High Voltage Safe Working Procedures
3.11 Safe Working Procedures
The safe working procedures are defined by International standards, classification society's rules, flag state administration rules and laws as well as the company policy and relevant rules. The person carrying out the work needs to check which procedure is valid in each working place. The most common reasons for arc related accidents are lack of communication, personnel carelessness, a person taking known risks and mechanical failure.
3.11.1 Working on High Voltage Apparatus
The competent person must be fully conversant with the nature and extent of the work to be done. The best approach for electrical safety is to only perform work on de-energised equipment that has been placed into an electrically safe condition. This should always be considered the ultimate safe work practice for electrical systems, when possible. With only a few exceptions, such as testing and start-up, or where de-energising a system produces an increased hazard or is infeasible, performing work on energized electrical equipment should only can be carried out taking all the precautions against an arc flash such as HRC-3 / 4 PPE
High Voltage Safe Working Procedures
No competent person is thus permitted to carry out work of any description on any part of a high voltage apparatus unless such part of the apparatus is:
1. Dead at the point of work.
2. Isolated and all practicable steps are taken to lock it off from live conductors and from dead conductors which may become alive.
3. Isolated and locked off from all voltage transformers which might normally be connected to them except where connections are bolted.
4. Earthed at all points of disconnections of high voltage supply to such apparatus and caution notices have been attached.
5. Proved dead by the appropriate testing equipment, confirming that no residual voltage exists on the HV conductors.
6. Screened where necessary to prevent danger, with caution and danger notices posted.
7. Released for work by the issue of a Permit to Work or Sanction for Test by an authorised person.
3.11.2 Working on HV Systems
The acronym “DIED will help you remember!
D Disconnect all points of isolation.
(Mechanical Interlock: The HV circuit breaker cannot be racked out while it is closed).
I Isolate (Rack-out) in order to prevent accidental re-energizing.
E Earth, using appropriate and approved equipment - by the Earthing Switch
(Mechanical Interlock: The earthing switch can be switched on until the circuit breaker is racked out / in the Test position; also, the circuit breaker cannot be racked in until the earthing switch is Off ).
D Dead prove it by checking with the voltage detector 15-20 minutes after the earthing
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M
M
M
M
M M
Live
Disconnected
Isolated
Earthed
Discharged
Dead
HV Bus Bar Switchgear Load
Figure 3.14 – HV Isolation Procedure
Racking Handle to withdraw the circuit breaker
Earthing Switch Handle
Figure 3.15 – The Front Panel of a HV Circuit Breaker
High Voltage Safe Working Procedures
A HV a a a a a a a
a a a a S . I a a a a
handle to operate the earthing switch when the breaker is in the Test / Disengage position.
3.11.3 Check of Completed Temporary Earthing
The Authorised person must inspect and ensure that the necessary earthing has been completed. To ensure that part of a high voltage plant is dead, it must be checked with a High Voltage Detector.
Prior to working on or close to high voltage plants, the Permit to Work, Action Plan and Electrical Equipment Checklist must be completed and signed by the Chief Engineer.
3.11.4 Procedure for the Use of Earthing Leads
Portable earthing cables are used where in-built earthing arrangements such as a transformer or bus bars are not available.
The following procedure should be observed when using earthing leads:
a) Verify that the circuit is dead by means of a voltage indicator of an approved type, the indicator itself being tested immediately before and after use.
b) Earthing leads should be connected to the earth system before being secured to the phase conductors. They should be secured to the phases only by means of a pole or other approved equipment. Care must be taken to ensure that good contact is made.
Figure 3.16 – High Voltage Portable Earthing Cable
c) All phases should be earthed, even if work is to be carried out on one phase.
d) Earthing leads should not be applied in any cell or compartment in which there is
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3.11.5 Checking for a Dead Condition and for Proving That a Circuit Is Dead
Prior to temporary earthing, it must be checked at the point of earthing that the section in question is dead.
When this high voltage electricity tester is moved within proximity of an energized line, the proximity voltage tester alert warns users with bright flashing lights and loud beeps. All functionality is available through push buttons designed for easy use with PPE gloves. A universal adapter Hot Stick is available for voltage higher than 1500 VAC.
Figure 3.17 – High Voltage Test Equipment – A Voltage Detector / Tester 3.11.6 Entry to Enclosures Containing High Voltage Apparatus
a) The cargo switchboard or transformer room and other enclosures containing High Voltage apparatus must be locked except when entry or exit is necessary.
b) The keys that permit the normal access to such enclosures must be available to authorised persons only.
c) No person except an authorised person or a competent person who is under the immediate supervision of an authorised person, who must be continuously present, is permitted to enter any enclosure in which it is possible to touch exposed high voltage conductors.
High Voltage Safe Working Procedures
d) Entry to other enclosures containing high voltage apparatus is limited to authorised persons or other persons only when they are accompanied by an authorised person.
3.11.7 Entry to Enclosures Containing High Voltage Equipment / Installations
Compartments and other enclosures containing high voltage equipment must be locked except when entry or exit is necessary. The keys that permit normal access to such enclosures must be available with authorised persons only. Entry to compartments containing high voltage equipment / installations that are not protected by insulated covers should only be made when the equipment / installation is isolated and earthed.
3.11.8 Precautions Prior to Live Voltage and Phasing Checks (Only in an Emergency) a) Where live-phasing is to be carried out, the area containing exposed live conductors
should be regarded as a high voltage test enclosure.
b) Approved equipment used for live voltage and phasing checks at high voltage should be tested immediately before and after use against a high voltage test supply.
c) Live voltage and phase-checking on high voltage equipment may only be carried out by a competent person acting on a sanction-for-test permit from the authorised person.
d) PPE-HRC 4 must be worn by a Competent Person performing the test.
e) The second competent man accompanying must be standing by with a rescue hook.
Figure 3.18
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3.11.9 High Voltage Test Enclosures Unauthorised access to a high voltage test enclosure should at least be prevented by red and white striped tape that is not less than 25 mm wide, suspended on posts and by the display of high voltage danger signs. A competent person (HV) should be present throughout the duration of the tests and the area should be continually watched while testing is in progress.
Figure 3.19 – A Safety Sign
And a Barrier in a High Voltage Test Enclosure
3.11.10 Working on Transformers
When work is to be carried out on any connections up to a point of isolation or the windings of a transformer, all windings irrespective of the voltage should be isolated.
Circuit main earths should be installed at the points of isolation from the high voltage supply.
Low voltage points of isolation should be locked in the open position.
3.11.11 Working on Ring Main Units
The design of ring main units usually prevents the use of a potential indicator, prior to earthing.
It is therefore extremely important that before any earth is applied, the appropriate remote end is isolated first.
The system diagram should be checked prior to any operations and the onsite labelling noted on an approved switching procedure, prior to commencing operations.
All work and switching on ring main units must be carried out in accordance with the
a a .
Work within the switching chamber of the ring main unit may require the isolation and earthing of all remote ends of the ring main unit.
High Voltage Safe Working Procedures
3.11.12 Working on Bus Bars and Directly Connected Bus Bar Equipment
a) Before any work commences on a bus bar or section of a busbar including any directly connected equipment, the bus bar should be isolated from any point of supply, including voltage transformers;
b) Any directly connected cable should be isolated and earthed at the remote end.
c) All switches on the bus bar or section of the bus bar must be withdrawn to their isolated position.
d) All isolating arrangements are to be locked and shutters covering high voltage contacts, contacts which may become alive and contacts where no work is to be done must be locked shut and warning notices posted.
e) The bus bar or section of the bus bar to be worked on must be proved to be dead with an approved potential indicator, in accordance with the rules for earthing.
f) A Circuit Main Earth shall be applied to the bus bar on at least one switch panel on the section of the bus bar on which work is to be done. An additional Circuit Main Earth shall be applied at any remote ends of directly connected equipment.
g) An additional Circuit Main Earth shall be applied at any such other position necessary to ensure that the busbar remains earthed at all times while work is being carried out.
h) A separate Permit to Work or Sanction for test shall be issued in respect of each section of bus bar. No more than one Permit to Work or Sanction for test shall be issued simultaneously in respect of any section of the bus bar or any electrical equipment directly connected to it.
i) Any orifices where work is to be done must be proved dead immediately before hand using an approved potential indicator.
3.11.13 Working on Bus Bar Spouts of Multi-Panel Switchboards
When work is to be carried out on bus bar spouts, the following operations should be carried out in strict sequence:
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c) The isolating arrangements should be locked so that they cannot be operated, and shutters of live spouts locked shut. Caution signs should be fixed to the isolating points;
d) Where applicable, danger signs should be attached on or adjacent to the live electrical equipment at the limits of the zone in which work is to be carried out;
e) Bus bars should be checked by means of an approved voltage indicator to verify that they are dead, the indicator itself being tested immediately before and after use. The checking with the voltage indicator should be done on the panel to which the circuit main earths are to be applied. This test should also be made on the panel on which the work is carried out;
f) Circuit main earths should be applied at a panel on the isolated section of the busbar other than that at which work is to be done using the method recommended by the switchgear manufacturers. The insertion of hands or any tool into the contact spouts for this purpose is not an acceptable practice;
g) An earth connection should also be applied to all phases at the point-of-work;
h) The permit-to-work should be issued to cover the work to be done. During the work, where applicable, the earth connection(s) at the point-of-work may be removed one phase at a time. Each phase to earth connection must be replaced before a second-phase to earth connection is removed;
i) On completion of the work, the permit-to-work should be cancelled.
3.11.14 Working on High Voltage Cables
a) No person shall touch the insulation which covers or supports any conductor subject to High Voltage unless such a conductor is earthed.
b) Before a Permit to Work is issued, a person who is authorised to issue permits shall identify the cable to be worked upon and prove it to be dead at the point of work. All cables shall be assumed to be live high voltage cables until they are proven otherwise.
c) Before issuing a Permit to Work to cut into or disturb the insulation of a High Voltage cable (except as required below) the person who is to issue the Permit to Work shall ensure compliance with the following and where practicable, shall involve the recipient of the Permit to Work.
i. Check cable records.
High Voltage Safe Working Procedures
ii. Visually trace the cable from the point of work to a point where the apparatus is clearly identified by permanent labelling and in such a way that there is no doubt about the cable identity. Where (ii) is not practicable then.
iii. Where (ii) is not practicable then the cable shall be identified by signal injection methods; the cable shall be spiked with an approved spiking gun as near to the point of work as practicable. When practicable the cable shall be cut with the spiking gun in position; tests shall be made to confirm that the cable that is cut, is the correct one. The above shall be carried out under a Sanction for test.
iv. Where work is to be carried out on cables where the conductors and / or sheath may be subject to induced voltages from live equipment in close proximity, then where practicable, the conductors and / or sheath shall be earthed and appropriate personal protective equipment (PPE) used.
v. Where the above procedures are not practicable then a special procedure shall be written and approved by the Electrical Engineer.
3.11.15 Re-energizing of a High Voltage Installation after Work
When work on a dead circuit is completed, the high voltage system must be restored to its operational state as follows:
a) Ensure that the zone / room / panel, etc., are clean and free from tools and any foreign objects.
b) Disconnect the portable earthing kit using the isolating rod. Start at the work location and move towards the earthing switch in the HV system. Remove all signs used for the work.
c) Open the earthing switch in the system panel.
d) C a HV activity
carried out.
e) Change over the circuit breaker to the service position.
f)