the tools or handling equipment might make contact with such conductors or parts

59 Special PPE s Cool Coat 11KV, 6.6KV Hand gloves Special Tools- Fuse Puller Discharge Rod Fuse Puller Power Tester Discharge Rod

60 Cable Design/Selection /Precaution

61 Cable Routing All electrical cables should be run either on trenches, trays or underground Cable routing layout map to be prepared so that it does not cause tripping hazards or accidents Welding and power cables not to be overlapped. 61

62 Design criterion of cable sizing Proper consideration of de-rating factor Current carrying capacity Voltage drop and short circuit calculation Type of grounding : solidly earthed or NGR earthed. Cable route

63 Precautions All cable should have tags at regular intervals. Underground cables to be laid with route markers. Minimum depth to be maintained for under ground cables Duct bank to be made while crossing roads/railway lines. Minimum Bending radius to be maintained Duct Bank All electrical cables should be run either on trenches, trays or underground Cable routing layout map to be prepared Welding and power cables not to be overlapped. 63

64 Temporary Installation

65 Check in General for Temporary DBs Neutral earthing(in case of DG) Protective shed Body earthing Earth pit for body earthing Earth resistance Fuses Loose connection of cable Housekeeping Fire extinguisher and sand buckets 65

66 Typical Earthing Scheme for Construction Power Facilities CLIENTS EARTH ELECTRODE 50 X 6 G.I. FLAT PIPE EARTH PIPE EARTH MAIN DB 25 X 3 G.I. FLAT SUB - DB NO. 8 SWG G.I. WIRE FDB EARTH ELECTRODE DRG NO. STD/GRD/021 INTERCONNECTION WITH CLIENTS EARTH GRID PIPE EARTH DRG NO. STD/CONP/002 PIPE EARTH EARTH CONTINUITY CONDUCTOR (SEPARATE OR AS THIRD / FOURTH CORE

67 Typical Sub Distribution Board ELCB 63 A 30 ma 67

68 PLUG TOPS Plug tops should be used to avoid shock danger. Three point plug in case of metallic body hand tools and twopointplugincaseofdoubleinsulatedhandtools. METALLIC BODY HAND TOOL 68

69 Statutory Requirements Electricity acts 2003-Guides for the public safety arising out of generation,transmission and distribution as well as plant maintenance. Building and other construction workers act 2003-Guide line for safety and health measures for construction workers. Factory act 1948-Guide line for health and safety of workmen in factory premises.

70 Safety is something you learn from the start, Being accident free is doing your part Thank You