Operating duty of a Circuit Breaker

According to ANSI/IEEE C37.4-1999, clause 5.6: "Rated standard operating duty (standard duty cycle). The standard operating duty of a circuit breaker is:

O - t - CO - t' - CO

Where:
O = Open;
CO = Close - Open
t' = 3 minutes
t = 15 seconds for circuit breakers not rated for rapid reclosing, and
t = 0.3 seconds for circuit breakers rated for rapid reclosing".


Sidharthan.G
Electrical Miracles.





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India's Powerful Locomotive WAG-9

India's Powerful Locomotive WAG-9 having capacity of hauling 6000 tonne at 120 km/hr.It is referred to as the Heavy Haul freight locomotive of the Indian Railways.
It is very similar to WAP-7,the only difference being the gear ratio (WAP -7 :- 72:20 ,WAG-9 77:15) which makes it suitable for heavy freight operations.

Around 400 of these locomotives have been put to service as of early 2013.They have GTO thyristor converters and 3-phase asynchronous motors.

Newer versions of WAG-9 feature full IGBT traction control.

They have better adhesion because of the computerized slip control which in turn increase their hauling capacity and initial starting torque of about 520KN.

They have Traction motors rated at 6,350 hp (4,735 kW) each,Continuous power at wheel rims 4500kW (6000hp).

Two units can haul 4500t on gradients of 1:60 and a single unit can start a 4700t load (58 BOXN wagons Max. axle load of 20.32t) on a gradient of 1:180.

Total weight of WAG-9 is 123t.

Starting Tractive Effort(TE) 520kN.
Continuous Tractive Effort(TE) 325kN.

Rated top speed is 120km/h (75 miles/hr) for 6000 tonne load (Operational).

Technical Specifications Of WAG-9 :-
Manufacturers: ABB, CLW

Power Supply: 25kV AC Supply

Traction Motors: ABB's 6FRA 6068 (850kW, 2180V, 1283/2484 rpm, 270/310A. Weight 2100kg) Axle-hung, nose-suspended.

Gear Ratio: 77:15 / 64:18

Transformer: ABB's 4x1450kVA.

Power Drive: Power convertor from ABB, SG 3000G X H24 GTO thyristors ,14 thyristors per unit (two units). Line convertor rated at 2 x 1269V @ 50Hz, with DC link voltage of 2800V. Motor/drive convertor rated at 2180V phase to phase, 971A output current per phase, motor frequency from 0 to 132Hz.

Hauling capacity: 4250t

Tractive Effort: 460kN

Bogies: Co-Co, ABB bogies; bogie wheel base 1850mm + 1850mm

Wheel base: 15700mm
Axle load: 20.5t
Unsprung mass per axle: 3.984t

Body width: 3152mmn
Cab length: 2434mm

Pantographs: Two Secheron ES10 1Q3-2500.
Pantograph locked down height: 4525mm.

India's Fastest Locomotive WAP-7

India's Fastest Locomotive WAP-7

India's fastest locomotive WAP-7 speeding upto 140km/h,6125hp max. power; 6000hp continuous at wheel rim. At 123t, it is much heavier than the 78t WAP-5. Intended to haul heavier, 26-coach passenger trains and passenger/parcel mixed trains.
Initial models were rated at 6125hp total power and 33000 kgf (323kN) tractive effort. Modifications during continuing trials resulted in improved performance with the loco now yielding 6350hp total power and 36000 kgf (352.8kN) tractive effort. In the trial runs,the upgraded WAP-7 #30203 was shown able to take a 24-coach train to 110km/h in just 235 to 245 seconds (compare: 324 seconds for a WAP-5). Braking systems as in the WAP-5, with regenerative braking rated at 183kN in the first units and 260kN in the later ones.
Earlier trials with WAP-7 locos had yielded times around 390 seconds for the same test, which had cast doubts on the future of this loco class which was designed to perform better than the WAP-5. After some trials with the Prayagraj Exp. in early 2002, now the WAP-7 is being used to haul the 24-coach rake of ER's Poorva Exp. and will presumably soon be used for other trains as well. Max. tested speed is 160km/h, rated for 140km/h.

Better performing variants of the WAP-7 have been under development changes are said to include higher capacity components (including the main transformer) to allow stall-free running on 1:100 gradients, and a higher tractive effort of 42000 kgf (411kN). Some of the units starting around #30212 are also thought to have some enhancements in comparison to the very first ones. [11/04] Other plans by CLW for this loco class are said to include the provision of IGBT control, greater automation of some control tasks, and in-cab signalling. MU operation possible with a maximum of two locos.

The WAP-7 appears to have returned to the older (WAM, earlier WAP) style of pantograph with a single collector bar instead of the double collector bar used for the WAG-9.

Manufacturers: CLW
Traction Motors: 6FRA 6068 3-phase squirrel-cage induction motors (850kW, 2180V, 1283/2484 rpm, 270/310A. Weight 2100kg, forced-air ventilation, axle-hung, nose-suspended. Torque 6330/7140Nm. 95% efficiency.)
Gear Ratio: 72:20
Axle load: 20.5t
Wheel diameter: 1092mm new, 1016mm worn
Wheel base: 15700mm
Bogies: Co-Co, ABB bogies; bogie wheel base 1850mm + 1850mm
Unsprung mass per axle: 3.984t
Length over buffers: 20562mm
Length over headstocks: 19280mm
Body width: 3152mmn
Cab length: 2434mm
Pantograph locked down height: 4525mm
Tractive Effort: 36.0t

A 24-coach (1430t) passenger rake can be accelerated to 110km/h in 240 seconds (over 4.7km) by a WAP-7; to 120km/h in 304 sec. (6.7km); and to 130km/h in 394 sec. (9.9km).

IP Code, Ingress Protection Rating

The IP Code, Ingress Protection Rating^, sometimes also interpreted as International Protection Rating, classifies and rates the degree of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in mechanical casings and with electrical enclosures
The standard aims to provide users more detailed information than vague marketing terms such as waterproof.
For example, an electrical socket rated IP22 is protected against insertion of fingers and will not be damaged or become unsafe during a specified test in which it is exposed to vertically or nearly vertically dripping water. IP22 or 2X are typical minimum requirements for the design of electrical accessories for indoor use.

Solid particle protection

The first digit indicates the level of protection that the enclosure provides against access to hazardous parts (e.g., electrical conductors, moving parts) and the ingress of solid foreign objects.

Level	Object size protected against	Effective against
0	—	No protection against contact and ingress of objects
1	>50 mm	Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part
2	>12.5 mm	Fingers or similar objects
3	>2.5 mm	Tools, thick wires, etc.
4	>1 mm	Most wires, screws, etc.
5	Dust protected	Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact
6	Dust tight	No ingress of dust; complete protection against contact

Liquid ingress protection

The second digit indicates the level of protection that the enclosure provides against harmful ingress of water.

Level	Protected against	Testing for	Details
0	Not protected	—	—
1	Dripping water	Dripping water (vertically falling drops) shall have no harmful effect.	Test duration: 10 minutes Water equivalent to 1 mm rainfall per minute
2	Dripping water when tilted up to 15°	Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.	Test duration: 10 minutes Water equivalent to 3 mm rainfall per minute
3	Spraying water	Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.	Test duration: 5 minutes Water volume: 0.7 litres per minute Pressure: 80–100 kPa
4	Splashing water	Water splashing against the enclosure from any direction shall have no harmful effect.	Test duration: 5 minutes Water volume: 10 litres per minute Pressure: 80–100 kPa
5	Water jets	Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.	Test duration: at least 3 minutes Water volume: 12.5 litres per minute Pressure: 30 kPa at distance of 3 m
6	Powerful water jets	Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.	Test duration: at least 3 minutes Water volume: 100 litres per minute Pressure: 100 kPa at distance of 3 m
7	Immersion up to 1 m	Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).	Test duration: 30 minutes Immersion at depth of at least 1 m measured at bottom of device, and at least 15 cm measured at top of device
8	Immersion beyond 1 m	The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.	Test duration: continuous immersion in water Depth specified by manufacturer

Types of Valves

Gate Valve :

The gate valve is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restric­tion is desired. Because of their ability to cut through liquids, gate valves are often used in the petroleum industry.

Globe Valve:

                                             

A globe valve different from ball valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.

Check Valve:

Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and/or inexpensive.

Butterfly Valve:

A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve designs as well as being lighter in weight, meaning less support is required. The disc is positioned in the center of the pipe, passing through the disc is a rod connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, therefore a pressure drop is always induced in the flow, regardless of valve position.

Angle Valve:

An angle seat piston valve is a pneumatically-controlled valve with a piston actuator providing linear actuation to lift a seal off its seat. The seat is set at an angle to provide the maximum possible flow when unseated. Angle seat piston valves are particularly suited to applications where high temperatures and large flowrates are required, such as steam or water. When used in reverse some models of angle seat piston valve will eliminate water hammer when operated.

Control valve:

Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.

The opening or closing of control valves is usually done automatically by electrical, hydraulic or pneumatic actuators. Positioners are used to control the opening or closing of the actuator based on electric, or pneumatic signals. These control signals, traditionally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems.

Solenoid Valve:

A solenoid valve is an electromechanically operated valve. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports.

Motor Operated Valve:

Motor Operated Valve (MOV) is an important item of Plant & Piping system. These valves are generally of large size and are used for different applications such as Pump discharge etc. Motor Operated Valves are often called as On-Off valves as the motors serve the purpose of fully opening or fully closing valves in pipelines.

Piston Valve:

A 'piston valve' is a device used to control the motion of a fluid along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder.

Safety Valve:

A safety valve is a valve mechanism which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits.

It is one of a set of pressure safety valves (PSV) or pressure relief valves (PRV), which also includes relief valves, safety relief valves, pilot-operated relief valves, low pressure safety valves, and vacuum pressure safety valves.

Relays IEEE Number

List of device numbers and acronyms

• 1 – Master Element
• 2 – Time Delay Starting or Closing Relay
• 3 – Checking or Interlocking Relay
• 4 – Master Contactor
• 5 – Stopping Device
• 6 – Starting Circuit Breaker
• 7 – Rate of Change Relay
• 8 – Control Power Disconnecting Device
• 9 – Reversing Device
• 10 – Unit Sequence Switch
• 11 – Multi-function Device
• 12 – Overspeed Device
• 13 – Synchronous-speed Device
• 14 – Underspeed Device
• 15 – Speed – or Frequency, Matching Device
• 16 – Data Communications Device
• 17 – Shunting or Discharge Switch
• 18 – Accelerating or Decelerating Device
• 19 – Starting to Running Transition Contactor
• 20 – Electrically Operated Valve
• 21 – Distance Relay
• 22 – Equalizer Circuit Breaker
• 23 – Temperature Control Device
• 24 – Volts Per Hertz Relay
• 25 – Synchronizing or Synchronism-Check Device
• 26 – Apparatus Thermal Device
• 27 – Undervoltage Relay
• 28 – Flame detector
• 29 – Isolating Contactor or Switch
• 30 – Annunciator Relay
• 31 – Separate Excitation Device
• 32 – Directional Power Relay
• 33 – Position Switch
• 34 – Master Sequence Device
• 35 – Brush-Operating or Slip-Ring Short-Circuiting Device
• 36 – Polarity or Polarizing Voltage Devices
• 37 – Undercurrent or Underpower Relay
• 38 – Bearing Protective Device
• 39 – Mechanical Condition Monitor
• 40 – Field (over/under excitation) Relay
• 41 – Field Circuit Breaker
• 42 – Running Circuit Breaker
• 43 – Manual Transfer or Selector Device
• 44 – Unit Sequence Starting Relay
• 45 – Abnormal Atmospheric Condition Monitor
• 46 – Reverse-phase or Phase-Balance Current Relay
• 47 – Phase-Sequence or Phase-Balance Voltage Relay
• 48 – Incomplete Sequence Relay
• 49 – Machine or Transformer, Thermal Relay
• 50 – Instantaneous Overcurrent Relay
• 51 – AC Inverse Time Overcurrent Relay
• 52 – AC Circuit Breaker
• 53 – Exciter or DC Generator Relay
• 54 – Turning Gear Engaging Device
• 55 – Power Factor Relay
• 56 – Field Application Relay
• 57 – Short-Circuiting or Grounding Device
• 58 – Rectification Failure Relay
• 59 – Overvoltage Relay
• 60 – Voltage or Current Balance Relay
• 61 – Density Switch or Sensor
• 62 – Time-Delay Stopping or Opening Relay
• 63 – Pressure Switch
• 64 – Ground Detector Relay
• 65 – Governor
• 66 – Notching or Jogging Device
• 67 – AC Directional Overcurrent Relay
• 68 – Blocking or "Out-of-Step" Relay
• 69 – Permissive Control Device
• 70 – Rheostat
• 71 – Liquid Level Switch
• 72 – DC Circuit Breaker
• 73 – Load-Resistor Contactor
• 74 – Alarm Relay
• 75 – Position Changing Mechanism
• 76 – DC Overcurrent Relay
• 77 – Telemetering Device
• 78 – Phase-Angle Measuring Relay
• 79 – AC Reclosing Relay
• 80 – Flow Switch
• 81 – Frequency Relay
• 82 – DC Reclosing Relay
• 83 – Automatic Selective Control or Transfer Relay
• 84 – Operating Mechanism
• 85 – Communications,Carrier or Pilot-Wire Relay
• 86 – Lockout Relay
• 87 – Differential Protective Relay
• 88 – Auxiliary Motor or Motor Generator
• 89 – Line Switch
• 90 – Regulating Device
• 91 – Voltage Directional Relay
• 92 – Voltage and Power Directional Relay
• 93 – Field Changing Contactor
• 94 – Tripping or Trip-Free Relay
• 95 – For specific applications where other numbers are not suitable
• 96 – For specific applications where other numbers are not suitable
• 97 – For specific applications where other numbers are not suitable
• 98 – For specific applications where other numbers are not suitable
• 99 – For specific applications where other numbers are not suitable
• AFD – Arc Flash Detector
• CLK – Clock or Timing Source
• DDR – Dynamic Disturbance Recorder
• DFR – Digital Fault Recorder
• ENV – Environmental Data
• HIZ – High Impedance Fault Detector
• HMI – Human Machine Interface
• HST – Historian
• LGC – Scheme Logic
• MET – Substation Metering
• PDC – Phasor Data Concentrator
• PMU – Phasor Measurement Unit
• PQM – Power Quality Monitor
• RIO – Remote Input/Output Device
• RTU – Remote Terminal Unit/Data Concentrator
• SER – Sequence of Events Recorder
• TCM – Trip Circuit Monitor
• SOTF – Switch On To Fault

Brushless DC Motor

What is a Brushless DC Motor?

A Brushless DC Motor (also known as a BLDC Motor), is a synchronous electric motor powered by a direct current. As the name implies, the Brushless DC Motor does not operate using brushes; rather it operates with a controller via electronic commutation.

Block Diagram for a Brushless DC Motor

How does a Brushless DC Motor Work?

A Brushless DC Motor is operated by means of an electronic six-step commutation system. Unlike its Brush DC Motor counterparts, the Brushless DC Motor does not contain any carbon brushes. Instead, the electromagnets within the motor remain stationary along with the armature, while the encased permanent magnets rotate, generating torque. The Brushless DC Motor is synchronous; both the stator and the magnetic field generate the same frequency, therefore avoiding any type of “slip” most induction motors exhibit.

What is Six-Step Commutation?

Six-step commutation is a cost-effective means of electronic commutation, due to the simple and relatively inexpensive feedback and drive devices. In six-step commutation, only two out of the three Brushless DC Motor windings are used at a time. Steps are equivalent to 60 electrical degrees, so six steps makes a full, 360 degree rotation. One full 360 degree loop is able to control the current, due to the fact that there is only one current path. Six-step commutation is typically useful in applications requiring high speed and commutation frequencies. A six-step Brushless DC Motor usually has lower torque efficiency than a sine-wave commutated motor.

How is a Brushless DC Motor Controlled?

An electronic Brushless DC Controller (also known as a Driver, or Electronic Speed Controller), replaces the mechanical commutation system utilized by a Brush DC Motor, and is required by most Brushless DC Motors to operate. In a Brushless DC Motor controller, either a Hall Effect Sensor or Back EMF (Electromotive Force) is used to identify the position of the rotor. Understanding the orientation of the rotor is crucial to operating the Brushless DC Motor.

The Hall Effect uses three hall sensors within the Brushless DC Motor to help detect the position of the rotor. This method is primarily used in speed detection, positioning, current sensing, and proximity switching. The magnetic field changes in response to the transducer that varies its output voltage. Feedback is created by directly returning a voltage, because the sensor operates as an analogue transducer. The distance between the Hall plate and a known magnetic field can be determined with a group of sensors, and the relative position of the magnet can be deduced. A Hall sensor can act as an on/off switch in a digital mode when combined with circuitry.

Back EMF, also known as the Counter-Electromotive Force, is caused by a changing electromagnetic field. In a Brushless DC Motor, back EMF is a voltage that occurs where there is motion between the external magnetic field and the armature of the motor. In other words, the voltage is developed in an inductor by an alternating or pulsating current. The polarity of the voltage is constantly the reverse of the input voltage. This method is commonly used to measure the position and speed of the Brushless DC Motor indirectly, and due to the lack of Hall Sensors within the controller, these are often referred to as sensorless controllers.

Optical Encoders can also be added to the Brushless DC Motor, allowing both direction and speed to be determined. More precise applications may use Optical Encoders with a third index signal, to determine pulse per revolution.

Physical Properties of a Brushless DC Motor

The Brushless DC Motor consists of a rotating rotor, Neodymium Iron Boron magnets, and a stator. Brushless DC Motors are considered to be an “inside-out” version of a Brush DC Motor; the commutator and brushes are nonexistent, and the windings are located externally, connected to the controller. There are typically two different construction types for the Brushless DC Motor: inrunner and outrunner configurations. The inrunner configuration consists of three stator windings located around the rotor, with permanent magnets as a part of the rotor. The outrunner has a reversed relationship between the magnets and the coils. The permanent magnets rotate inside a suspended rotor surrounding the core of the Brushless DC Motor.

Internally, a 3-phase motor can be configured to a “Wye” or “Delta” configuration. The primary advantage to the “Wye” configuration, also known as the Star configuration, is that the phase-to-neutral voltage is equal in all three legs. The arrangement is a parallel circuit in a shape of the letter Y, where all windings are connected at a central point, and power is applied to the remaining windings.

The Delta configuration creates a triangle-like figure, making it a series circuit. This configuration applies power to each of the connections.

How to Select a Brushless DC Motor

Selecting the appropriate Brushless DC Motor requires knowing the requirements of the application, such as torque, speed, size, power, length, etc. While determining which Brushless DC Motor best fits the requirements, the controller must be considered as well, as this goes hand in hand with the operation of the Brushless DC Motor.

Lastly, environment is important to consider. Applications requiring a harsh, damp environment may require motors with specific IP ratings. For more detailed information on this subject, see Brushless DC Motor Environmental Considerations.

Brushless DC Motor Applications

The cost of the Brushless DC Motor has declined since its introduction, due to advancements in materials and design. This decrease in price, coupled with the many advantages it has over the Brush DC Motor, makes the Brushless DC Motor a popular component in many different applications. Applications that utilize the Brushless DC Motor include, but are not limited to:

• Instrumentation

• Medical

• Appliances

• Automotive

• Factory Automation Equipment

• Aerospace

• Military

Advantages of a Brushless DC Motor

The absence of brushes in a Brushless DC Motor is perhaps its greatest advantage. The carbon brushes within a Brush DC Motor wear out rapidly and need replacing, which can be costly in the long run. The Brushless DC Motor generates less noise, and is less prone to sparking due to the lack of a commutator. The Brushless DC Motor is typically smaller and lighter than the Brush DC Motor, making it ideal for applications where weight and space are important factors. The Brushless DC motor is cleaner, more powerful, and requires lower maintenance than does the Brush DC Motor. It has higher speed ranges, higher dynamic responses, and ultimately outlasts the Brush DC Motor in total operating hours.

Disadvantages of a Brushless DC Motor

There are numerous applications using a Brush DC Motor that could instead utilize the Brushless DC Motor. However a few factors might prevent the changeover. The first factor is start-up cost. Although the Brushless DC Motor is lower-maintenance than the Brush DC Motor, initial cost is more expensive, due to its advantageous construction. Second is complexity. A controller is required in order to operate a Brushless DC Motor, and is usually more convoluted than most controllers. A Brushless DC Motor also requires additional system wiring, in order to power the electronic commutation circuitry.

Lifetime of a Brushless DC Motor

The Brushless DC Motor is often considered superior over the Brush DC Motor for its substantially longer lifespan. If run within the given specifications, the Brushless DC Motor can last over 20,000 operating hours based on bearing life. Running a Brushless DC Motor outside of its specifications shortens this lifespan.

Required Maintenance of a Brushless DC Motor

Due to the lack of brushes or a commutator, there is nothing to replace within a Brushless DC Motor, making it extremely low maintenance. The only requirement is that the motor be run within proper specifications, and in a clean environment to ensure it does not overheat or result in system failure.

Brushless DC Motor Environmental Considerations

Precaution must be taken by the user with respect to the environment of the Brushless DC Motor system during operation, repair, and service. The environment in which a Brushless DC Motor is used, must be conducive to good general practices of electrical equipment. Do not run a Brushless DC Motor system near flammable gases, dust, oil, vapor or moisture. The Brushless DC Motor must be protected by a cover if operated outdoors, ensuring the motor receives adequate air flow and cooling. Any presence of moisture may result in system failure and/or electric shock. Therefore adequate care should be taken to avoid any interaction between the Brushless DC Motor and any kind of moisture or vapors. A Brushless DC Motor should be installed in an environment free from vibration, shock, condensation, dust and electrical noise.

Formulas

What is the Kt Constant in a Brushless DC Motor?

Winding Power = Kt*Kt/R

Kv = 1000 rpm / Vrms

Kt = oz-in / Amp

Kt = Kb * 1.35

Ke = Vrms / 1000 rpm

Kb = V / 1000 rpm

Back EMF = V/KRPM

Transmission Lines Basics

Transmission Lines Basics

• Transmission towers also called pylons for supporting the conductors and other accessories
• Insulators
• Damping devices
• Earthing system

 

Transmission Tower and conductor


The transmission tower or pylon is one of the most important accessories of a transmission line. As the whole load of the line and accessories are taken by the towers so its design is crucial. For construction of a transmission line the type and numbers of  transmission towers required depends on many factors. Transmission tower is designed to carry the whole load of phase and grounding conductors in normal and abnormal conditions. The design requirements in icy, non-icy, coastal areas, cyclone prone areas and heavily air polluted areas are different. Due to the deposition of ice on conductor the weight of line is increased considerably resulting in heavy load on the tower. In the cyclone prone areas the conductors and towers experience severe wind loading. In such situations if these factors are not properly taken care of, then the conductor may snap and the tower may collapse. In the design process all these factors are taken care of.

Climatic condition plays an important role in tower and line design. For the purpose, climatic load data is collected. The tower foundation type depends on the soil. Also seismic data of the concerned region is collected for tower design. The tower types generally used are Lattice structure, Guyed V, Tubular pole type etc. We have already discussed about the conductor types used in transmission lines. 

Insulators


Insulators for use in transmission lines can be categorized different ways. The main function of insulator is undoubtedly to insulate the live conductor from the metallic tower at ground potential but the important thing is that the insulator should be able to carry the load/tension in the transmission line. At angle towers or at dead end the insulators should be able to carry large tensional force. The insulators used for transmission lines are mainly of porcelain or composite polymer types. Traditionally porcelain insulators are used for both transmission and distribution purposes.
In the coastal areas the climatic condition also influences the selection of materials . In the coastal areas salt deposits on the insulator surface, that results in increased leakage current on the insulator surface.  Similar situation arises where lots of suspended chemical particles are present in the atmosphere. While designing the transmission tower and selecting the conductor all these factors are taken into account.
We will devote one article about insulators.


Damping devices


Due to wind and ice, the transmission lines swing under different modes. The transmission lines may vibrate in three major ways.

• Galloping : Due to the deposit of ice above conductor surface, the conductor cross section resembles an aerofoil. The wind flowing across the conductor (aerofoil) results in Galloping of conductor. Galloping is the oscillation of the conductor at high amplitude and low frequency. The conductor may oscillate in vertical or horizontal plane. Generally the conductor oscillates in vertical plane. The amplitude of the oscillation may be more than a meter with frequency upto 3 Hz. Due to galloping the clearance between the conductors may reduce very much to initiate flashover. Structural damage may also happen due to conductor gallopping. Anti-gallopping devices may be fitted to reduce the affect of gallopping.
• Aeolian vibration : When wind flows across the line steadily then vortices are formed in the back side of conductor which is the cause of aeolian vibration. Here the amplitude is in milimeter or centimeter and frequency may be upto 150 Hz. Over a long time the aeolian vibration may cause damage to the strands of wire. Stockbridge Dampers in the shape of dumbbell with midpoint clamped to the line are used for damping the Aeolian vibration. As shown in the figure they are fitted at a position most effective in damping the vibration. In any conductor the dampers are used at both the ends of the span. Dampers are used both in the phase and ground conductors
• Wake induced vibration: Wake induced vibration takes place in bundled conductors. The aerodynamic forces in the downstraem of conductor gives rise to this form of oscillation. It has amplitude in centimeters.  The oscillation is reduced by keeping the spacing of bundled conductors large enough.

Earthing System
Every electrical system is equipped with a earthing system.  The ground wires (also called shield wire) run above the phase conductors and protect the line from direct lightning strokes as the lightning strikes first the ground conductor due to its position. The foot of the transmission towers are properly earthed so that the potential gradient near the tower remains within the limit and protects the human beings and animals around the tower in faulted condition. 

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