WAZIPOINT Engineering Science & Technology

Tuesday, August 13, 2024

MYSTERIOUS CORONA EFFECTS IN TRANSMISSION LINES

 Fig-Corona Effect in Transmission Line Visible at Night

What Is Corona Effects in Electrical Energy Transmission Line?

If you look along the high voltage power transmission line in a clear sky night, you will observe a dreamiest violet glow phenomenon embedded hissing noise along the transmission line conductors. This indefinable phenomenon causes nothing but a production of ozone gas surrounding on overhead electrical energy transmission lines is known as Corona or corona effect.

Usually you will find noticeable corona effects in EHV or Extra High Voltage transmission lines, like- 230kV, 400kV or higher grading. You may discover corona effects on normal voltages line if line overloaded or carry overestimated loads.

Theory and History of  Mysterious Corona

The mysterious corona factor equation was first derived by F.W. Peek and published in 1911. In a later a little modified from original the corona effect equation is published where he showed that the total amount of power loss in a wire due to the corona effect was equal to the equation as below:

where the parameter and the sample values are as below table:

ParameterSample Value
k0Fixed constant241
kdNormalized Air Density Factor
1 (25 °C, 76 cm pressure)
1
aRadius of Conductor3.5 cm (see Fig. 2)
dConductor Spacing1000 cm
fFrequency60 Hz
kiWire Irregularity Factor0.95 (weathered wires)
V0Line Voltage to Neutral
(1/1.73 x Voltage Between Conductors)
442 kV
(765 kV/1.73)
Disruptive Critical Voltage
(g0 ki a kd ln(d/a))
397 kv
Corona Loss kW/km/line25kW/km
Corona Loss %
(1000km line at 2.25 GW)
3.3%

The advantages of corona effects are- I) because of corona formation surrounding the conductor, virtually the conductor diameter becomes larger. As the diameter increases the electrostatic stress between the conductor decreases; ii) it reduces the surge voltage that created because of switching and thundering.

The disadvantages of corona effects on transmission lines are-

1. It reduces the transmission line’s efficiency;
2. Ozone created by this effect because corrosion of the conductors, health risk for human and animals;
3.  Due to corona effect non-sinusoidal voltage drop occurs across the line which causes inductive interference with neighboring communication lines, etc..

Features of Corona

• Conductor Size: The surface of the conductors decreases the breakdown voltage. Therefore, solid conductors are widely used for transmission lines;
• Line voltage: if the line voltage exceeding its limit or line become overloaded, a breakdown will occurs which creates Corona;
• Conductor’s spacing: To reduce corona more spacing is required between conductors;
• Atmospheric limitations: In Rainy, Foggy or Stormy weather Corona occurs at much less voltage at fair weather.

Factors Affecting Corona

The phenomenon of corona is affected by the physical state of the atmosphere as well as by the conditions of the line. The following are the factors upon which  coronadepends :

(i) Atmosphere: As corona is formed due to ionsiation of air surrounding the conductors, there fore, it is affected by the physical state of atmosphere. In the stormy weather, the number of ions is more than normal and as such corona occurs at much less voltage as compared with fair weather.

(ii) Conductor size: The corona effect depends upon the shape and conditions of the conductors. The rough and irregular surface will give rise to more corona because unevenness of the surface decreases the value of breakdown voltage. Thus a stranded conductor has ir regular surface and hence gives rise to more corona that a solid conductor.

(iii) Spacing between conductors: If the spacing between the conductors is made very large as compared to their diameters, there may not be any corona effect. It is because larger dis tance between conductors reduces the electro-static stresses at the conductor surface, thus avoiding corona formation.

(iv) Line voltage: The line voltage greatly affects corona. If it is low, there is no change in the condition of air surrounding the conductors and hence no corona is formed. However, if the line voltage has such a value that electrostatic stresses developed at the conductor surface make the air around the conductor conducting, then corona is formed.

Difference between Corona Effect and Skin Effect in Electrical Energy Transmission Lines

Corona is an electrical discharge causes by a liquefied ionization surrounding a conductor that is electrically charged. Corona is an electrical discharge caused by electrical over stress on the conductor. Corona which produce spark is one of the power loss during transmission due to ionization of air surrounding the conductors.

Skin effect is the tendency of an AC or Alternating Current to become more distributed over the conductor skin than inside the conductor. As a result the current density is largest near the surface of the conductor and decreases with greater depths in the conductor. Because of this case resistance of the alternating current carrying conductor increases which increases the power loss.

Typical Bus-Bar Arrangement System for High Voltage and Extra High voltage up to 400kV Capacity Substations.

Bus-Bar actually works as a matchmaker between higher voltage level transformers and lower voltage level transformers connecting others equipment to functional a co-relation between them.

The commonly used bus bar schemes for high voltage and extra high voltage at 132kV, 230kV, or 400kV Sub Stations are as below:
1. Single bus bar;
2. Main and Transfer bus bar;
3. Double bus bar;
4. Double main and transfer bus bar;
5. One and a half-breaker scheme.

You may be interested to read:

The schematic line diagram for the bus-Bar arrangement for each type of scheme is described below:

Single Bus-Bar Arrangement:

The single bus-bar arrangement is the simplest and easiest switching scheme in which each circuit is provided with one circuit breaker.

This arrangement can ensure limited security against bus bar faults and no switching flexibility, as a result, go into quite extensive outages of bus-bar and frequent maintenance of bus bar isolators.

In the single bus-bar scheme, in any bus-bar, isolator, or other equipment that needs maintenance or goes outage due to fault, the entire substation is lost or go in shutdown.

Another disadvantage of this switching scheme is that in case of maintenance of the circuit breaker, the associated feeder has also to be shut down.

Main and Auxiliary Bus-Bar Arrangement:

To overcome the disadvantages of a single bus-bar arrangement, additionally, a bus-coupler circuit is arranged as an Auxiliary bus that can be used during the main bus maintenance period without de-energizing the circuit controlled by that breaker as that circuit then gets energized through bus coupler breaker.

Main and Auxiliary Bus-Bar is technically a single bus bar arrangement with an additional bus bar called Auxiliary Bus energized from the main bus bars through a bus coupler circuit.

This bus-bar scheme also suffers like a single bus-bar system in the event of a fault on the main bus bar or the associated isolator, the entire substation is lost.

This type of arrangement is widely used for 132kV substations.

Double Bus-Bar Arrangement:

A Double Bus-Bar arrangement scheme is used to overcome the disadvantages of the single or main and auxiliary bus-bar schemes. The schematic diagram is shown below where each circuit can be connected to either one of these bus bars through the respective bus bar isolator.

The advantage of the double bus-bar arrangement is such away that the circuits can be switched on from one bus to the other on load.

This scheme suffers from the disadvantage that when any circuit breaker is taken out for maintenance, the associated feeder has to be shut down.

This bus-bar arrangement is widely used in 220kV or 230 kV substations.

Double Main and Auxiliary Bus-Bar Arrangement:

Using the double main and auxiliary bus-bar scheme, it is possible to overcome the limitation of the double bus-bar scheme.

In Double Main and Auxiliary Bus-Bar Arrangement, the feeder is transferred to the Auxiliary bus during maintenance of its controlling circuit breaker without affecting the other circuits.

This Bus bar arrangement is generally used nowadays in 220 or 230kV substations.

One-and-a-Half Breaker Arrangement:

In one and a half-breaker arrangement scheme three circuit breakers are used for controlling two circuits that are connected between two bus bars.

Normally both bus bars are in operation if a fault occurs then the associated circuit breaker opens and the fault remove.

Easily any circuit breaker can be taken out in need of any maintenance without causing an interruption.

The main advantage is to load transfer is achieved through the breakers and, therefore, the operation is simple.

The one-and-a-half breaker arrangement is best for those substations which handle large quantities of power and where the orientation of outgoing feeders is in opposite directions.

This scheme has been used in the 400 kV substations.

Hope, you got the idea to select the arrangement for your bus-bar system.

Why Should You Use Images in Your Blog?

Use a Good Image to Tell Your Story to Others People tend to respond better to visual cues, that’s why it’s important to use high qu...

Using images in your blog can have several benefits and enhance the overall quality of your content. Here are some reasons why you should consider incorporating images in your blog:

Visual Appeal: Images add visual appeal to your blog posts, making them more engaging and attractive to readers. A well-chosen image can grab attention, break up text-heavy content, and create a visually appealing layout.

Enhance Understanding: Images can help convey complex concepts or information more easily. They can act as visual aids to support your written content, making it easier for readers to understand and retain the information you are presenting.

Increase Readability: Large blocks of text can be overwhelming to readers. By incorporating images, you can break up the text and create a more visually pleasing layout. This improves readability and encourages readers to stay on your blog longer.

Emotional Connection: Images have the power to evoke emotions and create a connection with your readers. A compelling image can elicit an emotional response, making your content more memorable and relatable.

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Remember to use high-quality images that are relevant to your content, properly attribute any sourced images, and optimize them for web use to ensure fast loading times. Be mindful of copyright laws and use royalty-free or Creative Commons-licensed images whenever necessary.

In summary, incorporating images in your blog can improve its visual appeal, enhance understanding, increase readability, evoke emotions, boost SEO, facilitate social media sharing, and contribute to your brand's identity.

Saturday, June 29, 2024

Cable Pulling & Jointing Tools and Equipment

Cable pulling, Jointing, and Termination equipment play very important roles to ensure quality work to operate a safe and long-life operation. Cable pulling tools make for easy and safe cable laying, less cable sheath or screen damage/scarce, applying pulling tension correctly, and spacing cable in trench or duct properly. Cable Joint and Termination tools are very much special for cable jointing and cable sealing end termination.

How Use Cable Pulling Tools & Prepare Cable Trench?

Before laying cable, cable trench or cable duct must prepare as per site requirement. Cable ducts or trench measurements will not same for all, depending on the voltage rating, cable size, laying location, and other vicinity factors cable ducts or trenches' depth and width vary.

How Does a Small Size Damper Reduce Vibration in Transmission Lines?

Vibration dampers are usually used in high voltage and extra-high voltage electrical energy overhead transmission lines to handle aeolian and galloping or dancing vibrations in the transmission lines' conductors. The dampers are designed in such a way that they attenuate the line vibrations by reaching the same frequency as the cable that has wind-induced vibrations.

The overhead Transmission Line mainly experiences two types of vibrations in a vertical plane which can be categorized into two groups.

• Aeolian Vibration;
• Galloping or Dancing vibration.

Wednesday, May 8, 2024

Calculating the Resistance of a Wire

In many cases, we will know the length of a wire l and the AWG (American Wire Gauge) or
SWG (British Standard Wire Gauge) or IEC standard size of the wire, but not the resistance. It's easy to calculate the resistance though.

Wikipedia has a list of AWG specifications available here, which includes the resistance per meter in Ohms per kilometer or milli Ohms per meter. They also have it per kilofeet or feet.