Maintenance of transmission lines

This article covers information about the health diagnostic methods, as well as about preventive and predictive maintenance techniques in cold line and in hot line conditions
Maintenance of transmission linesThe transmission lines play a very important role in transmitting the huge quantum of electrical power generated at various generating stations to the whole area of the country from one end to other end over a distance of several hundreds of kilometers. By such transmission it is possible to distribute the power to the various types of customers through substations, at lowest possible line losses.
For uninterrupted power supply it is essential to maintain the transmission lines in trim and healthy condition.
For preventive and predictive maintenance of transmission lines following methods are applied.

Regular (monkey) thorough line patrolling with digital photography of the line components is carried out.
Thermo-graphic scanning for detecting Hot spots.
Punctured insulator detection by electric field measurement.
Punctured insulator detection by voltage measurement method.
Corona-Detection by Decor camera.
Resistance measurement of electric joint in live line condition (CRM).
Tower footing earth resistance measurement.
Various techniques for EHV line maintenance

Cold line maintenance
Deteriorated tower stub strengthening
Live Line Maintenance techniques  Live line maintenance by hot       stick method.  Bare hand technique for       system maintenance.  Hot line washing.
Ground patrolling is carried out by Inspection of the line, by walk down survey, and thorough patrolling by climbing on the tower through internal body of the tower and observing the line components keeping safe body clearance. While visual inspection thermo- scanning, digital photograph of the components and corona detection by Daycor camera is carried out.

Tower foundation
Tower earthing
Nut-bolts
Tower members
Anti climbing devices
Number plates, phase plate, danger boards
Clearances, as required by IE Rules
1956 for Ground / river /canal /dam/ structure/ Buildings / Road/ Tree/ Railway/ HT- LT lines/ telephone line crossing, etc. are checked
Broken disc insulator
Flashover disc insulator
Contaminated disc insulator
Split pins / cotter pins/ W pin/ hangers
Conductor and earth wire hardware (tension and suspension hardware, mid span joint)
Conductor condition
Jumper condition
Repair sleeve
Sag and ground clearance
Tack welding to the nuts and bolts of tower
Tower members missing
Armouring, suspension clamp, split pin
Conductor spacer
Vibration dampers for conductor and earth wire
Earth wire fittings flexible earth bond, jumper
Mid span joint and repair sleeve
Bird guard
Conductor and conductor fittings
Armour rod, suspension hardware
Insulator and insulator fittings, hanger, eye bolt, yoke plate, nut- bolts
Corona measurement
Thermo-vision scanning.
Modern health diagnostic methods for EHV linesThermo-vision scanning: By Thermo-vision scanning hot spots on the line live components can be detected.Electromagnetic spectrum having wave length bands of x-rays, ultra violate rays. Visible light, infra red rays and microwaves
Measurement of resistance of electric joint in live line condition (CRM): The sophisticated instrument (live line micro ohm meter) is designed to be attached directly to an energised EHV line through a hot stick and directly reads the resistance in micro ohms. Live line Micro ohm meter is designed to store up to 9 sets of readings.
It measures the voltage drop, the line current, and the calculated resistance is displayed. The ratio of the resistance of the joint (Rj) and the reference resistance of equal length of the conductor (Rc) indicates the condition of the joint. The value Rj / Rc should be < 1 for healthy joint. The ratio > 3 is serious, needs urgent replacement.
Punctured insulator detection using positron instrument by electric field measurement (PID): The positron instrument detects punctured insulator in the string by measuring the electric field across the insulator. The electric field across the punctured insulator is less as compared to healthy insulator.
Punctured insulator detection by voltage measurement method using Ritz’s instrument:
The Ritz’s instrument detects punctured insulator in the string by measuring the voltage across the insulator. The voltage across the punctured insulator is zero.
Coronagraphy by Daycor camera: When voltage on an electrical conductor exceeds threshold value, the air around it begins to ionise to form a blue or purple glow and produces hissing noise.Corona is the polarisation of air molecules due to energy on high voltage.

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