Before start of any construction activates all the working crew, site supervisors, engineers, and contractors should be made aware of activates to be done with all precautionary safety measures. The safety officers should ensure that the working crew members are fully aware of risk hazards and use of PPE articles. The PPE gadgets are to be use in invariably as per the type of activity. The stage wise safety measures to be taken are as under.
The Safety starts right at the first stage of excavation to charging of transmission line. The safety is not limited to the persons working for the transmission line but it is also inclusive for the persons staying nearby and passing nearby.
Depending upon the type of soil the design of tower is to be decided. During excavation as per the type of soil controlled blasting, excavation by JCB, Manual excavation, Excavation in water logged area is to be decided and accordingly with all safety measures excavation should be carried out. Wherever problem of land sliding is there proper shoring and shuttering is to be provided. Where the excavation area is big a slop method to be adopted. After excavation care should be taken to provide barricade / facing show as to avoid falling any human or animal.
Foundation
The design of tower foundation is based on type of soil, voltage capacity, crossings, wind zone etc. During foundation utmost care should be taken to see that when concreting activities are going on no persons may fall in the excavated pit. 1.5 Mtr. area around the pit should be kept free for easy movement. The mixture machine should be placed in such a way that the machine does not fall in the pit due to vibrations. All the persons working with concreting should use hand gloves, gumboots / safety shoes, face mask, escape ladder and safety helmets. If the foundation work continues in evening proper lighting arrangement must be available.
Erection
All the working staff should be acquainted / experienced to carry out erection work of tower structures. Before use of any tools and equipment the site engineer must ensure that all the tools are tested and the same are without any defects. All the tools tackles: Derrick, Guy wires, Winch machine, Pulleys, Ratchet, Pull lift, ropes, spanners etc. are in sufficient quantity and in good conditions. The working crew members are utilizing PPE articles viz. safety shoes, safety helmet, safety belts, full body harness, fall arrester etc.
Stringing
During stringing conductor pulling machines, winch machines, conductor drum table with its break device, dynamometer and all PPE gadgets are required. The rigging arrangement should be foolproof to avoid accident. The most use full tool in stringing is communication. The supervisors, foreman and leading crew member must have fully charged walkie talkie or mobile phones to communicate the stringing activities. Wherever the conductor is to be passed over any power line, telephone line, road or railways a pre-planned shutdown or arrangement must be done and at the time of crossing above points all the site engineers/ supervisor must remain present at that location.
Also utmost care should be taken that while pulling and lifting the conductor no public persons / animals are affected. For that, sufficient man power to be placed along the route of stringing the conductor span.
Require Point for Process of installation of transmission tower line
The supervisor should ensure that all the working staff are experienced, complete instructions are given to them, they are fully aware of electrical hazards due to crossing of power lines, induction of nearby lines and other hazards during crossing of roads, river, railway line etc.
The supervisor should ensure that all the staff are following the Safety Procedure and utilizing the suitable PPE (Personal Protective Equipment) without fail.
All the tools and tackles should have been checked & tested for its capacity and usage.
Where ever required, the line clear permit/PTW should be taken. Working area should be isolated from any power source and earthing should have been done in all the three phases.
During erection of transmission line, all the people residing / working near the line should be made aware by verbal, written, signboard regarding the accidence / dangers which may occur, during execution of work.
Whenever the work is stopped and if any pit is open, a barricade be provided to avoid any accident to nearby people due to falling in the pit.
During lifting of material on tower no person should remain exactly below lifting pulley to avoid any danger of falling material.
After the work is over, no extra material, scrap should remain at site which may cause any accident.
Hand groves should be used in erection and stringing work.
Suitable rubber hand gloves should be used by the concreting crew members to avoid damage to skin due to lime component in the cement.
Sunglasses should be used during stringing & tower erection in Hot Sun.
General rules for safety of transmission lines construction
The excavation for pad or pile type foundations in excess of 1.5-mtr. depth located on unstable earth, shall be either sloped to the angle of repose or shored if entry is required. Ladders shall be provided for access to paid or pile type-footing excavations in excess of 1.2 mtr.
Wherever the foundation is being constructed on unstable earth, the workmen shall not be permitted to enter the excavated pit unless shoring is done.
Only responsible and skilled employees shall be deployed for directing mobile equipment adjacent to footing excavations.
No workmen shall be permitted to remain in the excavated pit where concreting is done using machinery.
The mobile equipment shall be located only on levelled earth to assure stability.
Sufficient care shall be taken during tower erection to see that more than the minimum numbers of workmen are not deployed. This will minimize injury due to exposure of falling objects on workmen, when working at two or more levels. Proper protection such as use of helmets, safety belts etc., shall be insisted upon.
Tie ropes shall be used wherever necessary for maintaining steel sections or other parts in position to reduce the possibility of tilting etc.
Adequate supports shall be provided for the tower members and sections of panels during assembly.
The construction of transmission towers, erection of poles, the tools and machinery, employed for the work shall meet the requirements of the relevant Indian Standard Specifications and Code of Practices along with the CBIP manual on Transmission Lines. The wire ropes, pulley blocks etc., shall be of tested quality and inspected by a responsible employee for its fitness before commencing the work.
Other than the supervisory staff and such of the workmen required to guide and assist the section being erected, no one else shall be permitted to come under a tower being erected.
During erection of towers using hoisting equipment adjacent to existing Transmission Lines, the lines shall be de-energized wherever possible. When this is not practicable, extraordinary precautions shall be exercised to maintain more than the minimum clearances required for safe working.
Wherever cranes are used for erection, the same shall be set on firm foundations. The outriggers of the cranes shall be used wherever available. The wheels shall be locked in position to prevent dislocation during handling.
Suitable tie ropes shall be used to maintain control of tower sections being raised and positioned wherever possible and proper care shall be taken to see that they do not create a greater hazard.
The wire rope used for carrying the section shall not be detached before the section is adequately secured.
The erection or maintenance work shall not be carried out during high wind, thunderstorms or unfavorable weather condition, which would make the work hazardous, except during emergency restoration procedures where utmost precautions, shall be taken to avoid any accidents.
The Engineer in Charge shall regularly arrange to maintain all the equipment and tools and plant in safe operating conditions.
Stringing of Bundle Conductor shall be carried out with T & P Machine only except where not feasible.
Adequate traffic control shall be maintained wherever erection work is being carried out at highway crossings. The permissions required from the concerned authorities, such as the department of highway, police etc., shall be obtained prior to commencement of work. Similarly, for erection work at railway crossings, the permission of the railway authorities shall be obtained before commencing the work. The crossing of railway tracks under power lines shall be as nearly as possible at right angles.
The Engineer in Charge shall ensure the required clearances to be maintained in moving equipment under or near the energized Lines.
Before commencing the stringing operations or removal of conductors, In presence of Supervisor and workman
- Plan of operation
- The type of equipment and tools and plant to be used
- Grounding devices and procedures to be followed, Crossover methods to be employed
- The clearance authorization required.
Wherever there is a possibility of the conductor being handled coming in contact with an energized conductor, or there is a possibility of a dangerous voltage buildup due to induction, the conductor being handled shall be grounded, unless a provision is made to insulate or isolate the employee. If the existing line is de-energized, a Line Clear Permit shall be .obtained and the line grounded on both sides of the cross over. In case the Line Clearance Permit cannot be obtained the Line shall be considered as energized for all practical purposes.
While executing the work of crossing over an existing Line, suitable guard structures with rope nets shall be installed to isolate the conductors and workmen coming within the required minimum clearances specified for the voltage and if there is any auto re-closure installed on the energized line, the same shall be made inoperative. In addition the line being handled shall be grounded on either side of the cross over.
The conductors being strung or removed shall be kept under control by using adequate reels, guard structures, tie Lines, or any other appropriate means to prevent accidental contact with energized wires.
The guard structure shall have sufficient strength and have adequate dimensions and supported adequately.
The wire ropes, come-along clamps, anchors, guys, hoists shall have ample capacity to prevent failure and accidents. The load rating specified by the manufacturers for stringing equipment, pulley blocks and all other load bearing hardware and tools shall not be exceeded during operations.
These shall be inspected regularly and replaced and repaired when damaged or when dependability is doubtful.
Came along clamps designed for the specific conductor range only shall be used. During stringing or removal of conductors, no workmen shall be permitted to come directly under overhead operations, or on the cross arms. The dead end points of the conductors at section towers shall be adequately anchored before commencing operations. The grounds provided to the conductor shall be maintained intact until the conductors are hooked on to the insulators.
The reel handling equipment, including pulling and braking machines shall have ample capacity, operate smoothly, and levelled and aligned in accordance with the manufacturer’s operating instructions. Reliable communication between the operator of these machinery and the stringing operators shall be provided.
Each conductor shall be dead-ended at both ends before commencing stringing of the conductor in the next section.
The sequence of stringing of conductors and ground wires shall strictly follow the design conditions of erection loads considered for the structure. The method of erection followed shall not impose loads in excess of design loads on the structure.
Before commencing the stringing or releasing operations of any conductor adjacent to an energized line, the following precautions required
Only skilled and trained laborers competent to work on Transmission Line construction shall be deployed for the work. The workmen should be in good health, able bodied and normally sound mental state.
The possibility of dangerous voltages due to induction, particularly during switching and fault conditions, shall be investigated and attended.
The tension stringing method or such other methods shall only be used, which prevent unintentional contact between the lines being pulled and the employee.
All the pulling and tensioning equipment shall be isolated, insulated, or effectively grounded.
A ground rod shall be installed between the tensioning reel setup, and the first structure in order to ground each bare conductor, sub-conductor, or overhead ground wire during stringing operations.
During stringing or unstringing operations, each conductor or ground wire shall be grounded at the first tower adjacent to both the tensioning and pulling setup and in increments so that no point is more than 10 stringing spans away.
The grounds shall be left in place till the conductor installation is completed.
These grounds shall be removed at the last phase of cleanup operations. The grounds shall be placed or removed only with a Hot Line equipment/ insulating rod.
Conductors and ground wires shall be grounded at all dead-end points. A ground shall be located at each side and within 10 feet of working areas where conductors or ground wire are being jointed at ground level. The two ends to be jointed shall be bonded to each other. The jointing shall be carried out on either an insulated platform or on a conductive metallic grounding mat bonded to grounds. When grounding mat is used, the same shall be barricaded and an insulated walkway provided for access to the mat.
All the conductors and ground wire shall be bonded to the end tower where the work is to be completed. At the dead end tower, the de-energized line shall be grounded.
The grounds can be removed on completion of the work making sure that the Line is not left open circuited at any tower at which the work is carried out.
Precautions require for Hot-Line bare hand work in addition to all other applicable precautions
Only qualified and trained employees, trained for Hot-Line bare-hand technique and the pertinent safety requirements thereto, shall be permitted for the work as well as for supervision.
Hot line LCP be availed by Hot line crew engineer before commencement of work.
The information of Hot line LCP be informed to SLDC.
The following checks shall be made before commencing Hot-Line bare-hand work on energized high-voltage conductors or equipment to ensure adequacy of tools and capability of personnel:
The voltage rating of the circuit on which the work is to be carried out, The clearances to ground of the lines and other energized parts on which work is to be carried out, The voltage limitations of the aerial-lift equipment intended to be used.
The Hot Line equipment to be used shall be of proper design and tested. If any automatic reclosing feature is available on the circuit breakers or switches, the same shall be made inoperative before commencing the work on any energized line or equipment.
The work shall not be carried out during thunderstorms and cloudy atmosphere.
The employee shall be connected to the bucket liner of Hot Line equipment in use through conducting shoes, leg clips or by any other suitable means. Adequate electrostatic shielding for the rated voltage of the line or equipment on which work is being carried out shall be provided to the workmen wherever necessary or conducting clothing shall be provided.
Only tools and plant intended for Hot-Line bare-hand work shall be used, and these shall be kept clean and dry.
The outriggers on the aerial truck shall be extended and adjusted to stabilize the body of the truck before the boom is elevated. The body of the truck shall be bonded to an effective ground, or barricaded and considered as energized equipment for all purposes.
All the controls at ground level and Bucket available in the truck shall be checked and tested to determine their proper working condition before moving.
Every day, and each time, before commencing the work “arm current tests” shall be carried out. Aerial buckets used for hot-Line bare-hand work shall also be subjected to these tests.
This test shall be carried out by placing the Bucket in contact with an energized source equal to the voltage to be worked upon for a minimum period of three (3) minutes and the leakage current shall not exceed one (1) microampere per kilo-volt of nominal Line-to-Line voltage.
The work shall be suspended immediately if any indication of a malfunction in the equipment is noticed.
All the aerial lifts shall have reliable controls and shall be accessible for safe and secure operation.
Ground level lift control shall not be operated without the permission of the employee in the lift, except in case of emergency.
The conducting Bucket Liner of Hot Line equipment in use shall be bonded to the energized conductor by means of a reliable connection before the employee contacts the energized part.
This shall remain attached to the energized conductor until the work is completed.
The adequate minimum clearance shall be maintained from all grounded objects and from lines and equipment at a different voltage than, to which the insulated aerial device is bonded, unless such grounded insulated guards Cover objects or other lines and equipment. These distances shall be maintained when approaching, leaving, and when bonded to the energized circuit. These distance shall be in line with the prevailing standard practice and consistent with the manufacturer’s specification/ guidelines.
The adequate minimum distances shall also be maintained between all parts of the insulated boom assembly and any grounded parts including the lower arm or portions of the truck, while approaching, leaving or bonding to an energized circuit.
The table, comprising the minimum clearance for hot line bare handwork, shall be printed on a plate of durable non-conducting material, mounted in the buckets or its vicinity in such a position that the same is clearly visible to the operator of the boom. Insulated measuring sticks only shall be used to verify the clearances. During positioning the bucket alongside an energized bushing or an insulator string, the appropriate minimum Line-to-ground clearances must be maintained.
No conducting material longer than 0.9 meter, other than the jumpers of appropriate length, armor rods, and tools shall be placed in the Bucket. The non-standard and unsafe working methods must not be allowed by the supervisor in charge of the Hot Line crew.
The bucket and the upper insulated boom shall not be over stressed by attempting to lift or support weights in excess of the manufacturer’s rating. The recommendations of the manufacturer of the Hot-Line equipment being used shall be strictly followed.
