1.0 INTRODUCTION
In the modern age, the electricity has become a major essential commodity after air, food clothing and water. In the daily life any development of the country depends on the availability of the energy resources in abundance. Even though the other mineral and natural resources are available Electrical Power is contributing major role for the development of the country.
It is our bound duty to maintain the Electricity uninterruptedly to achieve not only revenue earnings for the organization but also for the major industrial growth and thus development of the country in four fold. For maintaining the uninterrupted power supply one of the preventive maintenance techniques used in our organization is Hotline Techniques. The details are discussed below.
1.2 WHAT IS HOTLINE
Hot lines mean energized electrical power lines. Any equipment or machinery suffers from minor ailments which leads to major breakdowns. To prevent this timely action is always required as the proverb says “Stitch in times saves nine”. Adoption of the Live Line maintenance techniques for the power lines will suit to this proverb.
1.3 MAINTENANCE METHODS
Following are the methods adopted by all the Electrical Utilities (Companies) either in generation, transmission or distribution.
i) Pre-arranged shut down methods after identifying the faults
ii) Sudden faults developed as break downs and rectification is a breakdown maintenance.
iii) Preventive Hotline maintenance
The paper is to study in detail and explain the august gathering the details of preventive maintenance of Electrical power lines by Hotline Maintenance Techniques.
2.0 HOTLINES
Hotlines techniques mainly deals with the maintenance of energized line without any interruption to the power from Low Voltage Line to Ultra High Voltage Line
2.1 Broadly there are two types of techniques at present in use.
i) Hot Stick Technique ii) Bare Hand Technique
Hot Stick technique can be used from 11 KV to 220 KV lines where as Bare Hand Method is a must for Ultra High Tension lines i.e., from 400 KV and above. This organization is proud to present that the Bare Hand Techniques are being used for the preventive maintenance of 132 KV and 220 KV EHT lines and sub-stations also which is an unique feature in our country.
2.2 HOT STICK METHOD
In the year 1935 the lengthy bamboo dry sticks were used to remove cartridge fuses and for disconnection of isolators. In later days, after research, two types of woods were discovered to serve the above purpose. They are (i) OAKWOOD (ii) SITCA SPRUCE AND HIMALAYAN SPRUCE.
2.3 OAK WOOD
Oak wood having a property of high mechanical strength and high dielectric strength was used till 70s. Since the weight of the sticks made by this wood has become a constraint, these sticks were used for tension relieving purpose only, where high mechanical strengths were required.
2.4 SITCA & HIMALAYAN SPRUCE
The laminated light wood like SITCA Spruce and Himalayan Spruce were found and with them the laminated pieces are gloved and tools were made for the requirement.
Eg. Tie sticks, Wire Tongs, Flexible Wrenches etc.
i) Tie stick will be used for tying or untying the insulator bindings where the pin binding were taken up and also in use for various applications.
ii) Wire tong holds the conductor or jumper and move them for a safe clearance of the crew who manipulates the works
iii) Flexible wrench – by fixing the suitable sockets of the required size, the bolt and nuts, of pad clamps, T clamps etc. can be tightened or loosened.
2.5 Likewise many more tools manufactured by this wood were in use upto 80s. But the above wood tools have got inherent property of absorbing moisture, even though they have outerly coated with Araldite and Teflon etc., looses their insulation values which requires heating chambers, air tight chambers and continuous insulation monitoring before use everyday at the work spot, which is a costly affair.
2.6 Even then, if the operation time is delayed, the wood sticks will absorb the moisture content present in the atmosphere and failures will occur and is dangerous to the crew members and may cause breakdown to the power line. Thereby the very purpose of preventive maintenance of the energized line by risking the crew will be lost.
2.7 To overcome the above constraints a further research was made on this and a new material i.e., Glass Fibre was introduced with trade name Epoxy Glass which is having very high dielectric strength, high mechanical strength and less weight than the wood sticks.
The glass Fibers have been soaked with Epoxy resin and wound to manufacture a hollow stick. The hollowed portion is filled with a Unicellular foam to prevent external moisture to enter inside the stick and thus insulation value of the Epoxy Glass Stick will be maintained.
2.8 With this advantage and inherent capacity of not absorbing moisture from the external atmosphere, though sudden rain comes the crew can leave the tools in engaged condition of the work and after rain lashes, they can complete the work.
Because of the presence of unicellular foam material the rain drop swill not creep inside the hollow portion of the stick thereby insulation value will not be affected.
Due to aberrations even though the water enters inside the hollow portion of the Epoxy Glass Stick, the water will not creep inside the stick due to stuffed unicellular foam material inside the stick. If the stick get watered in the rain, just wiping of the stick with moisture eater solution and little drying in the sun is quite enough to make the stick fit for the work.
Like wise, Epoxy Glass Sticks will all the above added advantages are better in use than the wooden sticks in the live line maintenance of the Hot lines.
For these Hot Sticks different suitable metal heads are fitted for carrying out number of operations like changing of broken insulators, flashed over insulators and all the connected parts of tension and suspension points of the live lines without interruption to the power or without availing any shut down. And also tightening or loosening of cut point jumper bolt and nuts, replacing vibration dampers, replacing suspension shoe clamps etc., of the EHT lines and Lifting up of the conductors, changing of cross arms upto 11 KV and 33 KV can be carried out by this Hot Stick method.
3.0 BARE HAND TECHNIQUE
Bare Hand Technique means to charge a person to the required voltage level on an insulated platform either by traversing the person by insulated ladder or by raising through an insulated boom, and carrying out the work on charged line with Hands.
The chargeable person will wear a conductive suit comprising of cotton, asbestos and stainless steel threads, along with conductive shoes of copper threaded carbon sole with conductive socks and conductive hand gloves. Total continuity will be maintained from ‘Head to Toe’ covering the head with hood except the face.
3.1 The Bare Hand Technique is not a single man operation, it requires both Hot Stick Method as explained previously and a bare hand person.
By the effective utilization of this method the APTRANSCO erstwhile APSEB was commissioned additional transformers in 220 kv and 132 kv Sub-stations and further equipment like capacitor bank etc. without interruption to any equipment or without Bus shut downs.
3.2 By this Bare Hand Technique damaged Bus jumpers, T Clamps, Isolator Pad Clamps, Female Contacts are being replaced without the interruption to the bus bars, and conductor damages also being attended when sufficient clearances are there for operation.
3.3 By adopting this Bare Hand Technique lot of problems like taking Bus shut downs, line clear etc. can be avoided and thereby lot of time and revenue and also interruption are being avoided. APTRANSCO and APGENCO are extensively using this technique to avoid interruption, there by the better consumer satisfaction and plant load factors are achieved.
4.0 THERMOGRAPHY
Thermography means projecting the Infra-red rays on an object and receiving the reflected image on the screen. Depends upon the temperature the colour intensity of the image will change. Depending upon the intensity of the colour, the fault is identified and predictivity is by human eye and experience only. Rectification will be carried out by depending upon gravity of the situation
4.1 With the latest version of Inframatics 760 system with Thermotroniks software, the condition of the line jumpers, insulators, metal parts, connectors of transformers and current transformers, where the change of temperature is there, can be identified well in advance and behaviour of the metal part can be analysed in the computer. The temperature rise of any connector since being identified well in advance by the Thermovision Camera the same is being rectified well in advance even before deformity or red hot occurs for the clamp or connector. With this latest version of thermal imaging system the APTRANSCO is able to identify the internal faults of any electrical system in the Generating Stations and EHT substations and by the analysis of computer the rectification action is also being initiated.
4.2 The following are the major identified by the Thermal Imaging System :
a) TURFOUNION 100 MVA transformer winding connectors at bushing end at Shapurnagar and Nellore EHT substations.
b) VTPS Generator Transformers 3,4 & 5 of BHEL make winding terminals at bushing are identified and due to emergency immediate action initiated and saved huge damage to the Transformer and connected equipment.
c) Sub-station equipment at almost all the EHT substations in the State and also major feeders connectors are scanned.
e.g Ghanapur-Chandrayanagutta 220 kv Line Chandrayanagutta-Shapurnagar 220 kv Line VTS- Narketpally-Hyderabad 220 kv Line VTS- Tadikonda-Ongole 220 kv Line
VTS-Nellore 220 kv Line
4.3 Rectification action already initiated and strengthened the weak points 5.0 OTHER HOTLINE WORKS
Apart from the above Hotline and Bare Hand Work, the Hotline sub-divisions are also taking up the special Hotline works, like removing and cleaning of the saline contamination of the insulators, cement dust deposits on the insulators and chemical deposits on the insulators by three types of methods.
a) Dry washing b) Hot Spraying c) Wet washing
5.1 DRY WASHING
The Dry Washing and Spraying will be undertaken with huge hot air along with corn husk or paddy husk on peanut husk with lime stone granules. The hot spray of air through nozzles will clean the cement contamination.
5.2 HOT SPRAYING
To avoid the cement dust pollution and other chemical pollution the spraying of chemical on the insulators will be taken up. When once the cleaning of the insulators by dry washing is completed a thin film of silicon compound will be deposited on the insulators by Hot Spray.
5.3 WET WASHING
Previously the wet washing of the live insulators is used to be carried out by a small cylinder with carbon dioxide along with water to a limited extent.
5.4 At present with latest equipment and trigger controls etc. the ordinary water having the conductivity of less than 2 mhos is being sprayed directly on the live insulator to clear the salt contamination, dust and chemical contamination which is soluble in water.
The above works are being taken up at all the coastal areas, by one Sub-division trained for this special nature of work to carry out the operation with special equipment. Due to cost constraint only one equipment is purchased and being used wherever necessary in the State.
5.5 The special nature work of thermal imaging equipment is with Hyderabad and used in entire state.
Vijayawada Hot Lines sub-division is having the special nature equipment of Hot Spray and Dry Washing Kit and being used.
Visakhapatnam Hot Line Sub-division is having the Wet Washing Kit and being used.
Visakhapatnam Hot Line crew has taken up several lines to clear the salt deposits on the insulators with the help of wet washing and maintained the supply of power and contributing much to the entire State.
On Macheeryala, Tadepally, Yerraguntla and Vadapally EHT Lines Cement deposits on Insulators have been cleared to much extent by Vijayawada Hot Line Sub-division.
Hyderabad Hot line Sub-division attended many works by Bare Hand Technique as noticed by Thermovision camera in changing female contacts, jumper clamps and jumpers, and provided many repair sleeves on the live conductors.
Many additional transformers of 50 MVA and 100 MVA were commissioned in the sub station system by connecting the HV side and LV side jumpers to the existing 220 KV /132 KV Buses without availing any bus shut downs and interruption to the equipment.
6.0 AUTHORISATION AND APPLICATION :
In this Hotlines field the crew is authorized to carryout insulatiors changing, jumpers both tightening etc., and all the connected works of Hotlines by way of
training at Hotline Training Centre and a Certification from the Competent Authority.
The personnel who were trained in Hotlines shall only carryout the work under the trained Supervisor.
6.1 CONSTRAINT:
The IE Act 1948 and IE rules 1956 insisted the working personnel to obtain license to work on live line, but the present Hotline Training Centre at Bangalore is imparting training on Hot Stick Methods only, But not in Bare Hand Techniques.
6.2 In this juncture it is worth mentioning that the APTRANSCO (erstwhile APSEB) is the only organization carrying out the works of Bare Hand Technique in the entire Country. In the absence of training facility in Bare Hand Technique all the Hot line trained people are trained in Bare Hand Techniques also by Sri K.S.N.Murthy, Divl.Engineer,APTRANSCO but certification is a major constraint.
6.3 By these two techniques, Hotlines and Bare Hand APTRANSCO is able to save the Revenue to the tune of 2.20 crores every month. By the adoption of these Techniques the transmission system can be maintained upto the standards.
7.0 SET BACKS:
a. At present the equipment like CTs, Wave Traps, Power transformers could not be attended without interruption to the equipment due to potential differences.
b. Hotlines experienced personnel even though they can perform Bare Hand Works due to rules prevailing certificates could not be issued.
c. Due to much risk involvement and extensive touring the new blood is not flowing into the Hotlines and this matter requires special attention.
d. Since the tools are of imported once, paucity of founds is of major setback to equip the working personnel with T&P required while opening new working groups or wings. The tools and vehicle costs Rs.30 lakhs for each working group and revenue is 2.2 crores.
7.1 If the above bottle necks are over come the transmission system can best utilize the Hotlines and bare hand techniques even upto 11 KV in the low level and 400 KV and above in the higher level and can maintain uninterrupted supply to the most extend and there by the reputation of the organization will go high.