Safety

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HV SAFEWORKING PRACTICE

OLADOKUN

EHV / May 2007 /

1

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OBJECTIVE 1. To understand the hazard and risk associated with high voltage electrical work 2. To understand the safe work procedure working on high voltage apparatus.

OLADOKUN

EHV / May 2007 /

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Definition High Voltage - exceeding 600 Volts Ф – E / 1000 Volts Ф – Ф Low Voltage – Not Exceeding 600 Volts Ф – E / 1000 Volts Ф – Ф (According to definition in Electricity Supply Act 447)

OLADOKUN

EHV / May 2007 /

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Personal Protective Equipments Employer should be provided PPE to employee for protection purpose. • Checked before and after used • Have procedures of use/defective.

OLADOKUN

EHV / May 2007 /

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Personal Protective Equipments

•Fire Retardant Suits (FRS) •Safety Helmet with Visor •Hand Gloves •Safety Shoes/Boots.

OLADOKUN

EHV / May 2007 /

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Chances of Survival Temperature during short circuit on high voltage( 8000OC – 10000OC) • Degree of burns : 1st, 2nd & 3rd • Surface area / percentage of burns • Age of victim

OLADOKUN

EHV / May 2007 /

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Chances of Survival

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on high voltage arcing depends on age of victim.

25% Burn

%

50% Burn

%

%

100

100

100

80

80

80

60

60

60

40

40

40

20

20

20

0

0

0

5-34

35-49

Age OLADOKUN

50-59

5-34

35-49

Age

75% Burn

50-59

5-34

35-49

50-59

Age EHV / May 2007 /

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Degree of burning due to arc depends on: • Arc Tempt – 8,000 -10,000 degree Celsius • Fault current – Arcing current depends on fault current than voltage system – Therefore both HV and LV can cause serious burn – “Arc in the box” s eg. Cubicle panel has 6 times more energy than open-arc. • Distance from arc (energy ~ 1/d2) • Duration expose to arc.

OLADOKUN

EHV / May 2007 /

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Severity due to electrical shock depends on: ● ●

Physical body of the victim, health, age and weight. Victim response. 2

J = I Rt

●

Electric flow through body

●

Duration of electric flow.

I = current, amperes

●

Capacity/magnitude of current

R = resistance of current path through the body, ohms

●

Frequency

●

Capacity/magnitude of voltage

OLADOKUN

J = energy, joules

t = time of current flow, seconds

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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High Voltage Zone?

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EHV / May 2007 /

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Entry to High Voltage Zone 3.All gates, doors or other device leading to High Voltage Zone shall be kept locked except when actually in use. 4.Only Competent Person may take charge of High Voltage Zone. 5.Members of a working party may be admitted to a High Voltage Zone by a Competent Person. OLADOKUN

EHV / May 2007 /

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DEFINITION H.V. Switching - Operation or other methods of making & breaking a circuit - Including switchgears controlling Tx (11/.415) L.V. equipment

OLADOKUN

EHV / May 2007 /

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DEFINITION

Dead - At or about 0 V & disconnected from any live system Note : A dead apparatus is not safe until it is isolated & earthed Earthed - Connected to general mass of earth - Ensure at all time an immediate discharge of electrical energy without danger - All Øs s/cct. & efficiently connected to earth

OLADOKUN

EHV / May 2007 /

19

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Precaution to be taken before work on High Voltage Apparatus. No person shall carry out work of any description on any part of High Voltage Apparatus unless such parts of the apparatus are: • Off • Isolated and all practicable steps taken to lock-off from live conductor including Low Voltage supplies,

• Proved dead • Connected to earth at all point of isolation • Physically screened where necessary to prevent danger and Danger Notices fixed. • Released for work by the issue of a Permit to Work. OLADOKUN

EHV / May 2007 /

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Withdraw able Apparatus

When withdraw able apparatus has been disconnected from all supplies and withdrawn from its normal live position, its conductor shall be discharged but need not remain connected to earth.

OLADOKUN

EHV / May 2007 /

21

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Feeder Spouts & Busbar Spouts Work On The Above Spouts ,Operations : i. Isolate from all points of supply ii. Lock - isolating mechanism - shutters of live spouts • Checked spout contacts dead by approved V.I. • Earth circuit with approved earthing equipment • Hang notice. Spouts Connected To O/H Circuit : • Dangerous induced V • Additional earths can safely be obtained

•

OLADOKUN

Forbidden to insert hand/any tool into contact spouts EHV / May 2007 /

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Making Dead and Isolating • Apparatus shall be made dead by opening the appropriate circuit breakers, oil switches, isolators, links or fuse gear • Ensure that the closing mechanism is inoperative by visual check • Isolation devices shall be locked immediately after isolation • Any supply from Low Voltage shall be removed by isolating the Low Voltage sides of the transformers,

OLADOKUN

EHV / May 2007 /

23

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Earthing Equipment • When High Voltage Apparatus is to be discharged and earthed it shall be done by the use of a circuit breaker, earthing switch, special equipment where provided or by other approved means. • Earthing lead and associated clamps used as Earthing Bonds shall be of approved type and adequate capacity for the duty at the point of application. • Earthing leads shall be properly maintained and always examined immediately prior to use.

OLADOKUN

EHV / May 2007 /

24

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Earthing Procedure • Before applying a Circuit Main Earth adequate steps shall be taken to identify the circuit, to ensure that the circuit is dead. • When a circuit breaker is used to make an earth connection the trip feature shall be rendered inoperative before closing unless this is impracticable. After closing, step shall be taken to lock off any means of tripping or opening the circuit breaker.

OLADOKUN

EHV / May 2007 /

25

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Earthing Procedure (contd..) 3. The procedure to be followed when using earthing leads shall be: (i) Earthing leads shall be connected to the earth system before being secured to the phases. (ii) All phases shall be earthed, even if work is to be carried out on one phase only. (iii) Earthing leads shall not be applied in any cell or compartment in which there is any exposed metal live at High Voltage. (iv)When earthing leads are being removed they shall be disconnected from the phases first and earth system last.

OLADOKUN

EHV / May 2007 /

26

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WORK ON REMOTELY AND AUTOMATICALLY CONTROLLED APPARATUS

Before work is carried out on remote or automatically controlled apparatus,, all remote control and automatic features shall be rendered inoperative. No work shall be carried out on the controlling equipment, wiring or relays of such apparatus except by a Competent Person acting under his direct instructions. WORK ON HIGH VOLTAGE CABLES

• No person shall touch the insulation which covers or supports any conductor is dead and earthed. • Where work is to be carried out on cable circuits in proximity to other live circuits and on cable circuits with fully insulated metalic sheaths, special precautions should be taken to avoid danger from induced voltages. OLADOKUN

EHV / May 2007 /

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DEFINITION Caution Notice - Warning against making apparatus live Danger Notice - Danger of approach or interfere Testing In Progress Notice - Warning : Danger testing in progress OLADOKUN

EHV / May 2007 /

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OLADOKUN

EHV / May 2007 /

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Recording of Switching Where log sheets are provided a record of all High Voltage Switching shall be entered therein.

OLADOKUN

EHV / May 2007 /

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MINIMUM CLEARANCE FROM EXPOSED CONDUCTOR TO GROUND LEVEL OR PLATFORM OR ACCESS-WAY :

Rated Voltage Not > 11 K.V. > 11 K.V. but not > 33 K.V. > 33 K.V. but not > 132 K.V. > 132 K.V. but not > 275 K.V.

Clearance Metric Imperial 2590 mm 8’ 6” 2740 mm

9’ 0”

3510 mm

11’ 6”

4570 mm

15’ 0”

The area to be defined at ground level shall only be that in which work is be carried out

b) Same min. clearance for nearest exposed H.V. conductor to points which work is carried out OLADOKUN

EHV / May 2007 /

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FIRE PROTECTION EQUIPMENT Portable Extinguishers • Approved • Handling extinguishers, maintain safety clearance • Discharge in enclose space - Personnel to leave space OLADOKUN

EHV / May 2007 /

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FIRE PROTECTION EQUIPMENT

CO2

OLADOKUN

EHV / May 2007 /

33

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General After explosion / fire / discharge of extinguishers in enclosed space & before entry of personnel • Ventilate thoroughly or • Wear suitable breathing apparatus

OLADOKUN

EHV / May 2007 /

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•HIGH VOLTAGE SAFETIES ON BOARD OLADOKUN

EHV / May 2007 /

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Precautions before work on HV

• Safety wearing must be used before proceeding to job. • Isolate power • Test HV live-line tester to prove its proper functioning. • The circuit on which work is to be carried out, must be tested and proved dead by an HV live-line testing equipment. • The circuit to be earthed down by connecting with hull. • Issue EPTW. • Minimum two people should work together. OLADOKUN

EHV / May 2007 /

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Safety precautions associated with operation of high voltage system •

Before start of work an Electrical Permit to Work must be issued.

•

EPTW is prepared and approve by the authorized officer.

•

The copied permit signed by the responsible person usually has at least 5 sections with the first stating the work to be carried out.

•

The next section is a risk assessment declaring where isolation and earthling has been applied and where danger/caution notices have been displayed then the permit is signed as authorized by the Chief Electrical Officer or Chief Engineer.

•

In the third section, the person responsible for the work (as named in section one) signs to declare that he/she is satisfied with the safety precautions and that the HV circuit has been isolated and earthed.

•

Section four relates to the suspension or completion of the designated work.

•

The last section cancels the permit with a signature from the authorizing officer.

•

The EPTW is valid only for 24 hours.

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EHV / May 2007 /

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Electrical Isolation Certificate

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EHV / May 2007 /

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Sanction-to-Test Certificate

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EHV / May 2007 /

39

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EARTHING-DOWN • CIRCUIT EARTHING • BUS-BAR EARTHING

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EHV / May 2007 /

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•

Procedure of megger testing (IR )

• Polarization Index or PI

OLADOKUN

EHV / May 2007 /

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